Fracture Analysis of Case Hardening in Kingpins Parts

Abstract

Kingpin parts are one of the critical products for heavy vehicles and are generally made of 20MnCr5 steel. A kingpin is a heavy metal cylindrical pin that is located underneath the front end of the trailer. The kingpin is the mechanism on the trailer that locks it to a road tractor. The parts in this study have undergone to case hardening heat treatment after the rough machining operation. During the operation in the assembly line, cracks have been realized on the surface of the parts. In this study, the kingpin parts are examined with optical microscopy, Scanning Electron Microscopy (SEM), hardness tests and %C potential analysis in order to determine the potential causes of the crack formations. By the help of the analysis, the presence of cracks became clear. There are no signs of hydrogen embrittlement. The exact outcome of the fracture could not be determined. It is seen that heat treatment of the parts is not homogeneously obtained throughout their surfaces or desired volume, and therefore fractures occur. With the present structure, it can be expected that even a low dynamic load can lead to breakage. As a result, the investigations suggest that the parts were exposed to inappropriate heat treatment parameters.