水冷均匀性对TMCP态Q500qE桥梁钢板性能的影响及其改进措施

Effect of Uniformity of Water Cooling on Mechanical Properties of TMCP Processed Q500qE Bridge Steel Plate and Its Improvement Measures

以TMCP工艺生产的Q500qE高性能桥梁钢为研究对象,采用光学显微镜、扫描电子显微镜、电子背散射衍射、拉伸及冲击试验等,研究了终冷温度对钢板组织和力学性能的影响。结果表明:随着终冷温度从600℃降至430℃,钢板粒状贝氏体含量减少,板条贝氏体含量增加,大角度晶界比例从28.5%提高至35.7%,M/A岛体积分数从5.8%降至1.2%,板条贝氏体尺寸从0.82μm减小至0.22μm;钢板屈服强度从478 MPa提高至627 MPa,抗拉强度从679 MPa提高至745 MPa,断后伸长率从23.0%降至16.5%,屈强比从0.70升至0.87,-40℃冲击吸收能量均值从115 J提高至305 J。同时,基于热成像仪分析,将钢板典型的终冷温度不均划分为头尾过冷、边部过冷、局部高温和波浪状温度分布4类,并针对性提出了头尾遮蔽工艺、水凸度、水冷集管维护以及板形控制等改进措施,可将Q500qE钢板终冷温度波动控制在80℃以内,钢板头、中、尾的抗拉强度波动控制在35 MPa以内。

Effect of final cooling temperature on the microstructure and mechanical properties of Q500qE high-performance bridge steel produced by TMCP process was studied by using optical microscope,scanning electron microscope,electron back scattering diffraction,tensile and impact tests,and so on.The results showed that as the final cooling temperature decreased from 600 to 430℃,the granular bainite content decreased and lath bainite content increased in the steel plate,the proportion of large angle grain boundary increased from 28.5%to 35.7%,the volume fraction of M-A island decreased from 5.8%to 1.2%,and the size of lath bainite decreased from 0.82 to 0.22μm;the yield strength of the steel plate increased from 478 to 627 MPa,the tensile strength increased from 679 MPa to 745 MPa,the yield-to-tensile strength ratio increased from 0.70 to 0.87,and the impact toughness at-40℃increased from 115 to 305 J,but the elongation decreased from 23.0%to 16.5%.Meanwhile,based on the analysis of thermal imager,the typical nonuniformity of final cooling temperature for the steel plates was divided into four types:head and tail supercooling,side supercooling,local high temperature and wave temperature distribution,and the targeted improvement measures were proposed for head and tail shielding,water crown,water header maintenance and shape controlling.The final cooling temperature fluctuation of Q500qE steel plate could be controlled within 80℃,and the tensile strength fluctuation at head,middle,and tail of the steel plate was controlled within 35 MPa.