管线用超低碳钢中针状铁素体的形成及强韧化行为

FORMATION AND STRENGTH-TOUGHNESS BEHAVIOR OF ACICULAR FERRITE IN AN ULTRALOW CARBON STEEL FOR LINE PIPE

通过对一种管线用超低碳钢的变形奥氏体相变工艺的分析,提出了能够获得针状铁素体为主的组织的控制热加工工艺(TMCP)制度,研究了针状铁素体的结构特征和力学性能.结果表明,与管线用中、低碳钢相比较,实验用钢尽管具有很低的碳含量(0.025％),但在当前优化的TMCP工艺下能够获得优良的力学性能,即具有相当的强度和高的冲击韧性.针状铁素体的结构特征提高了材料的力学性能.值得注意的是,在当前优化的TMCP工艺下,针状铁素体晶界上存在一层薄膜,这层薄膜对管线用超低碳钢的强韧性具有重要的作用.

The transformation process of deformed austenite was investigated to an ultralow carbon steel for line pipe on a Gleeble-2000 hot simulator. Based the obtained results, the improved thermo-mechanical control process (TMCP) was suggested to achieve the acicular ferrite dominated microstructure on a laboratory rolling mill. The microstructural characteristics and mechanical properties of acicular ferrite were analyzed. Compared with low carbon and/or medium carbon steels for line pipe, the experimental ultralow carbon steel for line pipe possessed the satisfied mechanical properties under the current improved TMCP, although this steel contained only 0.025% carbon. It was analyzed that microstructural characteristics of acicular ferrite enhanced the mechanical properties of steels. Furthermore, there existed a layer of thin film at the grain boundary of acicular ferrite under the current improved TMCP. The thin film should be attributed to the strength and toughness behaviors of the ultralow carbon steel for line pipe.