JPH0310686B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laser carburizing and quenching surface hardening method for forming a carburizing and quenching surface hardening layer on the surface of pure iron or low carbon steel by laser quenching in order to improve wear resistance. The conventional laser quenching surface hardening method applies laser quenching to the surface of workpiece materials such as medium- and high-carbon steels, alloy steels, and cast irons that have a high carbon content and are easily hardened, creating a high-hardness surface hardening layer. It was used to improve wear resistance and extend the lifespan of mechanical parts, equipment, etc. However, the conventional laser quenching surface hardening method as described above has the disadvantage that it cannot be applied to pure iron or low carbon steel. In other words, pure iron or low carbon steel has a low carbon content, so it hardly hardens, and even if the surface is hardened by laser hardening, a martensitic structure with high hardness cannot be obtained, so it has poor wear resistance. It is extremely difficult to obtain an excellent surface hardening layer. The purpose of the present invention is to eliminate the above-mentioned drawbacks, and provides a laser carburizing and quenching surface hardening method for forming a highly hard surface hardened layer with extremely excellent wear resistance on pure iron or low carbon steel. It provides: Hereinafter, the laser carburizing and quenching surface hardening method according to the present invention will be explained. (1) First, a substance that prevents laser reflection and that contains carbon and produces a carburizing effect (e.g., organic substances such as black paint, black printing ink, or graphite carbon) is applied to the workpiece of pure iron or low carbon steel. Coat the surface of the material and apply a black film treatment. Methods for coating the black film include spraying, dipping,
Select an appropriate method such as brush painting. (2) Next, the laser is irradiated at a fixed position and the workpiece is continuously moved. The laser irradiation conditions and the moving speed and direction of the workpiece are appropriately selected depending on the shape, hardness, and hardening depth of the intended hardened surface layer. In this way, the surface temperature of the workpiece that has been irradiated with the laser becomes high, so the black film thermally decomposes and generates carbon, which diffuses into the workpiece and causes carburization. It will be done. Further, the vicinity of the surface of the workpiece is heated to a high temperature and becomes an austenite structure. The irradiated area is heated to a high temperature by this laser irradiation method, and the irradiated area is rapidly cooled continuously by heat conduction to the non-irradiated area, so that the carburized area undergoes a crystal structure transformation from austenite to martensite, resulting in a high-temperature structure. Hard carburized and quenched surface to form a hardened layer. As described above, according to the method of the present invention, a hardened surface layer with excellent wear resistance can be extremely easily formed on the surface of pure iron or low carbon steel. This surface hardening layer can be made into any shape, hardness, hardening depth, and hardening width by appropriately selecting the laser irradiation conditions and the moving speed and direction of the workpiece. In addition, methods such as normal carburizing and quenching, tuftride treatment, and ion nitriding treatment all require the temperature of the entire workpiece to be raised.
Although there is a drawback that thermal deformation is large and therefore a re-polishing process is required as a post-process, the method of the present invention heats the surface of the workpiece locally, so thermal deformation of the workpiece is extremely small. , does not require a re-polishing process. Furthermore, it has excellent effects such as not requiring a water quenching or oil quenching step unlike ordinary heat treatment methods. As an example in which the method of the present invention has been applied to great effect, a friction disk for an electromagnetic brake/clutch will be described. The friction disc of the electromagnetic brake/clutch utilizes electromagnetic attraction, so pure iron or low carbon steel with good magnetic properties is used. However, pure iron or low carbon steel has the disadvantage of low hardness and poor wear resistance. As a result, the amount of wear increases and it becomes unusable, and the life of the electromagnetic brake/clutch is short and the amount of wear is large, causing undesirable phenomena such as fluctuations in electromagnetic attraction force and deterioration of torque characteristics and operating characteristics. was. Therefore, when we applied the carburizing and quenching surface hardening method according to the present invention to the friction discs of electromagnetic brakes, we were able to extend the life of the electromagnetic brakes by about three times compared to conventional ones, and obtain good torque and operating characteristics. We were able to achieve an extremely significant effect by stabilizing the braking time. Next, an embodiment of the method of the present invention will be described. As a test piece, an electromagnetic soft iron plate (material JIS
Using SUYPO; dimensions 100 mm x 100 mm x thickness 5 mm; Bitkers hardness Hv100), polish and thoroughly degrease. Next, a commercially available black printing ink containing carbon black as a coloring agent, phenolic resin as a printing film material, and alcohol as a drying agent is applied to the surface of an electromagnetic soft iron plate by a roller coating method to a width of about 3 mm and a thickness of about 3 mm. Apply to an area of approximately 10 μm in diameter and 80 mm in length, dry, and apply a black film treatment. after that,
While moving the specimen in a straight line at a speed of 700 mm/min, it is continuously irradiated with a laser (CO ₂ laser, output 1 kW) to form a carburized and hardened surface layer. A part of the surface-hardened portion of the test piece obtained in the above experimental example was cut to investigate the metallographic structure such as cross-sectional hardness distribution, hardening depth, hardening width, etc., but the formation of a high-hardness hardened surface layer was observed. Ta. The results are as follows.

[Table] In addition, the surface hardened part and the unhardened part of the test piece obtained in the above example were quenched, tempered, and polished to a high-speed tool steel disc (material SKH2; dimensions, outer diameter 30 mmφ, plate 2mm thick, Bitskers hardness
Hv600), pressing load 2Kg, friction speed 3
A wear test was conducted under conditions of m/sec. As a result, as shown in FIG. 1, it was found that the surface-hardened portion A exhibited far superior wear resistance than the unhardened portion B. As described above, the method of carburizing and hardening the surface of pure iron or low carbon steel using a laser according to the present invention can easily form a hardened surface layer with extremely excellent wear resistance on the surface of pure iron or low carbon steel. This has the excellent effect of significantly extending the life of mechanical parts, sliding parts, equipment, etc. that use these materials.

[Brief explanation of drawings]

Figure 1 shows a surface hardened part A of an experimental example of the method of the present invention.
It is a graph which shows the relationship of abrasion volume with respect to the friction distance of and unhardened part B. A: Surface hardened portion, B: Uncured portion.

Claims (1)

[Claims] 1 Laser treatment of pure iron and low carbon steel characterized by applying a black film treatment to the surface of pure iron or low carbon steel using a substance containing carbon, and then forming a carburized and hardened surface layer by laser hardening. Carburizing and quenching surface hardening method.