JPS62202022A - Manufacture of high toughness tool steel - Google Patents

Abstract

PURPOSE:To provide superior toughness to a conventional steel for a cutting tool by substituting Mo for Cr in the steel, increasing the Ni content and carrying out spheroidizing annealing as well as hot rolling in controlled rolling ratios in the longitudinal and lateral directions. CONSTITUTION:The composition of an alloy tool steel is composed of, by weight, 0.75-0.85% C, <0.35% Si, <0.6% Mn, 2-3% Ni, <0.5% Cr, 0.1-0.5% Mo and the balance Fe with inevitable impurities. The steel is hot rolled as stock so that the ratio of the rolling ratio (the ratio of length after rolling to length before rolling) in the longitudinal direction to the rolling ratio in the lateral direction is regulated to 0.33-3. The hot rolled steel is subjected to spheroidizing annealing, hardening and tempering.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a tool steel, particularly a tool steel with high toughness and low anisotropy, which is used as a circular saw material for cold cutting.

Conventional technology tool steel, JISG 44 as circular saw material for cold cutting
01 r carbon tool am material” SK5, JIS
5K specified in "G 4404 r alloy tool steel"
S5 and 5KS51 are commonly used.

Among these, SK5 is designed to increase hardness and improve wear resistance by containing a large amount of C, and is generally used for woodworking. On the other hand, 5KS5 and 5KS51
The toughness is improved by adding Ni so that it can be applied to cutting steel, and the toughness is improved by adding Cr.
With g4a, which improves wear resistance by forming carbides and also improves hardenability, the tempering temperature is set as high as 300 to 450"C in consideration of the temperature rise of the blade during cutting. This prevents softening.When actually using 5KS5 and 5KS51 as circular saw materials, in the case of woodworking, the cutting edge is often directly processed on the steel material and used as is after quenching and tempering. In the case of cutting, a sintered alloy such as tungsten carbide (Wc) is used for the cutting edge, and 5KS5 and 5KS51 are generally used as the base metal.

Purpose of the Invention However, in the 5KS5 and 5KS51 conventionally used as circular saw materials for cold cutting, in order to prevent tempering from softening due to the temperature rise of the blade when using a circular saw, it is necessary to Tempering temperature :=3.0O~450
However, as is well known, P is an element that promotes tempering embrittlement, and when tempering is performed at temperatures above about 250°C, the P content should be increased to α012% to prevent embrittlement.
It is also known that Cr contained in 5KS5 and 5KS51 in an amount of 0.20 to α5o% promotes tempering embrittlement caused by P. Therefore, the conventional 5KS5 and 5
KS51 has the disadvantage of being prone to so-called low-temperature tempering brittleness, and in order to prevent this low-temperature tempering brittleness, the P content is reduced to 0.
Reducing the temperature to 0.012% or less requires advanced technology, which raises the problem of high manufacturing costs.

Furthermore, when evaluating circular saws for cold cutting, not only machinability but also blade life are very important factors, and the cutting edge of a circular saw is usually reused by re-sharpening or replacing it.
In general, it depends on the wear, breakage, deformation, etc. of the alloy, but in addition to the drawback that the conventional 5KS5 and 5KS51 are susceptible to low-temperature tempering brittleness, they also do not have sufficient toughness and have anisotropy in mechanical properties. In other words, there may be a difference in mechanical properties between the length and width directions of the steel material.
There was also the problem that the alloy was prone to breakage and deformation, reducing the lifespan of the cutlery.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a tool steel that has improved resistance to low temperature tempering brittleness and toughness, as well as improved anisotropy of mechanical properties.

Structure of the Invention The present invention has been made for the above-mentioned purpose, and has the following features:
i amount %, C: α 50% or less, Si: α 35% or less, Mn: 0.80% or less, Ni: 2, oo to ao (1
%, Cr: α50% or less, Mo: 0.10-050%
The material is an alloy steel having a composition (hereinafter % indicates weight %) with the remainder consisting of Fe and other unavoidable impurities, and the rolling ratio in the length direction is 0. I was inspired by a method for manufacturing high-toughness tool steel, which involves hot rolling to obtain a toughness of 33 to 3.0, spheroidizing annealing, and then quenching and tempering.

The present invention will be explained in detail below.

First, the reason why the composition of the material used for the high-toughness tool steel of the present invention is limited as described above will be explained.

The C component is necessary to increase the hardness after quenching and tempering and ensure hardenability, but if it is less than 0.75%, the above hardness and hardenability cannot be secured, while if it exceeds 0.85%, Since the risk of quench cracking increases, the content is limited to α75 to 0.85%.

The Si component is necessary for deoxidation, but if it exceeds 0.35%, there is a risk of quench cracking, so its content was set at 0.35% or less.

Mn component increases strength and hardenability, but α60%
Since the risk of quench cracking increases when the content exceeds 0.60%, the content rate was set at 0.60% or less.

The Ni component improves toughness, but its effect is low below 200%, and the effect is saturated when it exceeds α00%, and no further increase in the effect can be expected, which is economically disadvantageous. The rate was limited to zOO~a00%.

It is effective in preventing tempering embrittlement due to the MOC component P, increasing strength by forming Mo carbides, and improving hardenability, but in grooves where the content is 10 times the P content, tempering embrittlement due to P occurs. If α exceeds 50%, a large amount of Mo carbide will precipitate, or it will become coarse precipitates, leading to deterioration of toughness, so the content was reduced to 0.10.
It was limited to ~0.50%. The lower limit was set to 0.010% because the minimum value of the P content that is mixed as an impurity when melting the material used for the high-toughness tool steel of the present invention is 0.010%, and this value is multiplied by 10. .

The Cr component improves hardness and furnace hardening properties, but in the present invention, Mo is added instead of Cr, so there is little need for Cr addition, so only the upper limit was set, and it was set to 0.50% or less. . As mentioned above, since Cr promotes tempering embrittlement due to P, it is desirable to have a smaller amount.

Both P and S components are impurities that are inevitably included, and their content is not limited, but it is preferable that both of them be 0.030% or less. In particular, P promotes tempering embrittlement and deteriorates toughness, and S forms sulfide inclusions such as MnS, which are elongated during rolling and promote anisotropy in mechanical properties. The less the better.

In addition to the above-mentioned components, Al, which is added for deoxidation, is included, but if the content of Afl increases, the toughness deteriorates, so it is preferable to limit the amount to the amount necessary for deoxidation.

Next, the rolling ratio (L) in the length direction of the material having the above-mentioned component composition is 033 with respect to the rolling ratio (C) in the width direction.
~3.0, i.e. L/C=
Hot rolling (hereinafter referred to as cross rolling) under the conditions of 0.33 to 3.0 is because rolling in only one direction causes inclusions and microstructures to be stretched in only one direction, resulting in anisotropic mechanical properties. This is because alloys made using the above-mentioned materials tend to break or deform, and when L/C is out of the above range, anisotropy becomes noticeable.

In addition, after performing the cross rolling, spheroidizing annealing is performed to spheroidize the carbide and improve the anisotropy by making the microstructure uniform.If the conditions are such that the carbide becomes spheroidal, heating There are no particular limitations on temperature, heating time, cooling rate, etc., but desirable conditions are heating temperature: 600°C to Ac, spot heating time: IHr or more and cooling rate: 50°C/Hr or less. In addition, since high carbon steel such as the high toughness tool steel of the present invention is easily decarburized during spheroidizing annealing, it is desirable to take measures to prevent decarburization.

The quenching and tempering after the spheroidizing annealing is the 5K
Under the conditions carried out in S5 and 5KS51,
Oil quenching is performed at a temperature above the Acs point at which crystal grains do not become coarse, and tempering is performed at a low temperature of 150 to 450°C.

The above description has been made regarding circular saw materials for cold cutting, but the high toughness tool steel of the present invention can be applied not only to the aforementioned circular saw materials, but also to drills, bits, etc. that require toughness and low temperature resistance and tempering brittleness. Needless to say.

Example The following will explain based on examples.

The alloy steel having the composition of the present invention and the alloy steel having the composition 5KS51 specified in JIs G 4404 were melted in a converter, made into a slab by continuous casting method, and then hot rolled to a thickness of 15 mm. After heat treatment, test pieces were cut out and various tests were conducted.Table 1 shows their chemical composition, L/C ratio in hot rolling, presence or absence of spheroidizing annealing, and quenching 'fA.
temperature, presence or absence of quench cracking, and tempering temperature. Spheroidizing annealing was performed by heating at 725° C. for 3 hours, followed by cooling at a cooling rate of 15° C./Hr, and quenching was performed by oil quenching. In the same table, A, B and C represent the composition of the high toughness tool steel of the present invention, cross-rolled so that L/C falls within the range of α33 to &0, and subjected to spheroidizing annealing and quenching and tempering. D is a comparative steel having the composition of the high toughness tool steel of the present invention but not subjected to the cross rolling and spheroidizing tA dulling, and E and F are conventional steels having the composition of 5KS51. In Comparative #D in which spheroidizing annealing was not performed, quench cracking occurred during quenching.

Example 1 Present invention @C and conventional f:! in Table 1 above. Regarding 14F, a Charpy impact test was conducted using a No. 3 test piece specified in JIS Z 2202 r Metal material impact test piece according to JIS Z 2242 r Metal material impact test method.

The test results are shown in Figure 1. In the figure, the horizontal axis shows the test temperature, the vertical axis shows the absorbed energy, the solid line in the figure is the measurement result for the present invention *C, and the broken line is the measurement result for the conventional mF. 1st
From the figure, it can be seen that the MC of the present invention has a larger absorbed energy than the conventional steel F over the entire test temperature range and exhibits good toughness.

Example 2 Regarding the invention steel C and conventional steels E and F in Table 1 above,
In addition to the tempering temperature of 400℃ shown in the same table, the tempering temperature is 100, 20℃.
A Charpy impact test was conducted in the same manner as in Example 1 except that the temperatures were changed to 0, 300, 500 and 600°C. However, the test temperature was 20°C.

The test results are shown in Figure 2. In the figure, the horizontal axis shows the tempering temperature and the vertical axis shows the absorbed energy, the solid line in the figure is the measurement result for the present invention #C, and the dashed line and broken line are the measurement results for the conventional fI4E and F, respectively. From Figure 2, the present invention g
4C has a higher absorption energy over the entire tempering temperature range than conventional IIE and F (shows good toughness, and also has a higher absorption energy than conventional IIE and F [127
It can be seen that there is no decrease in absorbed energy at 0 to 450°C.

Example 3 Regarding the invention steel C and conventional 1MF in Table 1, JIS
A hardenability test was conducted based on the JIS G
o5et-norm +a, JIS Z 22,4
5. The hardness was measured based on the "Rockwell hardness test method."

The test results are shown in Figure 3. In the same figure, the distance is the distance from the quenched end, and the vertical axis is Rockwell C hardness I (RC).
The solid line in the figure is the invention #C, and the broken line is the conventional one! 1
These are the measurement results for iiF. From FIG. 3, the present invention f
It can be seen that RC exhibits better hardenability than conventional steel F, has greater hardness, and therefore has greater wear resistance.

Example 4 A bending test was conducted on the mA, B and C of the present invention shown in Table 1 and the conventional g4F, and the maximum deflection in the length direction and width direction of the steel materials was measured.

Table fi2 shows the dimensions of the test piece, the distance between the supports, the bending radius, and the loading speed.

The test results are shown in Table 3. From the same table, it can be seen that in the conventional tI4F, the maximum deflection in the width direction is smaller than the maximum deflection in the length direction, and there is anisotropy.
It can be seen that in ffA, I3, and C of the present invention, the differences in the length direction and width direction are not so large, and the anisotropy is significantly improved.

Example 5 A carbon steel billet with a diameter of 187mm was cut using a cold-cutting circular saw using the tRC of the present invention and the conventional gllF shown in Table 1, and the cutting area until the blade was discarded was compared. Fourth
The table shows the cutting speed and blade diameter. In addition, the cutting edge of the blade has the present invention *C.

Conventional! A WC-based carbide blade was used in both cases.

The test results are shown in Table m5. From the same table, the cutting area until the blade is discarded is 3~3~3.
40% f''j, thicker (it can be seen that the blade life is significantly extended).

(Left blank space below) Table 4 As detailed in Table 5 of the invention, Cr in the conventional steel for cutting tools was replaced with Mo.
By using the tool steel of the present invention, which is replaced with Ni, increased Ni content, hot rolled by controlling the rolling ratio in the longitudinal direction and width direction, and subjected to spheroidizing annealing, toughness, Hardness after quenching, tempering brittleness resistance, hardenability, etc. are significantly improved, and anisotropy is also improved. As a result, it becomes possible to manufacture a cutting tool steel with good wear resistance and toughness, and it is possible to significantly extend the life of a tool using the tool steel.

[Brief explanation of drawings]

Figures 1, 2, and 3 are diagrams showing comparative examples of mechanical properties of the tool steel of the present invention and conventional tool steel, and Figure 1 shows the relationship between test temperature and absorbed energy in the Charpy impact test. 2 is a diagram showing the relationship between tempering temperature and absorbed energy in the Charpy impact test. FIG. 3 is a diagram showing the relationship between distance from the quenched end and hardness. Figure 1: V paper 31&c・c) Figure 2: Manto tsukishi L 攬C'e) Figure 3: 1f 2 tP φ 2

Claims (1)

[Claims] In weight%, C: 0.75-0.85%, Si: 0.35
% or less, Mn: 0.60% or less, Ni: 2.00 to 3.
00%, Cr: 0.50% or less, Mo: 0.10-0.
The material is alloy steel with a composition of 50% Fe and other unavoidable impurities, and the ratio of the length after rolling to the length before rolling in the longitudinal direction (hereinafter referred to as rolling ratio). 0.33 to rolling ratio in width direction
1. A method for producing high-toughness tool steel, which comprises hot rolling to obtain a toughness within the range of 3.0, spheroidizing annealing, and then quenching and tempering.