合金元素和工艺参数对非调质CT80钢组织性能影响

Effect of alloy elements and process parameters on microstructure and properties of non-quenched and tempered CT80 steel

研究了终轧温度、冷却速度和卷取温度等工艺参数对具有不同Mo、Nb含量的非调质CT80连续油管用钢组织性能的影响。结果表明,满足其强韧性要求的组织特征为针状铁素体和贝氏体复相组织,且弥散分布约4%的细小M/A岛。终轧温度主要影响组织均匀性。当冷却速度由40～45℃/s提高到60～70℃/s后,铁素体形态转变为针状,其内部亚晶面积增加,位错密度升高。卷取温度影响复相组织中强化相的形态与分布。为避免珠光体或马氏体而促进贝氏体组织转变充分,卷取温度应约为450℃。Mo元素含量提高至0.24%可促进针状铁素体转变并形成细小的强化相M/A岛,起到良好的亚结构强化和相变强化效果。Mo和Nb含量的增加使得实验钢对冷速的敏感性明显降低,增强了非调质CT80连续油管用钢控冷过程工艺稳定性。

In order to improve the performance of non-quenched and tempered CT80 steels with different Mo and Nb content, the effect of finish rolling temperature, cooling rate and coiling temperature on microstructure and properties of the steels were analyzed. The results show that the duplex phase microstructure of acicular ferrite and bainite dispersed with about 4% fine martensite-austenite （M/A） islands can meet the requirement of mechanical properties. Finish temperature affects the uniformity of microstructure. Morphology of ferrite becomes from polygonal shape to acicular shape when cooling rate increases from 40-45 ℃/s to 60-70 ℃/s, meanwhile, sub-grain boundary in acicular ferrite increases and dislocation density enhances. Coiling temperature influences the morphology and distribution of strengthening phase, and it should determine as 450 ℃ to promote bainite transformation and avoid appearance of pearlite and martensite. Increasing Mo content up to O. 24% can improve the transformation of acicular ferrite and M/A islands, and exhibits well sub-grain strengthening and phase transformations trengthening effect. High content of Mo and Nb decreases the sensibility of the non-quenched and tempered CT80 steel on cooling rate, and enhances the process stability of the steel during controlled cooling.