JPS5855553A - Tool steel - Google Patents

Abstract

PURPOSE:To provide tool steel to which excellent cutting property and toughness are imparted, by specifying S and Zr contents in steel, the configuration of sulfide inclusion and the area ratio of Zr(C, N). CONSTITUTION:Tool steel contains 0.40-1.5% C, 0.10-2.5% Si and 0.1-2.5% Mn as essential elements as well as 0.035-0.40% S and 0.001-0.5% Zr and comprises the remeinder Fe substantially. Among sulfide inclusions with a long diameter of 2mu or more present in this steel, at least 80% or more has an aspect ratio of 10 or less and the area ratio occupied with Zr(C, N) is limitted to 0.4% or less. The composition of this tool steel is selected in components and contents corresponding to the purpose of steel for a mold. In this tool steel, other than S as an element for improving cutting property, a specific amount of Zr is used together to adjust the configuration of sulfide inclusion and, at the same time, both of cutting property and toughness are imparted by limitting the amount of Zr(C, N).

Description

[Detailed description of the invention] The present invention relates to improvements in tool steel, particularly mold steel.

In general, it goes without saying that tool steel should have high toughness, hardness, and wear resistance, but in particular, tool steel, such as mold steel for die forging and plastic molding, must have high toughness, hardness, and wear resistance. Drinking water is exceptional in its rigidity. Regarding the force and the constant force 11, it is desirable that K due to the anisotropic linear direction is small.

Conventionally, in order to improve the machinability of steel, S, S (3, T
Addition of base threads such as e, Bi, Ca, etc. has been carried out. These have a negative effect on toughness, so their content must be selected appropriately. S is the most typical stiffness-improving element, and serves this purpose mainly by forming MnS-based inclusions. However, the shape of these sulfide-based inclusions is a problem, and if they exist in a form stretched in a certain direction due to processing, they will increase the anisotropy of the mechanical properties of the material, which is undesirable.

In view of these circumstances, the present invention aims to provide tool steels such as mold steels containing S as an element for improving machinability, while achieving excellent rigidity and improving mechanical properties such as toughness. This was done with the intention of providing a material with low anisotropy of properties. It is also within the intention of the invention to maintain high surface hardness and abrasion resistance.

The tool steel of the present invention, which satisfies such demands, contains S: 0.035 to 0.40% and Zr: 0.001 to 0.5%, with the remainder being substantially At least 80% of the sulfide inclusions with a major diameter of 2μ or more that are present in the steel and have a composition consisting of Fe.
is characterized in that the length ratio is 10 or less, and the area ratio occupied by Zr (C, N>) is 0.4% or less.

Generally, stiffness and toughness are contradictory properties, and it has traditionally been difficult to create tool steel that is excellent in both. In addition to an appropriate amount of machinability improving element S, a specific amount of Z
By using r together, we can control the morphology of sulfide-based inclusions, and at the same time, we know that Zr (C,N), which is inevitably generated due to the presence of zr, greatly impairs rigidity, so we control its scales. The present invention is the first attempt to put into practical use a tool steel with excellent machinability and toughness.

The S content of 0.035 to 0.40% is determined mainly by the limit at which the desired stiffness improvement effect can be obtained and the cleanliness of the steel, but it is also related to Zrl.

The lower limit of 0.5% is the minimum limit at which the above-mentioned effect of controlling the shape of sulfide-based inclusions is recognized, and the upper limit is the upper limit for the formation of a large amount of Zr (C, N). This is a value from the viewpoint of avoiding a decrease in stiffness and hot workability based on the above. Both were determined in relation to 81 in the previous 2.

Regarding the morphology of sulfide inclusions, it is known that they greatly affect the anisotropy of the mechanical properties of steel, but their relationship with the practical properties of tool steels, especially mold steels, especially toughness, is unknown. Therefore, the present inventors conducted a detailed investigation through numerous experiments. As a result, the major axis 2 of the sulfide inclusions
Large objects larger than μ have an influence on strength anisotropy, and there is virtually no negative effect as long as the length/breadth ratio is within 10 and the length is not extremely stretched. It has been found that if the number of sulfide-based inclusions that do not exist is 80% or more of the total number of sulfide-based inclusions, a practically desirable isotropy can be achieved.

Zr (C, N> In other words, Zr carbides and nitrides are extremely hard and cause significant wear on the cutting edge of the cutting tool, impairing machinability as mentioned above. The practically acceptable limit is the cutting of steel materials. The research conducted by the present inventors has revealed that the area ratio on the surface is 0.40%.

The tool steel of the present invention, which satisfies the above-mentioned conditions of S and Zr contents, the form of sulfide inclusions, and the area ratio of Zr (C, N>), also contains various additive elements necessary for tool steel. It goes without saying that it must contain a large number of combinations of the edge classes and content ranges of such elements, but the following are representative ones: be.

OC: 0.40-1.5%, Si: 0.1
0-265% and Mn: 0.1-2.5% ○ C: 0.30-0.60%, 3i: 0
．． 10-2.0%, Mn: 0.10-2.0%,
Cr: 0.2-2.0% and MO: 0.0
5-1.0%○ C: 0.20-0.50%, S
i: 0.10-2.0%, Mn: 0110-2.5%,
Cr: 1.5-3.5%, 1ylo: 0.
10-1.5% Oyohi v: 0.01-0.50% ○ C: 0.10-0.25%, Si: 0110
~1.0%, Mn: 0.40~2.0%, Ni
: '2.0~4.0%, Mo: 0.05~
1.0%, Cu: 0.50-1.5% and A: O, SO-1.5% OC: 0.30-0.9
0%, 3i: 0.10-1.5%, Mn:
0.10-1.5%, Cr:6.5-15%, Mo
: 0.01~1.5% OJ:ffV : 0.0
1-1. (1% ○ C: 0.95-2.0%, Si:, 0.1
0-2.0%, Mn: 0.10-2.5%,
Cr: 9.0-15%, MO: 0.20-1.5%
and y: o, oi ~1. .

%.

The respective roles played by these additive elements in the tool steel of the present invention are not fundamentally different from those known for conventional steels, but will be described below in relation to the features of the present invention.

C: In order to ensure the hardness and wear resistance of tool steel, especially mold steel, the content is selected depending on the purpose of use.
Excessive presence reduces toughness.

Si: In addition to having a deoxidizing effect during melting, Si is useful for strengthening the matrix, so it is contained in a relatively large amount in the steel of the present invention.
However, if it is too large, the toughness and resistance to softening at high temperatures will decrease, and the amount of base paper will increase. Moreover, it is also unfavorable in terms of stiffness.

Mn: In addition to deoxidizing and desulfurizing effects during melting, Mn is also effective in improving hardenability, and is also used in a relatively large amount in the present invention. The limitations are a decrease in stiffness and a decrease in toughness due to coarsening of crystal grains.

Ni: Effective in strengthening the base and ensuring hardenability, and is added in the required amount depending on the purpose of the steel.

However, there is a limit in terms of rigidity.

C: It strengthens the base and helps to ensure hardenability, wear resistance, and oxidation resistance, so it is also added more actively for the purpose of use. Establish limits.

CO: Still effective in strengthening the matrix and providing resistance to softening at high temperatures. However, if too much is added, the toughness will deteriorate and it will also be economically advantageous.

MOLW and V: These are both strong carbide-forming elements and are useful for increasing wear resistance, heat treatment hardness, and resistance to temper softening at high temperatures. Addition of a large amount also reduces toughness and makes manufacturing difficult, and also impractical in terms of machinability.

Cu: Promotes precipitation hardening and is effective in ensuring wear resistance. However, its presence in large amounts is unfavorable for toughness.

Furthermore, the steel included in the present invention includes alloys containing the following elements as necessary for tool steel.

○ C: 0.10% or less, 3i: 0.30% or less, Mn: 0.30% or less, Ni: 10 to 25%
, Cr near, 0% or less, MO: 3.0-15%, C
o: 5.0~25%, A: 0.01~1.
0%, Ti: 1.0% or less, B: 0.20% or less and (:, a: 0.10% or less, ○ C: 0.40-0.65%, Si: 0.10
~1.5%, 1yln: 0.10~1.5%, N
i: 1.0~3.0%, Cr: 0.50~
2.5%, MO: 0.10-1.0% and V: 0
．． 01-0.50% OC: 0.15-0.35%,
3i: 0.10-1.5%, Mn: 0.1
(1-1.5%, 'Ni: 0.20-2.5%,
Cr: 1.5~4.0%, MO: 0.20~
1.5% and V: 0.10-1.2%○ C: 0.1
5-0.60%, 3i: 0.10-2.0%, preferably 0.10-0.90%, Mn: 0.10-1
．． 50%, Cr: 3, O~6.0%, M
O2 0.30-4.0% J5yo (FV: fl, 0
5~'t, 0%, preferably 0.05~0.80%, and if necessary, Ni: 2.0% or less, C
u: 2.0% or less, Co: 5.0% or less and W: 3.0% or less, ○ C: 0.20-0.40%, Si: 0.1
0-1.5%, Mn: 0.10-2.0%, C"
:1.5~3.5%, W:4.0~12% and V:0
．． 10~1.0% QC: 0.30~0.50%, sr:
o, io~1.5%, Mn: 0.10~1.5%
, Cr: 3.0-5.0%, MO: 0.20
~2.0%, W:2.0~5.0%, V:0.50~2
, 5% and V: 1.5-5.0% QC: 0.
50-0.70%, 3i: 0.10-2.0%
, Mn: 0.10 to 2.0%
, Cr2 3.0-5.0%, MO:
3.5-5.5%, W: 1.5-6.5% and V:
O, S ~ 2.0% In the above alloy, Amin acts as a deoxidizing agent during melting, improves toughness through grain refinement, and ensures heat treatment hardness and wear resistance through precipitation hardening. It is effective for However, if too much is added, the base paper will increase, so there is a limit naturally.

In addition, among the above alloys, those that do not contain Ti
: 1.0% or less and or Nb: 1.
It can be contained in an amount of 0% or less. These elements also refine grains and increase toughness. However, A2
In the same way, excessive presence leads to an increase in base paper (not only that, but it also impairs toughness).

The steel of the present invention has the advantage of good machinability, but if a higher degree of stiffness is desired, in addition to a predetermined amount of S, p
b: 0.30% or less, 3e: 0.30% or less, 8i: 0.30% or less, Te: 0.1
5% or less and Ca: 0.01% or less of one or more types can be contained.

Hereinafter, the present invention will be described in detail with reference to Examples.

Steel 111-2 having the composition shown in Table 1 was melted. These are composed of the existing tool steel and the steel of the present invention, which has the basic composition of the existing tool steel and has adjusted the amounts of Si and Zr.

The relationship between the steel type group and the sample material number is as follows.

Sample material number, -L1 Ran-11JLIL I JIS 555C1, 23, 4 JIS 80M440 5' 6~8
JIS 5KD11 ♂, 10″ 11.12
Cr-MO-V 13" 14~1B
17 Fang 18-20 Blue 3Ni-I Cu-I A 21 22.23 Marage steel 24 25.26 Each specimen was subjected to the required heat treatment to reduce the hardness GF and remove sulfide-based inclusions. The shape of the object and the area ratio of Zr(C,N) were investigated.

Next, since these ropes are mainly used as mold materials for plastic molding, practical molds were made from each sample material and their workability was evaluated.

The above results are summarized in Table 2. In the table, "Inclusions (%)" means the percentage of large sulfide inclusions with a major axis of 2 μ or more that are not very elongated and have a major axis ratio of 10 or less. do.

The evaluation criteria for workability are as follows.

O Particularly good ○ Good 8 Average No1
-8, 13-16 and 21-23 are No. 8, 13-16 and 21-23 after heat treatment.
9-12, 17-20 and 24-26 were processed before heat treatment.

Steel having the composition listed in Table 3 was melted. Similar to Example 1, this is also a comparison of existing tool steel and its improvement according to the present invention, and the relationship between the steel type group and the sample material number is as follows.

Sample material number: L-J-Kita JL! l - prisoner l5
KT4 27''' 28.29 length piece Ni-CI-M, -V 30.31 32.33
Masu rice bowl 5KD61 34.35 36-41 rice bowl 5KD5 42.43 44.45ff
Fire high speed tool steel 50,51 52.53 These steels are mainly used for making molds for die forging, so after forging to give a forging ratio of about 10, some (NO27-39) are subjected to the necessary heat treatment,
In addition to measuring hardness, sulfide inclusions and Zr (
C, N) and also conducted an impact test.
This impact test is to examine the anisotropy of the toughness of the material, and two types of test pieces are prepared, one in the direction perpendicular to the forging direction and the other in the forging direction. It was used as a measure of gender.

The above results are summarized in Table 4.

Next, the forged and heat-treated steel materials were die carved, with some (No. 40 and above) being heat treated after processing, the workability was recorded, and the finished mold was used to carry out actual forging. , evaluated the durability of the mold and investigated the cause of damage.

The results are shown in Table 4 along with the products targeted for die forging.

Die engraving workability is the result of a comprehensive evaluation of machining efficiency (tool life, shape of chips, etc.) and required machining time when machining practical molds, and is based on conventional materials.
The smaller the number, the better.

Sample materials Nos. 38 to 41 had better results in die engraving workability and mold durability than Nos. 36 and 3 days. This shows that when the hardness of the work material is as high as H.040 grade, machinability can be significantly improved by slightly lowering the amounts of Sl and V. Furthermore, by reducing the amounts of Sl and V, heat check resistance is improved and mold durability is improved. For this reason, 3i
The preferable ranges are 0.10 to 0.90% for , and 0.05 to 0.80% for .

Table 5 Table 5 (continued)

Claims (16)

[Claims] (1) S: 0.03 with elements necessary for tool steel
5-0.40% and Zr: 0.001-0.5
%, with the remainder consisting essentially of Fe,
At least 80% of the sulfide inclusions with a major axis of 2 μ or more present in steel have a major axis ratio of 10 or less, and Zr
A tool steel characterized in that the area ratio occupied by (C, N) is 0.4% or less. (2) C: 0.40 as an element necessary for tool steel
1.5%, 3i: 0.10-2.5% and Mn: 0.1-2.5%. (3) C: 0.30 as an element necessary for tool steel
-0.60%, St: 0.10-2.0%, M
n: 0.10~2.0%, Cr: 0.2~
2.0% and MO: 0.05 to 1.0%. (4) C: 0.20 as an element necessary for tool steel
~0.50%, Si: 0.10~2.0%, M
n: 0.10~2.5%, Cr: 1.5~
3.5%, MO: 0.10-1.5% and Hv: 0
．． The tool steel according to claim 1, containing 01 to 0, SO%. (5) C: 0.10 as an element necessary for tool steel
~0.25%, St: 0.10~1.0%, M
n: 0.40-2.0%, Ni: 2.0
~4.0%, Mo: 0.05~1.0%, Co
: 0.50~1.5% and Ai:O,SG~1.
Tool steel according to claim 1 containing 5%. (6) C: 0.30 as an element necessary for tool steel
~0.90%, Si: 0.10~1.5%, M
n: 0.1 (1~L5%, Cr:6.5~15%
, Mo: 0.01~1.5096oJ=(FV
: [Claim 1] containing 0.01 to 1.0%. (7) C: 0.95 as an element necessary for tool steel
~2.0%, Si: 0.10~2.0%, Mn
Claim 1 contains: 0.10-2.5%, Qr: 9.0-15%, MO2 0.20-1.5% and V: 0.01-1.0%. tool steel. (8) C: 0.10 as an element necessary for tool steel
% or less, Si: 0.30% or less, Mn: 0.3
0% IX lower, Ni: 10.0-25%, Cr
: 7.0% or less, MO: 3.0-15%, Co
: 5.0-25%, AQ, : 0.01-1.0%
, Ti: 1.0% or less, B: 0.20% or less, and Ca: 0.10% or less. (9) C: 0.40 as an element necessary for tool steel
~0.65%, 3i: 0.10~1.5%, M
n: 0.10~1.5%, Ni: 1.0~
3.0%, Cr: 0.50-2.5%, Mo:
0.10-1.0% and V: 0.01-0.50
The tool steel of claim 1 containing % = (10) The principal amount required for tool steel is C: 0.
15-0.35%, Si: 0.10-1.5%
, Mn: 0.10 to L5%, Ni:
0.20-2.5%, Or: 1.5-4.
0%, Mo: 0.20-1.5% and V: 0.
Tool steel according to claim 1, containing from 10 to 1.2%. (11) As an element necessary for tool steel, C: 0.
15-0.60%, 3i: 0.10-2.0%, Preferably L, <4; tO, 10-0.90%, Mn:
0.10-1.50%, Cr: 3.0-6.
0%, 1ylo: 0.30-4.0% and V:
0.05-2.0%, preferably 0.05-0.80%
and, if necessary, Ni: 2.0
% or less, CLI: 2.0% or less, 'Co:
The tool steel according to claim 1, which contains one or more of the following: 5.0% or less and W: 3.0% or less. (12) As an element necessary for tool steel, C: 0.
20-0.40%, 3i: 0.10-1.5%
, Mn: 0.10-2.0%, Cr: 1.
5-3.5%, W: 4.0-12% FV:
Claim 1 containing 0.10-1.0%
Section 6 tools. (13) As an element necessary for tool steel, C: 0.
30-0.50%, 37: 0.10-1.5%
, Mn: 0.10-1.5%, Cr: 3.
0-5.0%, MO: 0.20-2.0%, W: 2
．． ．． 0-5.0%, -0.50-2.5% and Co
: The tool steel of claim 1 containing 1.50 to 5.0%. (14) As an element necessary for tool steel, C: 0.
50-0.70%, 3i: 0.10-2.0%
, Mn: 0.10-2.0%, Cr: 3.
0-5.0%, 1ylo: 3.5-5.5%, W
1.5 to 645% of V and 0.5 to 2.0% of V. (15) Furthermore, the tool steel with the tll shear force\ of Claims 1 to 14 containing NI): 1.0% or less and/or Ti: 1.0% or less (however, Regarding item 8, Nb:, 1.0%
(limited to the following cases). (16) Furthermore, pb: 0.30% or less, Se
: 0.30% or less, 3i: 0.30% or less, T
The tool steel according to any one of claims 1 to 15, containing one or more of e: 0.15% or less and Ca: 0.01% or less.