9Ni钢中回转奥氏体的形成规律及其稳定性

Formation of reversed austenite and its stability in 9Ni steel during tempering

采用XRD法测定了不同温度回火后9Ni钢中的回转奥氏体含量,并结合显微组织的变化,研究了回转奥氏体的形成规律及其对性能的影响。同时,采用多种方法研究了所形成的回转奥氏体的稳定性。结果显示:540℃回火时,回转奥氏体的生成比较困难;570℃回火后其含量达到4.47%,且稳定性较高;570～600℃之间回火,测得的回转奥氏体缓慢增加,稳定性则逐步降低;600℃以上回火,回转奥氏体快速增加,并在630℃左右达到峰值,但稳定性显著降低;回火温度超过630℃,保温期间生成的奥氏体更多,但稳定性更低,其中很大一部分在水冷过程中又发生相变,使最终测得的回转奥氏体含量又快速降低。结果也表明,通过分析回转奥氏体和基体点阵常数的变化趋势能够更加准确地确定回转奥氏体的稳定性。

The formation and stability of reversed austenite in 9Ni steel temped at different temperatures was studied by measuring its amount and lattice parameters with XRD and microstructure of the steel was examined by SEM. Results indicate that the formation of reversed austenite is difficult in 9Ni steel tempered at 540 ℃. Tempered at 570 ℃, 4.47% of stable reversed austenite in the steel is observed. Tempered between 570 ℃ to 600 ℃, the reversed austenite increases slowly and its stability deteriorates slightly. When tempering temperature above 600 ℃, the amount of reversed austenite increases rapidly with increasing tempering temperature and reaches to peak value at 630 ℃, but its stability decreases obviously. Tempered above 630 ℃, some reversed austenite transforms to martensite during cooling because of its lower stability, which leads to the decrease of the amount of reversed austenite. Results also show that the stability of reversed austenite can be determined exactly by analyzing the changes of lattice parameter of austenite and matrix.