Causes and Preventive Measures of Grinding Cracks of Carburized and Quenched Gear of Rolling Mill

In order to find out the causes of cracks on the gear surface of rolling mill after grinding in production, macro analysis, chemical composition analysis, hardness test and metallographic examination were carried out on the carburized and quenched gear of rolling mill. The results show that the improper grinding process led to the formation of secondary quenched cryptocrystalline martensite without tempering on the surface layer of gear, with high hardness and brittleness, and the carburized layer finally formed high-low-high typical hardness distribution characteristics of grinding quenching burn. When the thermal stress, tensile stress and microstructural stress on the ground surface are greater than the fracture strength of the gear surface, cracks will appear here. The generation of grinding crack can be prevented by controlling the martensite after carburizing and quenching to be cryptocrystalline or fine acicular, controlling the area fraction of retained austenite content to be less than 20%, the surface carbon content to be 0.7%~0.9%, and selecting reasonable tempering temperature, tempering time and grinding process.