Analysis of the causes of cracking of 700 MPa grade steel W brace

The stable quality of high-strength but low-alloy steel products has always been the goal pursued by automotive users and steel companies, especially high-strength automotive beam steel plates with a yield strength of 700 MPa. This article analyzed the microstructure, grain size, grain boundary orientation and precipitated phases of a 700 MPa grade beam steel W brace with different compositions by using light microscopy, electron microscopy and EBSD. The results showed that particles of the 700 MPa grade beam steel strengthened by niobium-titanium microalloying were smaller and more uniform than the single titanium strengthened beam steel, and the anti-crack ability was stronger during the bending process; stress concentration occurred around the large-size titanium nitride during the deformation process. The formation of holes became the source of cracks. The direct cause of the single-titanium-strengthened W brace cracking was that many precipitated phases and lath bainite structures at the grain boundary reduced the local plasticity, leading to the generation of local deformation cracks during the bending process. The above explained the reasons for the cracking during the processing of the trailer W brace and provided an important basis for the subsequent composition design of the beam steel and the selection of the environment.