加工条件对管线钢组织影响的实验研究

管线钢的最终组织和性能与控轧工艺以及加速冷却直接相关。采用一种新型的模拟轧制过程设备来研究X70级别管线钢在热变形冷却后的组织；设计了一系列的平面应变压缩实验来模拟板带轧制过程参数特别是精轧温度和冷却速率对最终组织的影响。采用恒定的变形速度70 s-1以及恒定的道次间隙时间，在850、900、950 ℃温度下的单道次和多道次压缩变形，随后研究2种不同冷却速率（3 ℃/s，6 ℃/s）获得的最终微观组织。观察发现，对于950、900、850 ℃的变温变形，出现了严重的混晶现象，而850 ℃下进行的3次压缩试样在6 ℃/s冷却到660 ℃后铁素体晶粒尺寸达到4.3 μm。

Research on Effect of Processing Conditions on Final Microstructure of a X70 Pipeline Steel

The final microstructure and subsequent properties of pipeline steel have been shown to be highly dependent of both controlled rolling and accelerated cooling conditions. This research utilized a novel physical deformation simulator to evaluate the final microstructure in an X70 grade pipeline steel after finishing hot deformation and cooling. A series of plane strain compression (PSC) tests have been designed to simulate the processes of plate rolling and strip rolling, with the influence of finishing temperature and cooling rate being of particular interest. Single and multi pass reductions at constant strain rates of 70s-1, together with constant delay times were used in this work. A total of three different deformation temperatures, namely, 950 ℃, 900 ℃ and 850 ℃ were used for the present experiments, in which multi pass isothermal or non isothermal deformation(i.e., descending temperature processing) took place, then subject to two different cooling rates, 3 ℃/min and 6 ℃/s respectively. The optical observations showed that the descending temperature processing in this study resulted in a mix grain size, and isothermal 850 ℃ with three hit deformation after 6 ℃/s accelerated cooling achieved uniform and fine ferrite grain with size down to 4.3 μm.