1 200 MPa级HSLA钢的SH-CCT曲线及其热影响区组织与性能

为在工程应用中对焊接工艺的合理选取与制定提供理论和试验依据，采用焊接热模拟技术研究了800~500 ℃冷却时间(t8/5)对1 200 MPa级低合金高强钢焊接热影响区粗晶区(CGHAZ)显微组织和性能的影响.结果表明：t8/5为6~20 s时，该钢热影响区的粗晶区组织为板条马氏体，硬度为477~456 HV5；随着冷却时间的延长，组织中开始出现板条贝氏体，在t8/5为60 s时硬度下降到380 HV5；当t8/5为60~600 s时，粗晶区组织为板条贝氏体和粒状贝氏体，硬度为380~300 HV5；t8/5>600 s时粗晶区组织主要为粒状贝氏体，硬度为300~315 HV5.试验钢碳当量为0.626%，冷裂纹敏感系数为0.335%，说明其淬硬倾向较大，焊接热影响区容易产生裂纹.
To provide theoretical and experimental basis for the proper selection of welding parameters in engineering application,the effect of cooling time from 800 to 500 ℃ (t8/5) on the microstructure and properties of the coarse grained heat affected zone (CGHAZ) of a 1 200 MPa grade HSLA steel was investigated by using the thermal simulation tests. The results indicate that the microstructure of the CGHAZ consisted of lath martensite with hardness 477~456 HV5 as t8/5 is 6~20 s. With prolonging cooling time,the lath bainite forms in the steel,and the hardness decreases to 380 HV5 as the t8/5 is 60 s. As t8/5 is 60~600 s,it shows a microstructure of lath granular bainites with hardness 380~300 HV5. When t8/5 is longer than 600 s,the CGHAZ mainly shows a microstructure of granular bainite with hardness of 300~315 HV5. The carbon equivalent and cold cracking susceptibity coefficient of this steel is 0.626% and 0.335%,respectively,indicating that the harden quenching tendency is strong and the cold crack can easily form in the HAZ of the steel.