关键词: 45钢, 销轴, 淬火裂纹, 亚温淬火

Abstract: Longitudinal cracked 45 steel pin shaft was analyzed by metallographic microscope, Rockwell hardness tester and direct-reading spectrometer. The results show that the chemical composition of the 45 steel pin shaft meets the standard requirements, the non-metallic inclusions near and at the crack are few, and the microstructure is tempered martensite. No obvious decarburization is found on both sides of the crack, which is a typical quenching crack. The quenching heating temperature of the pin shaft is high, the cooling time in water during quenching is too long, and the diameter $\phi$7 mm of the pin shaft is within the dangerous size range for quenching cracks in 45 steel during water quenching. The comprehensive effect of these factors leads to the longitudinal quenching crack of the pin shaft. In order to prevent the quenching crack of 45 steel pin shaft, the quenching heating temperature should be formulated according to the actual critical temperature Ac₃ of the 45 steel, the water cooling time of the pin shaft should be strictly controlled during quenching, or intercritical hardening process should be taken.

Key words: 45 steel, pin shaft, quenching crack, intercritical hardening