Decarbonization is a common surface defect of spring steel, which has a significant impact on the performance of spring.
The so-called decarbonization refers to the spring steel in the heating process or heat treatment, the steel surface in the furnace atmosphere under the action of all or in part decarbonization, resulting in the steel surface carbon content than the internal reduction of the phenomenon.
The surface decarbonization of the spring steel will significantly reduce its fatigue limit.
Moreover, fatigue life decreases significantly as the depth of the decarbonization layer on the surface of the steel increases. In particular, the presence of ferrite in the decarbonization layer of the steel surface can reduce the fatigue limit by 50%.
Due to decarbonization, the surface hardness of the spring is reduced, and cracks are easy to produce under the effect of alternating stress, which causes premature spring fatigue to fail.
In addition, the expansion coefficient is different when quenching different parts of the surface layer, causing stress concentration, causing the transition zone between the full decarbonization layer of the component and the partial decarbonization layer to produce microcracks, these visible or invisible microcracks become the stress concentration area, and as the origin of the crack continued to develop, causing the failure or rupture of the spring.