JPH0551629A - Hardening method for surface - Google Patents

Abstract

PURPOSE:To restore hardness and to enhance abrasion resistance and fatigue strength by allowing a small steel ball to collide against the beam overlapped part generated in the case of using high-energy beams to harden a sliding shaft. CONSTITUTION:A sliding shaft 1 is rotated at the specified velocity and simultaneously the sliding face 2 of the sliding shaft is irradiated with stationary laser beams. Successively small steel balls 7 are allowed to collide against the overlapped part AB of a starting point of irradiation and a finishing point thereof while blowing air 5. Thereby fine unevennesses are formed. The overlapped part AB receives fine plastic deformation and a lattice defect such as dislocation is concentrated. Further residual austenite is transformed into martensite and therefore the overlapped part AB is hardened. Further compression residual stress is generated on the surface. As a result, abrasion resistance and fatigue strength of the sliding shaft 1 are enhanced and the service life is prolonged. Furthermore since oxidative scale covering the surface of the sliding shaft is removed, finish working is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface hardening method using a high energy beam, and more particularly to a surface hardening method for improving fatigue strength and wear resistance of metal members such as machine parts.

[0002]

2. Description of the Related Art Surface hardening methods for machine parts include induction hardening, carburizing hardening, nitriding, and the like. In recent years, members that require local hardening and heat distortion are disliked. High-energy beams such as lasers and electron beams have been widely used for precision members. However, the overlapping portion where the beam irradiation traces overlap has a drawback that a tempering layer is formed and the hardness is significantly lowered.

For example, in the surface hardening method of a sliding shaft with a groove described in Japanese Patent Laid-Open No. 1-306526, a sliding surface of the sliding shaft is hardened by a laser beam machine with a groove interposed therebetween. At that time, the phases of the overlapping light receiving portions at the start and the end of the irradiation of the laser light moving along the circumferential direction of the plurality of sliding surfaces are shifted in the circumferential direction for each sliding surface. That is, by shifting the circumferential phase of the overlapping light receiving part at the start and end of laser irradiation for each sliding surface and only changing the stored information in the numerical control table format, intensive wear can be avoided. It is to quench.

As shown in FIGS. 12 and 13, the overlap portion AB of the laser beam 4 irradiation start portion A and the irradiation end B portion of the sliding portion 2 of the sliding shaft 1 is circumferentially arranged with the groove 3 interposed therebetween. To 30
Adjacent overlap portions AB are displaced while maintaining the phase of degrees. The sliding shaft is driven by a stepping motor, and each operation of the rotation angle and the rotation speed is accurately controlled by a numerical command, and the phase and length of the overlapping portion AB are arranged with extremely high accuracy.

[0005]

However, the quenching overlap portion of the sliding shaft has a low hardness. Therefore, if the ball bearing balls roll on the sliding surface, or if uneven load or sudden impact is applied, wear marks and dent marks will occur, resulting in poor accuracy and sliding starting from that part. The shaft may be fatigue fractured.

The present invention has been made in order to solve the above-mentioned problems, and is excellent in wear resistance and fatigue strength without lowering the hardness of the overlapping portion that occurs during high energy beam quenching. Another object of the present invention is to provide a surface treatment method.

[0007]

In order to achieve this object, a surface hardening method of the present invention is a method of hardening a sliding surface of a sliding shaft with a high-energy beam, and then forming a hardening overlapping portion of the sliding surface. It is characterized by performing shot peening.

[0008]

According to the present invention having the above structure, a laser beam, an electron beam, a TI beam can be used as the high energy beam.
An appropriate one is selected from G arc and plasma arc, and the surface of the sliding member is locally irradiated to form a quench hardened layer.

Next, the quenching overlap portion is subjected to shot peening treatment to increase the hardness and impart abrasion resistance.

In the shot peening treatment of the present invention, small particles such as steel are made to collide with the low hardness overlapping portions of the surface of the material to be treated to give microscopic unevenness.
A large amount of lattice defects such as dislocations are generated in the overlap portion and work hardening occurs. Furthermore, the untransformed austenite remaining in the softened layer also undergoes re-martensite transformation by impact, so that it hardens and wear resistance is improved. Further, since residual compressive stress is generated in the overlapping portion, fatigue strength is also improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as one embodiment embodying the present invention, a case where a sliding surface 2 of a sliding shaft 1 with a groove 3 is hardened by using a laser beam 4 which is a typical high energy beam is shown in FIG. It will be explained based on.

The sliding shaft 1 is made of SK3 and has a diameter of 15 mm. The sliding surface 2 has a width of 7 mm and the groove 3 has a width of 2 mm. This is rotated at a speed of 0.5 m / min, and a laser beam 4 having an output of 1.2 kw and a diameter of 7 mm is irradiated. Irradiation starts from point A and ends at point B. Therefore, irradiation between A and B is performed twice. FIG. 2 shows a side surface of the sliding shaft 1. This quenching operation is repeated for all the sliding surfaces 2.

Next, as shown in FIG. 3, the steel ball irradiating nozzle 6 is directed toward the overlap portion AB and its peripheral portion arranged in a line, and the grain size is 0.05 mm to 1 mm and the hardness Hv3.
A steel ball 7 of about 00 to 600 is pressed at a pressure of 3 kgf / cm ^{2 to} 7
Spray with air flow 5 of kgf / cm ² for tens of seconds. This operation is sequentially performed on the other overlap portion AB and its peripheral portion.

As a result, a concavo-convex portion having a depth of about 5 to 10 μm is formed near the overlapping portion AB. As shown in FIG. 4, the hardness of the overlap portion AB and its peripheral portion is as shown in FIG.
In some cases, it fell below the required quenching limit of Hv550. However, after the shot peening treatment, the hardness was restored to Hv 600 to 700 as shown in FIG. 5, and was almost equal to the hardness Hv 650 to 730 of the quench hardened layer.

Further, the 200-hour durability wear test result of the sliding shaft 1 which has been subjected to the shot peening treatment of this embodiment is shown in FIG.
Shown in. The wear depth in the vicinity of the overlap portion AB of the sliding surface 3 of the present invention was reduced to about 1/3 of that of the conventional sliding shaft 1 not subjected to shot peening. Since the shot peening process generally has the function of improving the fatigue strength of the member to be processed, the shot peening process may be performed not only on the overlapping part AB but also on the entire quenched part.
Further, the quenching oxide layer generated on the sliding surface 3 is not only removed cleanly, but also the conventional pickling after quenching becomes unnecessary.

According to the surface hardening method of the present embodiment, the hardness of the overlap portion which is tempered and softened can be restored to the level of the hardening layer. Therefore, the local wear of the sliding surface can be prevented, and the starting point of breakage is not created.

Next, as a second embodiment, a case of laser hardening the sliding shaft 1 in a spiral shape over the entire circumference will be described with reference to FIG.

In the figure, the quenching condition is that the beam size is φ6 mm and the moving speed of the laser beam 4 is 2.0 m / mi.
When n is an output of 0.8 kw, φ16 mm, the sliding shaft 1 is rotated at a constant speed, and the laser beam 4 is irradiated while moving in the axial direction of the sliding shaft 1 at a feed pitch of 3 mm so that the quenching irradiation traces overlap each other. ..

FIG. 8 is a cross-sectional photograph of the sliding shaft 1 after quenching under the above laser quenching conditions. The overlapping portion 8 where the one-pass beam and the two-pass beam overlap each other.
The shaded area in is equivalent to the tempered part. FIG. 9 shows a 500 times micrograph of a cross section of the quenching overlap portion 8 of the sliding shaft 1. It can be seen that it has a mixed structure of untransformed austenite and martensite with low hardness. FIG. 10 shows the hardness distribution of the sliding shaft 1 before the shot peening process. From the figure, the overlapping part is Hv550 (JIS
Hardness of the general quenching part in the standard).

Shot peening is applied to the overlapping portion 8 of the sliding shaft 1 under the same conditions as in the first embodiment. FIG. 11 shows the hardness distribution of the cross section of the sliding shaft 1 after the shot peening treatment. The hardness of the overlapping portion, which was less than Hv550, recovered to Hv550 or more.

The present invention is effective not only for the sliding shaft, but also for the flattened steel plate quenched by a high-energy beam and the hardened overlap portion generated in a steel material having a general complicated shape, and the hardness and fatigue strength are improved. Recover.

[0022]

As is apparent from the above description, the present invention provides shot peening treatment to the quenching overlap portion of the material to be treated that has been quenched by the high energy beam. According to such a surface treatment, the hardness of the overlapping portion on the surface of the metal member is increased, so that the wear resistance can be improved and local wear can be prevented. At the same time, since a high compressive residual stress is applied, cracks are less likely to occur and the fatigue strength of the metal member can be improved. Further, when the shot peening process is performed on the entire hardened portion, the hardened oxide layer covering the surface is removed by the shot action, so that the subsequent removal work is not required.

[Brief description of drawings]

FIG. 1 is a diagram of an example of laser hardening of a sliding shaft according to the present invention.

FIG. 2 is a diagram showing a state of laser hardening of the sliding shaft of the present invention.

FIG. 3 is a diagram illustrating shot peening processing according to the present embodiment.

FIG. 4 is a diagram showing the hardness distribution of the sliding shaft before the shot peening process of the present embodiment.

FIG. 5 is a diagram showing the hardness distribution of the sliding shaft after the shot peening process of the present embodiment.

FIG. 6 is a diagram showing wear characteristics of a sliding shaft.

FIG. 7 is a diagram showing laser hardening in a second embodiment.

FIG. 8 is a cross-sectional photograph showing the metallographic structure of the sliding shaft after laser hardening in the second embodiment.

FIG. 9 is an enlarged cross-sectional photograph showing a metallographic structure of a quenching sliding shaft.

FIG. 10 is a diagram of hardness distribution of a cross section of a sliding shaft before shot peening in the second embodiment.

FIG. 11 is a diagram of hardness distribution of a cross section of the sliding shaft after shot peening in the second embodiment.

FIG. 12 is a diagram showing a conventional example.

FIG. 13 is a diagram showing a conventional example.

[Explanation of symbols]

 1 Sliding axis 2 Sliding surface 3 Groove 7 Steel ball AB Laser beam overlap

Claims (1)

[Claims] 1. A surface hardening method, characterized in that, when quenching the surface of a metal member with a high-energy beam, shot peening is applied to the overlapping portion of the high-energy beam.