X120管线钢的相变组织及性能研究

Research of transformation microstructure and mechanical properties of X120 pipeline steel

为适应将来石油及天然气高效输送的需要,以及高级别管线对力学性能及焊接性能的要求,采用一种成分为0.05%C-2.01%Mn-0.30%Mo-0.48%Ni-0.35%Cu-0.076%Nb-Ti-B的试验材料,用于开发X120管线钢的试验研究.在Gleeble 1500热模拟机上,采用在奥氏体再结晶区和未再结晶区分别变形30%和35%和其后不同冷却速率的冷却对试样进行处理,经过对试样进行光学显微镜、透射电镜、维氏硬度计分析,研究了X120级别管线钢的相变温度、显微组织及维氏硬度.对试验钢坯控制轧制后,再经终冷温度370～500℃、冷却速度40～70℃/s的控制冷却处理.结果表明:当冷却速率为20～50℃/s时,试验钢可以得到以贝氏体和马氏体为主的组织,试验钢的硬度也随冷却速率增加而逐渐增加,硬度最高达到HV320;试验钢在控轧后控制冷却至终冷温度≤450℃后,除延伸率偏低外,其他力学性能均达到X120管线钢标准要求.

To meet the future needs of efficient oil and gas transportation and the requirement of mechanical properties and weldability of high grade pipeline steel,a test material with the chemical compositions of 0.05%C-2.01%Mn-0.30%Mo-0.48%Ni-0.35%Cu-0.076%Nb-Ti-B was experimentally studied for the development of X120 pipeline steels.The sample was formed in recrystallization and non-recrystallization zone with 30%and 35%reduction respectively and then be cooled in different cooling ratio by means of Gleeble 1500 thermal simulator.The change of transformation temperature,microstructure and Vickers hardness was studied the samples were analyzed by optical microscopy,SEM,micro-vickers hardness tester.After controlled rolled,the test steel billet was controlled cooled with 370～500℃finished cooling temperature and 40～71℃/s cooling ratio.The conclusion is that the microstructure is mainly low carbon martensite and low carbon bainite when the cooling rate is between 20～50℃/s.Meanwhile,the Vickers hardness of steel has also increased with the increasing cooling rate,the highest hardness is HV320.Except the low elongation,the other mechanical properties meet the requirements of X120 pipeline steel standard,after the steel treated by controlled rolling and controlled cooling to≤450℃finished cooling temperature.