550MPa级高强度高延性汽车方管用钢的显微组织与力学性能

Microstructure and Mechanical Properties of 550 MPa Grade High Strength and High Ductility Automobile Square Tube Steel

开发了一种550 MPa级高强度高延性汽车方管用钢,研究了其热轧带钢及方管平面、圆角、焊缝处的显微组织及力学性能。结果表明:热轧带钢的显微组织由均匀细小的铁素体与少量珠光体组成,基体中析出较多尺寸在1~110nm的(Nb,Ti)C相;方管平面与圆角部位显微组织与热轧态的基本相同;制管后钢中位错密度增加,晶界及第二相处发生位错塞积,圆角部位形成了位错墙与位错胞;制管后该钢发生加工硬化,方管平面、圆角、焊缝处的屈服强度、抗拉强度与屈强比依次增加,断后伸长率依次下降,焊缝处塑韧性相对较差。

A 550 MPa grade high strength and high ductility steel for automotive square tubes was developed.The microstructure and mechanical properties of hot rolled steel strip and plane,fillet and weld of square tube were studied.The results show that the microstructure of hot rolled steel strip was composed of uniform and fine ferrite and a small amount of pearlite,and a large number of(Nb,Ti)C phases with size of 1-110 nm were precipitated in the matrix.The microstructures of the square tube plane and fillet were basically the same as that of the hot rolled steel.The dislocation density in the steel increased after tube forming,dislocation plugging occurred at the grain boundary and the second phase,and dislocation walls and cells were formed at the fillet.Work hardening occurred in the steel after tube forming.The yield strength,tensile strength and yield ratio of the square tube plane,fillet and weld were increased in sequence,while the elongation decreased sequentially,and the toughness at the weld was relatively poor.