退火温度对CSP冷轧低碳高强钢带组织和性能的影响

Effect of annealing temperature on microstructure and properties of cold rolled low carbon high strength sheet by CSP

以低碳高强钢冷轧钢带为研究对象,利用光学显微镜、场发射扫描电镜、全自动拉伸试验机等设备对试验钢进行组织观察和性能测试。结果表明:试验钢带采用520~580℃退火后,铁素体晶粒形态变化较小,呈变形纤维状,组织中分布的渗碳体数量较少,其屈服强度、抗拉强度变化较小,屈强比维持在0.9以上,伸长率为1%左右;采用610~700℃退火后,变形的铁素体周围出现了无畸变的再结晶晶粒,再结晶晶粒会随着退火温度的升高而长大成等轴状铁素体,渗碳体的球化过程是导致组织中颗粒状渗碳体数量增多的主要原因,其屈服强度、抗拉强度迅速下降,伸长率迅速增加,屈强比呈下降趋势,在670℃时达到最小值0.86;采用730~760℃退火后,铁素体晶粒充分长大,晶粒形态变化较小,组织中几乎没有游离的渗碳体存在,渗碳体仅在晶界上聚集分布呈片层状,其屈服强度、抗拉强度缓慢下降,伸长率缓慢增加,屈强比呈上升趋势,在760℃时达到0.91。综合考虑,试验钢带的最佳退火温度为670℃。

Taking low-carbon high-strength cold-rolled sheet as the research object,the microstructure of the annealed cold sheet was observed by using optical microscope,field emission scanning electron microscope and the mechanical properties were tested by using automatic tensile testing machine.The results show that when the tested sheet is annealed between 520℃ and 580℃,the ferrite grain morphology changes little,it is still elongated;the number of cementite distributed in the microstructure is small,and the yield strength and tensile strength change little,yield ratio remains above 0.9,and the elongation is about 1%.When the tested sheet is annealed between 610℃ and 700℃,undistorted recrystallized grains appear around the deformed ferrite,the recrystallized grains will grow into equiaxed ferrite with the increase of annealing temperature.The spheroidization process of cementite is the main reason for the increase in the number of granular cementite in the microstructure,and the yield strength and tensile strength decrease rapidly,the elongation increases rapidly,the yield ratio shows a downward trend,reaching a minimum of 0.86 at 670℃.When the tested sheet is annealed between 730℃ and 760℃,the ferrite grains grow sufficiently,the grain morphology changes little,there is almost no freely distributed cementite in the microstructure,the cementite aggregates and distributes only in grain boundaries,and the yield strength and tensile strength decrease slowly,the elongation slowly increases,and the yield ratio increases,reaching 0.91 at 760℃.Based on the comprehensive consideration,the optimum annealing tmperature of the tested sheet is 670℃.