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一、热处理加热不足导致损毁的连杆螺栓工农11型手扶拖拉机在使用过程中,由于连杆螺栓的断裂,造成整台发动机破坏事故。从断裂螺栓的断口面观察,不是脆断,而属塑性变形后断裂。硬度为HRC22,金相组织为回火索氏体及小颗粒状分布的碳化物(见图1)。该连杆螺栓的技术要求是:采用40Cr钢,调质处理后硬度为HRC28～35,金相组织应该是回火索氏体,允许有很少量的小块铁素体。这只螺栓的材料是40Cr钢,但因采用冷镦锻六角头成型的,故要求原材
First, the lack of heat treatment lead to damage the connecting rod bolt Workers and peasants 11 type tractor in the use of the process, due to the link bolt fracture, causing the entire engine damage accident. From the broken bolt fracture surface, not brittle fracture, which is a plastic deformation fracture. Hardness of HRC22, microstructure of tempered sorbite and small particles of carbide distribution (see Figure 1). The connecting rod bolt technical requirements are: 40Cr steel, quenched and tempered after the hardness of HRC28 ~ 35, the microstructure should be tempered sorbite, allowing a small amount of small pieces of ferrite. This bolt material is 40Cr steel, but because of the use of cold forging hexagonal head shape, it requires raw materials