摘要
为了研究800MPa级低合金高强钢焊接粗晶区的组织转变规律,采用热模拟的方法,应用L78RITA相变热膨胀仪模拟了实验用钢的两次焊接热循环过程,对应的焊接线能量约为20kJ/cm。建立了该钢的奥氏体连续加热转变曲线(TTA),并对组织、硬度和热膨胀曲线进行分析,结果显示,实验用钢一次热循环粗晶区组织为板条马氏体和贝氏体,硬度为318HV,当第二次热循环峰值温度(Tp2)为1000℃时,第一次热循环后的组织发生完全重结晶,得到细小的贝氏体组织,硬度下降,当Tp2为900℃时发生部分重结晶,硬度最低(239HV),当Tp2为800℃时,在晶界和晶内相界生成链状分布的M-A组元,而Tp2小于A′c1时发生回火作用,M-A组元分解并析出碳化物。实验用钢的热影响区未出现组织遗传现象,因此为了更准确判断组织转变类型,应结合TTA曲线对焊接热影响区组织转变进行分析。
The microstructure evolution of the coarse grain heat affected zone（CG-HAZ）of 800 MPa grade high strength low alloy（HSLA）steel was investigated using thermal simulated method by L78 RITA phase change thermal dilatometer.The experimental steel was heated twice to simulate two welding-pass thermal cycles.The corresponding welding heat input was approximately 20kJ/cm.A time temperature austenization（TTA）curve was established for the experimental steel,and the microstructure,hardness and dilatational curve were analyzed.The results show that,for the CG-HAZ of the first pass thermal cycle,lath martensite and bainite are obtained,and the hardness is 318HV;When Tp2 is 1000℃,complete recrystallization occurs in the structure after the first cycle,fine bainite was obtained,and the hardness is decreased;When Tp2 is 900℃,partial recrystallization occurs,and the hardness is the lowest 239HV;When Tp2 is 800℃,some necklace-like M-A constituents are obtained at the grain boundary and intergranular phase boundary;When Tp2 is lower than Ac1,tempering occurs,the M-A constituents are resolved and carbides are precipitated.The structure heredity is not found in HAZ of this experimental steel,hence,in order to accurately determine the microstructure transformation type,analysis should be carried out on the microstructure transformation process of HAZ using TTA curve.
出处
《材料工程》
EI
CAS
CSCD
北大核心
2015年第7期93-99,共7页
Journal of Materials Engineering
基金
国家科技重大专项子课题(2009ZX04014-064-05)
内蒙古自治区高等学校科学研究项目(NJ10092)
