两阶段冷却工艺对基于应变设计X70管线钢组织的影响

 铁素体-贝氏体双相组织钢能够通过软硬相协调屈服抵抗大变形，这是基于应变设计管线钢的研究热点。为探究生产工艺对双相组织形态的影响规律，利用Gleeble-3800热模拟试验机，通过压缩试验模拟轧制和冷却，研究了两阶段冷却工艺对基于应变设计X70管线钢形变奥氏体组织转变的影响。结果表明：一阶段缓冷后的待温处理使铁素体形核温度降低，有效提高了铁素体形核率，起到细化晶粒作用；降低二阶段快冷开冷温度可以增加铁素体析出时间，从而增加铁素体的含量；二阶段快冷中，提高冷却速率和降低终冷温度均可细化贝氏体组织的板条间距以及板条间的碳化物，提高了贝氏体显微维氏硬度。

Influences of Two-Stage Cooling Processes on Microstructure of Strain-Based Designed X70 Pipeline Steel

Steel with ferrite-bainite dual phase has been extensively researched for the strain-based designed pipeline applications owing to the high deformation resistance through successively yielding of the two phases. In order to explore the relationships of processes and dual-phase microstructure, the influences of two-stage controlled cooling processes on the microstructure transformation of deformed austenite in strain-based designed X70 pipeline steel are investigated through compression experiments conducted by Gleeble-3800. The results indicates that holding temperature for a short time after slow cooling stage could effectively promote ferrite precipitation, thereby refine ferrite grain. In addition, with the accelerated cooling start temperature lowering, the ferrite fraction increased. During the accelerated cooling stage, either increasing the cooling rate or lowering the cooling finish temperature could decrease the lath width and the sizes of carbides in the bainite structure and then improve the microhardness.