Causes Analysis on Quenching Cracking of 45 Steel Gear Shaft Parts

For the phenomenon of batch quenching cracking of 45 steel gear shafts, instruments and devices such as optical microscope, scanning electron microscope and ICP spectrometer were used to analyze the cracking samples. The results show that the cracking of the 45 steel gear shafts were mainly due to the overheating caused by the high quenching heating temperature and fast cooling because of too long cooling time, which increased the thermal stress and structural stress. And when the stress exceeded the tensile strength of the material, quenching cracking would happen at the weak step positions. At the same time, the step position thickness of 45 steel gear shafts was in the easy quenching cracking range of 5 - 14 mm, which was another reason for the cracking.