1. The carbon content of steel is low;
2.In the quenching and heating stage, the required technical specifications were not met, the heating temperature was too low or the holding time was insufficient, resulting in insufficient austenite carbon and alloying elements in the forging structure, and even untransformed pearlite or undissolved ferrite, causing the hardness index of the forging to fail to meet the requirements after quenching;
3. The heating temperature of the forging is too high or the holding time is long, resulting in the decarburization of the surface and the hardness can not be reached;
4. Quenching cooling is not in place, cooling is the final process of heat treatment, and it is the most important process of heat treatment. The quenching hardness of 45 steel can be transformed into different structures at different cooling speeds, and its hardness will become lower if the quenching cooling is not in place.
