Method of increasing strength of cold worked part by ultrasonic shock treatment, and metal product with high fracture toughness and fatigue strength

Abstract

The invention provides a method for improving the strength of a cold-worked part by ultrasonic impact treatment. By implementing ultrasonic impact treatment on the surface of the stretched side of the metal cold-bending process, the surface hardness can be made higher than that of the surface without ultrasonic impact treatment. The surface hardness is increased by more than 10%, and the tensile residual stress can be reduced, and the fracture toughness and fatigue strength can be improved.

Description

technical field [0001] The invention relates to a method for improving the strength of a cold-worked part by ultrasonic impact treatment, and a metal product with high fracture toughness and fatigue strength manufactured by the method Background technique [0002] In recent years, in order to promote high performance, high functionality, and cost reduction, the strengthening of steel used for structural members has been progressing. However, for example, in ships, offshore structures, bridges, etc., which are subjected to repeated loads during service, generally, as the strength increases, the stress generated in the structural members increases, and the problem of significant metal fatigue often occurs. [0003] Therefore, due to the problem of metal fatigue, there may be restrictions on increasing the strength of steel. [0004] In general, in structures, fatigue cracks are a problem mainly in stress concentration parts or welded parts, but other than that, fatigue cracks...

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Problems solved by technology

However, the range of residual stress that can be improved by shot peening treatment is at best to a depth of about 300 μm, and the effect of shot peening treatment to inhibit crack progression has a limit.

[0016] Therefore, shot peening treatment is not necessarily a perfect method in terms of the effect of suppressing the progress of cracks. In addition, it is difficult to handle large objects because of the need to incorporate large machines and containers for processing objects.

[0017] In addition, shot peening treatment has low selectivity of the treatment target site, so it is difficult to treat only the surface of the steel plate to be treated.

That is, the shot peening treatment may leave traces of the treatment on parts that do not need to be treated, and damage the appearance of the metal product, so there is a problem that it cannot be used for objects requiring pattern design.

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