700 MPa级大梁钢W撑开裂原因分析

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

高强度低合金钢板产品的质量稳定一直是汽车用户和钢铁企业追求的目标,特别是屈服强度为700 MPa级的高强汽车大梁钢板。本文利用光镜、电镜和EBSD观察分析了不同成分的700 MPa级大梁钢W撑的显微组织、晶粒尺寸、晶界取向和钢中析出相。结果表明,铌钛微合金化强化的700 MPa级大梁钢较单钛强化的大梁钢晶粒细小均匀,折弯过程中的止裂能力强;加工变形过程中大尺寸的氮化钛周围产生的应力集中,形成孔洞并成为裂纹源;单钛强化的W撑开裂的直接原因是晶界处大量的析出相和板条贝氏体组织降低了局部塑性,导致折弯过程中局部产生变形裂纹。上述结果说明了挂车W撑加工过程开裂的原因,为后续大梁钢的成分设计和使用环境的选择提供了重要依据。

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.