回火温度对X80钢级热煨弯管组织性能的影响

Effects of tempering temperature on microstructures and properties of X80 grade heat-bending bend

采用热模拟试验方法、力学性能测试技术及显微分析技术研究了回火温度对X80钢级热煨弯管组织性能的影响规律。结果表明,当回火温度区间为550～650℃时,贝氏体铁素体及粒状贝氏体中板条宽化现象的增强及沉淀强化效应的降低不利于其强度的提高。位错亚结构的变化,Nb、V、Ti的碳、氮化物对位错及亚晶钉扎作用的降低及板条间M-A组元的逐渐分解等组织因素有利于其韧性的提高。当回火温度升高到700℃时,组织中板条宽化现象进一步增强,部分组织发生再结晶而出现多边形铁素体,以及位错密度的降低导致了材料强度和韧性的快速下降。综合考虑X80热煨弯管的强韧性,适宜的回火温度为650℃×1 h。

Effects of tempering temperature on microstructure and properties of X80 grade heat bending bend were investigated by means of thermal simulation method,mechanical property tests and microstructure analysis.The results show that the strength does not increase favorably due to the enhanced lath widening and the weakening of precipitation strengthening within bainitic ferrite and granular bainite when tempering temperature is in the range of 550-650 ℃.While the toughness increment benefits from the change of dislocation substructure,the weakening of pinning effect of carbide and nitride of Nb,V and Ti on dislocation and subgrain,and the gradual decomposition of M-A constituent among the laths.When tempering temperature is increased to 700 ℃,further-enhanced lath widening,some recrystallization-led polygonal ferrite,and reduction of dislocation density lead to a rapid decrement of strength and toughness.In general,a much better combination of strength and toughness of X80 heat-bending bend can be obtained when the steel is tempered at 650 ℃ for 1 h.