汽车用镀锌低合金高强钢HX550LAD+Z的研制与开发

Research and development of galvanized low alloy high strength steel HX550LAD+Z for automobile

为开发力学性能稳定、冷弯性能良好的汽车用镀锌低合金高强钢HX550LAD+Z,对HX550LAD+Z钢的化学成分、控轧控冷及镀锌退火工艺进行了设计,并采用拉伸试验机、金相显微镜、扫描电镜、透射电镜等分析了成品力学性能、冷弯性能、金相组织和析出物等。结果表明:采用低C同时添加微量Nb、Ti的化学成分设计,热轧终轧温度为920℃、卷取温度为550℃,镀锌均热温度为840℃、缓冷温度为700℃,镀锌光整采用0.5%恒延伸率模式,生产的镀锌低合金高强钢HX550LAD+Z组织为铁素体+珠光体,平均晶粒尺寸为7.5μm,晶粒度达11.2级,析出物主要为Ti(C,N)和(Nb, Ti)(C,N),抗拉强度Rm≥620 MPa,屈服强度Rp0.2=560~620 MPa,伸长率A80≥14%。开发的镀锌低合金高强钢HX550LAD+Z成功应用于汽车后梁上下件,零件产品表面质量、性能及尺寸外形等各项指标均达到相关技术要求,零件实现减重9%。

In order to develop a galvanized low alloy high strength steel HX550LAD+Z for automobile with stable mechanical properties and good cold bending property,the chemical composition,controlled rolling and controlled cooling,and galvanizing annealing process of HX550LAD+Z steel were designed.The mechanical properties,cold bending property,microstructure and precipitates of finishing product were analyzed by tensile testing machines,metallographic microscopes,scanning electron microscopes and transmission electron microscopes.The results show that the chemical composition design of low C and trace amounts of Nb and Ti added simultaneously is adopted,the final rolling temperature of hot rolling is 920℃,the coiling temperature is 550℃,the galvanizing soaking temperature is 840℃,the slow cooling temperature is 700℃,the galvanizing finishing adopts a constant elongation mode of 0.5%,and the microstructure of produced galvanized low alloy high strength steel HX550LAD+Z is composed of ferrite and pearlite,with an average grain size of 7.5μm.The grain size reaches 11.2 grade,and the precipitates are mainly Ti(C,N)and(Nb,Ti)(C,N).The tensile strength Rm is not less than 620 MPa,the yield strength Rp0.2 is 560-620 MPa,and the elongation A80 is not less than 14%.The developed galvanized low alloy high strength steel HX550LAD+Z has been successfully applied to the upper and lower parts of the automotive rear beam,and the surface quality,property,size and appearance of the parts have all met the relevant technical requirements,achieving a weight reduction of 9%.