超快冷下X65管线钢微观组织演变及强化机制分析

基于热连轧生产线开发了X65管线钢超快冷新工艺,系统表征了该工艺下实验钢的微观组织特征,并进一步讨论了其强化机制.结果表明,超快冷下X65管线钢微观组织为细小针状铁素体(AF)+准多边形铁素体(QPF)+M/A岛+弱化珠光体(DP)混合组织,有效晶粒尺寸为2.93μm,大角晶界百分比为31.5%;实验钢组织亚结构为细小的块状铁素体,铁素体尺寸分布在200~1000nm;在铁素体基体上析出了大量尺寸＜10nm的Nb(C,N)粒子;实验钢各项力学性能均满足API SPEC 5L标准要求.超快冷工艺下X65管线钢的主要强化机制为细晶强化、固溶强化、位错强化及纳米析出强化的耦合强化,其中纳米析出强化强度贡献值为96.1MPa.

Microstructural Evolution and Strengthening Mechanism of X65 Pipeline Steel Processed by Ultra-fast Cooling

Based on the hot-rolling production line, a novel processing of ultra-fast cooling(UFC)was developed to produce X65 pipeline strip. Microstructure of the experimental steel after the new processing was studied and the strengthening mechanism was further discussed. The results showed that microstructure of the UFC processed X65 pipeline strip primarily consists of fine acicular ferrite(AF), quasi-polygonal ferrite(QPF), martensite/austenite(M/A)and degenerate pearlite(DP). The effective grain size is 2.93μm and the proportion of the high-angle boundary in the microstructure is 31.5%. Small block ferrite with the size ranging from 200 to 1000nm is observed in the substructure. A large fraction of nano-sized Nb(C,N)particles(＜10 nm) are observed in the ferrite matrix. Moreover, mechanical properties of the experimental steel met to the API SPEC 5L standard. The main strengthening mechanism for the UFC processed X65 pipeline strip is composed by grain refining strengthening, solid solution strengthening, dislocation strengthening and precipitation strengthening, where the strengthening contributed by nano-sized precipitations is 96.1MPa.