JPS5983718A - Surface treatment of high speed steel - Google Patents

Abstract

PURPOSE:To enhance the cutting property of high speed steel without deteriorating the toughness thereof, by a method wherein the surface of high speed steel subjected to hardening treatment is irradiated with laser light to dissolve the primary carbide in the surface layer in a matrix to form a solid solution and the irradiated high speed steel is further tempered to finely precipitate the primary carbide. CONSTITUTION:After high speed steel is once subjected to hardening treatment, the surface thereof is irradiated with laser light of absorption energy density of 2,000J/cm<2> or more at a beam moving speed of 2m/min or more to be melted. Hard primary carbides of Mo, W, V or the like in the surface of the high speed steel are dissolved in a matrix to form a solid solution with a uniform crystal structure. The treated high speed steel is subjected to tempering treatment at 500-600 deg.C to precipitate the primary carbides in the solid solution in a fine form and a secondary hardening amount is increased to enhance anti-wear property, that is, cutting property without lowering toughness.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface treatment method for improving the properties of high-speed steel, particularly its cutting performance.

General high-speed steel contains a large amount of primary carbide made of alloying elements such as W, Mo, Cr, and V (usually around 10% by weight in the hardened state), which improves cutting performance. It has had a huge impact. Many studies on improving machinability have focused on the form of the primary carbide described above, and can basically be divided into the following two streams.

(1) Increasing the amount of primary carbides This is an attempt to increase wear resistance by adding a large amount of carbide-forming elements such as MOLWlv along with a corresponding amount of C to increase the amount of primary carbides. M
It is said that the effect of forming C-type carbide is the greatest. In 1968, the JISM rating system was established as high C-high V system (
DSKH5B, 5KH54, 5K) I57, etc. were added, and after that, products with further increased or adjusted alloy elements are being developed. However, in any case, products with increased primary carbide thickness tend to cause segregation, and angular coarse carbides also increase, resulting in an extreme deterioration of toughness.
Furthermore, because the amount of alloying elements is large and the price is soaring, it is currently only used for special purposes (machining difficult-to-cut materials).

(2) Reduction and refinement of primary carbide segregation In order to improve the cutting performance of high-speed steel, it is necessary to improve not only wear resistance but also toughness. In particular, for steels containing a large amount of primary carbides, such as high-V high-speed steels, improving toughness is particularly important, and for this purpose, it is necessary to reduce the segregation of primary carbides and refine the crystals. It is valid. ESR method and powder metallurgy method are cited as typical improvement measures based on this basic idea. However, in the former ESR method, although the segregation of primary carbides is considerably suppressed, the carbide grain size tends to become coarser, and it is less effective for small parts that originally have a uniform distribution of carbides, and the manufacturing process is Due to its complexity, the price also increases. In addition, in the case of the latter powder metallurgy method, there is no segregation of primary carbides and the particles are made finer, so toughness is considerably improved, but if the composition is the same as that of ordinary melted materials, wear resistance tends to deteriorate. Moreover, the manufacturing process is complicated and the product cost is high.

As described above, in conventional methods, when trying to increase the wear resistance of high-speed steel, toughness is sacrificed, and when trying to improve toughness, economical problems arise. Therefore, there is a need for the development of a technology that can increase wear resistance without deteriorating toughness and that can be produced easily and at low cost.

In view of this situation, the present inventors believe that it is difficult to achieve essential improvements simply by adjusting the amount of alloy components.
We have been conducting intensive research to improve surface properties by devising post-molding surface treatment methods. The present invention was completed as a result of such research, and its configuration is such that a laser beam is applied to the surface of hardened high-speed steel, the absorbed energy density is 200,037 cm or more, and the relative movement speed between the beam and the workpiece (hereinafter referred to as The steel surface is melted by irradiation at a beam moving speed of 2 m/min or more, and the primary carbides in the surface layer are dissolved in a solid solution in an IJ hook, and then tempered to finely precipitate the solid-dissolved carbides. There is a summary in .

In the present invention, after the high-speed steel is hardened, the surface is irradiated with a high-energy-density laser beam at a moving speed of a certain speed or higher, thereby dissolving the primary carbides on the surface into the 711 inx and improving its toughness. Forming a surface layer that contains almost no harmful primary carbides, and finely precipitating solid-dissolved carbides through subsequent tempering.
Wear resistance is improved by significantly increasing the amount of secondary hardening.
This also aims to improve cutting performance.

The structure and effects of the present invention will be clarified by following the experimental progress.

Lasers generally have very high energy density and can locally heat and cool the surface of a material. In particular, the structure of the rapidly solidified layer obtained by melting only the surface is expected to be significantly different from the normal heat-treated structure in terms of the morphology of primary carbides, solid solution precipitation state of alloying elements, crystal grain size, etc. It has the potential to significantly improve mechanical properties including hardness. Therefore, first of all, 5K is used as a high-speed steel.
A H9 hardened material was selected and subjected to laser beam irradiation treatment under the following conditions, and the internal structures of the laser irradiated area and the unaffected base material area were compared using an optical microscope.

[Irradiation conditions]

Heat source: CO2 laser output 8 KW to 5 KW Energy density: 2B00 to 4800 J/σ2 Beam travel speed Travel speed near m/part: Natural cooling The results are shown in Figure 1 (a photomicrograph of the laser irradiation area in place of a drawing), and As shown in Fig. 2 (micrograph substituted for a drawing of the base metal), primary carbides, which are often observed in ordinary heat-treated materials (base metal: Fig. 2), are found in the laser irradiated part (Fig. 1).
In this case, the primary carbide has completely disappeared, and the primary carbide is dissolved in the matrix by laser irradiation, resulting in an extremely uniform crystal structure.

When the relationship between the tempering temperature and the secondary hardening of this laser irradiation treated material was investigated, the results shown in FIG. 8 were obtained. This figure shows that in the base metal part that is not affected by laser irradiation, the hardness decreases as the tempering temperature increases.
In particular, when the tempering temperature exceeds about 600°C, the hardness decreases rapidly. On the other hand, a different tendency is observed in the laser irradiated area, and rapid secondary hardening occurs due to tempering at 500 to 600°C, and the tempering hardness of the final product surface layer (laser irradiated area) increases to Hv 1100, and the tempering It was confirmed that the softening resistance was also excellent. In addition, in Figure 4, the laser beam output direction is 8KW or 5KW, and the tempering temperature is 550.
This is an experimental graph obtained by examining the relationship between distance from the surface and hardness by performing the same processing as above except that the hardness was set to 'C. From this figure, when the laser output is 8KW, the surface hardened layer is obtained over a depth of approximately 700μm from the laser irradiation surface and when the laser output is 15KW, the surface hardened layer is approximately 1200μm deep, and as the laser output is increased, the secondary hardened layer becomes deeper. Can be done. However, the hardness of the hardened layer shows a constant value of approximately Hvlloo, and the influence of the laser output direction on the hardness is hardly recognized.

Figure 5 is an experimental graph comparing the wear resistance of the hardened surface layer (laser treated area) and base metal (normally heat treated area) for high cutting steel that was quenched at 550°C for 1 hour after laser irradiation. . The test conditions were as follows.

〔Test conditions〕

Test method: Large part type abrasion test Width Diameter mating material: 5UJ2.1.5 rts, X 80
(HiC=60 Friction distance: 400m Load: 8.8Kg As is clear from this figure, the surface hardened layer formed by laser irradiation showed excellent wear resistance, especially in the high-speed wear region.

FIG. 6 is an experimental graph in which a continuous cutting test was conducted under the following conditions using a cutting tool made using the laser irradiated material of the present invention and a conventional heat-treated material.

[Cutting conditions]

Bit installation angle: 0-15-6-6-15-15-Ro
, 4 Overhang amount: 84° Depth of cut: 1,5 Way feed 2 〇, 2 Harmonic cutting material: S
NCM8 (HRC82) Lubrication: None Life Judgment: Complete life. Figure 7 shows the same cutting conditions (however, the work material is grooved with a width of 10 m every 90', and the life judgment is V ma
This figure shows the results of an intermittent cutting test carried out at z = 0.6 m.

As is clear from FIG. 6.7, the material subjected to laser irradiation and tempering according to the method of the present invention has superior machinability compared to conventional heat-treated materials. It can be seen that it has excellent performance especially in interrupted cutting where a high degree of toughness is required.

In this way, in the present invention, by irradiating the surface with a laser beam after the hardening treatment, precipitation of coarse primary carbides in the surface layer is eliminated, and secondary hardening is significantly accelerated by the subsequent tempering treatment at a specific temperature. , thereby increasing both hardness and toughness and significantly improving machinability.

However, these effects tend to vary considerably depending on the absorbed energy density during laser beam irradiation and the beam movement speed.
00 J/am2 or more, and the beat movement speed must be set to 2m/min or more.

However, the absorbed energy density refers to a value calculated from the following formula.

Absorbed energy density (J74 shoulder) is as follows. That is, regarding the absorbed energy density, it was clarified in Fig. 6 above that the larger the density, the deeper the hardened layer can be. When we examined this in more detail, we obtained the results shown in Figure 8. As is clear from this figure, in order to form a hardened layer on the surface layer by laser irradiation, the absorbed energy density must be at least 2000 J/cm2 or more. If it is higher than this, as the absorbed energy density increases, the hardened layer after tempering becomes deeper and the machinability improves, but this irradiation effect is approximately 4000
A saturation state is reached at JkIn2, and any further increase in the absorbed energy density will only increase the output of the laser generator. On the other hand, Figure 9 is an experimental graph showing the relationship between the beam movement speed, the volume fraction of carbide as treated by the laser, and the hardness when the subsequent tempering treatment (550°C x 1 hr) is performed. It can be seen that in order to significantly exhibit the effect of accelerating curing by laser irradiation, the beam movement speed should be set to 200 z/'min or more.

By the way, a technique using laser beam irradiation to increase the surface hardness of high-speed steel is also disclosed in Japanese Patent Laid-Open No. 55-62119. However, as is clear from the description in the published specification, this technique involves irradiating the surface of a hardened and tempered high-speed steel tool with a laser beam to rapidly heat and self-cool it, and the present invention is similar to that of the present invention. (1) After the quenching process, the structure of the surface layer is made almost carbide-free by laser irradiation [carbide size is 1 μm or less: 1st
2% or less: FIG. 9], and (2) There is no idea at all that the surface hardness is dramatically increased by secondary hardening by tempering treatment after laser irradiation. Incidentally, in the present invention, in order to obtain the structure described in (■) above, the beam movement speed is set to 20
It is essential to set the speed to 0□□□/min or more, but the moving speed shown in the disclosed invention is extremely slow at 40 minutes, and the surface hardness of the final product is at most low in the disclosed invention. While HRC69 (Hv approx. 1000),
In the present invention, Hv can be increased to about 1100.

The present invention is roughly configured as described above, and it has been possible to provide a high-speed steel that can significantly improve hardness without reducing toughness and has excellent cutting performance.

[Brief explanation of drawings]

Figures 1.2 and 3 are micrographs used as drawings showing the steel structure.
The figure is a graph showing the relationship between tempering temperature and hardness, and Figure 4 is a graph showing the relationship between distance from the laser irradiation surface and hardness.
Figure 5 is a graph showing the relationship between friction speed and specific wear amount.
Figure 7 is a graph showing the relationship between the number of impacts and cutting speed, Figure 7 is a graph showing the relationship between cutting speed and cutting time, and Figure 8 is a graph showing the relationship between absorbed energy density and the depth of the molten layer (hardened layer). , FIG. 9 is a graph showing the relationship between beam moving speed, hardness, and carbide volume fraction. Part 1-: Fig. 2 and Fig. 3 quenching t-i + base material) Tempering temperature ("C) Xl
hr Distance from surface (pm) Friction speed (m/5ec) Number of impacts (X100 times) Cutting time (min)

Claims (1)

[Claims] (11 Melt the steel surface by irradiating the surface of the hardened high-speed steel with a laser beam at an absorbed energy density of 2000 J kn2 or more and a beam movement speed of 2 m/min or more,
A method for surface treatment of high-speed steel, characterized by dissolving primary carbides in a surface layer in a matrix, and then subjecting the matrix to a tempering treatment to finely precipitate the dissolved carbides.