JPH07316739A - Cold tool steel - Google Patents

Abstract

PURPOSE:To produce a tool material for the working of a hard-to-work material as a cold tool steel capable of obtaining hardness of >=64 HRC even in the case vacuum heat treatment is executed to a large one and capable of making the hardness and high toughness compatible. CONSTITUTION:An alloy compsn. having components contg. 0.75 to 1.15% C, 0,45 to 1.5% Si, <=1.5% Mn, 4.5 to 7.0% Cr, 3.0 to 6.0% Mo, <=3.0% W and 0.5 to 2.5% V, and the balance substantial Fe, and in which Weq(2MO+W) is regulated to 8 to 14 and does not exceed (-2.4Cr+26) is adopted. Thus, the cold tool steel high in hardenability can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold work tool steel, a cold work tool using the same, and a method for producing the same.
Since the cold work tool steel of the present invention has high toughness and hardenability and easily obtains high hardness, it is suitable for manufacturing tools and rolls for processing materials having low workability.

[0002]

2. Description of the Related Art As the cold working progresses, for example, the production of gears is changed from cutting to plastic working, and materials having high strength are used as materials for producing bolts by rolling. The load is increasing.

Conventionally, die-steel SKD11 type high carbon high chromium steel, high speed tool steel SKH51, etc. have been used as materials for cold working tools. SKD11
The hardness was about HRC62, and the number of usage conditions under which the load stress was high was high, and therefore the strength was unsatisfactory. SKH51 can obtain high hardness if it is ideally hardened, but since it is not originally hardenable, it becomes difficult to fully demonstrate its performance as tools become larger and vacuum hardening becomes widespread. ing.

[0004]

SUMMARY OF THE INVENTION One object of the present invention is to take a step forward from the current state of the art concerning cold work tool steel as described above, and to achieve a high hardness of HRC64 to 66 in a large-sized tool which has been vacuum heat treated. It is to provide a cold work tool steel that can be realized and can be manufactured with high toughness.

Another object of the present invention is to provide a method for producing a cold work tool of high hardness and high toughness from the above cold work tool steel.

[0006]

The cold work tool steel of the present invention comprises:
As a basic alloy composition, C: 0.75 to 1.15%, S
i: 0.45-1.5%, Mn: 1.5% or less, Cr:
4.5-7.0%, Mo: 3.0-6.0%, W: 3.
0% or less and V: 0.5 to 2.5%, with the balance being essentially Fe, an alloy component, Weq = 2Mo +
When W, 8 ≦ Weq ≦ 14, Weq ≦ −2.4C
It is a cold work tool steel having an alloy composition satisfying r + 26 and having high hardenability.

The amount of each alloy component is preferably as follows. C: 0.78 to 0.95%, Si: 0.6 to
1.0%, Mn: 0.1-1.5%, Cr: 5.1-
6.0%, Mo: 4.0-5.5%, W: 3.0% or less and V: 1.0-1.6%, with the balance being substantially F.
e.

Cold tool steels of the above basic alloy composition also
In addition to the above-mentioned components, one having a preferable alloy composition may also contain one or both of the following alloy components of group i) and b).

A) Ni: 0.25 to 1.5%, B: 0.
001 to 0.10%, Nb: 3.0% or less and Co:
1 type or 2 types or more selected from 5.0% or less, and b) REM: 0.60% or less, Y: 2.0% or less, Zr:
Selected from 2.0% or less and Hf: 2.0% or less 1
Seed or two or more.

The cold working tool manufacturing method of the present invention comprises forming a cold tool steel having any of the above alloy compositions, quenching it by vacuum heat treatment, and then high temperature tempering at 500 ° C. or higher to harden it. Is set to HRC 64 or more.

[0011]

The high-speed tool steel such as SKH51 has poor hardenability as described above. Therefore, it has been attempted to increase the amount of Cr to improve the hardenability, but it is known that if this is done, the toughness decreases. The inventor believes that this decrease in toughness is due to a change in the morphology of carbides in steel, and as a result of research on factors that influence the morphology of carbides,
By appropriately selecting the value of Weq = 2Mo + W and the amount of Si of the alloy, it has been found that the carbide can be made finer even if a high amount of Cr is adopted, and high hardness and high toughness can both be achieved. Came to.

More specifically, M ₂ C type carbides in high speed tool steel, when heated to high temperatures, M ₂ C → M ₆ C + MC
Caused a decomposition reaction of, and what was plate-shaped became granular,
Miniaturize. M ₂ C carbide is (Fe, Mo, W, V,
It is a double carbide of Cr) ₂ C, and by changing the proportions of the constituent elements, especially the amounts of Mo and W, and selecting the Si amount in a high range, it is possible to realize the refinement of the carbide by the above reaction. , The findings of the inventor.

The reasons for limiting the alloy composition of the present invention are as follows.

C: 0.75 to 1.15%, preferably 0.78 to 0.95% 0.75% in order to secure a tempering hardness HRC of 64 or more.
The above is required, and the content of carbides is kept at 1.15% or less so as not to be excessive.

Si: 0.45 to 1.5%, preferably 0.6 to 1.0% Si is solid-solved in M ₂ C type carbides to increase the amount of carbides, and at the same time, it has a high Cr content. The above-mentioned reaction of M ₂ C carbide in the above is promoted, and the region where fine carbide is obtained is expanded. Of course, it also forms a solid solution in the matrix and contributes to the increase in hardness. Therefore, in the present invention, the conventional Si amount (S
KH51 has selected a range higher than 0.3%).
However, an excessive amount of Si rather reduces the toughness, so the above-mentioned limit is set.

Mn: 1.5% or less, preferably 0.1
Add an appropriate amount as a 1.5% deoxidizing desulfurizing agent and as a hardenability improving element. The upper limit was determined from the viewpoint of not impairing hot workability.

Cr: 4.5-7.0%, preferably 5.
1-6.0% Solid solution in matrix to improve bainite hardenability. However, when the amount of Cr is large, the amount of not formed M ₂ C type carbides but M ₇ C ₃ type carbides that do not cause the above-mentioned refinement reaction even when heated increases, which is disadvantageous. I put it.

Mo: 3.0 to 6.0%, preferably 4.
0-5.5% W: 3.0% or less In order to realize an appropriate amount of carbide and a composition ratio of double carbide, the above range was selected. Mo has a high content range because it shifts the appropriate quenching temperature to the low temperature side and improves the bainite quenchability.

Weq = 2Mo + W: 8 to 14, and (-
2.4Cr + 26) or less In order to secure the wear resistance and hardness required for tools,
Weq must be 8 or more. An increase in the amount of Cr intended to improve hardenability leads to a decrease in toughness due to the carbide morphology. Weq is a condition for maintaining high toughness.
Should not exceed 14 and should not exceed the value of (−2.4Cr + 26), which decreases with increasing Cr content.

V: 0.5 to 2.5%, preferably 1.0
~ 1.6% V refines the crystal grains and improves wear resistance. Therefore, the lower limit amount required is 0.5%. On the other hand, if the amount of V is too large, a large amount of VC will be precipitated during solidification, or carbide will be significantly precipitated in the high temperature region during cooling during quenching. Therefore, there is a limit to the amount of V and the above upper limit. I set the value.

The action of the alloy components arbitrarily added and the reason for limiting the amount of addition are as follows.

Ni: 0.25 to 1.5%, B: 0.00
1 to 0.10%, Nb: 3.0% or less and Co: 5.
1 type or 2 types or more selected from 0% or less Ni and B enhance hardenability. Nb also forms stable carbides to suppress carbide precipitation in the high temperature region during quenching,
As a result, it works to prevent deterioration of quenching hardness.
If the amount of these elements is large, the hot workability is deteriorated or the annealing hardness is adversely affected, so the above-mentioned respective limits are set. While Co improves the hardness after heat treatment, it lowers the bainite hardenability, so the upper limit was set from this viewpoint.

REM: 0.60% or less, Y: 2.0% or less, Zr: 2.0% or less and Hf: 2.0% or less 1
Or two or more of these elements improve the hot workability by binding with impurities such as S and P in steel and fixing them.
Increase toughness. Further, it is also useful for miniaturization of VC by combining with N. If the amount is too large, the cleanliness of the steel will be impaired and the toughness will rather deteriorate, so an upper limit was set for each.

[0024]

Example A cold work tool steel having the alloy components shown in Table 1 (% by weight, the balance being substantially Fe) was melted. The values of Weq and -2.4Cr + 26 of each alloy are also shown in Table 1.

Table 1 No. C Si Mn Cr Mo WV Ni ... REM ... Weq -2.4Cr +26 Example 1 0.82 0.70 0.30 5.43 4.66 1.02 1.22 − − 10.3 13.0 2 1.00 0.45 0.64 4.95 4.95 1.93 2.13 Ni0.12 − 11.8 14.1 3 0.90 1.02 0.08 6.89 3.08 2.49 0.99 Ni0.22 − 8.6 9.5 4 0.77 1.03 0.32 5.72 4.88 1.89 1.66 Ni0.31 − 11.6 12.3 5 1.15 1.33 0.37 5.55 5.97 0.02 2.01 Ni0.20 − 12.0 12.7 6 0.99 0.83 0.94 5.31 4.13 1.88 0.51 Ni1.05 − 10.1 13.2 7 0.89 1.05 0.33 5.91 4.91 1.54 1.88 Nb1.31 − 11.4 11.9 8 0.84 0.71 0.55 5.39 4.22 1.99 1.38 B 0.01 Y0.08 10.4 13.0 Comparative Example 1 0.79 1.44 0.82 5.88 5.75 2.01 0.48 − − 13.5 11.9 2 1.00 0.34 0.35 5.62 7.21 2.12 1.93 − − 16.5 9.0 3 3 1.08 0.55 0.33 6.01 6.88 3.92 1.41 − − 17.7 11.6 4 0.85 0.34 0.41 4.13 5.03 6.41 1.91 − − 16.5 16.1 5 0.75 1.44 0.38 6.21 3.65 − 1.22 − − 7.3 11.1 Comparative Example 4 is a conventional SKH51 steel. It is considerable.

Each steel was forged, annealed and then quenched-tempered. Quenching was performed by vacuum heating / gas cooling. The cooling rate is 20 ° C / min. For tempering, a high temperature was used in consideration of the surface temperature reached when using the tool.

The hardness of each test material was measured, and its toughness was examined by a Charpy impact test. The wear resistance was measured by the Ogoshi rapid wear test under the following conditions: Counterpart material: SCM440 (annealed) Glide distance: 200 m Glide speed: 2.93 m / sec Load: 6.3 kgf The results were treated under heat treatment conditions. The results are shown in Table 2.

Table 2 No. Heat treatment temperature (℃) Hardness Charpy impact value Wear resistance Quenching Tempering HRC (J / cm ² ) (mm ² / kgf) Example 1 1140 540 66.2 34 12 × 108 2 1160 540 66.1 28 9 3 1140 540 65.3 31 20 4 1140 540 64.3 41 23 5 1140 540 66.5 29 9 6 1170 540 65.8 29 18 7 1140 540 65.2 27 19 8 1140 540 65.3 30 24 Comparative Example 1 1160 540 65.3 19 18 2 1160 540 65.1 15 16 3 1190 540 65.4 10 16 4 1190 540 62.7 19 25 5 1140 540 64.8 19 42

[0029]

According to the present invention, the above-mentioned embodiment is the HRC.
High hardness of 64 to 66 and Charpy impact value of 30 to 40 J
/ Cm ² class toughness is obtained. It was confirmed that sufficient quenching can be achieved even by the vacuum heat treatment, which tends to have a lower quenching effect than when using a conventional salt bath. Therefore, the present invention is a tool for processing difficult-to-machine materials, especially cold heading tools, cold rolling rolls,
Not only is it meaningful when applied to rolling dies, but it can also be applied to warm forging tools.

Claims (8)

[Claims] 1. C: 0.75 to 1.15%, Si: 0.4
5 to 1.5%, Mn: 1.5% or less, Cr: 4.5 to
7.0%, Mo: 3.0 to 6.0%, W: 3.0% or less and V: 0.5 to 2.5%, with the balance being substantially F.
It is composed of an alloy component of e, and when Weq = 2Mo + W, 8 ≦ Weq ≦ 14, Weq ≦ −2.4Cr + 26
A highly hardenable cold work tool steel with an alloy composition that satisfies the requirements. 2. C: 0.78 to 0.95%, Si: 0.
6-1.0%, Mn: 0.1-1.5% or less, Cr:
5.1-6.0%, Mo: 4.0-5.5%, W: 3.
0% or less and V: 1.0 to 1.6%, with the balance being an alloy component substantially Fe, Weq = 2Mo +
When W, 8 ≦ Weq ≦ 24, Weq ≦ −2.4C
A high hardenability cold work tool steel having an alloy composition satisfying r + 26. 3. An alloy, in addition to the alloy components of claim 1 or 2, Ni: 0.25 to 1.5%, B: 0.001 to
0.10%, Nb: 3.0% or less and Co: 5.0%
A cold work tool steel having high hardenability and having a composition containing one or more selected from the following. 4. An alloy, in addition to the alloy components of claim 1 or 2, REM: 0.60% or less, Y: 2.0% or less,
A highly hardenable cold work tool steel having a composition containing one or more selected from Zr: 2.0% or less and Hf: 2.0% or less. 5. An alloy, in addition to the alloy components of claim 1 or 2, Ni: 0.25 to 1.5%, B: 0.001 to
0.10%, Nb: 3.0% or less and Co: 5.0%
One or more selected from the following, and RE
M: 0.60% or less, Y: 2.0% or less, Zr: 2.0
% Or less and Hf: 2.0% or less, a cold work tool steel with a high hardenability having a composition containing one or more kinds. 6. The cold work tool steel according to claim 1, which is formed, quenched by vacuum heat treatment, and then tempered at a high temperature of 500 ° C. or higher to have a hardness of HRC 64 or higher. Manufacturing method of cold working tool. 7. A high hardness and high toughness cold working tool manufactured by the method according to claim 6. 8. The cold working tool according to claim 7, which is a rolling die, a Sendzimir roll or a cold forging die.