Method for shot peening a gas carburised steel

a gas carburized steel and peening technology, applied in the field of shot peening, can solve the problem that the methods of these studies are difficult to apply to gas carburized steel with a soft layer on the surface, and achieve the effect of high compressive residual stress and high fatigue strength

Inactive Publication Date: 2013-05-16
SINTOKOGIO LTD
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Benefits of technology

[0019]By the method for the shot peening of the first aspect of the present invention, the position where the maximum compressive residual stress is generated is estimated by multiplying the depth by a constant. The depth is determined as the depth where the maximum stress is generated by the collision of shot media. By shot-peening a gas carburized steel a maximum compressive residual stress that is equal to, or more than, 1,600 MPa, is produced. At that depth the gas carburized steel has a hardness that is equal to, or more than, 750 HV. The shot media have a hardness that is abov

Problems solved by technology

Thus the methods by these studies are difficult to be applied to a gas carburized steel that has a soft layer on the surface, since residual stresses are affected by pl

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  • Method for shot peening a gas carburised steel

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Embodiment Construction

[0027]Below, the embodiments of the present invention are described with reference to the drawings.

[0028]FIG. 1 is a graph showing the distribution of the hardness of the processed steels that were used in the embodiments. The abscissa denotes depths (micrometer) from the surface of the steel, and the ordinate denotes the Vickers hardness. A gas carburized steel is used for the processed steels. In the drawing, “TP.A” and “TP.B” denote the steels which have been tempered at 180 degree C. and 180 degree C., respectively.

[0029]FIG. 2 is a table showing the conditions and the results of shot peening that were used in the embodiments. A compressive-air shot peening system was used. Shot media that have a hardness of 700 HV to 1,000 HV and diameters (the mean diameters) of 0.2 to 1.0 mm were used.

[0030]The

“Maximum σR”

in the table denotes the maximum compressive residual stresses in the processed steels. The compressive residual stresses were measured by using a micro-stress analyzer that...

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Abstract

The present invention is to provide a method for shot peening for producing a high compressive residual stress in a gas carburized steel that has a soft layer. In this method, a depth where the maximum compressive residual stress is generated is estimated and the hardness on the surface or near the surface is not used. The depth where the maximum compressive residual stress is generated is estimated by multiplying the depth where the maximum stress is generated under contact stresses caused by the collision of shot media by the constant K. A processed steel that comprises a gas carburized steel and that has a hardness at that depth that exceeds 750 HV is used. Shot media that have a hardness that is greater than that of the processed steels at that depth by 50 HV or more are shot onto the processed steels to produce a high compressive residual stress in the processed steels.

Description

TECHNICAL FIELD [0001]The present invention relates to a method for shot peening. Specifically, it relates to a method for shot-peening a gas carburized steel.BACKGROUND ART [0002]Conventionally, shot peening has been known to produce compressive residual stresses and to increase hardness to improve the fatigue strength of gears (see authored by the Society of Shot Peening Technology of Japan; Fatigue of Metals and Shot Peening; published by Gendai Kogaku-sha; 2004). Further, to achieve high fatigue strength aimed at reducing the weight of parts, a method for increasing compressive residual stresses produced by shot peening has been known (see Kazuyoshi Ogawa and Takashi Asano; Theoretical Prediction of Residual Stress Produced by Shot Peening for Hardened Steel; Transactions of JSSR, No. 48 (2003) pp. 31-38).[0003]However, in these studies only the mean values of the hardness on the surface of, or near the surface of, the material are focused on. Thus the methods by these studies a...

Claims

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Application Information

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IPC IPC(8): B24C1/10
CPCC21D7/06B24C1/10C23C8/80C21D11/00
Inventor KOBAYASHI, YUJITSUJI, TOSHIYA
Owner SINTOKOGIO LTD
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