控轧工艺对厚壁X70管线钢低温止裂性能的影响

针对壁厚33 mm、管径φ1 422 mm管线用X70钢板在-30 ℃下DWTT性能异常问题,利用扫描电镜和背散射电子衍射技术,分析了两种不同控轧工艺下X70管线钢板的微观组织、晶粒大小及取向等因素对其低温止裂性能的影响。结果表明:粗轧采用7道次,道次压下量21~35 mm,轧后冷却速率19.4 ℃/s的条件下,钢板可获得细小的多边形铁素体、针状铁素体、以及弥散分布的M/A岛组织;同时,由于采用大压下率,提高了钢板心部变形渗透能力,可以细化心部奥氏体晶粒,增加了心部大角度晶界比例;还有,由于钢板厚度方向晶界取向差接近且心部存在38.2%的大角晶界,均有利于提高管线钢板的止裂性能。

Effect of controlled rolling process on low temperature crack arrest performance of thick wall X70 pipeline steel plate

Aiming at the abnormal DWTT performance at -30 ℃ of X70 steel plate for pipe with 33 mm wall thickness and φ1 422 mm diameter, the influence of microstructure, grain size and orientation on the low temperature crack arrest performance of X70 pipeline steel plates under two different controlled rolling processes was analyzed by scanning electron microscopy and backscattered electron diffraction techniques. The research show that under the conditions of 7 passes of roughing rolling, reduction of 21-35 mm per pass, and cooling rate of 19.4 ℃/s after rolling, the microstructure of fine polygonal ferrite, acicular ferrite and dispersed ferrite of plate can be obtained .Meanwhile, due to the use of a large reduction ratio, the deformation and penetration capacity of the core of plate is improved, and the austenite grains in the core can be refined, and the proportion of large angle grain boundaries in the core can be increased. In addition, because the grain boundary orientation difference in the thickness direction of the plate is close and there are 38.2% large angle grain boundaries in the core, it is beneficial to improve the crack arrest performance of the pipeline plate.