超快冷下厚规格X80管线钢显微组织与力学性能

Microstructure and mechanical properties of X80 pipeline steel heavy plate under ultra-fast cooling

针对厚规格X80管线钢,采用SEM、EBSD、TEM等方法,研究了不同超快冷终冷温度下厚规格管线钢显微组织演变规律及强韧化机制,并进一步给出了最佳超快冷工艺参数。结果表明,在相同控轧条件下,随着超快速冷却温度由650℃降低至350℃,显微组织经历了由AF＋QF＋GB＋DP向AF＋GB的转变,沿厚度方向组织均匀性得到改善,有效晶粒尺寸减小,铁素体板条亚结构细化;当超快速冷却温度为350℃时,沿厚度方向组织均匀性最优,有效晶粒尺寸及板条亚结构尺寸最小,分别为3.83μm及300~900 nm间,材料的主要强化机制为细晶强化与相变强化的综合强化,此时实验钢综合力学性能最优,拉伸、冲击力学性能均满足ASTM A370标准;实验钢轧后超快速冷却最佳工艺参数为：810℃精轧＋超快冷至350~400℃＋层流冷却至320~360℃＋卷取。

Ultra-fast cooling（ UFC） to different finish cooling temperatures was employed in the thermo-mechanical controlled process（ TMCP）,which aimed at for the fabrication of X80 pipeline steel heavy plate. The microstructure and mechanical properties of the experimental steel obtained under different UFC finish cooling temperature were studied by OM,SEM,EBSD technique and TEM,and the optimized controlled cooling parameters for the corresponding pipeline steel heavy plate were given based on the experiments. The results show that with the decrease of the finish UFC cooling temperature from 650 ℃ to 350 ℃,the microstructure varies from quasi-polygonal ferrite（ QF）,degenerate pearlite（ DP）,granular bainite（ GB） and acicular ferrite（ AF） to AF and GB,and the homogeneity of the microstructure along the cross section of the steel plate is improved. The effective grain size and substructure size is refined. When the UFC finish cooling temperature is 350 ℃,the excellent homogeneity of the microstructure is observed. The effective grain size of 3. 83 μm and the substructure grain size of 300 nm to 900 nm are obtained. The mechanical properties with a good combination of strength and ductility of the studied steel satisfy the ASTM A370 specification. The optimized UFC parameters after finish rolling are as follows： finish rolling at 810 ℃,UFC to 350-400 ℃,laminar cooling to 320-360 ℃,coiling.