Study of Carbide Banding in 51CrV4 Spring Steel

Abstract

51CrV4 is a spring steel commonly used for the production of trailing arms in the suspension assembly of trucks. It is essential for these products to be predictable and reliable. The presence of carbide banding in 51CrV4 steel can be detrimental to this predictable and reliable behavior. Therefore, in this research, the formation of carbide-banded microstructure in 51CrV4 steel will be investigated. The bending stresses undergone by trailing arms make it crucial to understand the relationship between surface depth and carbide band formation. Therefore, the goal of this research is to understand the relation between the surface depth and band formation in 51CrV4 steel and how banding differs among 51CrV4 steel from different manufacturers. This was done using a variety of testing methods which include microscopy, hardness, XRD, SEM, EDS and EPMA. These testing methods were used to understand the formation of carbide bands in 51CrV4 as well as the underlying physical properties that lead to the carbide band formation. Overall, a significant difference could be seen in the formation of carbide bands across the steel from different manufacturers. These differences in carbide banding properties could be clearly linked to the difference in the physical properties of the steels. The depth at which carbide band formation tends to start could be most clearly related to the micro-segregation peak concentration. Furthermore, the manner in which the carbide bands are built up along the surface depth could be most clearly related to the chromium concentration in the carbide banded regions. Finally, it was found that chromium is expected to be the primary carbide former in this steel as the formation of carbide bands is closely and consistently related to an increased presence of chromium.