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研究了临界淬火热处理(QLT)工艺对LNG工程用9Ni低温钢力学性能及精细组织的影响。与常规调质(QT)工艺的对比研究显示,QLT工艺在略微降低强度水平的情况下,显著提高9Ni钢的低温韧性水平及工艺稳定性,屈强比降低。随着两相区淬火温度的提高,9Ni钢的抗拉强度基本不变,屈服强度逐渐升高,低温冲击功在640~680℃范围达到最高值,为200 J以上。QLT工艺处理9Ni钢良好的低温韧性水平与层片化的细化马氏体组织及一定数量的稳定逆转变奥氏体直接相关。实验钢在640~680℃的两相区淬火,可获得10%以上含量的逆转变奥氏体,有利于低温韧性的改善。
The effect of critical quenching and tempering (QLT) process on the mechanical properties and fine structure of 9Ni cryogenic steel for LNG engineering was studied. Compared with the conventional quenching (QT) process, the QLT process significantly improves the low temperature toughness and process stability of the 9Ni steel with a slight decrease of the strength level, and the yield ratio decreases. With the increase of the quenching temperature in the two-phase region, the tensile strength of 9Ni steel keeps unchanged and the yield strength gradually increases. The low-temperature impact energy reaches the highest value in the range of 640 ~ 680 ℃, which is above 200 J. QLT process 9Ni steel good low temperature toughness level and delaminated martensite refinement and a certain number of stable reverse austenite are directly related. Experimental steel in the 640 ~ 680 ℃ two-phase quenching, available for more than 10% of the content of reverse austenite, is conducive to the improvement of low temperature toughness.