JP2005325407A - Cold working tool steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide cold working tool steel having a hardness (by HRC) of ≥61 after tempering and excellent in processability. <P>SOLUTION: The cold working tool steel has a K-value of 0.4-2.6 (wherein, K-value = Cr(wt%)-6.8C(wt%)) and a L-value of 15.5-21.0 (wherein, L-value = Cr(wt%)+15.5C(wt%)), contains, by weight, >0.60 to 2.0% Si, 0.10-1.0% Mn, >0.03 to 0.2% S, >1.25 to <3.0% of Mo+0.5W, and 0.05-1.0% V, and the balance Fe with inevitable impurities, and exhibits a maximum hardness (by HRC) of ≥61 after tempering at a temperature of ≥450°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to cold tool steel, and more particularly, cold forging punch dies, high-tensile steel plate forming dies, bending dies, cold forging dies, swaging dies, screw rolling dies, punch members, slitter knives. , Lead frame punching die, gauge, deep drawing punch, bending die punch, shear blade, stainless steel bending die, drawing die, plastic working tools such as forging, gear punch, cam parts, press punching die, progressive punching die , Surface treatment such as seal plate of earth and sand feeder, screw member, rotary plate for concrete spraying machine, IC sealing mold, precision press mold requiring high dimensional accuracy, CVD treatment, PVD treatment, TD treatment, etc. The present invention relates to a cold tool steel suitable for the various cold molds and the like used above.

  Cold tool steel represented by JIS steel SKD11 is a high-hardness carbide that is dispersed by crystallization or precipitation in a large amount to improve wear resistance, and various types that require wear resistance and galling resistance. (For example, cold forging punch dies, cold forging dies, etc.). However, the conventional cold tool steel has (1) lack of toughness, (2) as the molding process conditions become severe, the hardness of the mold may become insufficient, (3) wire There were problems such as cracking during EDM.

  In order to solve this problem, various proposals have heretofore been made. For example, in Patent Document 1, C: 0.75 to 1.75 wt%, Si: 0.5 to 3.0 wt%, Mn: 0.1 to 2.0 wt%, Cr: 5.0 to 11.0 wt% , Mo: 1.3 to 5.0 wt%, V: 0.1 to 5.0 wt%, the balance is made of Fe and impurities, and a cold tool steel tempered at a temperature of 450 ° C or higher is disclosed. ing. In this document, tool life and electrical discharge machining are achieved by improving the toughness by reducing the primary eutectic carbide, and by increasing the secondary hardening hardness by adjusting each component and tempering at 450 ° C or higher. It describes that the performance is greatly improved.

  Patent Document 2 discloses a cold tool steel having a predetermined composition and an aggregate size of carbide aggregate portions of 100 μm or less. This document describes that when the aggregate size is 100 μm or less, crack generation and crack propagation in the carbide are suppressed, and the tool life is improved.

  Patent Document 3 has a predetermined composition, and an α value (= 0.706 + 0.541C−0.063Cr + 0.033Mo−0.232V) is 0.7 to 1.0, and a β value (= A high hardness cold tool steel having a Mo equivalent of 1.9 V equivalent) of 3.0 to 6.0 is disclosed. This document describes that by setting the α value and β value in this range, the formation of coarse carbides and aggregated carbides is suppressed, and the adhesion to the hard surface layer is improved.

  Patent Document 4 discloses a cold tool steel having a predetermined composition and finely dispersing 5-35 vol% retained austenite to an average particle size of 0.01 to 2 μm. This document describes that fatigue resistance is improved by finely dispersing a predetermined amount of retained austenite.

  Furthermore, Patent Document 5 discloses that a free-cutting element is contained in order to improve the machinability, and the C content is reduced in order to improve the machinability. Further, it is described that residual stress is removed by high-temperature tempering and cracking due to electric discharge machining can be prevented.

JP 59-179762 A JP 2002-12952 A JP 2000-073142 A JP 2004-035920 A JP 2000-355737 A

  In the case of a prototype mold or a mold with a small number of lots, workability superior to the mold life is particularly required. In other words, the machining methods include cutting, electric discharge machining, wire electric discharge machining, etc., but in certain applications, HRC60 is easily machined by any machining method and has the same hardness as a normal mold. There is a need for cold work tool steel that can ensure the above.

  However, since the conventional cold tool steel represented by SKD11 has a large amount of crystallized carbide dispersed in order to ensure a predetermined wear resistance, it is inferior in machinability even in the annealed state. There is a problem. Moreover, a wire may be cut | disconnected by the crystallization carbide | carbonized_material at the time of wire electric discharge machining.

  In addition, a material in which the amount of crystallized carbide is reduced in order to improve workability is also known, but it is difficult to ensure HRC 60 or more at high temperature tempering with conventional materials. On the other hand, in such a material, if low temperature tempering is performed in order to obtain high hardness, the residual stress generated in the material during quenching cannot be removed. Therefore, when electric discharge machining or wire electric discharge machining is performed on such a material, the residual stress may lose balance, and the material may crack or crack.

  On the other hand, the cold tool steel disclosed in Patent Document 1 reduces the amount of crystallized carbide as compared with SKD11, and at the same time, adjusts the components, so it can secure hardness of HRC60 or higher and workability. Has also been improved to some extent. However, even with the cold tool steel disclosed in Patent Document 1, improvement in workability is insufficient. Patent Documents 2 to 5 do not disclose specific means for improving workability while maintaining high hardness.

  The problem to be solved by the present invention is to provide a cold tool steel having a hardness after tempering of HRC60 or more and excellent workability.

In order to solve the above problems, the cold work tool steel according to the present invention,
0.4 ≦ K value ≦ 2.6 (where K value = Cr (wt%) − 6.8 C (wt%)),
15.5 ≦ L value ≦ 21.0 (where L value = Cr (wt%) + 15.5 C (wt%)),
0.60 wt% <Si ≦ 2.0 wt%,
0.10 wt% ≦ Mn ≦ 1.0 wt%,
0.03 wt% <S ≦ 0.2 wt%,
1.25 wt% <Mo + 0.5 W <3.0 wt%, and
0.05 wt% ≦ V ≦ 1.0 wt%,
And the balance consists of Fe and inevitable impurities,
The gist is that the maximum hardness obtained by tempering at 450 ° C. or higher after quenching is HRC 61 or higher.

  Since the cold tool steel according to the present invention has a K value in a predetermined range, the maximum hardness after high-temperature tempering can be HRC 61 or more. Moreover, since L value was made into the predetermined range, machinability improves and the wire cutting at the time of wire electric discharge machining can be suppressed. Furthermore, since 0.6 wt% or more of Si is added in addition to S, machinability equivalent to or higher than that of conventional free-cutting steel can be obtained.

  Hereinafter, an embodiment of the present invention will be described in detail. The cold tool steel according to the present invention contains the following elements, with the balance being substantially composed of Fe and inevitable impurities. The kind of additive element, its component range, and the reason for limitation are as follows.

(1) 0.4 ≦ K value ≦ 2.6 (where K value = Cr (wt%) − 6.8 C (wt%)).
The K value represents the amount of residual Cr in the matrix at an appropriate quenching temperature. When the K value is less than 0.4 or exceeds 2.6, the amount of carbides that contribute to secondary hardening during tempering is reduced, and the hardness is HRC 61 or more at high temperature tempering of 450 ° C. or higher. It becomes difficult to obtain. The K value is more preferably 0.45 or more and 2.5 or less, and further preferably 0.6 or more and 2.4 or less.

(2) 15.5 ≦ L value ≦ 21.0 (where L value = Cr (wt%) + 15.5 C (wt%)).
The L value represents the amount of crystallized carbide contained in the material, and means that the amount of crystallized carbide increases as the L value increases. When the L value is less than 15.5, not only crystallized carbides are hardly formed, but also the matrix component at an appropriate quenching temperature changes, so that the required hardness cannot be obtained. On the other hand, when the L value exceeds 21.0, the amount of crystallized carbide becomes excessive, and the machinability, electrical discharge machinability, and toughness are reduced. However, if the crystallized carbide is completely eliminated, the crystal grains become coarse or mixed during quenching, so it is better that the crystallized carbide remains to some extent. The L value is more preferably 15.8 or more and 20.8 or less, and further preferably 16.0 or more and 20.5 or less.

The crystallized carbide is a large carbide having an equivalent circle diameter exceeding about 10 μm, and is mainly expressed by M ₇ C ₃ (M is Cr, Mo, etc.). The L value of 15.5 to 21.0 corresponds to 0.20 wt% to 4.0 wt% in terms of the weight ratio occupied by the crystallized carbide.

(3) 0.60 wt% <Si ≦ 2.0 wt% or less.
Since Si is added as a deoxidizing element, it is usually contained in steel. In the present invention, Si is positively added to facilitate cutting. The improvement of machinability by adding Si can be obtained not only in a low hardness state after annealing (around HRB95) but also in a high hardness state after quenching and tempering (HRC 61 or higher). Moreover, Si addition contributes also to the improvement of high temperature tempering hardness.
In order to obtain such an effect, Si needs to be added exceeding 0.6 wt%. On the other hand, even if Si is added excessively, the effect is saturated. Accordingly, the Si amount is preferably 2.0 wt% or less. The amount of Si is more preferably 0.65 wt% or more and 1.8 wt% or less, and further preferably 0.70 wt% or more and 1.5 wt% or less.

(4) 0.10 wt% ≦ Mn ≦ 1.0 wt%.
Mn has the effect of increasing the hardenability and improving the hardness and strength. Moreover, it reacts with S which is a free-cutting element, forms an inclusion, and has the effect of improving machinability. In order to obtain such an effect, Mn needs to be added in an amount of 0.10 wt% or more. On the other hand, when Mn is added excessively, the hot workability is lowered. Therefore, the amount of Mn is preferably 1.0 wt% or less.

(5) 0.03 wt% ≦ S ≦ 0.20 wt%.
S is a free-cutting element and combines with Mn to form inclusions, thereby improving machinability. The improvement in machinability by adding S can be obtained not only in a low hardness state after annealing (around HRB95) but also in a high hardness state after quenching and tempering (HRC 61 or more).
In order to obtain such an effect, S needs to be added in an amount of 0.03 wt% or more. However, if the amount of S is too large, the Charpy impact test in the material cross-sectional direction is greatly reduced, and hot workability is also reduced. Therefore, the amount of S is preferably 0.20 wt% or less.

(6) 1.25 wt% <Mo + 0.5 W <3.0 wt%.
Mo and W form carbides and increase the amount of secondary hardening in tempering at 450 ° C. or higher. Mo and W bring about the same effect, but in order to obtain the same effect as Mo, twice the amount of W is required. Therefore, it is defined by the Mo equivalent described by Mo + 0.5W.
In order to obtain hardness HRC61 or more after quenching and tempering, the Mo equivalent needs to be greater than 1.25 wt%. However, if the Mo equivalent is too large, the hot workability, the toughness, and the machinability are reduced. Therefore, the Mo equivalent is preferably less than 3.0 wt%.

(7) 0.05 wt% ≦ V ≦ 1.0 wt%.
V forms a stable carbide and is effective in preventing crystal grain coarsening. In addition, the formation of carbides contributes to improved wear resistance and hardness. In order to obtain these effects, V needs to be added at 0.05 wt% or more. However, if the amount of V becomes too large, the machinability and hot workability deteriorate due to an increase in the amount of carbide. Therefore, the V amount is preferably 1.0 wt% or less.

  Moreover, in addition to the element mentioned above, the cold tool steel which concerns on this invention may further contain the following 1 type, or 2 or more types of elements. The component ranges of each element and the reasons for limitation are as follows.

(8) 0.005 wt% ≦ Se ≦ 0.10 wt%.
(9) 0.005 wt% ≦ Te ≦ 0.10 wt%.
(10) 0.0002 wt% ≦ Ca ≦ 0.010 wt%.
(11) 0.005 wt% ≦ Pb ≦ 0.10 wt%.
(12) 0.005 wt% ≦ Bi ≦ 0.10 wt%.

Se, Te, Ca, Pb, and / or Bi can be added for the purpose of improving machinability. In addition, any of these elements does not hinder improvement in machinability due to the addition of Si.
Se and Te can be used as substitute elements for S in Mn sulfide. Moreover, Ca improves the machinability by forming an oxide or forming a protective film on the surface of the cutting tool at the time of cutting by forming a solid solution in Mn sulfide. Furthermore, since Pb and Bi are substances having a low melting point, they are melted by the heat generated by the cutting process, provide a lubricating effect between the cutting tool and the chips, and improve the machinability.
In order to obtain these effects, addition above the lower limit described above is necessary. However, if the addition amount is too large, the mechanical properties are deteriorated, so the addition amount is preferably set to the upper limit or less.

(13) 0.01 wt% ≦ Cu ≦ 2.0 wt%.
(14) 0.01 wt% ≦ Ni ≦ 2.0 wt%.
(15) 0.20 wt% ≦ Co ≦ 1.0 wt%.
(16) 0.0003 wt% ≦ B ≦ 0.010 wt%.

Cu, Ni, Co, and B are all dissolved in the matrix and have the effect of improving the hardenability. Ni also has an effect of improving toughness by lowering the impact transition temperature and preventing deterioration of weldability by improving toughness. Furthermore, in the cold mold, depending on the high-tensile steel and the processing conditions, the mold temperature may rise locally due to processing heat generation. Co has the effect of improving the high-temperature strength and preventing the mold from sagging due to such a temperature rise.
In order to obtain these effects, it is preferable that the amount of these elements added be equal to or higher than the lower limit value described above. However, if the addition amount is too large, the mechanical properties are deteriorated, so the addition amount is preferably set to the upper limit or less.

(17) 0.001 wt% ≦ P ≦ 0.030 wt%.
(18) 0.0050 wt% ≦ N ≦ 0.050 wt%.
(19) 0.001 wt% ≦ Al ≦ 0.10 wt%.
(20) 0.0002 wt% ≦ O ≦ 0.010 wt%.

P, N, and O are inevitably contained in the steel. P segregates at the grain boundaries, O forms an oxide, and N forms a nitride. Al reacts with O and N in steel to form oxide grains and nitrides. These elements can improve toughness by reducing the addition amount. In order to obtain such an effect, it is desirable that the addition amount of these elements be equal to or less than the above-described upper limit value. Desirably, P ≦ 0.020 wt% or less, N ≦ 0.030 wt% or less, Al ≦ 0.050 wt% or less, and O ≦ 0.050 wt% or less.
However, Al oxides and nitrides contribute to prevention of coarsening of crystal grains. Therefore, if these elements are excessively reduced, the crystal grains are conversely coarsened and toughness is lowered. Moreover, reducing these elements more than necessary leads to an increase in manufacturing costs. Furthermore, when these elements are below a certain value, the effect of improving toughness is saturated. Therefore, these elements are preferably set to be equal to or higher than the lower limit value described above.

(21) 0.010 wt% ≦ Nb ≦ 0.10 wt%.
(22) 0.005 wt% ≦ Ta ≦ 0.10 wt%.
(23) 0.005 wt% ≦ Ti ≦ 0.10 wt%.
(24) 0.005 wt% ≦ Zr ≦ 0.10 wt%.
(25) 0.005 wt% ≦ Mg ≦ 0.10 wt%.
(26) 0.005 wt% ≦ REM ≦ 0.10 wt%.

Nb, Ta, Ti, Zr, Mg, and REM are all effective in improving toughness. Among these, Nb, Ta, Ti, and Zr have the effect of improving toughness by forming fine carbonitrides and making crystal grains finer. On the other hand, Mg and REM have the effect of improving toughness by reducing the amount of oxygen in the matrix.
In order to obtain such an effect, the amount of these elements added is preferably equal to or greater than the lower limit value described above. However, if the amount added is too large, the toughness and weldability are reduced. Therefore, it is preferable that the addition amount of these elements is not more than the above-described upper limit value.

  When the material having the above composition is quenched and tempered, the cold tool steel according to the present invention is obtained. In this case, if the tempering temperature is low, the residual stress introduced at the time of quenching is insufficiently released, and the electric discharge processability is lowered. Accordingly, the tempering temperature is preferably 450 ° C. or higher. In the cold tool steel according to the present invention, the alloy components are optimized, so that even when tempering is performed at a high temperature of 450 ° C. or higher, high hardness (specifically, the maximum hardness is HRC 61 or higher) is obtained. .

  Moreover, the crystal grain size of prior austenite affects toughness. In order to obtain a cold work tool steel having high toughness, the crystal grain size of prior austenite is preferably smaller. However, even if the crystal grain size becomes too small, the effect is small, and the cost is rather increased. Therefore, the grain size of the prior austenite is preferably 3.0 or more and 8.0 or less in terms of the crystal grain size Gq. The “crystal grain size Gq” is the crystal grain size of prior austenite after quenching, measured using the method described in JIS G0551.

  The carbide contained in the cold tool steel has an effect of preventing the crystal grain size from becoming coarse during quenching. However, in the present invention, the amount of carbide is reduced as compared with the conventional cold tool steel such as SKD11, so that the crystal grain size is relatively likely to become coarse. Therefore, in order to optimize the crystal grain size Gq and obtain high toughness, it is necessary to perform a quenching process at an appropriate temperature. Specifically, the quenching temperature is preferably 950 ° C. or higher and 1080 ° C. or lower. When quenching is performed within this temperature range, the crystal grain size can be prevented from becoming coarse.

  Since the present invention is basically free-cutting by adding S, it is desirable that the A-based inclusions are in a certain range. Here, “A inclusions” are inclusions determined using the inclusion evaluation method described in JIS G0555, and mainly sulfides.

  In order to obtain a cold tool steel excellent in machinability, dA60 × 400 is preferably 0.10% or more and 1.50% or less. Here, “dA60 × 400” is the cleanliness of the A-based inclusions measured based on the method described in JIS G0555, and the cleanliness when 60 fields are observed with an optical microscope 400 times field of view. It is. In order to obtain even higher machinability, the ratio of A-based inclusions having a maximum length of 20 μm or less is preferably 30% or more of the entire A-based inclusions.

  In order to form such A-based inclusions, an amount of Mn suitable for the amount of S must be added. The minimum amount of Mn is 1.7 × S or more. However, since Mn is also required for enhancing the hardenability, it is usually added more than the Mn amount suitable for the S amount.

In addition, B-based inclusions and C-based inclusions (alumina, other oxides, etc.) not only cause adverse effects of free cutting, but also cause a decrease in Charpy impact value, so it is preferable to reduce them as much as possible. Here, “B inclusions” and “C inclusions” refer to inclusions determined using the inclusion evaluation method described in JIS G0555.
In order to obtain a cold tool steel excellent in free cutting property and impact resistance, d (B + C) 60 × 400 is specifically preferably 0.05% or less. Here, “d (B + C) 60 × 400” is the cleanliness of B-type inclusions and C-type inclusions measured based on the method described in JIS G0555, and the optical microscope has a 400 × field of view. The cleanliness when 60 fields of view are observed.

  Next, the operation of the cold tool steel according to the present invention will be described. Since the crystallized carbide has high hardness, the wear resistance of the cold tool steel can be increased by dispersing the crystallized carbide in a large amount. However, a large amount of crystallized carbide not only lowers machinability but also causes wire breakage during wire electric discharge machining. In addition, the crystallized carbide is generally large in size, and therefore tends to be a starting point of cracking. On the other hand, if the amount of crystallized carbide is too small, the hardness decreases, the crystal grains become coarse, and the toughness decreases.

  On the other hand, the cold tool steel according to the present invention optimizes the L value and relatively reduces the amount of crystallized carbide, so that the machinability is improved and the trouble of wire breakage during wire electric discharge machining is also reduced. To do. Further, since the amount of coarse crystallized carbide that becomes the starting point of cracking is reduced and the crystal grains are also refined, high toughness can be obtained.

  Further, as described above, the K value represents the amount of residual Cr in the matrix at an appropriate quenching temperature, and the necessary secondary hardening can be obtained by optimizing the K value. Si is a free-cutting element and at the same time contributes to the improvement of hardness over the entire tempering temperature. Further, the Mo equivalent affects the secondary curing hardness.

In the cold tool steel according to the present invention, in addition to optimizing the K value, other components such as the Si amount and the Mo equivalent have been optimized. Therefore, the hardness HRC61 required as a cold tool steel during quenching and tempering The above can be ensured.
Moreover, since high temperature tempering is possible, the residual stress inside the material generated during quenching can be sufficiently released. Therefore, not only is it excellent in machinability, but also generation of cracks and cracks can be prevented when electric discharge machining or wire electric discharge machining is performed.

  Furthermore, in the cutting process in a high speed range (high rotation speed), the material is likely to be welded onto the rake face. Therefore, formation and detachment of the welded portion are repeated, and tool wear tends to proceed. On the other hand, since the cold tool steel according to the present invention is added with 0.6 wt% or more of Si, welding hardly occurs and tool wear can be suppressed. Therefore, it becomes possible to have workability higher than that of conventional free-cutting steel.

  80 kg of steel materials (Examples 1 to 20 and Comparative Examples 1 to 10) having the composition shown in Table 1 were melted in a high-frequency vacuum melting furnace. Next, this was ingoted, and the steel ingot was hot forged to obtain a square bar having a side of 35 × 55 mm. After hot forging, spheroidizing annealing was performed in which cooling was performed at a cooling rate of 880 ° C. to 7 ° C./hr.

  About each obtained steel material, machinability test (end mill processing test), wire electric discharge machining test, hardness evaluation, Charpy impact test, crystal grain size Gq after quenching, and cleanliness of inclusions were evaluated.

In addition, the machinability test (end milling test) was performed on a test piece cut out from an annealed steel material. The test conditions are as follows.
Tool: Carbide M20 (φ32 mm).
Speed: 200 m / min.
Feed: 0.15 mm / rev.
Cutting width: 4.5 mm.
Cutting height: 1.2 mm.
Cutting oil: None.
Tool life: Cutting distance when the maximum amount of side flank wear reaches 0.3 mm.
Evaluation method: Comparative steel No. Relative evaluation with 1 tool life as 100.

  The wire electric discharge machining test was performed according to the following procedure. That is, a 30 × 50 × 200 mm test piece was cut out from the steel material after annealing, and the test piece was quenched and tempered under predetermined conditions. Next, after a hole of φ4 mm was drilled in the test piece, a 10 × 20 mm square shape was stuck with a wire electric discharge machine. After electric discharge machining, the sample was left for 1 day, and the number of cracks generated in the test piece was measured.

  The hardness was measured after cutting a 20 mm square plate-shaped test piece from the annealed steel material and quenching and tempering at a predetermined temperature. The hardness is a value when tempering at a specific temperature shown in Table 2 (test hardness) and a maximum value (maximum hardness) of hardness when tempering at 100 to 600 ° C. Was measured.

  The Charpy impact test was performed at room temperature after producing a 10R-notch-shaped Charpy impact test piece from the annealed steel material, quenching and tempering at a predetermined temperature. The impact value was an average value of three test pieces.

  Furthermore, the crystal grain size Gq was measured by the method described in JIS G0551. The cleanliness of inclusions was measured for A-type inclusions and (B + C) -type inclusions by the method described in JIS G0555 (magnification of optical microscope: 400 times, number of fields of view: 60).

  Table 2 shows the quenching temperature, the tempering temperature, and the results of various evaluation tests. FIG. 1 shows the relationship between the L value and the amount of crystallized carbide.

  As shown in FIG. 1, the L value has a correlation with the amount of crystallized carbide. When the L value exceeds 21.0, the amount of crystallized carbide exceeds 4.0 wt%. Comparative Examples 1 and 6 to 10 all have a relatively high L value and a large amount of crystallized carbide. Therefore, the impact value is low and the machinability is poor. In particular, in Comparative Examples 7 and 8, the wire was disconnected during wire electric discharge machining. Moreover, since the tempering temperature was less than 450 degreeC in Comparative Examples 3, 9, and 10, all generated cracks after electric discharge machining. Further, in Comparative Examples 2, 4, and 5, since the alloy elements such as Mn, Mo, and V are outside the scope of the present invention, the maximum hardness was less than HRC61. Further, in Comparative Example 6, since the K value was too large, sufficient secondary curing could not be obtained, and the maximum hardness was less than HRC61.

On the other hand, since the inventive steels 1 to 20 are optimized in K value and L value, and the amount of other alloy elements, all have a maximum hardness of HRC 61 or more, machinability and electric discharge machining. Excellent in impact and high impact value.
FIG. 2 shows the relationship between Si addition amount and machinability. FIG. 2 shows that the machinability is greatly improved when the Si amount is 0.6 wt% or more. This is because tool wear due to welding is suppressed by adding a predetermined amount of Si.

  The embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the present invention.

  The cold tool steel according to the present invention can be used as various cold working dies and various cold working tools.

It is a figure which shows the relationship between L value and the quantity of a crystallization carbide | carbonized_material. It is a figure which shows the relationship between Si amount and machinability.

Claims (7)

0.4 ≦ K value ≦ 2.6 (where K value = Cr (wt%) − 6.8 C (wt%)),
15.5 ≦ L value ≦ 21.0 (where L value = Cr (wt%) + 15.5 C (wt%)),
0.60 wt% <Si ≦ 2.0 wt%,
0.10 wt% ≦ Mn ≦ 1.0 wt%,
0.03 wt% <S ≦ 0.2 wt%,
1.25 wt% <Mo + 0.5 W <3.0 wt%, and
0.05 wt% ≦ V ≦ 1.0 wt%,
And the balance consists of Fe and inevitable impurities,
A cold work tool steel whose maximum hardness obtained by tempering at 450 ° C. or higher after quenching is HRC 61 or higher. 0.005 wt% ≦ Se ≦ 0.10 wt%
0.005 wt% ≦ Te ≦ 0.10 wt%
0.0002 wt% ≦ Ca ≦ 0.010 wt%,
0.005 wt% ≦ Pb ≦ 0.10 wt%, and
0.005 wt% ≦ Bi ≦ 0.10 wt%,
The cold tool steel according to claim 1, further comprising one or more elements selected from the group consisting of: 0.01 wt% ≦ Cu ≦ 2.0 wt%,
0.01 wt% ≦ Ni ≦ 2.0 wt%,
0.20 wt% ≦ Co ≦ 1.0 wt%, and
0.0003 wt% ≦ B ≦ 0.010 wt%,
The cold tool steel according to claim 1 or 2, further comprising one or more elements selected from the group consisting of: 0.0010 wt% ≦ P ≦ 0.030 wt%,
0.0050 wt% ≦ N ≦ 0.050 wt%,
0.0010 wt% ≦ Al ≦ 0.10 wt%, and
0.0002 wt% ≦ O ≦ 0.010 wt%,
The cold tool steel according to any one of claims 1 to 3, further comprising one or more elements selected from the group consisting of: 0.010 wt% ≦ Nb ≦ 0.10 wt%,
0.005 wt% ≦ Ta ≦ 0.10 wt%,
0.005 wt% ≦ Ti ≦ 0.10 wt%,
0.005 wt% ≦ Zr ≦ 0.10 wt%,
0.005 wt% ≦ Mg ≦ 0.10 wt%, and
0.005 wt% ≦ REM ≦ 0.10 wt%,
The cold tool steel according to any one of claims 1 to 4, further comprising one or more elements selected from the group consisting of: 0.10% ≦ dA60 × 400 ≦ 1.50%
The cold work tool steel according to any one of claims 1 to 5.
However, “dA60 × 400” is the cleanliness measured based on the method described in JISG0555. Obtained by quenching at a temperature of 950 ° C. or higher and 1080 ° C. or lower,
3.0 ≦ Gq ≦ 8.0
The cold work tool steel according to any one of claims 1 to 6.
However, “Gq” is the crystal grain size of prior austenite after quenching, measured based on the method described in JIS G0551.

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