稀土耐候钢中的夹杂物及耐点蚀性能研究

Study on Nonmetallic Inclusions and Pitting Corrosion Resistance of RE Weathering Steel

利用电子探针、扫描电镜及能谱仪、图像分析仪对含稀土和不含稀土耐候钢中夹杂物的成分、形貌、尺寸等进行了研究。钢中加入稀土后,小球状的稀土硫化物和稀土氧硫化物夹杂取代了钢中原有的有害的长条硫化锰夹杂。对于低硫低氧(S:～0.004%,O:～0.002%)的耐候钢,0.0065%～0.016%的稀土含量保证了钢中夹杂物的良好变质效果,变质后的夹杂弥散分布而且85%以上的稀土夹杂物都小于2μm。通过干湿周期浸润实验室加速腐蚀试验研究了Cu-P-RE耐候钢和对比Q235钢的耐蚀性能。通过电化学极化试验和扫描电镜分析研究了稀土耐候钢中的夹杂物诱发点蚀行为。结果表明,微米级弥散分布的稀土夹杂取代了易腐蚀的长条硫化锰夹杂,减弱了钢中的微区域电化学腐蚀,从而抑制了钢中点腐蚀的发生和扩展。并可以诱发耐候钢表面发生均匀的全面腐蚀,促进均匀致密保护性锈层的生成。Cu-P耐候钢中加入适量稀土提高了钢的点蚀电位和耐点蚀能力,降低了耐候钢的腐蚀速率,提高了其耐蚀能力。

The type,shape and size of nonmetallic inclusions in rare earth weathering steel and weathering steel without rare earth were analyzed through electron probe micro-analyzer（EPMA）,quantitative image analyzer and scanning electron microscope（SEM）.The results show that the small spherical rare earth oxysulfides and rare earth sulphides replace the elongated MnS inclusions in the RE weathering steel.The RE content range of 0.0065%～0.016% plays a very good role on the modification of inclusions in the clean RE weathering steels with about 0.002% oxygen and 0.004% sulfur,which not only on elongated manganese sulfides but also on stringers of brittle oxides.The modified inclusions by RE in the clean weathering steels are predominated by the dispersive spherical RE sulfides and duplex of RE sulfides and RE oxysulfides in size of 2μm.The corrosion resistance of Cu-P-RE weathering steels and Q235 steel were studied by dry-wet cyclic immersion test.The pitting corrosion behaviors of weathering steels with and without rare earth were measured by means of polarization test,and pitting characteristics of RE inclusions during pitting initiation were studied through SEM.Fewer rare earth inclusions heavily decrease pitting susceptibility and rate of pit propagation in the RE weathering steel.It results in the general uniform corrosion on the surface of steel and the formation of compact rust layer.The pitting potential and the resistance to pitting corrosion of the RE weathering steel are significantly improved because of the modification of rare earth to inclusions.The micro-area electrochemical corrosion is weakened,and the corrosion resistance of Cu-P weathering steels is improved by adding an appropriate amount of rare earth.