Research On Decarburization Of Spring Steel

Generally, there is decarburized layer on the surface of spring steel, decarburized layer has a strong impact on spring steel's material properties, especially fatigue strength and fatigue limit. The current research on decarburization is mainly about qualitative analysis through experiment, but lack of theoretical research, especially numerical computation of decarburization depth, however, decarburization depth can't be predicted. This paper has mainly studied numerical computation of decarburization depth, Process Improvement to reduce decarburization depth, Non-destructive testing methods for decarburization depth.Based on the diffusion theory and Fick's law, we analyzed the principle of atomic diffusion in the solid, summarized its macro-mechanism and micro-mechanism, established a non-steady-state semi-infinite model of diffusion, deduced the numerical computation of decarburization depth, used empirical approach to prove it with spring steel 60Si2MnA.The results show that between 800 degrees to 1050 degrees, in 90 minutes, theoretical results with experimental data is less than 10% deviation.According to requirement of spring steel heat treatment technology, we researched and improved the current spring steel heat treatment process, put forward medium frequency induction heating technics and anti-oxidation, decarburization heat treatment technics, and the improved scheme was proved feasible. The results show that after process improvement the performance met the requirements, decarburization has 50 percent decline in depth.Stand on law of conservation of mass and law of crystal organizational change, we have done the research of the relationship between the decarburized depth and size of spring steel before and after heat treatment. Proposed a non-destructive method on measure the decarburized depth by this relationship, which was also proved by theory and experiments. The results show that as the decarburized depth changes from 0.1mm to 0.4mm, the diameter of spring steel increases by 0.0545mm.