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研究了新型20Cr11MoVNbNB 马氏体耐热钢在1130℃淬火及200～750℃回火后的析出相和力学性能,证明该钢淬火态下残留相基本上全由 Nb(C,N)组成;<400℃回火主要析出物是M_3c,其析出量在400℃达最大;400℃回火观察到 M_7C_3型碳化物,600℃时其量最多;500℃回火发现有 Mo_2C,Nb_2(C,N)和 VC 存在;550℃出现 M_(23)C_6型碳化物,它是该钢600℃以上温度回火时含量最多的析出相;>700℃回火出现少量 MoFe_2。电解萃取法证实,<400℃时,析出相总重量随回火温度升高而逐渐增加,在400～500℃范围,因 M_3C 回溶,析出物总量则逐渐减少,500～680℃大量 M_(23)C_6出现,析出物量迅速增加,≥680℃后,相的析出过程基本完成;该钢约在500℃具有明显二次硬化现象,引起二次硬化的碳化物不是 M_7C_3,而是 Mo_2C,Nb_2(C,N)和 VC。为保证组织稳定及获得较好综合力学性能,推荐该钢采用680～720℃回火≥4h 的工艺处理。
The precipitation phase and mechanical properties of a new type of 20Cr11MoVNbNB martensitic steel after quenching at 1130 ℃ and tempering at 200-750 ℃ were studied. The results show that the residual phase is basically composed of Nb (C, N) The main precipitates at 400 ℃ are M_3c, and the precipitates reach the maximum at 400 ℃. The M_7C_3 carbides are observed at 400 ℃ and the maximum amount is at 600 ℃. The results show that there are Mo_2C, Nb_2 (C, N ) And VC were present. M_ (23) C_6 carbides appeared at 550 ℃, which was the most precipitated phase when the steel was tempered above 600 ℃. Electrolysis extraction confirmed that the total weight of precipitated phase increased gradually with the increase of tempering temperature at <400 ℃. The total amount of precipitates decreased gradually due to the re-solution of M_3C in the range of 400-500 ℃, (23) C_6, the amount of precipitates increased rapidly, and the precipitation process was basically completed after ≥680 ℃. The steel had obvious secondary hardening at about 500 ℃. The secondary hardened carbides were not M_7C_3 but Mo_2C, Nb_2 (C, N) and VC. In order to ensure the stability of the organization and obtain the better comprehensive mechanical properties, it is recommended that the steel be tempered at a temperature of 680 to 720 DEG C for processing for 4 hours or more.