高强度厚壁H型钢轧后快冷组织及性能

Microstructure and mechanical properties of high strength thick wall H-beam steel after controlled rolling and fast cooling

研究海洋石油平台专用H型钢(55C钢)轧后快冷产生的显微组织特征及其对力学性能的影响,探索实际生产中提高大尺寸厚壁H型钢强韧性的有效途径。测定了55C钢的动态CCT曲线;结合生产现场实际,通过优化控轧控冷工艺参数,特别采用比空冷和风冷快的轧后冷却,对试验钢进行了试轧;对轧后试样进行了力学性能测试、显微组织观察以及晶粒大小的测定。试验结果表明,轧制工艺参数特别是轧后冷却工艺对55C钢的显微组织和力学性能具有重要影响。采用适宜的终轧温度、道次变形量以及提高轧后冷速可以获得铁素体、珠光体和粒状贝氏体混合组织,使55C钢的强度得以大幅提升,获得良好的强韧性配合。通过轧后快冷获得高强韧性的贝氏体组织和细化晶粒都是大尺寸厚壁H型钢中重要的强韧化机制。55C钢的TMCP工艺(Thermo MechanicalControlled Processing)具有较宽的终轧温度和道次变形量范围,可根据不同的使用性能要求选择轧制工艺参数。

Effects of fast cooling after controlled rolling on microstructure transformation and mechanical properties of high strength thick wall H-beam steel（55C steel） for offshore oil drilling platform were studied for exploring the effective process to improve strength and toughness of the steel in practical production.The dynamical CCT curves of 55C steel were tested.The tested steel was tentatively rolled and cooled according to measured CCT characteristics and actual production process using optimizing process parameters in laboratory.Especially,the cooling rate after rolling higher than air cooling and wind cooling was adopted.Mechanical properties,microstructure and grain size of the specimens after rolling were tested.The results show that the effects of processing parameters on mechanical properties and microstructures of 55C steel are significant.With proper final rolling temperature,deformations and cooling rate after rolling,mixed microstructure of ferrite,pearlite and bainite can be obtained and the strength of 55C steel obviously enhanced with excellent strength-toughness matching.To obtain tenacious bainite and refine grains through fast cooling after controlled rolling all are important strengthening and toughening mechanisms in the tested thick wall H-beam steels.TMCP（Thermo Mechanical Controlled Processing） parameters of 55C steel can be selected in wider ranges of final rolling temperature and deformation according to different demand for service performance.