900 MPa级管线钢热处理工艺优化及韧性波动分析

Heat treatment process optimization and toughness fluctuation analysis of 900 MPa grade pipeline steel

通过三因素三水平正交热处理试验,探索新型900 MPa级低合金高强韧管线用钢的最优热处理工艺,借助OM、SEM、TEM等手段,对管线钢韧性波动原因进行了全面分析。结果表明,各因素(淬火温度、回火温度、回火时间)对钢的力学性能(冲击功、强度性能和延伸率)的影响具有不同优先级,确认了最优工艺参数为淬火温度890℃、回火温度590℃、保温时间60 min。随着回火温度的升高和保温时间的延长,析出物数量增多且趋于球化,同时组织软化,位错密度降低,这些因素是管线钢韧性提高的主要原因。相比之下,细小弥散分布的夹杂物对韧性的提升贡献较小。尽管回火温度升高和保温时间延长也会导致析出相尺寸增大和组织粗化,使管线钢韧性降低,但这种降低效果远小于前述增韧因素带来的正面影响。

Through a three-factor,three-level orthogonal heat treatment experiment,the optimal heat treatment parameters for a noval 900 MPa grade low-alloy high-toughness pipeline steel were determined,and the causes of toughness fluctuation were comprehensively analyzed by means of OM,SEM,and TEM.The results reveal that the factors including quenching temperature,tempering temperature,and holding time,have an impact on the mechanical properties(impact toughness,strength properties,and elongation)of the pipeline steel with varying priorities.The optimal parameters identified are a quenching temperature of 890℃,a tempering temperature of 590℃,and a holding time of 60 min.As the tempering temperature increases and the holding time extends,precipitates increase in quantity and tend to spheroidize,alongside microstructural softening and reduced dislocation density.These are the primary factors enhancing the toughness of the pipeline steel.Conversely,the minor role of fine,dispersed inclusions in improving toughness is noted.While the larger precipitate size and coarser microstructure could potentially diminish toughness,these effects are markedly less significant than the improvements wrought by the primary toughening mechanism.