X80管线钢边部横裂纹成因分析

Cause analysis of transverse crack in X80 pipeline steel

利用金相显微镜、扫描电镜并结合轧制工艺,对X80管线钢存在的边部横裂纹缺陷位置的微观组织进行分析。研究发现:在粗轧阶段由于板材边部与轧辊、冷却水和空气进行着强烈的三维热传导和热交换,导致边部温度比中间低,随着温度的降低和变形量的增加,诱导铁素体相变,边部进入两相区,X80管线钢在两相区轧制过程中导致先共析铁素体变形成扁平状,先共析铁素体在轧制过程中产生变形,成流线型组织,而心部仍为奥氏体,此类先共析铁素体从奥氏体相变得到,奥氏体塑性优于先共析铁素体,变形铁素体未来得及发生动态回复,当轧制变形力超过变形极限时导致边部开裂;此外,Nb在奥氏体中固溶度高于铁素体,边部处于两相区时,NbC和TiC钉扎在晶界,抑制了钢的动态再结晶,且存在于晶界的析出物弱化晶界,导致塑性变形能力差,作为应力集中源,均会导致开裂。

Metallographic microscope and rolling process were used to analyze the microstructure of the edge transverse crack defect existing in X80 pipeline steel.The research found that in the roughing stage,the edge temperature is lower than the middle because of the intense three-dimensional heat conduction and heat exchange between the edge of the plate and the roller,the cooling water and the air,induced ferrite phase transition,the edge into the two-phase zone,during the rolling process of X80 pipeline steel in two-phase zone,the pre-eutectoid ferrite is deformed into a flat shape,and the pre-eutectoid ferrite is deformed into a streamline structure,while the austenite is still in the center,this kind of pre-eutectoid ferrite is obtained from austenite transformation,and the plasticity of austenite is better than that of pre-eutectoid ferrite;in addition,when the solid solubility of NB in austenite is higher than that of ferrite,and the edge is in the two-phase zone,NBC and TIC are pinned at the grain boundary,which inhibits the dynamic recrystallization of steel,and the precipitates existing at the grain boundary weaken the grain boundary,as a source of stress concentration,it can lead to cracking.