超快冷下X70管线钢热轧工艺及显微组织

研究了14.2 mm X70管线钢轧后经超快冷+层流冷却、层流冷却两种冷却制度后的显微组织及力学性能,讨论了超快冷+层流冷却下实验钢强韧化机制.结果表明:两种冷却制度下实验钢力学性能均满足API SPEC 5L X70要求,超快冷+层流冷却下实验钢强度、塑性及韧性较高,综合力学性能良好;不同冷却制度下显微组织均为贝氏体铁素体+针状铁素体+M-A岛混合组织,其中超快冷+层流冷却下针状铁素体、M-A岛组织更加细化;超快冷+层流冷却下实验钢主要强韧化机制为细晶强化与纳米析出强化;实验钢理想轧后冷却工艺为:820~840℃终轧+超快冷至450~500℃+层流冷却至350~400℃+卷取.

Hot Rolling Process and Microstructures of X70 Pipeline Steel Under Ultra-Fast Cooling

The microstructures and mechanical properties of 14.2 mm X70 pipeline steel， which undergoing ultra-fast cooling+laminar cooling and single laminar cooling after finish rolling， were compared and analyzed. The strengthening and toughing mechanisms were discussed for ultra-fast cooling methods. The results indicate that the mechanical properties of the experimental steel at both cooling methods can meet the API SPEC 5L X70 criterions. The microstructures consist of bainitic ferrite， acicular ferrite and M-A island， and the mixture microstructures of acicular ferrite and M-A island can be refined at the condition of ultra-fast cooling+ laminar cooling. The main strengthening mechanisms are grain refinement strengthening and nano-scale precipitation strengthening. The ideal cooling method after rolling for 14.2mm X70 pipeline steel is listed as: finish rolling at temperature of 820~840℃+ ultra-fast cooling to temperature of 450~500℃+laminar cooling to 350~400℃+ coiling.