焊接峰值温度对X80管线钢焊接接头热影响区性能影响的热模拟

摘要

In order to study the effect of welding peak temperature on softening of single-pass welded joint heat affected zone of X80 pipeline steel with excellent deformability,a thermal simulation testing machine was used to study the effects of peak temperature on microstructure and mechanical properties at 500-1 300 ℃ by simulating single-pass welding test.The results show that,when the temperature was 500-700 ℃,yield strength and impact toughness of the welded joint increased,tensile strength and hardness decreased,the content of pearlite decreased, black M/A island appeared and its distribution was along the grain boundaries.When the temperature was 800-1 000 ℃,softening phenomenon appeared,yield strength,tensile strength and impact toughness all reduced,the hardness drop was significant,the contents of M/A island gradually increased;The reasons for softening was incomplete recrystallization,the microstructure of matrix was given priority to with ferrite,and with the increase of temperature,carbide dispersion degree decreased,strength and hardness decreased.When the temperature was 1 100-1 300 ℃,yield strength and tensile strength of welded joint increased obviously,percentage reduction of area significantly reduced,hardness increased,the microstructure consisted of lath bainite and ferrite,M/A island transformed from fine and disordered arrangement to long striped and ordered arrangement.%为了研究焊接峰值温度对大变形X80管线钢单道次焊接接头热影响区软化的影响,利用热模拟试验机在500~1300℃下对X80钢的单道次焊接试验进行热模拟,研究了峰值温度对其组织和力学性能的影响。结果表明：当峰值温度从500℃升至700℃时,接头的屈服强度和冲击韧性升高,抗拉强度和硬度降低,组织中的珠光体含量减少,出现黑色的 M/A 岛,且其有沿晶界分布的特征；当温度从800℃升至1000℃时,接头出现软化现象,屈服强度、抗拉强度和冲击韧性都降低,硬度的下降较为显著,M/A岛逐渐增多；出现软化的原因是发生了不完全重结晶,显微组织以铁素体为主,并且碳化物的弥散度随着温度升高而逐渐减小,故而强度和硬度下降；当峰值温度从1100℃升高至1300℃时,接头的屈服强度和抗拉强度明显增大,断面收缩率显著减小,硬度增加,显微组织以板条贝氏体和铁素体组成,M/A岛由细小、无序状排列向长条、有序状排列转变。