ES2781465T3 - Hot stamping steel sheet, manufacturing method, and hot stamping molded body - Google Patents

Abstract

A steel sheet for hot stamping, comprising a composition containing: in mass %, C: from 0.100% to 0.600%; Yes: from 0.50% to 3.00%; Mn: from 1.20% to 4.00%; Ti: from 0.005% to 0.100%; B: from 0.0005% to 0.0100%; P: 0.100% or less; S: from 0.0001% to 0.0100%; Al: from 0.005% to 1,000%; N: 0.0100% or less; Ni: from 0% to 2.00%; Cu: from 0% to 2.00%; Cr: 0% to 2.00%; Mo: from 0% to 2.00%; Nb: from 0% to 0.100%; V: from 0% to 0.100%; W: 0% to 0.100%, and a total of one type or two or more types selected from a group consisting of REM, Ca, Ce, and Mg: 0% to 0.0300%, the remainder being Fe and impurities, in in which the surface roughness of the steel sheet satisfies 8.0 μm > Rz > 2.5 μm, and coating oil in an amount of 50 mg/m2 to 1500 mg/m2 is applied on a surface, and in which an amount of S contained in the coating oil which is applied on the steel sheet is 5% or less in mass %, in which the Rz was determined by measuring the region of a length of 10 mm with n=3, with the use of a contact surface roughness measuring instrument (SURFCOM2000DX/SD3 manufactured by TOKYO SEIMITSU CO., LTD) with a probe tip angle of 60°, and an R point of 2 μm and determining the mean value as the roughness of the surface Rz of each of the steel sheets

Description

DESCRIPTION

Hot stamping steel sheet, manufacturing method, and hot stamping molded body Technical field

The present invention relates to a hot stamping steel sheet excellent in inlay adhesion at the time of hot stamping and to a method for producing the hot stamping steel sheet, and to a hot stamping formed body which is a body formed from the steel sheet for hot stamping.

Background of the technique

Weight reduction of members, such as door crash bars and car side members, is being studied to address the recent trend of improving fuel efficiency, and in terms of a material, it is promotes an increase in the resistance of a steel sheet from the point of view of resistance and safety against shocks that must be guaranteed even when the thickness is reduced. Hereinafter, "strength" means both the tensile strength and the elastic limit. However, the formability of a material deteriorates as the strength increases and, therefore, to achieve a reduction in weight of the members described above, it is necessary to produce a steel sheet that satisfies both the formability and the high resistance. As a method to obtain high formability simultaneously with high strength, there are TRIP steels (TRansformation Induced Plasticity) that take advantage of the martensitic transformation of retained austenite that is described in the patent literature 1 and the bibliography of 2 patents, and the application of TRIP steels has expanded in recent years. However, in steel, although the deep drawing ability and elongation are improved at the time of forming, due to the high strength of the steel sheet, it has the problem of low fixability of the shape of a member after forming. formed under pressure.

To form a high strength steel sheet, which is inferior in formability, with good shape fixability, there is a method called hot pressing which is described in patent literature 3 and in patent literature 4. The method performs forming at a temperature of 200 ° C to about 500 ° C at which the strength of the steel sheet is reduced. However, when considering the forming of the high-strength steel sheet of 780 MPa or more, the method has problems in the fact that even when the forming temperature is increased, the strength of the steel sheet can still be high in some cases, and thus the shaping is difficult, and by the fact that the strength of the steel sheet after shaping is reduced by heating, and thus the predetermined strength cannot be obtained in some cases.

As a method of solving the problems, there is a method called hot stamping which cuts a soft steel sheet of a predetermined size, then heats the steel sheet to a single phase region of austenite at 800 ° C or more, at This is followed by press-forming in the austenite single phase region as described in patent literature 5, followed by hardening. As a result, it is possible to manufacture a member having a high strength of 980 MPa or more and excellent in shape fixability.

However, in hot stamping, a steel sheet is inserted into a heating furnace, or heated to a temperature exceeding 800 ° C by electrical heating or far-infrared heating in the atmosphere, and thus the Hot stamping has a problem of fouling generated on a steel sheet surface. A die can wear out due to the generated scale released at the time of hot stamping and therefore excellent adhesion of the inlays is required at the time of hot stamping. As a technique that solves these problems, a technique for restricting the generation of scale by making an atmosphere in the heating furnace a non-oxidizing atmosphere is known in patent literature 6, for example. However, it is necessary to strictly implement the control of the atmosphere in the heating furnace, and thus the cost of the installation is increased and the productivity is reduced. Furthermore, the steel sheet that is removed is exposed to the atmosphere, and thus the technique has an unavoidable fouling problem. Furthermore, in recent years, in order to improve the productivity of hot stamping, the method of electrically heating a steel sheet in the atmosphere has been developed. At the time of heating in the atmosphere, it is difficult to prevent oxidation of the steel sheet, and thus a die wear problem due to loose scale at the time of hot stamping becomes easily apparent. As a result, regular repair of the womb is essential.

A technique is known to restrict die wear caused by loose scale by the use, in hot stamping, of a zinc-plated or Al-plated steel sheet applied to a steel sheet surface as a steel sheet that solve these problems. However, since zinc plating or Al plating melts into a liquid phase at the time of heating, the technique has a problem that the zinc or Al stick to the interior of the heating furnace and the matrix in the time of transportation of the steel sheet or pressing moment. A bonded zinc or Al deposit has the problem of causing indentation failure in a hot stamp formed body and sticking to the formed body to worsen the external appearance. Consequently, it is necessary to repair the matrix regularly.

Consequently, it is required to develop a steel sheet for hot stamping in which the scale does not come off at the time of hot stamping, and adhesion of a molten metal to a die does not occur.

Appointment list

Patent Bibliographies

Patent Bibliography 1: Japanese Patent Publication Open to Public Inspection No. 01-230715 Patent Bibliography 2: Japanese Patent Publication Open to Public Inspection No. 02-217425 Patent Bibliography 3: Japanese Patent Publication Open to Public Inspection No .2002-143935 Patent Bibliography 4: Japanese Patent Publication Open to Public Inspection No. 2003-154413 Patent Bibliography 5: Japanese Patent Publication Open to Public Inspection No. 2002-18531 Patent Bibliography 6: Japanese Patent Publication Open To Public Inspection No. 2004-106034 Patent Bibliography 7: Japanese Patent Publication Open to Public Inspection No. 2002-18531 Patent Bibliography 8: Japanese Patent Publication Open to Public Inspection No. 2008-240046 Patent Bibliography 9: Publication Japanese Patent Laid-Open No. 2010-174302 Patent Bibliography 10: Japanese Patent Laid-Open Publication a to public inspection No. 2008-214650 Summary of the invention

Technical problem

In light of the above-mentioned problems, the present invention has an object to provide a hot stamping steel sheet which is excellent in scale adhesion at the time of hot stamping, without adhesion of a molten metal occurring. to a die, a method of making the steel sheet for hot stamping, and a body formed by hot stamping.

Solution to the problem

The present inventors have seriously studied methods to solve the problems described above. As a result, in order to improve the scale adhesion of a steel sheet, from 0.50% by mass to 3.00% by mass of Si is contained in the steel sheet, the amount of corrosion inhibiting oil that is applied to the steel sheet is set within a range of 50 mg / m2 to 1500 mg / m2, and the surface roughness of the steel sheet is set as Rz> 2.5 pm. Furthermore, a content of S included in the corrosion inhibiting oil is preferably set to 5% by mass or less. Therefore, it has been found that the adhesion of the scale is improved at the time of heating and at the time of hot stamping. In general, the inclusions in the coating oil concentrate at an interface between the base iron and the scale, thereby impairing the adhesion of the scale. However, it has been found that it is possible to ensure adhesion of the scale by using restrictions on the amount of inclusions and an anchoring effect by using irregularities in the surface of the steel sheet in combination.

The present invention is based on the knowledge described above, and is set forth in the claims.

Advantageous effects of the invention

According to the present invention, the hot stamping steel sheet has excellent scale adhesion at the time of hot stamping, in which adhesion of a molten metal to the die does not occur, the method to produce the steel sheet for hot stamping and the body formed by hot stamping.

Brief description of the drawings

[Fig. 1] Fig. 1 is a diagram illustrating a relationship between an amount of coating oil in a steel sheet and the surface roughness Rz of the steel sheet.

[Fig. 2] Fig. 2 is a diagram to explain that when the concentration of S in the oil of lining, scale comes off easily.

[Fig. 3] Fig. 3 is a diagram illustrating the relationship between a pickling time period and the surface roughness Rz of the steel sheet.

[Fig. 4A] Fig. 4A is a photograph showing a microstructure of a surface layer of a hot rolled steel sheet before pickling.

[Fig. 4B] Fig. 4B is a photograph showing the microstructure of the surface layer after pickling.

[Fig. 5] Fig. 5 is a diagram illustrating the relationship between an amount of coating oil and a scale thickness.

[Fig. 6A] Fig. 6A is a photograph showing a section of a surface of the hot stamping body of an example of the present invention.

[Fig. 6B] Fig. 6B is a photograph showing a section of a surface of the body formed by hot stamping of a comparative example.

[Fig. 7] Fig. 7 is a diagram to explain that when the surface roughness Rz before hot stamping heat treatment is less than 2.5, a number density of irregularities after hot stamping heat treatment is less than 3.

Description of achievements

A steel sheet for hot stamping of the present invention contains from 0.5% by mass to 3.0% by mass of Si in the steel sheet, an amount of corrosion inhibiting oil applied to the steel sheet is in a range of 50 mg / m2 to 1500 mg / m2, and the surface roughness of the steel sheet is Rz> 2.5 gm. A content of S contained in the corrosion inhibiting oil is 5% by mass or less.

First, the reason why the present inventors paid attention to coating oil will be described.

In order to improve the scale adhesion of steel sheets to which no plating is applied (cold rolled steel sheets or hot rolled steel sheets), the present inventors have investigated the surface properties of the sheets. steel and the influences of various types of treatment. As a result, the present inventors have found that although steel sheets after degreasing show excellent scale adhesion, scale adhesion is significantly deteriorated after applying corrosion inhibiting oil. When the present inventors investigated the relationship between scale adhesion and corrosion inhibiting oil in more detail, it was found that when the amount of S contained as impurities in the corrosion inhibiting oil is increased, scale tends to come off easily. It is conceivable that the S in the corrosion inhibiting oil has an influence on the adhesion of the scale, although the detailed reason is not clear.

On the other hand, it is necessary to apply corrosion inhibiting oil such as mineral oil, to a pickled hot rolled steel sheet for hot stamping, and to a cold rolled steel sheet for hot stamping after cold rolling or annealing. to prevent corrosion in the period from production to use. In particular, a steel sheet after pickling has generally been coated with oil of more than 1500 mg / m2, assuming that the period from delivery to a user to use is long. When the present inventors investigated the influence of the amount of coating oil in order to make scale adhesion and corrosion inhibition properties compatible, the present inventors have found that, as illustrated in Fig. 1, adhesion The fouling is improved by strictly controlling the range of the coating oil amount and the surface roughness of a steel sheet. The effect is exhibited by setting the amount of coating oil at 50 mg / m2 to 1500 mg / m2. A lower limit of the amount of coating oil is set at 50 mg / m2, because it is difficult to ensure excellent corrosion inhibition properties with an amount of coating oil less than the amount of coating oil of 50 mg / m2. The lower limit of the amount of coating oil is preferably 100 mg / m2 or more, and more preferably 200 mg / m2 or more. An upper limit is set at 1500mg / m2 for excellent scale adhesion effect. The upper limit of the amount of coating oil is set at 1500 mg / m2 because when the amount of coating oil exceeds 1500 mg / m2, scale adhesion deteriorates. The upper limit is preferably 1000 mg / m2, it is more preferably 900 mg / m2, and most preferably it is 800 mg / m2. In addition, the oil coated on the surface of the steel sheet is burned at the time of heating, and thus becomes the cause of soot generation. Based on this, a lesser amount of coating oil is more preferable.

The scale adhesion illustrated in Fig. 1 was evaluated by a hot shallow draw test in a cylindrical die of F 70 mm and a depth of 20 mm. After a steel sheet was heated to a temperature range of 800 ° C to 1002C at 50 ° C / s in an electric heater, and held for from 0 seconds to 120 seconds, the energization was stopped, the steel sheet was cooled to 650 ° C by allowing it to cool, and hot shallow drawing was made into the above-described die. The samples after formation were visually observed, and the samples in which an area where the scale peeled off accounted for 5% or less were determined to have good scale adhesion (circle), the samples in which the area where the incrustations represented 5 to 15% were determined as poor (triangle), and samples in which the area where the incrustations were separated represented more than 15% were determined as very poor (X). Samples in which the area where the scale separated represented 5% or less were determined within the range of the present invention.

It is possible to evaluate the adhesion of the scale without particularly limiting the heating method. For example, conditions of any of a heating furnace, far infrared rays, near infrared rays and electric heating can be adopted. Also, when a steel sheet is heated in a heating furnace, more excellent scale adhesion can be obtained by decreasing scale by controlling the atmosphere in the heating furnace and restricting oxidation of the steel sheet.

Note that a shallow draw test temperature can be in any temperature region as long as a steel sheet can be processed, but in general, a hot stamping steel sheet has high strength and excellent fixability of formed by processing in an austenite region and subsequent matrix hardening. From this, the evaluation of the characteristics was carried out by hot shallow drawing at 650 ° C exceeding Ar3.

As the oil coating method, electrostatic oil coating, spraying, a coating roller and the like are generally used, but the oil coating method is not limited as long as the amount of coating oil can be ensured.

Although the type of oil is not specified, NOX-RUST530F (manufactured by PARKER INDUSTRIES, INC.) Or the like is generally used if the oil is mineral oil, for example, and if the amount of coating oil meets the range herein. invention, the type of oil is not limited.

Although the amount of coating oil can be measured by any method as long as the amount of coating oil can be measured, the present inventors measured the amount of coating oil by the following method. The corrosion inhibiting oil coated steel sheet was first cut into a 150mm square, and then tape was applied so that a 100mm by 100mm region was exposed. Subsequently, the weights of the coating oil and the steel sheet to which the sealing was performed (including the weight of the tape) were measured in advance. Subsequently, degreasing was carried out by wiping the corrosion inhibiting oil on the surface of the steel sheet with a cloth containing acetone, the weight of the degreased steel sheet was measured, the weights before and after degreasing were compared, and, therefore, the amount of coating oil per unit area was calculated. The measurement was carried out at three points on each of the steel sheets, and an average value of the bound amounts was determined as an amount of coating oil of each of the steel sheets.

The content of S contained in the corrosion inhibiting oil is restricted to 5% by mass or less. When the present inventors investigated the relationship between the S content in the coating oil and a percentage of scale spaced area as illustrated in Fig. 2, the present inventors have found that as the S content in the oil Coating becomes smaller, scale adhesion is increased, and especially when the S content in the coating oil is 5% by mass or less, the area of dislodged scale becomes substantially 0%. It is conceivable that while the oil contained in the corrosion inhibiting oil is burned and removed during heating, the S contained as an impurity remains on the surface of the steel sheet to concentrate on the scale, thereby impairing adhesion. of the inlays, although the detailed mechanism is unclear. Therefore, it is preferable to reduce the content of S contained in the corrosion inhibiting oil. The content of S is preferably 4% by mass or less, and is more preferably 3% by mass or less. Although the analysis of S in the corrosion inhibiting oil can be performed by any method as long as the S can be analyzed, the present inventors extracted 5 ml of the corrosion inhibiting oil which is applied to the steel sheet, and carried out X-ray fluorescence analysis (X-ray Fluorescence Sulfur-in-Oil Analyzer SLFA-2800 / HORlBA). In the measurement, the measurement was carried out with n = 3, and its mean value was defined as the content of S.

The roughness of the surface of the steel sheet will be described below. To ensure adhesion of the scale, the surface roughness of the steel sheet needs to satisfy Rz> 2.5 gm. A result obtained by investigating a relationship between the surface roughness Rz of the steel sheet and the adhesion of the scale is as illustrated in Fig. 1 described above. By providing irregularities in an interface between scale that are generated at the time of hot stamping heat treatment and a base iron, the irregularities are formed at the interface between the base iron and scale, resulting in a higher increase in the accession. The effect is generally known as the anchor effect. In particular, the scale that is generated at the time of heating in the present steel sheet is thin. As a result, in the present steel sheet in which the thickness of the inlays is thin, inlays having irregularities are formed by being influenced by the surface condition of the base iron. Therefore, the Steel sheet surface roughness before hot stamping needs to satisfy Rz> 2.5 gm. When Rz <2.5 gm, the surface roughness of the steel sheet is small, and the anchoring effect is insufficient, so that excellent adhesion of the inlays cannot be guaranteed at the time of hot stamping. Although the effect of excellent adhesion of the scale of the present invention can be obtained without particularly providing the upper limit, if the adhesion of the scale is excessively increased, it becomes difficult to remove the scale in a downstream process, such as shot blasting, for example. Thus, it is set to Rz <8.0 gm. It is more preferable to set Rz <7.0 gm. However, even if Rz is set> 8.0 gm, it is possible to guarantee excellent scale adhesion which is the effect of the present invention. Note that in the steel sheet in which the Si content is less than 0.50% by mass, even if the surface roughness is set to Rz> 2.5 gm, thick Fe scale is formed at the time of heating, and thus even when the irregularities are on the surface of the steel sheet, the interface between the base iron and the scale becomes flat by excessive oxidation. As a result, the irregularities in the interface between the scale and the base iron are eliminated, and the effect of excellent adhesion of the scale which is the effect of the present invention is not exhibited.

Although the measurement of the surface roughness Rz can be carried out by any method, the present inventors measured the region of a length of 10 mm with n = 3, with the use of an instrument for measuring the roughness of the contact surface. (SURFCOM2000DX / SD3 manufactured by TOKYO SEIMITSU CO., LTD) with a probe tip angle of 60 ° and an R point of 2 gm, and they determined the mean value as the surface roughness Rz of each of the sheets of steel.

Next, an inlay structure of the hot stamping body will be described. The hot stamping steel sheet of the present invention ensures scale adhesion by controlling irregularities at the interface between the scale and the base iron. Consequently, the scale can be mainly composed of an oxide of Si, Fe3O4, Fe2O3 and FeO. There is an oxide of Si at the interface between the base iron and the iron scale (FeO, Fe2O3, Fe2O3), and therefore controls the thickness of the iron scale. Consequently, the scale needs to contain an oxide of Si. Since the main goal is to control the thickness of the iron oxide, even if the Si oxide is very thin, it is enough if the Si oxide exists, and even with 1 nm, the Si oxide exhibits the effect.

Analysis of the composition of the inlays of the formed body was carried out by X-ray diffraction cutting the foil from a bottom of the cylindrical portion of a shallow inlay sample piece. From the peak intensity ratio of the respective oxides, the volume ratios of the respective Fe oxides were measured. Si oxide hardly existed, and the volume percentage was less than 1%, and thus quantitative evaluation in X-ray diffraction was difficult. However, it is possible to confirm that there is a Si oxide at the interface between the scale and the base iron by online analysis from EPMA (Electron Probe Micro Analyzer).

The thickness of the inlays is 10 gm or less. When the thickness of the inlays is 10 gm or less, the adhesion of the inlays is further improved. When the thickness of the inlays exceeds 10 gm, the inlays tend to come off easily due to a thermal stress that operates at the time of cooling at the time of hot stamping. Next, in a scale removal process, such as shot peening or wet blasting, cracks occur between the Fe scale, and scale existing on an external side is dislodged. As a result, the scale also has the problem of being inferior in removability of the scale. Therefore, the thickness of the inlays is 10 gm or less. The thickness of the inlays is more preferably 7 gm or less, and it is more preferably 5 gm or less. The thickness of the scale is achieved by controlling the amount of coating oil within the predetermined range simultaneously with controlling the Si content of the steel sheet within a predetermined range. Fig. 5 illustrates a relationship between the amount of coating oil and the thickness of the scale.

At the interface between the base iron and the inlays in the hot stamp formed body of the present invention, three or more irregularities of 0.2 gm to 8.0 gm per 100 gm are present. Fig. 6A shows a photograph of an interface between a base iron and inlays of a formed body excellent in inlay adhesion, and Fig. 6B shows a photograph of an interface between a base iron and bottom inlays in inlay adhesion. Since the irregularities contribute to the improvement of the adhesion of the scale at the time of hot stamping, and thus, excellent adhesion of the scale can be ensured by controlling the irregularities within the range described above. Irregularities of less than 0.2 gm provide insufficient anchoring effect and provide inferior scale adhesion. With irregularities of 8.0 gm or more, the adhesion of the scale is so strong that the scale is difficult to remove in the subsequent scale removal procedure, for example by shot peening or wet blasting, and therefore it is preferable to do irregularities in the interface between the scale and the base iron of 8.0 gm or less. The irregularities are more preferably 6.0 gm or less, and more preferably 4.0 gm or less. Please note that even if the unevenness exceeds 8.0 gm, excellent scale adhesiveness can be guaranteed which is the effect of the present invention.

When the number of irregularities from 0.2 gm to 8.0 gm per 100 gm is less than three, a scale adhesion enhancing effect is not sufficient, and thus the number of irregularities per 100 gm is set to three or more . It is possible to ensure excellent scale adhesion, which is the effect of the present invention, without particularly setting an upper limit on the number of irregularities per 100 gm. Note that the irregularities of the formed body are correlated with the surface roughness Rz of the steel sheet as illustrated in Fig. 7, and are controllable by setting the surface roughness of the steel sheet as Rz> 2.5 gm.

Next, the chemical compositions of the steel sheet and the hot stamping body of the present invention will be described. Note that% hereinafter means% by mass. C: 0.100% to 0.600%

The C represents an element that is contained to improve the strength of the steel sheet. If a C content is less than 0.100%, a tensile strength of 1180 MPa or more cannot be guaranteed, and a high-strength formed body that is the goal of hot stamping cannot be guaranteed. When the C content exceeds 0.600%, the weldability and processability become insufficient, and thus the C content is set to 0.100% to 0.600%. The C content is preferably 0.100% to 0.550%, and more preferably 0.150% to 0.500%. However, if the strength of the formed body is not required, excellent scale adhesion can be guaranteed even if the C content is less than 0.150%.

Yes: from 0.50% to 3.00%

Si improves scale adhesion by controlling scale composition at the time of hot stamping, and therefore Si is an essential element. If the Si content is less than 0.50%, the thickness of the Fe scale cannot be controlled and excellent adhesion of the scale cannot be guaranteed. Consequently, it is necessary to set the Si content to 0.50% or more. In addition, when considering the application to a member that is difficult to form at the time of hot stamping, it is preferable to increase the Si content. Accordingly, the Si content is preferably 0.70% or more, and it is more preferably 0.90% or more. Meanwhile, Si increases a point Ae3, and the heating temperature necessary to make martensite a main phase, and thus, if Si is contained in excess, productivity and economic efficiency are reduced. Therefore, an upper limit of the Si content is set to 3.00%. The upper limit of the Si content is preferably 2.5%, and the upper limit is more preferably 2.0%. However, it is possible to ensure excellent scale adhesion, except productivity and economic efficiency.

Mn: from 1.20% to 4.00%

Mn delays the transformation of ferrite in a quenching process at the time of hot stamping, and converts a shaped body by hot stamping into a structure having a main martensite phase, and thus it is necessary to contain 1.20% o more than Mn. If the Mn content is less than 1.20%, the martensite cannot be converted into a main phase, and it is difficult to guarantee high strength, which is a target of the hot stamping formed body, and thus a limit. Lower Mn content is set to 1.20% However, if the strength of the formed body is not required, excellent scale adhesion can be ensured even if the Mn content is less than 1.20%. When the Mn content exceeds 4.00%, the effect becomes saturated, embrittlement is caused and fracture is caused at the time of casting, cold rolling or hot rolling, thus establishing an upper limit of the content of Mn at 4.00%. The Mn content is preferably within a range of 1.50% to 3.50%, and more preferably it is within a range of 2.00% to 3.00%.

Ti: from 0.005% to 0.100%

Ti is an element that combines with N to form TiN and thus prevents B from being a nitride to improve hardenability. The effect becomes noticeable when the Ti content is 0.005% or more, and thus the Ti content is set as 0.005% or more. However, when the content of Ti exceeds 0.100%, a carbide of Ti is formed, an amount of C is reduced that contributes to strengthening the martensite, and a reduction in strength is caused, and thus an upper limit. of the Ti content is set to 0.100%. The Ti content is preferably within a range of 0.005% to 0.080%, and more preferably it is within a range of 0.005% to 0.060%.

B: from 0.0005% to 0.0100%

B improves hardenability at the time of hot stamping and contributes to making a martensite main phase. The effect is noticeable when the content of B is 0.0005% or more, and thus it is necessary to set the content of B to 0.0005% or more. When the content of B exceeds 0.0100%, the effect becomes saturated, an iron boride precipitates, and the effect of hardenability of B is lost, and thus the upper limit of the B content is set at 0.0100%. The content of B is preferably within a range of 0.0005% to 0.0080%, and more preferably it is within a range of 0.0005% to 0.0050%.

P: 0.100% or less

The P is an element that segregates in a central portion of the sheet thickness of the steel sheet, and is an element that embrittles a welded portion. Consequently, an upper limit of a P content is set at 0.100%. A more preferable upper limit is 0.050%. The lower the P content, the more preferable, and although the effect of the present invention is exhibited without particularly setting the lower limit, but it is economically disadvantageous to reduce the P to less than 0.001% from the viewpoint of productivity and of the cost of dephosphorization, and thus the lower limit is preferably set at 0.001%.

S: from 0.0001% to 0.0100%

The S exerts a great influence on the adhesion of the scale and thus, it is necessary to restrict a content in the steel sheet. Consequently, an upper limit of an S content is set at 0.0100%. A lower limit of the S content is set at 0.0001% because it is economically disadvantageous from the point of view of productivity and cost of dephosphorization. The content of S is preferably within a range of 0.0001% to 0.0070%, and more preferably it is within a range of 0.0003% to 0.0050%.

Al: from 0.005% to 1.000%

Al acts as a deoxidizer and thus the Al content is set to 0.005% or more. When the Al content is less than 0.005%, a sufficient deoxidation effect cannot be obtained and there is a large amount of envelope (oxide) on the steel sheet. These wraps become starting points for destruction at the time of hot stamping and breakage causes, and are therefore not preferable. The effect becomes noticeable when the Al content reaches 0.005% or more, and thus it is necessary to set the Al content to 0.005% or more. When the Al content exceeds 1,000%, the Ac3 point is increased and the heating temperature is increased at the time of hot stamping. That is, hot stamping is a technique for obtaining a high strength shaped body having a complicated shape by heating a steel sheet to an austenite single phase region, and subjecting the steel sheet to hot die pressing of excellent formability and cooling rapidly using a die. As a result, when a large amount of Al is contained, the Ac3 point is significantly increased, there is an increase in the heating temperature required for heating the austenite single phase region, and the productivity is reduced. Consequently, it is necessary to set an upper limit of the Al content at 1,000%. The Al content is preferably within a range of 0.005% to 0.500%, and is more preferably within a range of 0.005% to 0.300%.

N: 0.0100% or less

N is an element that forms coarse nitrides and impairs bending ability and hole expandability. When N content exceeds 0.0100%, the bending ability and hole expandability are significantly deteriorated, and thus, the upper limit of the N content is set at 0.0100%. Note that N becomes a cause of blowing hole generation at the time of welding, and thus the lower the N content, the more preferable it is. Accordingly, the content of N is preferably 0.0070 or less, and it is more preferably 0.0050% or less. Although it is not necessary to particularly set a lower limit of the N content, the manufacturing cost increases significantly when the N content is reduced to less than 0.0001%, and thus a practical lower limit is 0.0001%. From the manufacturing cost viewpoint, the N content is more preferably 0.0005% or more.

Please note that other unavoidable items may be contained in extremely small quantities. For example, O forms an oxide and exists as an inclusion.

The steel sheet of the present invention further contains the following elements as needed.

Ni: from 0.01% to 2.00%

Cu: from 0.01% to 2.00%

Cr: from 0.01% to 2.00%

Mo: from 0.01% to 2.00%

Ni, Cu, Cr and Mo are elements that contribute to increase resistance by improving hardenability at the time of hot stamping, and making a main phase of martensite. The effect becomes noticeable by containing 0.01% or more of each of one type or two or more types selected from a group consisting of Ni, Cu, Cr and Mo, and thus the content of the elements is preferably 0.01% , respectively. When the content of each of the elements exceeds a predetermined amount, the weldability, hot workability and the like deteriorate, or the strength of the steel sheet for hot stamping is so high which can cause a manufacturing problem and thus the upper limits of the contents of these elements are preferably set at 2.00%.

Nb: from 0.005 to 0.100%

V: from 0.005 to 0.100%

W: 0.005 to 0.100%

Nb, V and W are elements that strengthen fine grains by inhibiting the growth of austenite at the time of hot stamping, and contribute to increase strength and improve toughness. Accordingly, one type or two or more types selected from a group consisting of these elements may be contained. The effect becomes more noticeable when 0.005% or more of each of the elements is contained, and thus it is preferable that 0.005% or more of each of the elements is contained. Note that when more than 0.100% of each of these elements is contained, it is not preferable because carbides of Nb, V and W are formed, an amount of C is reduced that contributes to strengthening the martensite and causes a reduction of the resistance. Each of the elements is preferably in a range of 0.005% to 0.090%.

A total of one type or two or more types selected from a group consisting of REM, Ca, Ce and Mg: 0.0003% to 0.0300%

In the present invention, 0.0003% to 0.0300% of one type or two or more types selected from a group consisting of REM, Ca, Ce and Mg may be further contained in total.

REM, Ca, Ce and Mg are elements that improve resistance and contribute to the improvement of the material. When the total of one type or two or more types selected from the group consisting of REM, Ca, Ce and Mg is less than 0.0003%, a sufficient effect cannot be obtained and thus it is preferable to set a lower limit of the total at 0.0003%. When the total of one type or two or more types selected from the group consisting of REM, Ca, Ce and Mg exceeds 0.0300%, the moldability and hot workability are likely to deteriorate, and thus it is preferable set an upper limit of the total at 0.0300%. Note that REM is an abbreviation for Rare Earth Metal and refers to an element that belongs to a lanthanum system. In the present invention, REM is often added in misch metal, and in addition to Ce, elements of a lanthanum system are sometimes contained in combination.

In the present invention, the effect of the present invention becomes evident even when the elements of a lanthanoid system other than La and Ce are contained as unavoidable impurities, and the effect of the present invention becomes evident even when the other elements such as metals are contained as impurities.

Next, the characteristics of the microstructures of the hot stamping steel sheet and the hot stamping shaped body of the present invention will be described.

As long as the chemical composition, the surface roughness of the steel sheet, and the amount of coating oil meet the ranges of the present invention, the effect of the present invention can be exhibited by any of a rolled steel sheet. hot pickled, rolled steel sheet obtained by cold rolling a hot rolled steel sheet, or a cold rolled steel sheet to which an anneal is applied after cold rolling.

These steel sheets are heated to an austenite region exceeding 800 ° C at the time of hot stamping, and therefore exhibit performance as hot stamping steel sheets having excellent scale adhesion that is the effect of the present invention without particularly limiting the microstructure. However, when mechanical cutting of the steel sheets and cold punching is carried out before hot stamping, the strength of the steel sheets is preferably as low as possible to reduce wear of the dies, edges cutting blades or punching dies. Accordingly, the microstructure of the hot stamping steel sheet is preferably ferrite and pearlite structures, or a bainite structure and a structure obtained by quenching martensite. However, if the wear of a punch and dies at the time of mechanical cutting and cold punching does not become a problem, it is possible to guarantee excellent adhesion of the inlays, which is the effect of the present invention, even if one type or two or more types of retained austenite, hardened martensite and bainite are contained. Furthermore, to reduce the strength of the steel sheet, a heat treatment can be carried out in a box-type annealing furnace or in a continuous annealing facility. Alternatively, even when cold rolling is carried out after the above softening treatment, and the thickness of the sheet is controlled to a predetermined sheet thickness, excellent adhesion of inlays is guaranteed, which is the effect of the present invention.

When the strength of the formed body is improved after hot stamping, and a high strength of the component is obtained, the microstructure of the formed body preferably has a main phase of martensite. In particular, to ensure a tensile strength of 1180 MPa or more, a volume ratio Martensite which is a main phase is preferably made of 60% or more. Martensite can be quenched after hot stamping, and made tempered martensite. A structure other than martensite, bainite, ferrite, pearlite, cementite and retained austenite can be contained as structure. Furthermore, even if the volume percentage of martensite is less than 60%, it is possible to ensure the excellent adhesion of the scale of the present invention.

The following methods are used in the identification of the microstructures (tempered martensite, martensite, bainite, ferrite, pearlite, retained austenite and a remaining structure) that make up the structure of the steel sheet, confirmation of the existence positions and measurement of the area percentages. For example, it is possible to corrode a section in a steel sheet rolling direction or a section in a direction perpendicular to the rolling direction with a nital reagent and the reagent described in Japanese Patent Laid-Open Publication No. 59 -219473, and observe the structure with a 1000 to 100000 power scanning electron microscope (SEM: Scanning Electron Microscope) and transmission electron microscope (TEM: Transmission Electron Microscope). The present inventors determined the thickness section of the sheet parallel to the rolling direction of the steel sheet as the observation surface, took a sample, polished the observation surface, etched with nital, observed a thickness range of And at% with a% of the thickness of the sheet as the center with a Field Emission Scanning Electron Microscope (FE-SEM), they measured an area fraction, and the area fraction was taken as a volume fraction. Regarding the volume fraction of retained austenite, the volume fraction was measured by performing X-ray diffraction with the surface that was parallel to the surface of the main steel sheet and had a% thickness, used as the observation surface .

Next, a method for producing the hot stamping steel sheet of the present invention will be described.

Although the other operating conditions are based on a usual method, the following conditions are preferable in terms of productivity.

To produce the steel sheet in the present invention, a slab having the same component composition as the above-mentioned composition of components of the steel sheet is first cast. As the slab provided for hot rolling, a continuously cast slab, the slab produced by a thin slab caster or the like can be used. The method for manufacturing the steel sheet of the present invention is adapted to a process such as continuous casting direct rolling (CC-DR) which performs hot rolling immediately after casting.

Slab heating temperature: 1100 ° C or higher

Hot rolling termination temperature: transformation point Ar3 or higher

Winding temperature: 700 ° C or lower

Cold rolling ratio: 30 to 70%

The heating temperature of the slab is preferably set at 1100 ° C or more. The heating temperature of the slab in a temperature region lower than 1100 ° C causes a reduction in the finish rolling temperature, and thus the resistance at the time of finish rolling tends to be high. As a result, there is a possibility that rolling becomes difficult, poor shape of the steel sheet is produced after rolling, and thus the heating temperature of the slab is preferably set to 1100 ° C or more.

The finish rolling temperature is preferably set at the Ar3 transformation point or higher. When the finish rolling temperature becomes lower than the transformation point of Ar3, the rolling load becomes high, and there is a possibility that the rolling becomes difficult, and poor shape of the sheet of steel after rolling, and thus a lower limit of the finish rolling temperature is set preferably at the transformation point Ar3. It is not necessary to set an upper limit on the finish rolling temperature, but if the finish rolling temperature is set to be excessively high, the slab heating temperature has to be made excessively high to guarantee the temperature, and hence Thus, the upper limit of the finish rolling temperature is preferably 1100 ° C.

The winding temperature is preferably set at 700 ° C or lower. When the winding temperature exceeds 700 ° C, the thickness of the oxides formed on the surface of the steel sheet is excessively increased, and the pickling property deteriorates, and thus the winding temperature higher than 700 ° C is not preferable. When cold rolling is performed thereafter, a lower limit of the winding temperature is preferably set at 400 ° C. When the winding temperature is lower than 400 ° C, the strength of the hot-rolled steel sheet is extremely increased, and sheet fracture and bad shape easily occurs at the time of cold-rolling, and thus , the lower limit of the winding temperature is preferably set at 400 ° C. However, if the rolled steel sheet Hot coil is desired to be softened by heating the hot wound steel sheet in the box-type annealing furnace or continuous annealing facility, the steel sheet can be wound at a temperature lower than 400 ° C. Please note that at the time of hot rolling, the rough rolled sheets can be joined to each other and the final rolling can be done continuously. Also, the raw laminated sheet can be temporarily wound.

Then the pickling is applied to the hot rolled steel sheet which is produced in this way for 30 seconds or more in an aqueous solution with a temperature of 80 ° C to 100 ° C where the acid concentration is 3% by mass to 20% by mass and an inhibitor is included. In the present invention, pickling under the present conditions is extremely important, and to control the surface roughness Rz of the steel sheet to more than 2.5 gm, pickling under the conditions described above is necessary. Note that an aqueous solution of a hydrochloric acid, a sulfuric acid or the like is generally used as the acid, and aqua regia or the like can be used.

The temperature of the aqueous solution is set at 80 ° C to less than 100 ° C, because with a temperature less than 80 ° C, the reaction rate is low, and it takes a long time to bring the surface roughness of hot rolled steel sheet to an appropriate range. Meanwhile, heating to a temperature of 100 ° C or more is dangerous and not preferable because the solution boils and splashes although the pickling reaction has no problem.

Also, the reason why the acid concentration is set to 3% by mass to 20% by mass is to control the surface roughness Rz of the hot rolled steel sheet within the appropriate range. When the acid concentration is less than 3% by mass, it takes a long time to control the irregularities on the surface by stripping. When the acid concentration exceeds 20% by mass, the pickling tank is significantly damaged and the handling of the facility becomes difficult, so it is not preferable. A preferable range of the acid concentration is a range of 5% by mass to 15% by mass.

Furthermore, the reason why the pickling time period is set to 30 seconds or more is to stably give predetermined irregularities (irregularities of Rz> 2.5 gm) to the surface of the steel sheet by pickling. When the pickling tank is divided into a plurality of tanks, if the pickling time period of any of the pickling tanks or the total pickling time period satisfies the conditions described above, the surface roughness Rz of the sheet Hot rolled steel can be brought into the range of the present invention, even if the concentrations or temperatures of the individual pickling tanks differ from each other. Furthermore, pickling can be carried out by dividing it into a plurality of times. Note that in the experiment of the present inventors, a hydrochloric acid including an inhibitor was used, but the effect of the present invention can be obtained by using another acid such as hydrochloric acid without using an inhibitor, a sulfuric acid and a nitric acid. , or a mixture of these acids, provided that the surface roughness Rz can be controlled by etching.

Furthermore, the irregularities formed by pickling the hot rolled steel sheet also remain even after temper rolling, cold rolling or annealing, and thus it is extremely important to control the pickling conditions and give irregularities to the surface of the foil after pickling. Accordingly, the temper rolling can be carried out on the hot rolled steel sheet after pickling.

Also, even with cold rolled steel sheet that is only cold rolled, or cold rolled steel sheet heat treated in continuous annealing facility or box type annealing furnace after cold rolling , irregularities are formed on the surface when carrying out pickling before cold rolling, and the predetermined effect can be obtained. Please note that cold rolling is preferably done with Rz roll roughness for cold rolling within a range of 1.0 gm to 20.0 gm, and the cold rolling roll also includes a temper rolling roll.

Cold rolling is applied to the pickled hot rolled steel sheet under the conditions indicated above with a section reduction of 30% to 80%, and the steel sheet can be passed through a continuous annealing facility. When the section reduction is less than 30%, it becomes difficult to maintain the shape of the flat steel sheet, and the ductility of the finished product deteriorates, and thus, a lower limit of the section reduction is preferably set at 30%. When the section reduction exceeds 80%, the rolling load becomes excessively large, and cold rolling becomes difficult, and thus an upper limit of the section reduction is preferably set at 80%. The section reduction is more preferably 40% to 70%. The effect of the present invention becomes apparent even without particularly specifying the number of times of rolling pass and the section reduction of each pass, and thus it is not necessary to specify the number of times of rolling pass, and the reduction section at each step. After that, the cold rolled steel sheet can be passed through the continuous annealing line. An object of the treatment is to soften the steel sheet which is highly hardened by cold rolling, and thus, any condition can be adopted as long as the condition is such that the steel sheet is softened. For example, when the annealing temperature is in the range of 550 ° C to 750 ° C, the dislocation introduced at the time of cold rolling is released by recovery, recrystallization or phase transformation, and thus annealing is preferably carried out in this temperature region.

By annealing by a box-type furnace for a similar purpose, the excellent scale adhesion hot stamping steel sheet of the present invention can be obtained.

After that, oil coating is carried out. As an oil coating method, electrostatic oiling, spraying, a coating roller and the like are generally used, and as long as an amount of coating oil in a range of 50 mg / m2 to 1500 mg / m2 can be ensured, the method is not limited. In the present invention, the coating of a predetermined amount of oil was carried out by an electrostatic oiling machine. Furthermore, as long as the amount of coating oil can be ensured in the range of 50 mg / m2 to 1500 mg / m2, a corrosion inhibitor can be applied in an amount equal to or greater than the amount of coating oil, and degreasing can be done.

Excellent scale adhesion which is the effect of the present invention and a corrosion inhibiting property can be made compatible without particularly limiting the hot stamping conditions. For example, when producing by the production method shown below, the compatibility of the excellent performance of the tensile strength of 1180 MPa or more and the productivity is achieved. At the time of hot stamping, heating is preferably carried out in a temperature region of 800 ° C to 1100 ° C at a heating rate of 2 ° C / second or more. By heating at a rate of 2 ° C / second or more, the generation of scale at the time of heating can be restricted, and the effect of improving the adhesion of scale is provided. The heating rate is preferably 5 ° C / second or more, and is more preferably 10 ° C / second or more. Furthermore, increasing the heating rate is also effective for the purpose of improving productivity.

The annealing temperature at the time of hot stamping is preferably within the range of 800 ° C to 1100 ° C. By conducting annealing in this temperature region, it is possible to make the structure become a single-phase austenitic structure, and the structure can be converted to a structure having martensite as the main phase by cooling which is carried out subsequently. When the annealing temperature at this time is lower than 800 ° C, the structure at the time of annealing becomes ferrite and austenite structures, the ferrite grows in the cooling process, the volume percentage of ferrite exceeds 10% and the tensile strength of the hot stamping body is less than 1180 MPa. Consequently, a lower limit of the annealing temperature is preferably set at 800 ° C. When the annealing temperature exceeds 1100 ° C, not only is the effect saturated, but also the thickness of the scale is significantly increased, and the fear arises that the adhesion of the scale will be reduced. Accordingly, it is preferable to anneal at 1100 ° C or lower. The annealing temperature is more preferably in a range of 830 ° C to 1050 ° C.

After heating, retention can be carried out in the temperature region from 800 ° C to 1100 ° C. When the retention is carried out at a high temperature, the melting of the carbides included in the steel sheet is possible, and it contributes to increasing the strength of the steel sheet and improving the hardenability. Retention includes residence, removal of heating, and removal of cooling in the present temperature region. Since the objective is to melt the carbides, the objective is achieved as long as the residence time period in the present temperature region is guaranteed. Although the limitation on the retention time period is not particularly provided, 1000 seconds is preferably set as an upper limit, because when the retention time period is 1000 seconds or more, the thickness of the scale becomes excessively large and scale adhesion is impaired.

After that, a temperature of 800 ° C to 700 ° C is preferably reduced to an average cooling rate of 5 ° C / second or more. Here, 700 ° C is a die cooling start temperature, and the reason why the temperature from 800 ° C to 700 ° C is reduced to 5 ° C / second or more is to avoid ferrite transformation, bainite transformation and pearlite transformation and converting the structure into a martensite main phase. When the cooling rate is less than 5 ° C / second, these soft structures are formed, and it is difficult to ensure the tensile strength of 1180 MPa or more. Meanwhile, the effect of the present invention is exhibited without particularly setting the upper limit of the cooling rate. The reason why the temperature range that is reduced to 5 ° C / second or more is set from 800 ° C to 700 ° C is that in this temperature range, the ferrite or similar structure is likely to be formed that causes reduction in resistance. The cooling at this time is not limited to continuous cooling, and even when holding and heating is performed in the temperature region, the effect of the present invention is exhibited as long as the average cooling rate is 5 ° C. / second or more. The effect of the present invention can be exhibited without particularly limiting the cooling method. That is, the effect of the present invention can be exhibited either by cooling using a matrix or cooling the matrix using water cooling in combination.

Examples

Next, examples of the present invention will be described, and the conditions in the examples are just one example of the conditions adopted to confirm the implementability and effect of the present invention, and the The present invention is not limited to one example of a condition.

First, slabs of the component compositions from A to S and from a to an shown in Table 1 were melted, and after the slabs were temporarily cooled to room temperature, heating was carried out for 220 minutes in a heating oven. With oven temperature = 12302C, hot rolling was carried out with finish rolling temperature = 920 ° C to 960 ° C, and winding was carried out under the temperature conditions shown in Table 2.

A1 FH 500 8 83 160 NOX503F ^- 0 ^{Comparative steel} A2 FH 600 6 B7 200 NOX503F 80 0 ^{Steel of the present invention} A3 FH 590 8 85 160 NQX50QF 140 1 ^{Steel of the present invention} A4 FH 6BQ 7 80 680 NOX503F 270 1 ^{Steel of the present invention} A5 FH 590 9 89 160 NOX503F 490 1 ^{Steel of the present invention} A6 FH 600 9 86 160 NOX5O0F 780 1 ^{Steel of the present invention} A7 FH 580 8 64 240 NGX503F 1020 1 ^{Steel of the present invention} AS FH 550 9 86 40 NOX503F 1480 5 ^{Steel of the present invention} A9 FH 510 6 82 _M NOX503F 1000 2 ^{Comparative steel} A10 FH 520 7 85 _{£ 1} NOX503F 970 1 ^{Comparative steel} Al 1 FH 510 6 85 _28. NÜX5Q3F B20 1 ^{Comparative steel} Al 2 FH 620 10 84 180 NOX503F 1790 i ^{Comparative steel} A13 FH 580 8 89 65 NOX503F 2050 _£ ^{Comparative steel} A14 FH 600 9 85 200 NOX503F 3720 ₁ ^{Comparative steel} AIS FH 570 8 87 240 NOX504F 4890 _í ^{Comparative steel} B1 HR 5B0 12 85 230 NOX503F 490 1 ^{Steel of the present invention} C1 CR 590 6 86 160 NOX503F 420 1 ^{Steel of the present invention} 01 FH 560 8 85 100 NOX5O0F 550 1 ^{Steel of the present invention} E1 FH 560 7 83 100 NOX503F 1030 2 ^{Steel of the present invention} F1 FH 570 6 88 140 NOX503F 1200 3 ^{Steel of the present invention} G1 FH 610 8 93 200 NOX503F 820 1 ^{Steel of the present invention} H1 FH 600 10 89 130 NQX503F 670 1 ^{Steel of the present invention} 11 FH 580 8 86 240 NOX503F 980 0 ^{Steel of the present invention} ai FH 550 9 90 80 NOX503F 1180 2 ^{Steel of the present invention} K1 FH 570 8 84 160 NOX503F 630 1 ^{Steel of the present invention} L1 FH 590 9 88 220 NOX503F 940 0 ^{Steel of the present invention} M1 FH 600 6 90 200 NOX503F 430 1 ^{Steel of the present invention} NI FH ESO S 83 200 NOX503F 570 1 ^{Steel of the present invention} N2 FH 560 9 89 80 NOX503F 090 1 ^{Steel of the present invention} N3 FH 550 11 92 70 NOX503F 700 1 ^{Steel of the present invention} N4 FH 000 10 94 120 NOX503F 800 1 ^{Steel of the present invention} N5 FH 520 7 02 _m NOX503F 760 1 ^{Comparative steel} N6 FH 530 7 83 _28. NOX503F SO 1 ^{Comparative steel} N7 FH 59 0 8 06 210 NOX503F ^- 0 ^{Comparative steel} N6 FH 570 9 87 190 NOX504F 3560 _£ ^{Comparative steel N9 FH 600 9 82 200 NOX503F 4820} a ^{Comparative steel} N10 FH 580 8 88 240 NOX503F 6090 _i ^{Comparative steel} 01 HR 590 8 94 240 NOX503F 1220 2 ^{Steel of the present invention} P1 CR 580 7 86 200 NOX503F 890 1 ^{Steel of the present invention} Q1 FH 580 9 86 180 NOX503F 300 1 ^{Steel of the present invention} R1 HR 590 8 83 200 NOX503F 1370 3 ^{Steel of the present invention} _SI FH 560 9 B9 200 NOX503F 880 1 ^{Steel of the present invention} _al FH 590 8 85 240 NOX503F 590 1 ^{Comparative steel bl = * 2 = * 2. = S 2 = * 2} = * 2 ^{= 232. = 52.} = * 2 ^{Comparative steel} GÍ FH 580 8 84 240 NOX503F 1260 2 ^{Comparative steel} di FH 480 7 86 _{i ñ} NOX503F 2450 2 ^{Comparative steel} _{© 1} FH 570 9 90 270 NOX503F 990 1 ^{Comparative steel f!} = 22 z ££ L = 3 £ = 22 = 22 = 22 ^{= * 2.} = * 2 ^{Comparative steel ei FH 580 9 88 210 NOX503F 1210 1 Comparative steel} h1 ^{FH 560 8 92 180 NOX503F 1040 0 Comparative steel} _n FH 580 7 89 220 NOX503F 1300 1 ^{Comparative steel} _Ji FH 570 8 88 200 NOX503F 1230 2 ^{Comparative steel} k1 FH 640 8 85 190 NOX503F 840 1 ^{Comparative steel} n FH 610 9 82 80 NOX503F 900 2 ^{Comparative steel} _m1 FH 560 9 93 280 NOX5O0F 1000 1 ^{Comparative steel} _n1 FH 560 9 86 180 NOX503F 570 1 ^{Comparative steel} * 1 means that FH: left as cold rolled, HR: hot rolled steel sheet, and CR: hot rolled steel sheet tempered after cold rolling * 2 means that the Mn is excessively high, many fractures occur during casting and rolling time hot rolled, and could not produce hot rolled steel sheet

The finished sheet thickness of the hot rolled steel sheet provided for hot stamping as the hot rolled steel sheet was made 1.6mm. The sheet thickness of the hot rolled steel sheet provided for cold rolling was made 3.2 mm. When pickling was carried out under the conditions of Table 2 below, and cold rolling was carried out, the thickness of the sheet was made 50% (3.2mm ^ 1.6mm). After that, annealing was carried out for some of the steel sheets in a continuous annealing facility, and the steel sheets were converted into cold rolled steel sheets. After that, using NOX-RUST503F (manufactured by PARKER INDUSTRIES, INC.), NOX503F (manufactured by PARKER INDUSTRIES, INC.) Was applied to the hot rolled steel sheets and cold rolled steel sheets by means of a machine. electrostatic oiled, in a non-oil coating range up to 6090 mg / m2.

After that, the steel sheets were cut into a predetermined size, after which, electric heating was carried out up to 900 ° C at 50 ° C / second, retention was carried out for 10 seconds at 900 ° C, it was then allowed to cool for 10 seconds and hardening was carried out in the hot shallow drawing dies described above at a temperature of 650 ° C or higher. The obtained hot stamping formed bodies were visually observed, and the steel sheets without scale peeling were determined as the steel sheets with excellent scale adhesion.

Regarding the corrosion inhibiting property, retention was carried out for 30 days at room temperature, and the steel sheets without corrosion generated on the surfaces of the steel sheets were defined as the steel sheets with excellent corrosion inhibition property. In combination, with the use of flat sheet test pieces, hot stamping was performed under the conditions mentioned above, and the tensile characteristics were evaluated. The result of the evaluation is shown in Table 3.

A1 FH 3.7 4 6 0 O Presence 1555 Comparative steel A2 FH 3.6 5 5 0 O Absence 1562 Steel of the present invention A3 FH 4.0 4 8 0 _O Absence 1560 Steel of the present invention A4 FH 4.4 5 9 0 _O Absence 1559 Steel of the present invention A5 FH 4 2 4 6 0 _O Absence 1555 Steel of the present invention A6 FH 4.5 6 8 0 _O Absence 1550 Steel of the present invention ^{A7 FH 3 J3 6 7 0} o ^{Absence 1557 Steel of the present invention A8 FH 26 5 4 3} or ^{Absence 1562 Steel of present invention} A9 FH 22 2 Q. 11 A Absence 1562 Comcarative steel A10 FH UL 3 1 11 x Absence 1554 Comcarative steel Alt FH ZA 2 2 a. A Absence 1504 Comparative steel A12 FH 46 1 í 7 14 A Absence 1548 Comparative steel AIS FH 2.6 11 4 m _X Absence 1556 Comparative steel A14 FH 3.8 15 3 14. x Absence 1560 Comparative steel AIS FH 36 _ia 7 _{ea X} Absence 1567 Steel comparative 61 HR 58 4 13 0 _O Absence 1549 Steel of the present invention C1 O í 4.1 4 6 0 _O Absence 1403 Steel of the present invention D1 FH 3.7 3 5 0 _O Absence 1529 Steel of the present invention The FH 38 3 8 0 _O Absence 1550 Steel of the present invention ^{F1 FH 3.7 7 7 0} o ^{Absence 1625 Steel of the present invention £ 31 FH 45 4 0 0} o ^{Absence 1572 Steel of the present invention H1 FH 4.6 4 6 0} o ^{Absence 1645 Steel of the present invention 11 FH 4.4 5 6 0} o ^{Absence 1687 Steel of the present invention U1 FH 38 5 8 0} o ^{Absence 1639 Steel of the present invention K1 FH 4.0 3 7 0} o ^{Absence 1752 Steel of the present invention L1 FH 45 4 8 0} o ^{Absence 1624 Steel of the present invention MI FH 43 4 7 0} or ^{Absence 1715 Steel of the present invention N1 FH 4.4 4 7 0} o ^{Absence 1834 Steel of the present invention N2 FH 3.9 3 6 0} o ^{Absence 182B Steel of the present invention N3 FH 32 3 5 0} o ^{Absence 1833 Steel of the present invention m FH 45 4 10 0} o ^{Absence 1829 Steel of the present invention} m FH Z2 2 Q. _a A Absence 1830 Comparative steel N0 FH 18 3 1 _ta A Absence 1826 Comparative steel N7 FH 3.9 4 B 0 _O Presence 1834 Comparative steel NB FH 46 m 8 _aa X Absence 1823 Comparative steel N9 FH 43 m 7 _{4 Z} X Absence 1035 Comparative steel N10 FH 45 _{2 1} B 4 & _X Absence 1830 Comparative steel 01 HR 5.3 4 13 0 O Absence 1054 Steel of the present invention P1 CR 4.4 4 8 0 _O Absence 1847 Steel of the present invention ^{01 FH 4.7 4 9 0} o ^{Absence 2100 Steel of the present invention R1 HR 6.0 4 12 0} o ^{Absence 2138 Steel of the present invention S1 FH 39 3 7 0} o ^{Absence 2505 Steel of the present invention to FH 4.3 4 B 0} or ^{Absence 1054 Comparative steel} b1 FH Z * 2 Z52. = & _{= * £} Comparative steel el FH _M m _{Q aa} X Absence 1483 Comparative steel _di FH 18 _{i QMX} Absence 1598 Comparative steel _el FH 33 4 9 0 _O Absence 987 Comparative steel _n FH z * 2 Z * 2 1 * 2 1 * 2 - * £ Comparative steel et FH 43 5 8 _{92 X} Absence 1604 Comparative steel h1 FH 4.1 4 6 0 _O Absence U § 6 Comparative steel ^{II FH 4.0 5 7 0} or ^{Absence 1095 Comparative steel} _J1 ^{FH 46 4 7 0} o ^{Absence 1023 Comparative steel k1 FH 4.4 7 11 0} or ^{Absence 1154 Comparative steel n FH 4.1 5 8 0} or ^{Absence 1072 Comparative steel m1 FH 33 4 5 0} or ^{Absence - * 3 Comparative steel n1 FH 45 4 7 0} or ^{Absence 1006 Steel comparative} * 1 means that FH: left cold rolled, HR: hot rolled steel sheet, and CR: hot rolled steel sheet tempered after rolling * 2 means that Mn is excessively high, many casting fractures and hot rolling time, and could not produce hot rolled steel sheet

* 3 means that at the time of hot stamping, a fracture occurred with inclusion as the starting point, and the tensile test could not be carried out with forming

Regarding the tensile characteristics, the tensile test pieces that were in accordance with JIS Z 2201 were extracted, the tensile test was carried out in accordance with JIS Z 2241, and the maximum tensile strength. The formed bodies having the maximum tensile strength of 1180 MPa or more were determined as the formed bodies of the present invention.

Analysis of the composition of the inlays of the formed bodies was carried out by X-ray diffraction cutting sheets from the bottoms of the cylindrical portions of the shallow drawn test pieces. From the maximum strength ratios of the respective oxides, the volume ratios of the respective Fe oxides were measured. Si oxides were hardly present and the volume ratio was less than 1%, and thus quantitative evaluation by X-ray diffraction was difficult. However, it could be confirmed that Si oxides were present at the interface between scale and base iron by linear analysis of EPMA.

Regarding the evaluation of the irregularities in the interfaces of the inlays and the base irons formed in the formed bodies, a built-in polishing was carried out for the steel sheets cut from the position described above, and then the observation was made by SEM with a power of 3000 of the section perpendicular to the rolling direction. Five visual fields were observed in each of the test pieces, and the numerical density of the irregularities was measured in the range of 0.2 pm to 1.0 pm per 100 pm length.

The bodies formed satisfying the conditions of the present invention were able to make compatible excellent corrosion inhibition properties and excellent scale adhesion. The bodies formed that did not satisfy the conditions of the invention were inferior in scale adhesion, or inferior in corrosion resistance.

Industrial applicability

According to the present invention, the steel sheet of excellent inlay adhesion at the time of hot stamping can be provided, the problems of wear and tear of the die at the time of hot stamping, plating adhesion to the matrix and accompanying indentation defects, and thus the present invention can produce significant productivity improvement and is of industrially great value.

Claims (12)

1. A steel sheet for hot stamping, comprising a composition containing: in% by mass, C: from 0.100% to 0.600%; Yes: from 0.50% to 3.00%; Mn: from 1.20% to 4.00%; Ti: from 0.005% to 0.100%; B: from 0.0005% to 0.0100%; P: 0.100% or less; S: from 0.0001% to 0.0100%; Al: from 0.005% to 1,000%; N: 0.0100% or less; Ni: from 0% to 2.00%; Cu: from 0% to 2.00%; Cr: 0% to 2.00%; Mo: from 0% to 2.00%; Nb: from 0% to 0.100%; V: from 0% to 0.100%; W: from 0% to 0.100%, and a total of one type or two or more types selected from a group consisting of REM, Ca, Ce and Mg: 0% to 0.0300%, the remainder being Fe and impurities, in which the surface roughness of the steel sheet satisfies 8.0 pm> Rz> 2.5 pm, and a coating oil is applied on a surface in an amount of 50 mg / m2 to 1500 mg / m2, and in which a amount of S contained in the coating oil that is applied on the steel sheet is 5% or less by mass%, where The Rz was determined by measuring the region of a length of 10 mm with n = 3, with the use of an instrument for measuring the roughness of the contact surface (SURFCOM2000DX / SD3 manufactured by TOKYO SEIMITSU CO., LTD) with an angle of probe tip of 60 °, and a point R of 2 pm and determining the mean value as the roughness of the surface Rz of each of the steel sheets. 2. The steel sheet for hot stamping according to claim 1, in which the composition of the steel sheet contains, in% by mass, one type or two or more types selected from a group consisting of Ni: from 0.01% to 2.00%; Cu: from 0.01% to 2.00%; Cr: from 0.01% to 2.00%; Mo: from 0.01% to 2.00%; Nb: from 0.005% to 0.100%; V: from 0.005% to 0.100%; Y W: from 0.005% to 0.100%. 3. The steel sheet for hot stamping according to claim 1 or 2, in which the composition of the steel sheet contains, in% by mass, a total of 0.0003% to 0.0300% of one type or two or more types selected from the group consisting of REM, Ca, Ce and Mg. 4. A method of producing a steel sheet for hot stamping, comprising: a step of casting a slab containing, in% by mass, C: from 0.100% to 0.600%; Yes: from 0.50% to 3.00%; Mn: from 1.20% to 4.00%; Ti: from 0.005% to 0.100%; B: from 0.0005% to 0.0100%; P: 0.100% or less; S: from 0.0001% to 0.0100%; Al: from 0.005% to 1,000%; N: 0.0100% or less; Ni: from 0% to 2.00%; Cu: from 0% to 2.00%; Cr: from 0% to 2.00%; Mo: from 0% to 2.00%; Nb: from 0% to 0.100%; V: from 0% to 0.100%; W: from 0% to 0.100%, and a total of one type or two or more types selected from a group consisting of REM, Ca, Ce and Mg: 0% to 0.0300%, the remainder being Fe and impurities, and hot rolling the slab directly or allowing the slab to cool and heating the slab to obtain a hot rolled steel sheet; a step of pickling the hot rolled steel sheet for 30 seconds or more in an aqueous solution having a temperature of 80 ° C to less than 100 ° C and which includes an inhibitor being an acid concentration of 3% in mass to 20% by mass; Y a step of applying a corrosion inhibiting oil to the steel sheet after pickling. wherein a remaining amount of corrosion inhibiting oil on a steel sheet surface is limited to 50 mg / m2 to 1500 mg / m2, and wherein an amount of S in the corrosion inhibiting oil that is applied to steel sheet is 5% or less by mass%. The method of producing a hot stamping steel sheet according to claim 4, further comprising: a stage of cold rolling the hot rolled steel sheet that has been pickled to obtain a cold rolled steel sheet, wherein the corrosion inhibiting oil is applied to the cold rolled steel sheet. The method for producing a hot stamping steel sheet according to claim 4, which further includes: a stage of cold rolling the hot-rolled steel sheet that has been pickled, and further carrying out a heat treatment in a continuous annealing facility or in a box-type annealing furnace to obtain a cold-rolled steel sheet, wherein the corrosion inhibiting oil is applied to the heat treated cold rolled steel sheet. The method for producing a hot stamping steel sheet according to any one of claims 4 to 6, wherein a slab composition contains, in mass%, one type or two or more types selected from a group consisting of Ni: from 0.01% to 2.00%, Cu: from 0.01% to 2.00%, Cr: from 0.01% to 2.00%, Mo: from 0.01% to 2.00%, Nb: from 0.005% to 0.100%, V: from 0.005% to 0.100%, and W: from 0.005% to 0.100%. The method for producing a hot stamping steel sheet according to any one of claims 4 to 7, wherein a slab composition contains, in mass%, a total of 0.0003% to 0.0300% of one type or two or more types selected from the group consisting of REM, Ca, Ce and Mg. 9. A body formed by hot stamping, comprising a composition containing: by mass%, C: from 0.100% to 0.600%; Yes: from 0.50% to 3.00%; Mn: from 1.20% to 4.00%; Ti: from 0.005% to 0.100%; B: from 0.0005% to 0.0100%; P: 0.100% or less; S: from 0.0001% to 0.0100%; Al: from 0.005% to 1,000%; N: 0.0100% or less; Ni: from 0% to 2.00%; Cu: from 0% to 2.00%; Cr: from 0% to 2.00%; Mo: from 0% to 2.00%; Nb: from 0% to 0.100%; V: from 0% to 0.100%; W: from 0% to 0.100%, and a total of one type or two or more types selected from a group consisting of REM, Ca, Ce and Mg: 0% to 0.0300%, the remainder being Fe and impurities, in which three or more irregularities in a range of 0.2 gm to 8.0 gm in depth are present per 100 gm at an interface between the scale and a base iron, and the tensile strength is 1180 MPa or more, and in which a thickness of the inlays is 10 gm or less. 10. The body formed by hot stamping according to claim 9, wherein an oxide of Si, FeO, Fe3Ü4 and Fe2Ü3 are included in a surface of the body formed by hot stamping. The body formed by hot stamping according to claim 9 or 10, wherein the composition of the hot stamping body contains, in mass%, one type or two or more types selected from a group consisting of Ni: from 0.01% to 2.00%, Cu: from 0.01% to 2.00%, Cr: from 0.01% to 2.00%, Mo: from 0.01% to 2.00%, Nb: from 0.005% to 0.100%, V: from 0.005% to 0.100%, and W: from 0.005% to 0.100%. 12. The body formed by hot stamping according to any one of claims 9 to 11, wherein the composition of the hot stamping body contains, in mass%, a total of 0.0003% to 0.0300% of one type or two or more types selected from the group consisting of REM, Ca, Ce and Mg.