When grinding a part with high heat treatment strength, if the processing pressure is too large, cracks are likely to occur in many cases because the temperature rises too fast during processing, and the surface martensite and other mixed structures are formed. And cause cracks. 55CrSi is a kind of high-quality spring steel. The addition of Cr and Si alloy elements makes it have good hardenability. It is completely possible to produce quenched structure during vigorous grinding. To illustrate this problem, the author intercepts a wire of the same material and the same state, and grinds the end face with a grinding wheel. When grinding, use two different forces to grind out two parts of the surface on the end face. One is to use a small force to grind out the metallic (silver-white) surface (A), and the other is to use a larger force to grind out the blue-black. s surface. The metallographic observation of the surface was observed, and it was found that the structure of the A region was a normal tempered troostite, and the structure of the B region was a mixed structure containing martensite and bainite. The reason for the spring break in a spring factory may be that the individual springs are slightly larger in size or improperly assembled during grinding, and they are subject to greater grinding force when the same amount of grinding is applied. Another reason may be grinding during grinding. Caused by improper volume control.
Improper control of the grinding process, possible hazards: (1) If a) Zone A tempered troostite structure @500b) Zone B martensite, bainite mixed structure @500 crack, that is, the spring is serious Surface defects will directly lead to early fracture; (2) brittle structures such as martensite, which are prone to cracks when springs are deformed, affecting fatigue life; (3) martensite and other tissues exist, hardness is high, and cannot be realized Shot peening, the surface can not form compressive stress, also affects fatigue life. The broken spring sample was close to the fracture position, the shot blasting trace was not obvious, and shot peening did not work. In order to ensure product quality, it is recommended to take measures: (1) strict standard operation; (2) springs with blue-black and oxidized color on the grinding surface should be treated with caution, on the one hand, another tempering treatment should be carried out immediately to improve the organization. Then, blasting treatment is carried out; on the other hand, further inspection is to be carried out to check whether cracks are present. Conclusion (1) The reason why the spring pressure of a factory is broken is that the spring generates quenching structure and crack during grinding. (2) The spring end face grinding should be standardized to avoid quenching structure or cracks. (3) For springs with a blue-black oxidized color on the ground surface, the spring should be treated with caution. On the one hand, it should be tempered in time, and on the other hand, it should be checked for cracks.
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