Nb对Fe-Mn-Al-C低密度钢显微组织及耐蚀性的影响

Effect of Nb on microstructure and corrosion resistance of Fe-Mn-Al-C low density steel

为探究Nb合金化对Fe-28Mn-10Al-C低密度钢显微组织和耐腐蚀性能的影响规律及作用机理,采用金相显微镜、扫描电子显微镜、透射电子显微镜等手段观察了Nb质量分数分别为0、0.3%、0.5%的试验钢微观显微组织和析出相特点;通过电化学极化测试与浸泡腐蚀法研究了Nb含量对试验钢在3.5%NaCl溶液中耐腐蚀性能的影响,并观察分析了腐蚀后的形貌特征及元素分布规律。结果表明,Nb合金化后的Fe-28Mn-10Al-C-xNb低密度钢中沿奥氏体晶界析出了fcc-NbC第二相,随着Nb质量分数由0增加至0.5%,试验钢中奥氏体晶粒尺寸由39.49μm减小到13.67μm,腐蚀电流密度由6.17×10^(-6) A/cm^(2)降低到6.31×10^(-7) A/cm^(2);在72 h的腐蚀周期内,腐蚀失重由5.750 mg/mm^(2)降至4.625 mg/mm^(2),表明Nb合金化细化了奥氏体晶粒尺寸,增强了电化学极化过程中试验钢表面稳定性,降低了电化学腐蚀速率,试验钢的耐腐蚀性能得到改善。经浸泡腐蚀后,试验钢表面生成氧化膜,且氧化膜与金属(O/M)界面处以Al氧化物为主;与不含Nb试验钢相比,加Nb试验钢O/M界面Al氧化物的偏聚更为明显,表明Nb能够促进腐蚀过程中试验钢表面Al氧化膜的形成,降低试验钢的腐蚀速率。通过试验研究所获得的数据和结论,可为进一步改善Fe-Mn-Al-C系低密度钢耐腐蚀性能提供理论依据与研究基础。

In order to explore the influence of Nb addition on the microstructure and corrosion resistance of Fe-28Mn-10Al-C low density steel and make clear its mechanism,the microstructure and precipitation characteristics with different Nb content(0,0.3%,0.5%)were investigated by means of OM,SEM and TEM.The effect of Nb content on the corrosion resistance of Fe-28Mn-10Al-C alloy in 3.5%NaCl solution was investigated by electrochemical polarization test and immersion corrosion.The microstructure of the test steel and the element distribution after corrosion were observed and analyzed.The results show that the second phase of fcc-NbC is precipitated along the austenite grain boundary after Nb is adding.As the Nb content increases from 0 to 0.5%,the austenite grain size decreases from 39.49μm to 13.67μm,and the corrosion current density decreases from 6.17×10^(-6)A/cm^(2) to 6.31×10^(-7)A/cm^(2).In addition,within the 72 hours corrosion period,the corrosion weight loss of the test steel decreases from 5.750 mg/mm^(2) to 4.625 mg/mm^(2).The results confirm that the austenite grain size is refined in the Nb-containing alloys,and the surface stability of test steel during electrochemical polarization process is enhanced,which indicates that the electrochemical corrosion rate is also reduced with the increase of Nb content,and the corrosion resistance of test steel is further improved.The oxide film is formed on the surface of test steel after immersion corrosion.Al oxides mainly gather at the interface between oxide film and metal(O/M).Compared with the Nb-free test steel,the gather of Al oxides at the O/M interface is more obvious with Nb added.This indicates that the addition of Nb can promote the formation of Al oxide film on the surface of Fe-28Mn-10Al-C low density steel and reduce the corrosion rate of the alloy.The data and conclusions obtained by experimental research can provide theoretical and research basis for further improving the corrosion resistance of Fe-Mn-Al-C low density steel.