JP2009293081A - Tool steel suitable to die for aluminum working and die for aluminum working - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool steel having excellent wear resistance and aluminum erosion resistance in which the coarsening of crystal grains and the precipitation of intergranular carbides caused by carburizing are suppressed, so as to remarkably improve its toughness, and to provide a die for aluminum working. <P>SOLUTION: The tool steel suitable to the die for aluminum working and the die for aluminum working are characterized in that a steel has a composition comprising, by mass, 0.31 to 0.60% C, 0.1 to 0.6% Si, 0.3 to 1.0% Mn, 0.05 to 0.6% Ni, 3.0 to <5.0% Cr, one or two selected from Mo and W so as to satisfy an Mo equivalent (Mo+1/2W): 0.8 to 4.0% and one or two selected from V and Nb so as to satisfy a V equivalent (V+1/2Nb): 0.5 to 1.5%, and the balance Fe with inevitable impurities, and in forging and rolling, end temperature is controlled to 900 to 1,150°C and cooling velocity is controlled to ≥0.05°C/sec. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a tool steel and an aluminum machining die which are excellent in wear resistance and aluminum corrosion resistance by carburizing.

  In recent years, due to efforts to reduce the weight of automobiles, trucks, vehicles, etc., the use of high-Si high-strength aluminum alloys has increased in die-casting and aluminum extrusion, and large parts have increased. Furthermore, from the viewpoint of improving productivity, the usage environment of molds is becoming severe, such as shortening of cycle time, and improvement of mold life is a major issue.

  In aluminum die cast punch pins and aluminum extrusion dies, contact with an aluminum alloy often results in severe seizure and wear, leading to early die life. Nitrogen (gas soft nitriding, salt bath soft nitriding, plasma nitriding, plasma nitriding, nitrosulphurizing, etc.) is used as a surface treatment for the purpose of improving the service life of these molds. Developed steel with improved PVD coating (TiN, TiAlN, TiCN, CrN, etc.) and improved component of JIS SKD61, which is a general-purpose steel, has been studied.

  In addition, in aluminum extrusion dies, contact with the aluminum billet extruded by heating and pressurization causes wear and seizure in the die-shaped part, leading to life, but nitriding for the purpose of improving lubrication and wear resistance. In many cases, it is reworked according to use and renitrided. However, in nitriding, since the thickness of the hardened layer is as thin as about 50 to 200 μm, a sufficient improvement in wear resistance cannot be expected, the surface hardness exceeds 1000 HV, and the hardness gap with the base material increases. There are problems such as early cracking and peeling. In addition, PVD coating is generally about 1-5 μm TiN, TiCN, CrN, etc., but local aluminum alloy seizure and melting damage from pinholes and droplets on the film surface are sufficient. The effect is not acquired.

  Under the circumstances as described above, for example, a steel for die-casting die for carburization and a die-casting die and a manufacturing method of the die-casting die as disclosed in Japanese Patent Application Laid-Open No. 2003-119544 (Patent Document 1) have been proposed. ing. Moreover, a casting mold or a welded molten member having excellent resistance to erosion with respect to molten Al or molten Zn as disclosed in Japanese Patent Laid-Open No. 8-144039 (Patent Document 2) has been proposed. Further, a repeated gas soft nitriding steel of a first nitriding treatment step and a second nitriding treatment step as disclosed in JP 2007-56368 A (Patent Document 3) has been proposed.

  In addition, steel for manufacturing a tool for cold working by plasma carburizing and a tool manufactured from the steel as disclosed in Japanese Patent Laid-Open No. 10-158780 (Patent Document 4) have been proposed. Yes. Further, carburization disclosed in JP-A-11-50190 (Patent Document 5) that can be applied under severe conditions such as a forging die and a sliding member used cold, warm and hot. Steel for a wide range of uses has been proposed as a member. In addition, a method for manufacturing a cold working die for vacuum carburization, which is disclosed in Japanese Patent Application Laid-Open No. 57-134554 (Patent Document 6), has been proposed.

Furthermore, a surface hardened steel disclosed in JP-A-57-164977 (Patent Document 7) has excellent machinability in the annealed state and excellent wear resistance after carburizing treatment. ing.
JP 2003-119544 A JP-A-8-144039 JP 2007-56368 A JP-A-10-158780 Japanese Patent Laid-Open No. 11-50190 JP-A-57-134554 JP-A-57-164977

  In the steel for die-casting die for carburizing of Patent Document 1 as described above, the C content is low, the internal hardness and strength are insufficient, and the die-casting die die is used for die-casting die so as to emphasize toughness. The wear resistance and aluminum meltability are not improved sufficiently. In addition, in the casting mold having excellent resistance to melting of Al and Zn in Patent Document 2, Mn is very high, the productivity and the machinability are poor, and the mother layer is austenite. Hardness decreases and strength is insufficient.

  Further, in the repeated gas soft nitrided steel of Patent Document 3, a certain improvement effect is obtained by the formation of the compound layer, but the steel material component has not been studied, the problem of peeling of the compound layer, and hardening The layer is shallow and the wear resistance is not sufficiently improved. Moreover, in the cold tool steel for carburizing of Patent Document 4, Cr is reduced, V is significantly increased, and a large amount of VC and V (CN) are precipitated during carburizing to obtain wear resistance and hardness. ing. However, Cr is too low, and the improvement of wear resistance is insufficient. In steel as a wide range of applications such as cold, warm, hot molds and sliding members of Patent Document 5, the depth of the carburized hardened layer has not been studied, and the toughness improvement is insufficient. is there.

  Further, the C content (Example) is low, and the internal hardness and strength are insufficient. Moreover, in the die steel for cold work which performs the vacuum carburizing of patent document 6, Cr content is high and toughness improvement is inadequate. Furthermore, in the cold working mold and blade steel of Patent Document 7, it is optional addition of Mo, V, etc., the technical idea is different, and the addition amount of C, Cr is high (Example), Each of them has problems such as insufficient improvement of impact value.

  In order to solve the above-mentioned problems, the inventors have made extensive developments in order to improve wear resistance and aluminum erosion resistance in aluminum processing molds. I came up with the idea of getting. Therefore, it was found that the toughness was greatly improved by suppressing the coarsening of crystal grains and precipitation of grain boundary carbides due to carburization, and the steel material components, production conditions, and hardness gradient of the hardened layer were controlled.

  That is, the precipitation of grain boundary carbides during carburization is suppressed by reducing the Cr content, the C diffusion during carburization is promoted by reducing the Si content, and the amount of finely precipitated carbide in the carburized layer is increased by increasing the Mo and V content. While improving the wear resistance and softening resistance, the diffusion of the Al alloy was suppressed and the meltability was improved. Moreover, the manufacturing conditions and the manufacturing method of the tool steel suitable for the aluminum processing metal mold | die which ensured toughness by suppressing the coarsening of the crystal grain during the carburization by Mo, V precipitation carbide | carbonized_material, and the aluminum processing metal mold | die are provided.

The gist of the invention is that
(1) By mass%, C: 0.31 to 0.60%, Si: 0.1 to 0.6%, Mn: 0.3 to 1.0%, Ni: 0.05 to 0.6% , Cr: 3.0 to less than 5.0%, any one or two of Mo or W is equivalent to Mo (Mo + 1 / 2W): 0.8 to 4.0%, any one of V or Nb Alternatively, two kinds of V equivalent (V + 1 / 2Nb): 0.5 to 1.5%, a steel composed of the balance Fe and unavoidable impurities, an end temperature of forging and rolling of 900 to 1150 ° C., a cooling rate of 0.05 ° C. / Tool steel suitable for molds for machining aluminum, characterized by a sec or longer.

(2) A mold for aluminum processing which is made of the steel described in (1) and has a carburized hardened layer on the surface.
(3) The relationship between the hardness and depth of the carburized hardened layer is 0.03 <(ΔHV / D) ≦ 0.15. .
However, ΔHV = (surface hardness) − (internal hardness), D = (depth of carburized hardened layer)
Here, the internal hardness is an average value measured arbitrarily at 5 points inside the cured layer, and the cured layer depth is measured when the hardness ± 30 HV is continuous for 5 points or more when the hardness is measured from the surface portion. Indicates the distance from the surface of the point closest to the surface.

  As described above, surface treatment and quenching can be performed together by vacuum carburizing according to the present invention, the work period can be shortened, and energy can be saved. Also, in die casting pins and extrusion dies, melting, wear, cracking, breakage This provides an extremely excellent effect that makes it possible to extend the life while suppressing the above.

Hereinafter, the reasons for limiting the component composition according to the present invention will be described.
C: 0.31 to 0.60%
C is an element necessary for hardness and strength by giving a sufficient matrix hardness by quenching and tempering and forming a carbide by combining with Cr, Mo, V, Nb and the like. However, if it is less than 0.31%, the effect is not sufficiently obtained, and if it exceeds 0.60%, the toughness and hot workability are lowered, so the range is 0.31 to 0.60%. It was. Preferably it is 0.35 to 0.55%.

Si: 0.1-0.6%
Si is an element necessary as a deoxidizer during steelmaking. However, if it is less than 0.1%, the effect cannot be sufficiently obtained, and if it exceeds 0.6%, the toughness is lowered and C diffusion is inhibited by carburization. 6%. Preferably it is 0.2 to less than 0.5%. Mn: 0.3 to 1.0%
Mn is a deoxidizer and an element imparting hardenability. However, if it is less than 0.3%, the effect is not sufficient, and if it exceeds 1.0%, the machinability is lowered, so the range was made 0.3 to 1.0%.

Ni: 0.05-0.6%
Ni is an element useful for improving hardenability and toughness. However, if it is less than 0.05%, the effect is not sufficient, and if it exceeds 0.6%, the machinability is lowered, so the range was made 0.05 to 0.6%.

Cr: 3.0 to less than 5.0% Cr is an element necessary for hardness and hardenability. In particular, carbides are deposited during carburizing to improve wear resistance and erosion resistance. However, if it is less than 3.0%, the effect is not sufficient, and if it is 5.0% or more, coarse carbides are likely to be generated during solidification, and grain boundary carbides are likely to precipitate and grow during carburization, and toughness Reduce. Therefore, the range was made 3.0 to less than 5.0%. Preferably, the content is 3.6 to 4.6%.

Mo + 1 / 2W: 0.8-4.0%
Mo and W can be added alone or in combination, and are elements that precipitate fine carbides during tempering to increase softening resistance, hardness, and high-temperature strength. In addition, fine carbides are precipitated during carburizing to improve wear resistance and erosion resistance, and the fine carbides have an effect of suppressing crystal grain coarsening during carburizing and ensuring toughness. However, if the content is less than 0.8%, the effect is not sufficient. If the content exceeds 4.0%, fine carbides precipitate during tempering, and the toughness and hot workability are deteriorated. It was 8 to 4.0%. Preferably it is set to 2.0 to 3.6%.

V + 1 / 2Nb: 0.5-1.5%
V and Nb can be added singly or in combination, and dissolve in the base during quenching heating, precipitate fine carbides that are difficult to agglomerate during tempering, increase softening resistance in a high temperature range, and provide high high-temperature strength. And has the effect of suppressing the coarsening of crystal grains and ensuring toughness. However, if it is less than 0.5%, the effect is not sufficient, and if it exceeds 1.5%, the toughness and hot workability are lowered, so the range was made 0.5 to 1.5%.

Final temperature in forging and rolling 900-1150 ° C
The reason why the end temperature in forging and rolling is 900 to 1150 ° C. is a condition necessary for ensuring hot workability, and the effect is not sufficient when the temperature is lower than 900 ° C., and the crystal grain is higher than 1150 ° C. Increases and decreases toughness. Moreover, the grain boundary carbides during carburizing become coarse. Therefore, the range was made 900-1150 degreeC. Preferably it is 1000-1100 degreeC.

With a cooling rate of 0.05 ° C./sec or higher and a constant temperature or higher, the matrix structure becomes martensite and fine bainite, and the toughness is improved. However, slow cooling causes carbides to precipitate at the grain boundaries, reducing toughness. Therefore, it is set to 0.05 ° C./sec or more. Preferably, it is 0.1 ° C./sec or more.

The relationship between the hardness and depth of the carburized hardened layer is 0.03 <(ΔHV / D) ≦ 0.15.
The relationship between the hardness and depth of the carburized hardened layer is that, by applying carburizing, it is possible to obtain wear resistance and durability by obtaining a hardened layer having a depth of 500 to 4000 μm. In addition, in order to obtain a balance between wear resistance, durability and toughness, it is necessary to regulate the steel material composition, manufacturing conditions, and hardness gradient of the hardened layer, and the one that defines the hardness gradient of the hardened layer is the above It is a relationship. If it is 0.03 or less, the toughness is inferior and the optimum balance between the two cannot be obtained. Moreover, even if it exceeds 0.15, toughness is inferior, and an optimal balance between the two cannot be obtained. Therefore, in order to obtain a balance between the two, it is more than 0.03 and not more than 0.15.

  FIG. 1 is a diagram showing a structure state of a micrograph in the depth direction from the surface of the steel of the present invention and a comparative steel. FIG. 1A is a structural state of a steel according to the present invention as a micrograph, and FIG. 1B is a structural state of a conventional steel as a micrograph. As shown in this figure, it can be seen that in the steel of the present invention, the carburized layer on the steel surface is finely precipitated carbide, whereas the carburized layer of the comparative steel is coarsely precipitated carbide.

Hereinafter, the present invention will be specifically described with reference to examples.
Each test material shown in Table 1 was melted in a 100 kg vacuum induction melting furnace, then steeled and ingot, heated to 1150 ° C. and forged (forging end temperature 1020 ° C.), then gradually increased at 0.05 ° C./sec. After cooling and producing a round bar with a diameter of 32 mm, an annealed sample (held at 800 to 900 ° C. for 5 hours and then gradually cooled) was processed, carburized and heat-treated for evaluation. . The carburizing conditions at that time were that the vacuum carburizing furnace was used to carry out vacuum carburizing and quenching as it was for quenching. After raising the temperature at 10 ° C./min and holding at 900 ° C. for 30 minutes in a vacuum carburizing furnace, the temperature was further raised to 1000 to 1150 ° C., and a carburizing treatment was performed by flowing a hydrocarbon-based gas such as acetylene gas. Thereafter, quenching was performed by quenching with nitrogen gas. Furthermore, tempering at 550 to 650 ° C. was performed, and the internal hardness (average value arbitrarily measured at five points inside the cured layer) was set to 400 to 660 HV. The results are shown in Table 2. The measurement and test methods are described below.

The surface hardness was measured by using a micro Vickers hardness tester to measure the surface hardness 0.03 mm from the surface that does not affect the indentation shape such as surface sag.
Hardened layer depth is measured using a micro Vickers hardness tester, measuring the hardness from the surface at an interval of 0.05 mm, up to the point closest to the surface when the hardness ± 30 HV continues for 5 points or more. The distance from the surface was taken as the hardened layer depth.

In the Charpy impact test, a 2 mmU notch test piece (10 mm × 10 mm × 55 mm) was produced from the center L direction of the specimen, and the test was carried out after carburizing heat treatment.
In addition, the aluminum erosion test was performed by preparing an aluminum erosion test piece (diameter 20 mm × length 100 mm) from the longitudinal direction (L direction) of the center portion of the test material, and using ADC12 (Al-11Si-2Cu) as an aluminum alloy. ) Was immersed in a molten metal heated to 720 ° C., and the amount of melting loss was measured by rotating at a peripheral speed of 3.2 m / min for 2 hours. The amount of melting loss (%) was calculated from [(weight of test piece before test) − (weight of test piece after test)] / (weight of test piece before test) × 100.

  In the Ogoshi abrasion test, a test piece of 15 mm × 20 mm × 5 mm was prepared from the L direction of the center portion of the specimen, and the test was carried out after carburizing treatment. The test conditions were as follows: SCM420 (surface hardness 86HRB) was used for the ring of the counterpart material, the friction distance was 200 mm, the final load was 61.7 N, and the friction speed was 2.38 m / sec. The width of the wear scar after the test was measured, and the specific wear amount was calculated.

表２に示すように、Ｎｏ．１〜１３は本発明例であり、Ｎｏ．１４〜２０は比較例である。

As shown in Table 2, no. Nos. 1 to 13 are examples of the present invention. 14 to 20 are comparative examples.

  Comparative Example No. 2 shown in Table 2 No. 14 has a low C content, a high Si content, a low Cr content, and a high V + 1 / 2Nb content. Therefore, ΔHV / D is large, toughness is poor, and the aluminum loss is high. In addition, the wear resistance is inferior. Comparative Example No. No. 15 has low C content, high Mn, Ni, Cr content and high V + 1 / 2Nb content, so the carburized hardened layer depth is shallow, ΔHV / D is large, toughness is poor, aluminum Loss is high and wear resistance is poor.

  Comparative Example No. No. 16 has a high C, Si, Mn content, a high Mo + 1 / 2W content, no Ni content, and a high end temperature, so the carburized hardened layer depth is slightly shallow, and ΔHV / D is large. Poor toughness, high aluminum melt loss, and poor wear resistance. Comparative Example No. No. 17 has a low Si and Mn content, a high Cr content, a low Mo + 1 / 2W content, a high V + 1 / 2Nb content, and a low cooling rate, so the internal hardness and surface hardness are low. .DELTA.HV / D is small, but since the Cr content is high, the toughness is poor, the aluminum melt loss is high, and the wear resistance is poor.

Comparative Example No. No. 18 has a high Si, Ni, Cr content, so that the carburized hardened layer depth is shallow, ΔHV / D is large, the toughness is poor, the aluminum erosion amount is high, and the wear resistance is inferior. Comparative Example No. Since No. 19 has a high end temperature, the carburized hardened layer depth is shallow, ΔHV / D is large, toughness is poor, and the amount of aluminum erosion is high. Comparative Example No. 20 shows that ΔHV / D is large, toughness is poor, and the amount of aluminum erosion is high because the cooling rate is slow.
On the other hand, No. which is an example of the present invention. Since 1 to 13 satisfy the requirements of the present invention, it can be seen that they are excellent in any performance.

  As described above, instead of conventional nitriding (depth 50 to 200 μm) and PVD coating (thickness 1 to 5 μm), carburization is applied to improve wear resistance and durability by a deep hardened layer of 500 to 4000 μm. In order to suppress the deterioration of toughness at that time, the mold life without melting, abrasion, cracking, and breakage was improved by controlling the steel composition, manufacturing conditions, and hardness gradient of the hardened layer. The present invention provides a tool steel suitable for an aluminum machining die and a method for producing an aluminum machining die.

FIG. 1 is a diagram showing a structure state of a micrograph in the depth direction from the surface of the steel of the present invention and a comparative steel.

Claims (3)

% By mass
C: 0.31 to 0.60%,
Si: 0.1 to 0.6%,
Mn: 0.3 to 1.0%
Ni: 0.05-0.6%,
Cr: 3.0 to less than 5.0%,
Any one or two of Mo or W is Mo equivalent (Mo + 1 / 2W): 0.8 to 4.0%, and one or two of V or Nb is V equivalent (V + 1 / 2Nb): 0 Aluminum for processing aluminum, characterized in that steel comprising 5 to 1.5%, balance Fe and inevitable impurities is set to a finish temperature of 900 to 1150 ° C. and a cooling rate of 0.05 ° C./sec or more in forging and rolling. Tool steel suitable for the mold. An aluminum processing mold comprising the steel according to claim 1 and having a carburized hardened layer on a surface thereof. The mold for aluminum processing according to claim 2, wherein a relationship between hardness and depth of the carburized hardened layer is 0.03 <(ΔHV / D) ≦ 0.15.
However, ΔHV = (surface hardness) − (internal hardness), D = (depth of carburized hardened layer)

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