JPH01222019A - High-speed steel tool - Google Patents

Abstract

PURPOSE:To improve wear resistance of a tool by irradiating the surface of steel material with high energy density beam, by melting and rapidly cooling and successively, making martensitic structure substantially containing no delta- ferrite of the high hardness layer after heat-treatment. CONSTITUTION:The solidified layer is formed after melting and rapidly cooling by irradiating the surface of steel material with the high energy density beam of laser beam, etc., and successively the heat treatment is executed, to form the high hardness layer. Then, by adjusting contents of C, Cr, Mo, W, V, Ni, Co, etc., in the steel composition, the high hardness layer is made to the martensitic structure substantially containing no delta-ferrite. By this method, especially, the high speed-steel tool having excellent wear resistance can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a high-speed steel tool having particularly excellent wear resistance.

[Prior art] The demand for higher efficiency and precision in cutting and plastic working has been increasing in recent years, and various improvements have been made to high-speed steel cutting tools and plastic working tools. Efforts are being made to improve the wear resistance, toughness, or hardness of the moving surface.

For example, Japanese Patent Laid-Open No. 59-83718 discloses the following method.

First, a high-speed steel tool material is hardened and irradiated with a laser beam (hereinafter simply referred to as laser) to locally melt and rapidly solidify, thereby removing a large amount of primary carbide contained in the material steel. to reduce or eliminate coarse carbides in the surface layer structure. After that, by tempering at a constant temperature, the solid solution carbide is finely precipitated,
Hardness, toughness, and wear resistance are improved by promoting secondary hardening (hereinafter, this treatment is referred to as laser treatment).

[Problem to be solved by the invention] However, 5KH of high speed steel that is generally used
When applying the above laser treatment to materials such as No. 2 and 5KH51, the laser treatment effects such as improved wear resistance may not be obtained depending on the laser treatment conditions. After investigating and investigating the cause, we found the following.

In order to obtain the laser treatment effect, the structure of the rapidly solidified layer formed by laser irradiation needs to be a martenside structure similar to the conventional hardened structure. However, once melting and rapid solidification are carried out, martensite has an area ratio of 20 to 3
0% δ-ferrite may occur. The generation of δ-ferrite causes a decrease in hardness, making it impossible to improve wear resistance. This problem occurs not only with laser-treated materials but also with laser-treated and tempered materials. The occurrence of such δ-ferrite is 5KH5
In cases such as No. 1, the amount is so small that it has been overlooked.

However, it has been found that in laser processing such as 5KH2, a large amount of δ-ferrite is generated in some cases.

The present invention was made under these circumstances, and provides a high-speed steel tool that does not generate δ-ferrite even when subjected to laser or other high-energy density beam processing and has particularly excellent wear resistance. The purpose is to In the present invention, the high energy density beam refers to a laser beam that can irradiate high speed steel to form a rapidly solidified layer.

Although the term refers to electron beams and other beams, in this specification, a laser beam will be explained as a representative beam.

[Means for Solving the Problems] The high-speed steel tool of the present invention has a high-hardness layer that is a melted and rapidly solidified layer that has been heat-treated by irradiation with a high-energy density beam, The gist of the present invention is that the material has a martensitic structure substantially free of δ-ferrite.

[Effect] When high-speed steel is melted and rapidly solidified by laser irradiation, the following changes are thought to occur in the structure. In other words, when high-speed steel is cooled and solidified from the liquid phase at a normal cooling rate (approximately 10°C/min), as shown in Figure 2 (A) (schematic structure diagram), almost without exception δ changes from the liquid phase. - Ferrite 1 is generated, and then austenite 2 is generated as shown in FIG. 2(B) by a peritectic reaction between the remaining liquid phase and δ-ferrite 1. Generally, the reaction rate of the peritectic reaction is slow, so the austenitization is not completely completed before the material is cooled to room temperature. Therefore, as shown in Fig. 2(C), the liquid phase becomes an austenite-carbide mixed layer P while the δ-ferrite 1 remains in a frozen state. As shown in D), austenite 2 transforms into a martensite-carbide mixed phase Q, and austenite 2 transforms into martensite 3.

In contrast, in the present invention, only austenite 2 is generated without generating δ-ferrite as the primary crystal, as shown in FIGS. 1(A) to 1(D), and the subsequent temperature drop As a result, austenite 2 is transformed into martensite 3, and therefore a structure containing no δ-ferrite and having high hardness and excellent wear resistance can be obtained.

When rapidly solidifying high-speed steel, solidification begins from a supercooled liquid phase that is lower than the normal melting point. The types of phases that appear during rapid solidification are determined by the free energy of each phase at this temperature. That is, even in a supercooled state, if the free energy of austenite becomes lower than that of 6-ferrite, austenite appears directly from the liquid phase and δ-ferrite does not appear.

The high-speed steel tool of the present invention can be obtained from such a viewpoint, and the manufacturing method thereof is exemplified as follows.

It is preferable to melt and rapidly cool by laser irradiation, and then adjust the composition so that the rapidly solidified layer after heat treatment has the following composition range.

That is, when Cr, Mo, W, V, C, N, and Co represent weight percent, m = 0.26X Cr + 0.111X M O
+0.14X W +0.6 x V-2,7X C
-0,70X N i -0,13xCo -1,02
... (I), m≦0.05 ... (Ia) It is desired that the following component composition conditions be satisfied.

... (!■) V2O, 5% ・(nr) cr≧2.5%・
(IV) C50.5% ... (V) Co51
5%... (Vl)Ni≦5%... (■
) Remainder: Fe and unavoidable impurities The basis of the above formula will be explained below.

The inventors of the present invention have studied in detail the mechanism by which δ-ferrite is generated, and have found the following facts.

(a) δ-ferrite occurs relatively near the surface of the rapidly solidified layer.

c) The amount of δ-ferrite generated is related to the amount of alloying elements in the rapidly solidified layer, and the smaller the amount of Cr, Mo, W or V, and the larger the amount of C, Co or Ni, the more δ-ferrite The amount of ferrite decreases.

FIG. 3 is an enlarged cross-sectional view of the rapidly solidified layer, where 5 is the base material, 6
is a rapidly solidified layer, Q is the maximum depth from the surface of the material in the δ-ferrite existing layer, and b is the maximum depth of the rapidly solidified layer.

Steel types in Table 1 (St, Mn<0.4%, P, S<
0.01%, remainder: Fa) was subjected to laser treatment, and δ
- The correlation between the amount of ferrite produced and the relational expression m of the alloying elements was determined.

Table 1 Metal composition values are weight%. Figure 4 shows the maximum depth a of the δ-ferrite existing layer with respect to the maximum depth b of the rapidly solidified layer on the vertical axis for m types (1) to (21) in Table 1. The actual measured value of the ratio is taken, and the value of m in the above equation (1) is plotted on the horizontal axis.

If you want to suppress the generation of δ-ferrite by adjusting the value of m, it is most preferable to adjust the value of m so that a = O, that is, a / b = O. However, if δ-ferrite is not generated, However, the amount generated is extremely small, and a /
A case where the value of b is approximately O and does not cause a decrease in wear resistance is also within an acceptable range.

The value of m was found from Figure 4, and m≦0.05. I found out that it's fine.

However, if the content of Mo, W, or V is small, the secondary hardening due to tempering will be small, and the hardness may be reduced even when the generation of δ-ferrite is observed. Therefore, as mentioned above, each of these contents is Mo0%W≧6.5%... (1■)■≧0.5
%·(III) is preferable.

In addition, if the content of C, Co, or Ni is excessive, a large amount of residual austenite will be generated in the rapidly solidified layer, and this will not be decomposed by tempering and wear resistance and toughness may deteriorate. As mentioned above, the contents are preferably C50.5%... (V) 00515%... (Vl) Ni55%... (■).

Furthermore, if the Cr content is low, the corrosion resistance may deteriorate, making it difficult to use as a tool. Therefore, as mentioned above, it is preferable that the content is Cr≧2.5%-(IV).

As a result of the above, h) the alloying elements in the solidified layer are
It turns out that it is sufficient to satisfy the relationship of equation (■). In addition, FIG. 5(A) shows the case where δ-ferrite is not generated [invention example (No. 4 in Table 1), 4 in the figure is the base material, 5 is the rapidly solidified layer], and FIG. 5(B) are the cross-sectional macrostructure and microstructure diagram of the case where δ-ferrite is generated [conventional composition (Table 1 No. 6)], and Fig. 6 (A) and (B
) shows the cross-sectional hardness distribution after tempering, and Figure 6 (
A) corresponds to Fig. 5(A), and Fig. 6(B) corresponds to Fig. 5(A).
Corresponding to B), the hardness is significantly reduced in the latter case where a δ-ferrite layer is formed.Examples will be described below, but the present invention is not limited to the following examples, and the hardness is significantly reduced in the latter case where a δ-ferrite layer is formed. It is within the technical scope of the present invention to make appropriate design changes based on the spirit of the above.

[Example] Example 1 A cutting tool was manufactured using the materials shown in Table 2, its flank surface was laser-treated, and after tempering was performed at 550°C for 1 hour 3 times, the cooling solidification phase formed on the cutting edge. Finishing was performed so that it would look like this, and a cutting test was conducted.

Table 2 Metal composition values are weight %, The laser treatment conditions and cutting test conditions were as follows.

(Laser processing conditions) (Cutting test conditions) Output
=5KW Work material: 545C (HB200) speed
Degree: 2m 7 minutes Depth of cut: 0.07 mm Spot diameter: 2 mm Cutting speed: 6.8 m7
Figure 7 shows the amount of wear on the flank surface due to minute cutting.

The material compositions in Table 2 (a) to (8) are all the same as the above (I).
A tool that satisfies formula a) and also satisfies formulas (TI) to (■) above, and does not cause the formation of δ-ferrite.
Compared to the comparative tool using the material (2) which does not satisfy formula Ia) and produces δ-ferrite, the amount of flank wear was considerably reduced and excellent wear resistance was exhibited.

Example 2 Composition shown in Table 2 (However, Si, Mn<0.4%, P, S<
After laser treatment under the same conditions as the cutting tool (0.01%, balance: Fe) and tempering 3 times at -560 t x 1 hour, it was made with 15 teeth, a land width of 3 mm, and a multi-blade step with 0. A 07 mm broach was produced and a cutting test was conducted.

The cutting test conditions were as follows.

Work material: 545C (HB200) Cutting speed: 7 m Figure 8 shows the measurement results of the amount of wear on the flank surface during 7 minutes of cutting. The broaches using the materials in Table 2 (a) to (viii) do not produce δ-ferrite as in Example 1, while the comparative example uses the material in (d) and produces δ-ferrite. Compared to a broach, the amount of flank wear was significantly reduced, demonstrating excellent wear resistance.

Example 3 After hardening a cold punch material having the composition shown in Table 2, it was subjected to laser treatment and tempered 3 times at 560°C for 1 hour before finishing processing was performed. Cold working was carried out on an actual machine using these cold punches. As a result, the cold punch of the comparative example using the material in Table 2 (d) had a lifespan of about 25,000 punches due to the formation of δ-ferrite, whereas In the cold punch of the example using
A lifetime of ~40,000 pieces was obtained.

[Effects of the Invention] Since the present invention is configured as described above, it is possible to provide a high-speed steel tool with particularly excellent wear resistance.

[Brief explanation of the drawing]

Figures 1 and 2 are structural change diagrams due to laser irradiation in the present invention and conventional example, Figure 3 is an enlarged cross-sectional view of the rapidly solidified layer, and Figure 4 is the maximum depth of the δ-ferrite layer relative to the maximum depth of the rapidly solidified layer. Graphs showing the correlation between the depth ratio and the correlation equation m of alloying element content, Figures 5 (A) and (B)
are enlarged cross-sectional views of the rapidly solidified layer of the present invention example and the conventional example, respectively, and FIGS. 6(A) and 6(B) are FIG. 5(A), respectively.
, FIG. 7 is a diagram showing the cutting test results of an example, and FIG. 8 is a diagram showing the cutting test results of another example. 1...δ-ferrite 2...Austenite 3
... Martensite 5 ... Rapidly solidified layer Figure 1
Figure 2 Figure 3 Figure 5 GA) Figure 5 (B) Procedural amendment (method) % formula % 2. Name of the invention High speed steel tool 3. Relationship with the person making the amendment Case Patent applicant Kobe City 1-3-18 Wakihama-cho, Chuo-ku (119) Kobe Co., Ltd.! ! Steelworks representative Sokichi Kametaka 4, agent 5, date of amendment order

Claims (1)

[Claims] A layer that is melted and rapidly solidified by irradiation with a high energy density beam, and has a high hardness layer that has been subjected to heat treatment, and the high hardness layer is made of a martensitic structure that does not substantially contain δ-ferrite. A high speed steel tool characterized by: