湿H₂S环境中L360MCS钢焊接热影响区的应力导向氢致开裂行为

来源期刊：金属学报2010年第5期

论文作者：周成双 郑树启 陈长风

文章页码：547 - 553

关键词：管线钢； 热影响区(HAZ)； 应力导向氢致开裂(SOHIC)； H₂S； 拉应力

Key words：pipeline steel； heat affected zone(HAZ)； stress oriented hydrogen induce cracking(SOHIC)； H₂S； tension stress

摘    要：利用裂纹面分离及SEM和EDS研究了L360MCS钢焊接热影响区(HAZ)在湿H₂S环境中的应力导向氢致开裂(SOHIC)行为.结果表明:应力导向氢致开裂裂纹由轴向和纵向两种裂纹组成,先形成轴向裂纹,后形成纵向裂纹,两种裂纹均独立形核.裂纹带有明显的阶梯状氢致开裂特征,裂纹面呈现准解理型断口形貌.拉应力在裂纹形核和扩展方面起主要作用,拉应力不仅增加了拉伸区的过饱和氢浓度,而且直接推动纵向裂纹的扩展.轴向裂纹在MnS和CaS夹杂以及析出相处形核,以氢压为主要的裂纹扩展动力.而纵向裂纹则主要在析出相处萌生,裂纹扩展受拉应力和氢压双重控制,拉应力为主导.

Abstract: Stress oriented hydrogen induced cracking(SOHIC) behavior of heat affected zone (HAZ) of L360MCS steel in wet H₂S environment was studied by separating crack,SEM and EDS. The cracks are formed by four point bending test in wet H₂S environment.The microstructure of HAZ is obviously different from the base metal,and the hardness of HAZ is lower than those of the base metal and welding joint.The fracture surface of the cracks was separated and the hydrogen blisters were torn off.The cross section and fracture surface of the cracks are analyzed by SEM and EDS.Results show that the cracks of SOHIC appeared as axial crack and vertical crack, and the former is preferential.The appearance of cracks is associated with the low hardness value of HAZ.The dimension of hydrogen blasters in tension stress zone of bended specimen is bigger than that in unstressed specimen,which is due to hydrogen concentration in bended specimen is higher.Both axial and vertical cracks nucleate independently and propagate in the quasi-cleavage manner.Tension stress not only increases the supersaturated hydrogen concentration in tension stress zone but directly promotes vertical crack propagation.Axial crack nucleates at MnS,CaS and precipitated phase,and propagates under internal hydrogen pressure.Vertical crack mainly nucleates on precipitated phase and propagates under both internal hydrogen pressure and tensile stress.