JPS61265271A - Shot peening method of cemented product - Google Patents

Abstract

PURPOSE:To permit an abnormal layer of a cement product to be removed and greatly improve fatigue strength of the cemented product by shot-blasting the cemented product with a blast material of a small specific gravity after shot-peening it at a high arc hide. CONSTITUTION:A workpiece (cemented product) 4 is placed on a rotary table 3 in a pressurized tank 3 of a pressurized tank type shot peening machine 1 to be rotated. Shot grains 6 from a nozzle 8 collide with the workpiece 4 in rotation for shot peening the workpiece 4. Next, the workpiece 4 is transferred to a rotary table 10 of a self-supply type shot blast machine 9 and the rotary table 10 is rotated by a motor 11. A blast material composed of average grains having a size less than 0.5mm and a specific gravity less than 5.0 is shot from a nozzle 13 to the workpiece 4 for removing an abnormal layer of the workpiece 4 and giving compressed residual stress to the portion of the workpiece 4 ranging from the surface to the depth thereof so that fatigue strength of the workpiece is greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shot peening method for carburized products.

[Conventional technology]

Shot peening treatment is a technique in which shot particles accelerated at high speed are struck on the surface of a workpiece to impart compressive residual stress to the surface layer of the workpiece, thereby improving the fatigue strength of the workpiece.

Therefore, it is the compressive residual stress that determines the fatigue strength of shot peened products, and obtaining a high residual stress distribution deep into the treated product, even to the outermost surface, is
This leads to obtaining high fatigue strength. For example, as in the two-stage shot method, the workpiece is first subjected to shot peening using steel shot particles to obtain a deep or thick compressive residual stress layer on the workpiece, as shown in Figure 6. Afterwards, if shot peening is performed using shot peening grains with low specific gravity such as alumina or glass peas, a shallow but high compressive residual stress will be obtained in the surface layer as shown in Figure 7, so treatment with steel shot grains will be performed. The processed product is then shot peened using glass beads, etc.

As shown in FIG. 8, there is a method of obtaining high fatigue strength of the paper or processed product by further increasing the compressive residual stress near the surface.

[Problem that the invention seeks to solve]

However, even if a carburized product is subjected to shot peening treatment as described above, an incompletely quenched layer called an abnormal layer exists on the surface layer of the carburized product, and this layer is different from the internal martensitic structure. The troostite structure or the bainite IJL structure has the second lowest hardness, and as shown in FIG. 9, the compressive residual stress near the surface does not increase much.

Therefore, even if a two-stage shot treatment is performed on a treated product such as a carburized product in which an abnormal layer exists, its fatigue strength cannot be significantly improved.

The present invention is a companion to solving the above-mentioned problems, and aims to provide a shot peening method for carburized products that can significantly improve fatigue strength.

[Friendly means of solving problems]

The shot peening method for carburized products of the present invention is characterized by subjecting the carburized products to shot peening treatment at a high arc height, and then shot blasting the carburized products with a blasting material having an average particle diameter of 0.5 m or less and a specific gravity of 10 or less. shall be.

That is, the method of the present invention subjects a carburized product to shot peening treatment at a high arc height to give #! After forming 16 residual layers of low pressure #l, shot blasting is performed using a blasting material with low specific gravity such as alumina to remove the abnormal layer of the carburized product and create a new surface as shown in Figure 10. This increases the compressive residual stress near the surface of the carburized product, significantly improving the fatigue strength of the carburized product.

In the method of the present invention, shot peening treatment is performed to form a thick compressive residual stress layer deep to the carburized product.
It is preferable to conduct the process at a high arc height of 0.4 tm or more in mm). For this purpose, the shot grains need to have a large mass, and examples thereof include cast steel shot and cut wire shot, with cast steel shot being preferred.

The particle size of shot grains is α5~1.2■, especially α8~LO■
is preferred.

The blasting material used for shot blasting is preferably particles used for abrasive materials, such as alumina, zirconia,
Examples include angular particles such as glass. The particle size of the blasting material is 0.5 square meters or less, preferably 0.5 to 0.1 m.

[For production]

In the shot peening of a carburized product of the present invention, a deep, ie, thick compressive residual stress layer can be formed in the carburized product by subjecting the carburized product to shot peening treatment at a high arc height.

Next, by subjecting this treated carburized product to shot plus treatment, the abnormal layer that exists on the surface layer of the carburized product, where the compressive residual stress does not increase much, can be removed. The compressive residual stress of the outermost surface layer can be increased. Since a blasting material having a particle size of a5ss or less is used in this shot blasting treatment, the surface after removing the abnormal layer has little roughness and does not cause a decrease in strength. Furthermore, since the blasting material has a specific gravity of 5.0 or less, high compressive residual stress can be obtained in the outermost layer. As a result, a high compressive residual stress can be obtained from the surface to the depth of the carburized product, and the fatigue strength of the carburized product can be significantly improved.

〔Example〕

The present invention will be explained by way of one embodiment with reference to the drawings.

This embodiment is an example in which the present invention is applied to a carburized and hardened gear. First, as shown in FIG.
A workpiece 4 consisting of a carburized and hardened gear with a module of 2.55 and an effective hardening depth αEIIB was placed, and the rotary table 3 was rotated by the motor 5. Then, cast steel shot grains 6 with an average grain size α81 m are supplied to a nozzle 8 through a hose 7 with air pressurized to 5.0 Kf/-, and are struck from the nozzle 8 against a rotating workpiece 4 for 5 minutes to create an arc. Shot peening treatment was performed under the condition of a height cL of 55 m.

Next, as shown in FIG. 2, the treated workpiece 4 was transferred to a rotating table 10 of a self-contained shot blasting machine 9 and rotated by a motor 11. And 5. OKp/c+dK By sending pressurized air from the hose 12 to the nozzle 13, #60 alundum (alumina grain) abrasive material 14 is supplied to the nozzle 15 through the hose 15, and from the nozzle 15 the rotating workpiece 4 is Shot blasting was performed by hitting the surface for 2 minutes.

Comparative Example This comparative example was treated in the same manner as in the example except that shot peening treatment was performed using glass beads instead of the shot blasting treatment using alundum in the example.

FIG. 4 shows a microscopic photograph of the t,1 structure of the gear obtained in the above example, and FIG. 5 shows a microscopic photograph of the metallographic structure of the gear obtained in the comparative example. The comparative example has an abnormal layer on the surface, but the abnormal layer is removed in the example by the above treatment.

In addition, as shown in the residual stress distribution shown in Figure 3, as a result of the two-stage shot treatment, the comparative example with an abnormal layer on the surface layer has a low residual stress near the surface, but the abnormal layer due to alundum with a small specific gravity Due to the removal and peening effect, high residual stress was obtained from the surface to the depth in the example. Therefore, the carburized and quenched gear treated according to the example has a fatigue strength of
It was 50 inches better than the gear before the treatment and 20 inches better than the gear treated in the comparative example.

〔Effect of the invention〕

In the present invention, as described above, the carburized product is subjected to shot peening treatment with a high arc height and then shot blasted with a blasting material having a small specific gravity. A high compressive residual stress can be applied from the surface to the depths, and as a result,
The fatigue strength of carburized products can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing shot peening treatment according to an embodiment of the present invention, FIG. 2 is a diagram depicting shot blasting treatment according to an embodiment of the present invention, and FIG. 3 is a diagram showing shot blasting treatment according to an embodiment of the present invention and a comparative example. A graph showing the residual stress distribution of the treated gear. FIG. 4 is a micrograph of the metallographic structure of the gear treated according to an example of the present invention. FIG. 5 is a micrograph of the metallographic structure of the gear treated according to the comparative example. Figure 6 is a schematic diagram of the residual compressive stress distribution of a product shot peened with steel shot, Figure 7 is a schematic diagram of the residual stress distribution of a product shot peened with glass bead shot, and Figure 8 is a diagram of the residual compressive stress distribution of a product shot peened with glass bead shot. Figure 9 is a schematic diagram of the residual stress distribution of a carburized product that has been shot peened with a glass bead shot. Figure 10 shows a schematic diagram of the residual stress distribution of a carburized product that was subjected to a steel shot shot peening treatment and was further shot blasted with an alumina blasting material. In the figure, 1... Pressurized tank type shovel beaning machine 2...
...Pressure tank 3,10...Rotary table 4...Workpiece 5.11...
・Motor 6...Shot grain 7,12.
15...Hose 8.16.111. ·nozzle
9...Shot blasting machine 14...
...Abrasive material patent applicant Toyota Motor Corporation and 1 other talented person -y! 2 Figure 3 Figure 0 0.1 0.2 03 Board length from Table 5J (mm) Figure 21.5, 1 31! 6 Figure Fang 8 Surface force ＼ Uno 1 Giant Bell 1 - Ichiga 10 Figure Surface 50 Range t → Fang 7 Figure Age 9 Surface O' Wound Range ◆

Claims (1)

[Claims] After shot peening the carburized product at a high arc height, the carburized product has an average particle size of 0.5 mm or less and a specific gravity of 5.
A shot peening method for carburized products, characterized by shot blasting with a blasting material of 0 or less.