CN100471595C - Hot pressing method of high-strength parts using steel plate and hot-pressed parts - Google Patents

Abstract

The present invention provides a hot-pressing method and hot-pressed parts using hot-rolled and cold-rolled steel sheets, Al-based steel sheets, or Zn-based coated steel sheets that can obtain a strength of 1200 MPa or more after high-temperature forming and have a very low possibility of hydrogen embrittlement. The hot pressing method of high-strength automobile parts according to the present invention is characterized in that a steel sheet containing 0.05 to 0.5% by mass of C in the steel composition, or a steel sheet coated mainly with Al or Zn is used, and the hot pressing method is used. When manufacturing automotive parts, the heating temperature before stamping is specified to be not less than Ac ₃ and not more than 1100°C, the hydrogen concentration in the heating atmosphere is not more than 6% by volume, and the dew point is not more than 10°C. The hot-pressed part of the present invention is made by using the above-mentioned hot-pressing method.

Description

Hot pressing method of high-strength parts using steel plate and hot-pressed parts

technical field

The invention relates to a hot-pressing method and hot-pressing parts when using cold-rolled or hot-rolled steel sheets or Al- or Zn-plated steel sheets to manufacture automobile pillars, door inner anti-collision beams, bumper beams and other strength parts.

Background technique

In order to reduce the weight of automobiles due to global environmental problems, it is necessary to increase the strength of steel sheets used in automobiles as high as possible. However, when the strength of steel sheets is generally increased, the elongation and r-value decrease, and the formability deteriorates. In order to solve such a problem, Japanese Unexamined Patent Application Publication No. 2000-234153 discloses a technique of forming at a medium temperature and utilizing the heat at this time to improve the strength. In this technique, the components in the steel are appropriately controlled, heating is performed in the ferrite temperature range, and the strength is improved by precipitation strengthening in the temperature range.

In addition, JP-A-2000-87183 proposes a high-strength steel sheet whose yield strength at the forming temperature is significantly lower than that at normal temperature for the purpose of improving press forming accuracy. However, in these techniques, there is a possibility that the strength obtained is limited. On the other hand, for the purpose of obtaining higher strength, Japanese Patent Application Laid-Open No. 2000-38640 proposes an austenite single-phase region heated to a high temperature after forming, and the phase transformation becomes hard during the subsequent cooling process. phase technology.

However, when heating and rapid cooling are performed after forming, there is a possibility that problems may arise in shape accuracy. As a technique to overcome this disadvantage, documents (SAE, 2001-01-0078) and Japanese Patent Application Laid-Open No. 2001-181833 disclose a technique in which a steel plate is heated to the austenite single-phase region, and thereafter, during press forming , Cooling is carried out at a cooling rate above the critical cooling rate of the martensitic transformation determined by the steel composition. The former document discloses that an Al-plated steel sheet is used in order to suppress the generation of scale on the surface during heating. In the present invention, such a pressing process is called hot pressing.

The following techniques are mentioned as the prior art related to the hot pressing using such a plated steel sheet. In Japanese Patent Application Laid-Open No. 2003-147499, an example of using a steel plate coated with a Fe-Zn alloy for hot pressing is disclosed. An example of a hot-pressed Al-based steel plate coated with a coating layer.

In addition, JP-A-2002-282951 discloses an example in which, as a method of punching a heated metal sheet using dies and punches, the gap between dies is specified from the viewpoint of formability and hardenability.

Contents of the invention

In this way, the higher the strength of the high-strength steel sheets used in automobiles, the more the above-mentioned formability problems. In particular, in high-strength materials exceeding 1000 MPa, hydrogen embrittlement (also sometimes called Strain aging cracking, hysteresis failure) is an essential subject. Therefore, when using it as a steel sheet for hot pressing, it is important to reduce the hydrogen content of the billet.

The present invention is an invention made to solve the above-mentioned problems, and provides a hot-rolled cold-rolled steel sheet, an Al-based steel sheet, or a Zn-plated steel sheet that can obtain a strength of 1200 MPa or more after high-temperature forming and has a very small possibility of hydrogen embrittlement. The invention relates to a hot pressing method and hot pressing parts of a steel plate.

The inventors of the present invention conducted various studies in order to solve the above-mentioned problems. As a result, it was found that controlling the atmosphere and temperature during heating to the austenite single-phase region before stamping is extremely important for producing hot-pressed parts excellent in hydrogen embrittlement resistance. That is, when hydrogen is contained in the atmosphere during heating, the hydrogen penetrates into the steel sheet, and even if moisture is contained, hydrogen may similarly penetrate into the steel sheet, so it is important to reduce these components. In addition, in order to prevent hydrogen embrittlement, it is important to properly select the gap of the mold. The gist of the present invention based on the above-mentioned findings is as follows.

(1) A hot pressing method for high-strength automobile parts, characterized in that a steel sheet containing 0.05 to 0.5% by mass of C in the steel composition, or a steel sheet mainly coated with Al or Zn is used, and hot pressing is used. When manufacturing auto parts by press method, the heating temperature before stamping is specified to be not less than Ac ₃ and not more than 1100°C, the hydrogen concentration in the heating atmosphere is not more than 6% by volume, and the dew point is not more than 10°C.

(2) The method for hot-pressing high-strength automobile parts according to (1), wherein the hydrogen concentration in the heating atmosphere is 1% by volume or less, and the dew point is 10°C or less.

(3) The hot pressing method as described in (1) or (2), characterized in that when the heated steel plate is introduced into a press for forming, the clearance between the die and the punch is equal to the plate thickness of the steel used. 1.0 to 1.8 times of that.

(4) A hot-pressed part produced by using the hot-pressing method described in any one of (1) to (3).

Description of drawings

FIG. 1 is an outline view of a hat-shaped mold used in a processing test of an example.

Detailed ways

The reasons for the limitations of the present invention will be described below.

As mentioned above, in the present invention, after heating hot-rolled or cold-rolled steel sheets, or Al-based or Zn-based coated steel sheets to 700°C or higher, they are hot-formed, cooled and quenched in a mold immediately to obtain desired strength, and then In the present invention, the steel sheet before heating and press forming is specified. As a steel sheet component, excellent hardenability is required, and for this purpose, the amount of C needs to be 0.05% or more, preferably 0.1% or more. Regarding other elements in steel, elements such as Si, Mn, Ti, B, Cr, Mo, Al, P, S, and N are sometimes added. Si has an effect on fatigue properties, and when Si is contained, it is preferably 0.05 to 1%. Mn, B, Cr, and Mo contribute to the improvement of hardenability. When these elements are contained, Mn: 0.5 to 3%, B: 0.05% or less, Cr: 2% or less, and Mo: 0.5% or less are preferable. Ti and Al improve the oxidation resistance of the Al-plated steel sheet, and when these elements are contained, Ti: 0.5% or less and Al: 0.1% or less are preferable.

Steel sheets with Al-based or Zn-based plating as the type of plating are conceivable, and when these steel sheets are used for hot pressing, the generation of iron oxide on the surface can be suppressed and corrosion resistance can be imparted.

First, the structure of the Al-based plating layer will be described. Al-based plated steel sheets have been manufactured for various applications, and the present invention can use these steel sheets. There is a steel sheet that contains Al as a main component in the composition of the Al-based coating, and preferably contains 3 to 15% of Si in order to suppress the formation of an alloy layer during hot-dip Al plating. In addition, there are Cr, Mg, Ti, Sn, and the like as elements that further improve the corrosion resistance of the plating layer, and these elements may be added. In this case, it is preferable to contain Cr: 0.1 to 1%, Mg: 0.5 to 10%, Ti: 0.1 to 1%, and Sn: 1 to 5%. In addition, the Al-based plating layer contains Fe as an impurity, and the amount of this Fe is usually 0.05 to 0.5%.

Furthermore, intermetallic compounds such as FeAl ₃ , Fe ₂ Al ₅ , Fe ₃ Al, Fe ₂ Al ₈ Si can be formed on the surface after heating. These phases tend to form a multilayer structure, typically a five-layer structure, but the phase structure of these phases does not impair the gist of the present invention. In addition, as its composition, Al and Fe are the main components, and when Si is added to the Al plating bath, about 5 to 10% of Si is also contained. The total composition of these elements accounts for more than 90%. In addition, a trace amount of unalloyed AI may remain, but if it is a small amount, there is no particular influence on performance. Al-based oxides and nitrides cover the surface after heating, but their amounts are not particularly specified.

Next, the constitution of the Zn-based plating layer will be described. As the Zn-based plated steel sheet, steel sheets with various compositions have been produced, and the present invention can use these steel sheets. As a typical composition of Zn-based coatings, the following compositions can be cited: Zn-0.2%Al, Zn-5%Al-0.1%Mg, Zn-5%Al-0.1%Mg-mixed rare earth alloy, Zn-7 %Al-3%Mg, Zn-11%Al-3%Mg-0.1%Si, Zn-55%Al-1.6%Si and so on. In addition, Zn-0.1%Al bath plating followed by heating to have a configuration such as Zn-10%Fe. In addition, there are Cr, Mg, Ti, Sn, and the like as elements that further improve the corrosion resistance of the plating layer, and these elements may be added. In this case, it is preferable to contain Cr: 0.1 to 1%, Mg: 0.5 to 10%, Ti: 0.1 to 1%, and Sn: 1 to 5%.

Furthermore, after heating, intermetallic compounds such as ζ, δ ₁ , Γ, Γ _1, etc., and a ferrite phase in which Zn is solid-dissolved can be formed on the surface. These phases may be distributed in a layered form or in a granular form, but what kind of phase structure they have does not impair the gist of the invention of the present application. In addition, if it is a plating layer containing Al as its composition, the above-mentioned Fe—Al-based compound may be generated in some cases. In the case of Zn-based plating, a Zn-based or Al-based oxide film is formed after heating, but even if these substances are formed, the gist of the present invention is not impaired.

There are no particular limitations on the deposition amount, pre-plating treatment, and post-plating treatment of the Al-based and Zn-based plating layers, but the deposition amount of the plating layer is preferably 50 g/m ² or more on one side. The reason is that the more the amount of plating is deposited, the more effective the effect of inhibiting oxidation during heating and the corrosion resistance when forming parts after heating and forming is improved. As the post-plating treatment, for the purpose of primary rust prevention and lubricity, there may be chromate treatment, resin coating treatment, etc., but since the organic resin disappears when heated, it is not preferable. In the chromate treatment, considering the hexavalent chromium restriction in recent years, a trivalent treatment film such as electrolytic chromate is also preferable. In the case of an Al-based plated steel sheet having excellent corrosion resistance, only oil coating may be performed without providing a chromate film.

In the present invention, the temperature and atmosphere at the time of heating are specified, and the temperature is specified to be not less than Ac ₃ and not more than 1100°C. This is because, in order to completely transform the steel plate into the austenite single-phase region, it needs to be above the Ac ₃ temperature. On the other hand, if the heating temperature is too high, the surface will be oxidized, or the intrusion of hydrogen into the steel will become active. . When using a Zn-based coating, in addition, since the boiling point of Zn is about 910°C, if the temperature is too high, Zn will completely evaporate and the oxidation of the steel sheet will become intense, so 1000°C is preferably the upper limit. More preferably, the upper limit temperature is 920°C. The lower limit temperature is preferably 800°C. The reason is that even if the steel plate is heated to Ac ₃ temperature or higher, the temperature will drop when the steel plate is taken out from the furnace and transferred to the press after heating, and ferrite will be formed.

In the heating atmosphere, the hydrogen concentration is set to be 6% by volume or less. This is because, as described above, hydrogen penetrates into the steel to increase the possibility of hydrogen embrittlement. The lower limit of the hydrogen concentration is not particularly set, and the hydrogen concentration is preferably low. More preferably, the amount of hydrogen is 1% or less. The present invention finds that the moisture in the atmosphere can also easily intrude into the steel in the form of hydrogen. Therefore, it is preferable that the moisture in the atmosphere is also low. From a practical point of view, the moisture content is measured by measuring the dew point, and the upper limit of the dew point is made 10°C. In addition, the following formula is known about the conversion of a dew point and a moisture content, and the moisture content at this time is 1.2 volume%. In particular, when a Zn-based plated steel sheet is used, when oxygen is contained in the atmosphere, Zn oxides tend to be formed on the surface of the steel sheet to suppress evaporation of Zn. Therefore, when using a Zn-based plated steel sheet, it is preferable to contain 1 to 21% of oxygen in the atmosphere. In addition, not only coated steel sheets but also uncoated steel sheets (bare materials) have hydrogen intrusion during heating, so it is necessary to manage the hydrogen concentration and moisture content in the heating atmosphere.

Mathematical formula 1

$\mathrm{<span\; class="notranslate">\; p</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; o</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 44016</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 118.774</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; Tdp</span>}}{\mathrm{<span\; class="notranslate">\; 8.314</span>}<span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; Tdp</span>}}<span\; class="notranslate">\; )</span>$

pH ₂ O: hydrogen concentration (volume fraction); Tdp: dew point (absolute temperature)

There are no special regulations on the heating method, and radiation heating can be carried out by using a radiant tube, etc., or induction heating, electric heating, etc. can be used. The heating rate at this time is not limited, either. This of course greatly depends on the plate thickness, shape.

Hot pressing is characterized in that it cools from the austenite phase to obtain a quenched structure, and of course the cooling rate after heating also has a large influence. In the present invention, it is necessary to cool at or above the critical cooling rate for obtaining a martensitic structure determined by steel components, and the average cooling rate from 700°C to 350°C as a target value is preferably 15°C/s or more. It can be considered that the cooling rate depends on the steel composition. For steel with good hardenability, the desired martensite-based structure can be obtained even if the cooling rate is about 20°C/sec. , Sometimes a cooling rate of about 30°C/sec is required.

During punching, the clearance between the die and the punch is one of the important factors, and in the present invention, the clearance is preferably 1.0 to 1.8 times the thickness of the plate. It is considered that, if the gap is narrow, the sheet becomes difficult to enter, and the steel sheet surface becomes sticky, which may become a starting point of hydrogen embrittlement. Also, if the gap is wide, it tends to be difficult to be hardened, uneven strength occurs in the part, residual stress remains in the part, and the possibility of hydrogen embrittlement increases.

Example

The present invention will be described in more detail below using examples.

Example 1

Cold-rolled steel sheets with a thickness of 1.4 mm having the steel components shown in Table 1 were heated under various conditions, and formed using a hat-shaped die shown in FIG. 1 . The gap is specified as 1.1 times the thickness of the plate. Then, 10 points of Φ5 mm and a gap of 0.5 mm (both sides) were punched on the edge of the cap. After 7 days, the punched part was observed with a magnifying glass of 20 times to determine whether there were micro cracks. Heating is performed by inserting the sample into an electric furnace with a controlled atmosphere. The heating time up to 900°C is about 4 minutes, the time from the furnace to the press is about 10 seconds, and the pressing start temperature is about 750°C. Cooling is carried out in the mold with an average cooling rate of 40°C/sec from 700°C to 350°C. Table 2 shows the heating conditions and the presence or absence of microcracks. Furthermore, a part was cut out after cap forming and measured for Vickers hardness under a load of 10 kgf. As a result, the overall level was in the range of Hv: 410 to 510, and the structure showed a martensitic structure. In addition, iron oxide was generated on the surface of these steel sheets after hot pressing.

No. 7 of Example 1 had five or more microcracks due to its high dew point. In No. 1 and No. 3, since the amount of hydrogen was 1% or more, a small amount of cracks occurred.

Table 1

symbol C Si mn P S Al N Ti Cr Mo B A 0.15 0.1 2.1 0.01 0.004 0.03 0.004 0.02 0.4 0.01 0.003 B 0.21 0.2 0.9 0.02 0.005 0.015 0.005 0.01 0.9 0.4 0.004 C 0.27 0.15 0.88 0.01 0.002 0.02 0.004 0.02 0.23 0.5 0.003

Table 2

Scoring of Microcrack Occurrence

Total number of microcracks in 10 points: o: 0; ○: 1; △: less than 5; ×: 5 or more.

Example 2

Hot-dip Al plating was performed using cold-rolled steel sheets (sheet thickness: 1.4 mm) having the steel components shown in Table 3 that had undergone normal hot-rolling and cold-rolling processes as materials. Hot-dip Al plating uses a non-oxidizing furnace-reduction furnace type production line. After plating, the coating adhesion is adjusted to 80g/m ² on one side by gas friction method, and then cooled. The composition of the plating bath at this time was Al-10%Si-2%Fe, and the bath temperature was 660°C. Fe in the bath is an unavoidable element supplied by the plating equipment or lath. The appearance of the plating layer was good because there was no non-plating or the like. The hot-dipped Al-coated steel sheets produced in this way were heated under various conditions, and then formed using a hat-shaped die as shown in FIG. 1 . The gap is specified as 1.1 times the thickness of the plate. Then, 10 points of Φ5 mm and a gap of 0.5 mm (both sides) were punched on the edge of the cap. After 7 days, the punched part was observed with a magnifying glass of 20 times to determine whether there were micro cracks. Heating is performed by inserting the sample into an electric furnace with a controlled atmosphere. The heating time up to 900°C is about 4 minutes, the time from the furnace to the press is about 10 seconds, and the pressing start temperature is about 750°C. Cooling is carried out in the mold with an average cooling rate of 40°C/sec from 700°C to 350°C. Table 4 shows the heating conditions and the presence or absence of microcracks. Furthermore, a part was cut out after cap forming and measured for Vickers hardness under a load of 10 kgf. As a result, the overall level was in the range of Hv: 410 to 510, and the structure showed a martensitic structure. In addition, iron oxide did not occur on the surface of these steel sheets after hot pressing.

table 3

C Si mn P S Al N Ti Cr Mo B 0.22 0.21 1.20 0.02 0.003 0.027 0.003 0.002 0.18 0.02 0.0018

Table 4

Scoring of Microcrack Occurrence

Total number of microcracks in 10 points: ○: 0; ○: 1; △: less than 5; ×: 5 or more.

As shown in Table 4, depending on the heating atmosphere and temperature, the amount of hydrogen intruded into the steel also changes, and the sensitivity to microcracks also changes. In No. 5 having a hydrogen concentration of 10 vol%, and No. 7 having a dew point of 15° C., five or more cracks were observed. As the hydrogen concentration and dew point decrease, the occurrence of cracks is more suppressed, but in the case of Nos. 6, 10, and 15, a little cracks occurred.

Example 3

Various Zn-based platings were performed using cold-rolled steel sheets with a sheet thickness of 1.4 mm having the steel components shown in Table 5. FIG. Table 6 shows the coating type, bath composition, and bath temperature at this time. Using these Zn-based plated steel sheets, cap forming was carried out in the same manner as in Example 1, and the penetration mode of microcracks was observed after punching. Table 7 shows the relationship between the heating conditions and the occurrence of cracks at this time. Cooling is carried out in the mold with an average cooling rate of 20°C/sec from 700°C to 350°C. The cross-sectional hardness after forming was measured in the same manner as in Example 1, all of which were between Hv: 410 to 510, and the structure also showed a martensitic structure. In addition, iron oxide did not occur on the surface of these steel sheets after hot pressing.

table 5

symbol C Si mn P S Al N Ti Cr Mo B A 0.15 0.1 2.1 0.01 0.004 0.03 0.004 0.02 0.4 0.01 0.003 B 0.21 0.2 0.9 0.02 0.005 0.015 0.005 0.01 0.9 0.4 0.004 C 0.27 0.15 0.88 0.01 0.002 0.02 0.004 0.02 0.23 0.5 0.003

Table 6

symbol Coating composition Single side adhesion (g/m²) Bath temperature (℃) GI Zn-0.2%Al 85 460 GA Zn-10.5%Fe 70 460 GL Zn-55%Al-1.6%Si 75 610 GAM Zn-6%Al-3%Mg 65 420 GAMS Zn-11%Al-3%Mg-0.1%Si 80 430

Table 7

Scoring of Microcrack Occurrence

Total number of microcracks in 10 points: ○: 0; ○: 1; △: less than 5; ×: 5 or more.

As in Examples 1 and 2, No. 7 in Table 7 had a high dew point, so fine cracks occurred. In No. 1 and No. 3, since the amount of hydrogen was more than 1%, some microcracks occurred. Moreover, since No. 1-3 had a low oxygen concentration, contamination in the furnace and deterioration of the steel plate surface accompanied by evaporation of Zn in the furnace were observed.

Example 4

As a material, cold-rolled steel sheets (sheet thickness: 1.4 mm) having the steel components shown in Table 8 were used through normal hot-rolling and cold-rolling processes. Some of them were subjected to Al hot-dip plating or Zn-based hot-dip plating. Hot-dip plating uses a production line of the non-oxidizing furnace-reduction furnace type. After plating, the gas friction method is used to adjust the coating adhesion amount, and then cooled. The appearance of the obtained coating is not uncoated, which is good. Table 9 shows the coating type, bath composition, and bath temperature.

Table 8

C Si mn P S Al N Ti Cr Mo B 0.22 0.21 1.20 0.02 0.003 0.027 0.003 0.002 0.18 0.02 0.0018

Table 9

symbol Coating composition Single side adhesion (g/m²) Bath temperature (℃) AL Al-10%Si-2%Fe 80 660 GI Zn-0.2%Al 85 460 GA Zn-10.5%Fe 70 460

The steel sheet produced in this way was heated under various conditions, and then formed using a hat-shaped die as shown in FIG. 1 . The gaps during hot pressing are shown in Table 10. Then, 10 points of Φ5 mm and a gap of 0.5 mm (both sides) were punched on the edge of the cap. After 7 days, the punched part was observed with a magnifying glass of 20 times to determine whether there were micro cracks. Heating is performed by inserting the sample into an electric furnace with a controlled atmosphere. The heating time up to 900°C is about 4 minutes, the time from the furnace to the press is about 10 seconds, and the pressing start temperature is about 750°C. Cooling is carried out in the mold with an average cooling rate of 40°C/sec from 700°C to 350°C. Table 10 shows the heating conditions and the presence or absence of microcracks. Furthermore, a part was cut out after cap forming and measured for Vickers hardness under a load of 10 kgf. As a result, the overall level was in the range of Hv: 410 to 510, and the structure showed a martensitic structure.

Table 10

Scoring of Microcrack Occurrence

Total number of microcracks in 10 points: ○: 0; ○: 1; △: less than 5; ×: 5 or more.

For Nos. 1, 7, and 13 in Table 10, five or more microcracks were observed because the die gap during hot pressing was below the predetermined lower limit. For Nos. 6, 12, and 18 in Table 10, since the die gap during hot pressing was more than the specified upper limit, uneven strength occurred, residual stress remained in the part, and five or more microcracks were observed. Nos. 5, 11, and 17 showed a tendency to produce uneven strength and residual stress in the parts due to the large gap between the molds during hot pressing, and thus a few microcracks occurred.

Industrial availability

According to the present invention, hot-rolled, cold-rolled steel sheets, Al-based plated steel sheets, or Zn-based plated steel sheets can be used to manufacture high-strength components by hot pressing, and can be used without hydrogen embrittlement.

Claims (4)

1. the hot-press method of high-strength vehicle parts, it is characterized in that, use following hot rolling Cr, that do not implement plating or the cold-rolled steel sheet of C, 2 quality % that contains 0.05～0.5 quality % in the composition of steel, when adopting pressure sintering to make automobile component, the heating-up temperature before the punching press is defined as Ac ₃More than, below 1100 ℃, the hydrogen concentration of heating atmosphere is defined as below the 2 volume %, dew point is defined as more than-10 ℃, below 6 ℃, and oxygen concentration is defined as 0.3～21 volume %.

2. the hot-press method of high-strength vehicle parts, it is characterized in that, use on the steel plate of the C, the Cr below the 2 quality % that in composition of steel, contain 0.05～0.5 quality % and implemented the steel plate as the plating of main body with Al, when adopting pressure sintering to make automobile component, the heating-up temperature before the punching press is defined as Ac ₃More than, below 1100 ℃, the hydrogen concentration of heating atmosphere is defined as below the 2 volume %, dew point is defined as more than-20 ℃, below 7 ℃, and oxygen concentration is defined as 0.3～21 volume %.

3. the hot-press method of high-strength vehicle parts, it is characterized in that, use on the steel plate of the C, the Cr below the 2 quality % that in composition of steel, contain 0.05～0.5 quality % and implemented the steel plate as the plating of main body with Zn, when adopting pressure sintering to make automobile component, with the heating-up temperature before the punching press be defined as more than 800 ℃, below 1000 ℃, the hydrogen concentration of heating atmosphere is defined as below the 2 volume %, and dew point is defined as more than-10 ℃, below 6 ℃, and oxygen concentration is defined as 1～21 volume %.

4. a hot press parts is characterized in that, uses wantonly 1 described hot-press method of claim 1～3 to make.

Images