Fracture Analysis of Crosshead Screw Made of SWRCH22A Wire Rod

Crosshead screws made of SWRCH22A wire rod were fractured in the torque force and drilling tests. The fracture reason was discussed by means of the microstructure of wire rod and screw examination and the fracture mode analysis.The results showed that severe surface cracks formed in the teeth valleys of screw during threading process were the main reason for the fracture. In addition, poor protection of spheroidizing annealing resulted in severe decarburization and coarse ferrite grain in wire rod surface; and then the following excessive carburization treatment made the surface layer highly brittle. Meanwhile, a transitional zone consisting of ferrite, martensite and carbide network formed below the brittle carburized layer. Thus, the cracks in surface could easily propagate intergranularly under the maximum shear stress around screw surface and finally caused the screw failure during torque force test.