Study on Influencing Factors of Surface Decarburization of Spring Steel 55SiCr During Heating

55SiCr is a high-grade steel used in automobile suspension springs. Suspension springs undergo reciprocating compression during the driving process of the automobile, playing a buffer and shock absorption function, and have high requirements on the performance of steel. Decarburization is one of the main problems in the hot working process of spring steel. Decarburization of the spring steel surface will seriously damage the fatigue performance of the spring. Especially when the full decarburization of ferrite occurs on the surface of the spring steel, the fatigue limit of the spring can be reduced. 50%. At present, the research reports on the surface decarburization of spring steel mainly focus on the two influencing factors of heating temperature and heating time, but there are few reports on the influence of heating furnace atmosphere on the decarburization of spring steel. Researchers at the University of Science and Technology Beijing refer to the actual production conditions of the on-site heating furnace to study the effects of heating temperature, holding time and atmosphere in the heating furnace on the surface decarburization of spring steel 55SiCr in the laboratory, and conduct a thermodynamic analysis of the decarburization reaction. The results show that the thickness of the fully decarburized layer of spring steel first increases and then decreases when the temperature increases in the range of 950℃～1250℃. The thickness of the fully decarburized layer reaches the maximum at 1200℃, and the oxidation rate is greater than the decarburization rate at 1250℃. , The completely decarburized layer disappears. The thickness of the fully decarburized layer of spring steel increased significantly with the increase of heating time, the increase of CO2 content, the increase of O2 content and the increase of H2O(g) content in the atmosphere, respectively. When the temperature is 950℃, the O2 content in the atmosphere is 1%, and the heating time is 35 minutes, the formation of a completely decarburized layer can be avoided.