材料期刊网

利用光学显微镜、X射线衍射仪等仪器对Ti-IF钢进行了微观组织观察及宏观织构的检测;利用拉伸试验机检测钢板的拉伸性能及加工硬化指数n和塑性应变比r;利用TE-SMF金属板材综合成形试验机进行刚性凸模胀形试验和杯突试验;研究了Ti-IF钢板在热轧、冷轧、退火等不同状态下微观组织与成形性能之间的关系.研究发现,试验钢板热轧态微观组织为等轴铁素体晶粒,晶粒尺寸平均为20～25 μm;冷轧后钢板的微观组织呈拉长、压扁的纤维结构,退火后钢板发生了回复、再结晶及晶粒长大,微观组织以等轴晶为主,晶粒尺寸约为15～20μm.退火后钢板的织构以｛111｝面织构为主,有部分｛100｝织构存在,说明该试样具有良好的冲压成形性能.拉伸试验结果显示,退火后钢板拉伸曲线无明显的屈服平台,屈服强度R..2约为130～150 MPa,抗拉强度Rm约为280～290 MPa,断后伸长率A80为43％～45％,屈强比小于0.51,加工硬化指数n值平均为0.21,塑性应变比r值平均为3.07.低的屈强比、高的n值和r值保证了材料良好的冲压性能.材料的刚性凸模胀形试验及杯突试验结果也证明了这一点.

Microstructures and macro texture of Ti-IF steel sheet used for car body were observed by optical microscopy,X-ray diffractometer and other instruments.Tensile properties,strain hardening exponent n and plastic strain ratio r of the steel sheets were measured by tensile testing machine.The rigid punch bulging test and the cupping test were done by TE-SMF sheet metal composite forming machine.The relationship between microstructures and formability of the Ti-IF steel sheet in hot-rolled,cold-rolled and annealed conditions was investigated.It was found that the microstructure of the hot-rolled steel sheet was equiaxed ferritic grains whose average grain size was 20 μm to 25 μm,and that the microstructure after being cold-rolled was a stretched and flattened fiber structure,and after annealing,the recovery,recrystallization and grain growth occurred in the steel sheet whose average equiaxed grain size was 15 μm to 20 pm.Apart from a little {100｝ texture,most of the annealing textures were { 111 ｝ plane texture,which confirmed that the sample has good stamping formability.The tensile test results of the annealed steel sheet showed that the tensile curve has no obvious yield point elongation,and the steel sheets exhibited the yield strength Rp0.2 of 130 MPa to 150 MPa,the tensile strength Rm of 280 MPa to 290 MPa,the elongation As0 of 43％ to 45％,the yielding-to-tensile ratio of less than 0.51,the strain hardening exponent n of 0.21,and the plastic strain ratio r of 3.07.The lower yielding-to-tensile ratio,higher n and r values make it possible to guarantee the better stamping formability of the Ti-IF steel sheet.The foregoing also was confirmed by the rigid punch bulging test and cupping test results of the steel sheet.