铌对奥氏体耐热钢组织和高温抗氧化性能的影响

Effect of Nb on Microstructure and High Temperature Oxidation Resistance of Austenitic Heat Resistant Steel

采用OM、SEM、EDS和XRD研究了铌对奥氏体耐热钢组织及高温抗氧化性能的影响。结果表明,未添加Nb元素的耐热钢基体组织为奥氏体+第二相(M_(23)C_6和M_7C_3),奥氏体晶粒比较粗大,碳化物呈链状和骨骼状;添加Nb元素后的耐热钢基体组织不变,但奥氏体晶粒明显细化,晶粒细化程度随Nb含量增加而提高,组织中出现片状Nb C和Nb N,其数量随Nb含量的增加逐渐增多,但当铌含量达到1.5%时,组织中各类碳化物出现长大粘连的现象。在1 000℃和1 200℃条件下,Nb元素的添加不利于抗氧化,随着Nb含量的增加,耐热钢的抗氧化性逐渐下降,并且随着温度升高,抗氧化性能下降越显著。1 000℃×150 h高温氧化试验后,未添加Nb元素的耐热钢为完全抗氧化的,添加Nb元素的耐热钢为抗氧化的;1 200℃×150 h高温氧化试验后,未添加Nb元素的耐热钢为弱抗氧化的,添加Nb元素的耐热钢为不抗氧化的。

Effects of Nb on microstructure and high temperature oxidation resistance ofaustenitic heat resistant steel were studied by OM, SEM, EDS and XRD. The results show that the matrix structure of heat resistant steel without Nb is composed ofaustenite and second phase （M23C6,M7C3）. The austenite is coarse and the carbide has chain and skeletal structures. After adding Nb, the matrix structure of heat resistant steel remains unchanged. However, the austenite grains are obviously refined and the grain size decreases with the increase of Nb content. In addition to M23C6 and M7C3, slice NbC and NbN appear, the quantity of which increases with Nb content increased, but these carbides/nitrides grow up and are adherent to each other when the Nb content reaches 1.5%. At 1 000℃ and 1 200℃, the addition of Nb is disadvantageous to the oxidation resistance. The oxidation resistance gradually decreases with the increase of Nb content and sharply decreases with the increase of temperature. After the high temperature oxidation test at 1 000℃×150 h, the specimen without Nb is completely antioxidative and that with the addition of Nb is antioxidative. After the high temperature oxidation test at 1 200℃ × 150 b, the specimen without Nb is weakly antioxidative and that with Nb is not antioxidation.