JPS6220854A - Tool steel excellent in toughness - Google Patents

Abstract

PURPOSE:To develop a high-hardness tool steel for high-speed cutting excellent in strength and toughness by adding specific amounts of Al to a tool steel containing Cr, W, Mo and V so as to prevent deterioration in toughness caused by the addition of V. CONSTITUTION:As the tool steel for use in cutting edges for high-speed cutting such as stationary knives for steel fiber cutting etc., an alloy steel having the following composition is used: the steel containing, by weight 1.5-3.5% C, 0.2-2.0% Si, <1.0% Mn, 3-8% Cr, <10% Mo, <10% W and 5.5-10.0% V and having balance consisting of Fe, which satisfied relations in C>=0.2V and W+2Mo>=4 and to which Al in an amount satisfying 0.5+0.2[C-0.2 V]<=Al<=2.65-[W+2Mo]/40 or further <10% Co is added and incorporated. In this way, the tool steel for cutting edges having high hardness and excellent in wear resistance and toughness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tool steel with excellent hardness and toughness, and particularly to a tool steel suitable as a cutting blade for high-speed cutting such as a fixed blade for cutting steel fibers.

[Conventional technology and its problems]

Hardness and toughness are the basic properties required of tool steel, and hardness, along with precipitated carbides, is deeply involved in wear resistance. That is, wear resistance depends on the type and amount of precipitated carbides. Furthermore, this wear resistance is also affected by the hardness of the martensite base, and it is said that the higher the base hardness, the better the wear resistance.

On the other hand, toughness is a property that is contradictory to hardness; as the hardness increases, the toughness decreases, and conversely, as the total toughness increases, the hardness decreases. This mainly depends on the nature of the martensitic structure.

It has been well known that (2) is effective in improving hardness. This is because V combines with C to form precipitated carbides. However, the addition of (2) significantly lowers the toughness, and since the amount added is limited from the standpoint of toughness, it is not possible to achieve a significant improvement in hardness.

The cutting blade for high-speed cutting described above is required to have high hardness in terms of wear resistance and high performance in terms of toughness, but there have been extremely few tool steels that meet both of these requirements.

The purpose of the present invention is to achieve both high strength and high toughness by compensating for the decrease in toughness caused by the addition of At with the addition of At, to be able to withstand use as a cutting blade for high-speed cutting, and to be economical. We also provide excellent tools W4.

[Means for solving problems]

By the way, tool steels using both V and At'r are well known.

For example, the tool steel proposed in Japanese Patent Publication No. 89-25271 has a ktTh of 0.6 to 4. Although it contains 0 wt%, its purpose is to increase temper softening resistance and improve cutting performance and wear resistance performance as a high-speed tool, that is, hardness, not to improve toughness. Therefore, V, which causes toughness reduction, is 0.8 to 5.0.
The hardness is kept low at wt%, and the hardness is not sufficient.

In addition, the tool steel proposed in Japanese Patent Application Laid-Open No. 53-94215 contains 0.1 to s, o wt% of total M, and 1
Contains ~7 wt%. The effect of these additions is that when At is contained, the wear resistance is improved due to the synergistic effect with the large amount of V solidified in the matrix due to the Zr content.
It is explained. That is, At in this tool steel
and V are also aimed at improving hardness or wear resistance,
Not only are measures regarding toughness insufficient (,zr
Since the aim is to have a synergistic effect with Zr, the high cost associated with the addition of Zr is a problem.

The tool steel of the present invention solves these problems by:
By adding in a large amount, we aim to greatly improve hardness and wear resistance, and also reduce the decrease in toughness caused by adding large amounts of (■).
This was supplemented by the addition of At, which was strictly controlled in terms of C1 and W equivalents, thereby achieving both strength and toughness at a high level.Moreover, the hardness improvement was achieved without the need for iZr, and economical efficiency was also improved. It is something.

That is, the present invention contains C: 1.5 to 8.5 wt%, Sl
:0.2~2. owt, %, m: 1. o wt%
Below, Cr: s, o ~ s, o wt%, W: 10
wt% or less, Mo: 10% or less, V: 5.5-1
0.0wt%, satisfies C≧0.2V1W+2Mo≧4, and 0.5+0.2rc-0.2V)≦At≦16
5-aHrW+2Mo], and further contains c as necessary.
o: 10.0 wt.% or less, and the remainder is Fe and unavoidable impurities, making it a tool steel with excellent toughness.

The reasons for limiting the additive components in the tool steel of the present invention are as follows.

A part of C is solidly bathed in the matrix and forms a martensitic structure, retaining the hardness and strength of the matrix, but most of the rest is carbide-forming elements such as Cr, Mo, W,
Combines with Fe to improve hardness and wear resistance. In particular, ■ is easy to produce carbide, and ■ CO per I wt%
, 2wt%. In addition, the amount of solid solute C mentioned above is 0
．． 4-0.5 wt% is optimal. From these, the lower limit of ① is the C-1i required for V5.5wt%, that is, cl, the lower limit of 5wt%'ftC, and the upper limit is V, Cr
The CB, 5Wt, and % required to completely generate carbides for all SMo, W, and Fe were set.

Sl: Used as a deoxidizing agent, it forms a solid bath in the matrix in steel, and at 0.2 wt% or more, it increases resistance to temper softening and contributes to improving hardness. However, even if it is added in excess of 2.0e%, not only the hardness improvement effect is saturated, but also
Hot forgeability is completely inhibited. For this reason, the amount of Sl added was determined to be in the range of 0.2 to 2.0 wt%.

Mn: Used as a deoxidizing agent like S5-,
If added in excess of 1.0 wt%, Mn will completely stabilize and expand the austenite structure, increasing the amount of retained austenite and causing a total decrease in quenching hardness.
The content was set to 1.9 wt% or less.

Cr: Stone that improves hardenability, wear resistance, and oxidation resistance.
If the content is less than a, o wt%, these improvement effects are small;
On the other hand, if it exceeds s, owt%, the toughness and tempering hardness will decrease, so it was limited to a range of 3.0 to s, owt%.

Mo, W: These are C (!: Combined into M2O type,
Forms MJC type carbide to improve wear resistance. In addition, secondary hardening is performed by tempering. Furthermore, it also imparts heat resistance. However, if the W equivalent (W-)-2Mo) is less than 4, these effects are not sufficient, so W+2Mo≧4. Also, when W and M○ are fully recovered by towt%, At
The upper limit was set at 10 wt% for each, since adding them would cause a decrease in toughness.

(2) = One of the characteristic elements in the tool steel of the present invention, which combines with C to form a hard VC carbide and provides total wear resistance. ■ Penetrates into the substrate and causes secondary tempering hardening. When V is less than 5.5 wt%, these effects are not suitable for use as a cutting blade for high-speed cutting, which is beyond the range of conventional tool steels. This remarkable hardness improvement effect is 10.0w
If it exceeds t%, it becomes saturated, and if it exceeds 10.0wt%, it is uneconomical. Therefore, ■ was limited to a range of 5.5 to 10.0 wt%. However, from the viewpoint of achieving both hardness and toughness, it is recommended to limit the amount to 7.0 to 8.0 wt%. In addition, as mentioned in the section on C, in the formation of VC carbide, 2 wt% of co is required for VIWt'X, so to avoid a shortage of C, it is necessary to replace it so that V is not added unnecessarily. It was decided to satisfy C20.2Vi.

At: This is another characteristic element in the tool steel of the present invention. Conventionally, this M has been added as a deoxidizing agent with a grain-refining effect, and has been limited to an amount of about 0, i wt% at most, and even when added in a relatively large amount, it was intended to improve hardness. (Japanese Patent Publication No. 89-25271 and Japanese Patent Application Laid-Open No. 58-94215).

However, according to experiments conducted by the present inventors, as the amount of At increases, the carbide morphology changes during casting, and the Ms point increases, resulting in a decrease in retained austenite, and as a result, the toughness decreases. It was found to improve. Moreover, the range of this effect cannot be determined only by the amount of M added;
It has become clear that this phenomenon occurs only in a specific range that is closely related to the W equivalent. That is, M is 0.5-)-0,2
If it is less than [C-0.2V), the above-mentioned toughness improvement effect is not sufficient, and if it exceeds 2.65-rW+zMo'), the above-mentioned toughness improvement effect not only disappears, but also results in a total decrease in hardness. It will become. Therefore, At is 0.5
+0.2 [C-0.2V) or more, 2.65--! −
c−w+2Mo) It was limited to the following range 1.

C: Does not form carbides, and by adding as necessary, increases the solubility of C in Fe, increases high-temperature hardness, and improves toughness. This effect becomes clear when C4 is added at 0wt% or more, and when added in excess of 10.0wt%, the effect is saturated and conversely, hardenability and hot forgeability are reduced, so when adding C4, is 4. The content is preferably 0 wt% or more, and the upper limit is 10.0 wt%.

〔Example〕

Next, a non-inventive example will be described. The composition of the steel used in the examples is listed in Table 1.

Example I A sample (
For the first expressions 1 to 6), the amount of wear was measured under the conditions shown in Table 2. Since the amount of wear is affected not only by the carbide but also by the hardness of the base, each sample was oil quenched at 1175°C and then
Hardness i HRC54 by re-refining at 50-600°C
, 5±5, and the test was conducted.

All results are shown in Table 3 and Figure 1. As is clear from this result, the amount of V is within the non-inventive range (5.5 to 10.01%)
Those in 2 have extremely low abrasion loss and excellent abrasion resistance. It is also clear that this effect does not change with the addition of At.

Example 2 Samples with W equivalent (W+2M0) of 4.16.26 and V claw metal changes for each (first expression 7-11.1-
6. Regarding 12-16), after oil quenching at 1175℃,
The hardness HRCf after tempering at 550°C was investigated. The results are shown in Table 4 and Figure 2.

As is clear from this result, for any W equivalent, as the amount of ■ increases, the hardness increases due to secondary hardening.
t%).

Example 3 For each sample in Table 1 Nn5, 30 to 54, 1175
After oil quenching at °C and tempering, bending test specimens with a thickness of 5 layers, a width of 1 layer, and a length of 55 layers were prepared, and three bending tests were conducted on each with a gauge distance of 40 mm. When the claw metal is constant, M
The effect of addition on toughness was investigated.

The results are shown in Table 5 and Figure 3.

As is clear from Table 5, A
The addition of t increases the transverse rupture strength, and the ratio to the transverse rupture strength when A4 is not added is 1 for all non-invention steels.
．． It is 1 or more. Moreover, the lower limit of At at this time depends on the amount of C and the amount of v, as shown in FIG. 3, and At≧
0.5+0.2 [C-0.2V].

Example 4 For each sample in Table 1 Nn5.151.17-29,
The same transverse rupture strength test 1p2 as in Example 3 was conducted to investigate the influence of W current on the relationship between the A7 amount and transverse rupture strength. All results are shown in Table 6 and Section 4C.

In particular, as is clear from Fig. 4, when A/= becomes excessive, the transverse rupture strength decreases;
M0), and At≦2.65−(W+2M0).

The non-inventive steels in Examples 3 and 4 had a ■ of 5.5 to 10.
．． It is clear from Examples 1 and 2 that the content of 0 wt % in this range has high hardness and excellent wear resistance. Therefore, it can be seen that the material No. 11 has high hardness and high toughness.

Example 5 The same transverse rupture strength test as in Examples 3 and 4 was performed on each sample of Nn5.28.55 to 6o in Table 1 to fully investigate the effect of Co addition on transverse rupture strength of 1.1Y. did. As shown in Figure 5, the transverse rupture strength increasing effect due to the addition of Co is Co4, 0.
It is large at wt% or more, and when adding Co, it is 4.0wt.
% or more is found to be effective.

Table 2 Table 3 (W equivalent: 16) Table 4 Table 5 Note: The upper column shows cw2. owt%, bottom column is C-2,5wt%
Table 6 [Effects of the Invention] As is clear from the above description, the tool steel of the present invention not only contains a large amount of v, has high hardness and excellent wear resistance, but also has improved toughness due to the addition of a large amount of It is effectively supplemented by At, which is strictly regulated by the reducing element, C1■, and W equivalent, and has a high degree of hardness and toughness, so it can be used under severe conditions, such as with fixed blades for cutting steel fibers. It exhibits excellent durability as a material for metal materials.

[Brief explanation of the drawing]

The drawings are graphs showing all the effects of implementing the invention. Figure 1 shows the relationship between the amount of wear and test time for samples with a W equivalent of 16, and Figure 2 shows the relationship between the amount of wear and test time for samples with a W equivalent of 4, 16, and 26.
Figure 8 shows the relationship between quantity and hardness.
Figure 4 shows the effects of V and M amounts on the transverse rupture strength in each t%C sample, and Figure 4 shows the effects of W equivalent and Atfi on the transverse rupture strength in the 8.0wt%C sample. Figure 5 shows the influence of Cot on transverse rupture strength in a sample with a W equivalent of 4.26. Figure 1 @ Figure 2 →, wt% ■ Figure 3 Amount wt (va)

Claims (2)

[Claims] (1) C: 1.5-3.5wt%, Si: 0.2-2.
0wt%, Mn: 1.0wt% or less, Cr: 3.0-8
．． 0wt%, W: 10wt% or less, Mo: 10wt% or less, V: 5.5 to 10.0wt%, C≧0.2V, W
+2Mo≧4 and 0.5+0.2 [C-0.
2V〕≦Al≦2.65-(1/40) [W+2Mo]
A tool steel with excellent toughness, the balance being Fe and unavoidable impurities. (2) C: 1.5-3.5wt%, Si: 0.2-2.
0wt%, Mn: 1.0wt% or less, Cr: 3.0-8
．． 0wt%, W: 10wt% or less, Mo: 10wt% or less, V: 5.5 to 10.0wt%, C≧0.2V, W
+2Mo≧4 and 0.5+0.2[C-0.
2V〕≦Al≦2.65-(1/40) [W+2Mo]
, Co: 10.0 wt% or less, and the balance is Fe and unavoidable impurities, making the tool steel excellent in toughness.