新型25Cr-20Ni奥氏体耐热不锈钢750℃持久实验过程中析出相演变  

Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During Creep Rupture Test at 750 ℃

作　　者：胡国栋 王培[1] 李殿中[1] 李依依 HU Guodong;WANG Pei;LI Dianzhong;LI Yiyi(Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China;School of Materials Science andEngineering,University of Science and Technology of China,Shenyang 110016,China)

机构地区：[1]中国科学院金属研究所,沈阳110016 [2]中国科学技术大学材料科学与工程学院,沈阳110016

出　　处：《金属学报》2018年第11期1705-1714,共10页Acta Metallurgica Sinica

基　　金：国家自然科学基金项目No.U1708252~~

摘　　要：研究了一种新型25Cr-20Ni奥氏体耐热不锈钢在750℃不同拉应力持久实验中析出相演变及其对性能的影响。结果表明,当持久应力为180 MPa时,持久寿命为32.6 h,析出相包括M_(23)C_6和(Nb, V)(C, N)相。其中M_(23)C_6主要分布在晶界位置,(Nb, V)(C, N)相在晶内弥散析出。当持久应力为150和120 MPa时,随着持久时间延长至98.1 h以上,晶界位置的M_(23)C_6发生长大和Ostwald熟化,但(Nb, V)(C, N)相具有较好的尺寸稳定性。同时,在持久应力为120 MPa条件下,组织中出现s相。s相首先在晶界位置析出,当持久应力为100 MPa时,随持久时间延长至752.3 h,s相也会在晶内析出。研究还发现,大量s相依附于(Nb, V)(C, N)相析出,这是由于(Nb, V)(C, N)相的析出导致附近奥氏体基体中局部位置C和N元素含量减少,从而促进了s相的形核。不同应力条件下试样断裂方式均为沿晶断裂,当持久时间较短时,裂纹在晶界M_(23)C_6处产生,引起沿晶开裂。随着持久时间延长,s相在晶界析出后,裂纹更容易在晶界s相处产生,导致持久延伸率随持久寿命延长而减小。25Cr-20Ni austenitic heat resistant stainless steels are widely used as structural materi- als in nuclear industries and power plants for their excellent corrosion resistance and creep properties at elevated temperature. It is generally accepted that the precipitation during creep is a key factor influenc- ing the creep properties. However, the evolution of precipitates is complicated due to the interaction of the alloy elements. To investigate the precipitation behaviors, a modified 25Cr-20Ni austenitic heat resis- tant stainless steel has been crept at 750 ℃ under different stresses varying from 100 MPa to 180 MPa. The microstructure observation indicates that M23C8 and （Nb, V）（C, N） precipitates are formed during 32.6 h creeping deformation under 180 MPa. M23C6 precipitates are mainly generated at grain boundaries and （Nb, V）（C, N） particles are dispersively distributed in austenitic matrix. The grain boundary M23C8 car-bides are significantly coarsened and Ostwald ripening process happens during 98.1 h creeping deforma- tion under the stress of 150 MPa and 353.0 h creeping deformation under stress of 120 MPa, while （Nb, V）（C, N） carbonitrides show high dimensional stability. With the creep rupture time further prolonging to 353.0 h and 752.3 h under the creep stress of 120 and 100 MPa, respectively, σ-phases are generated first at grain boundaries and then at inner grains. Meanwhile, large amounts of σ-phases are formed around （Nb, V）（C, N） particles, indicating the σ-phase precipitation is accelerated by （Nb, V）（C, N） carbo- nitrides. Composition analysis and thermodynamic calculation are subsequently performed to elucidate the precipitation mechanism of σ-phase. Carbon and nitrogen depleted zone is detected at the interface between （Nb, V）（C, N） precipitates and austenitic matrix. A correlation between σ-phase and C/N con- tents has been calculated by Thermo-Calc, which shows that the mass fraction of σ-phase increases with the decreasing C/N contents.

关 键 词：奥氏体耐热不锈钢 持久 析出相演变 Σ相 MX 

分 类 号：TG142.1[一般工业技术—材料科学与工程]