高速重轨钢组织对重轨大气腐蚀性能的影响

There produces brand heavy rail steel in Baotou iron and steel company which is the important enterprise of producing heavy rail in China. According to the response of technician of Bao steel, the heavy rail steel is corroded a little seriously under damp climate in south. Whereas there is few study on corrosion to heavy rail steel under the condition of atmosphere and there is much less referring on relation between corrosion and microstructure. In the project, the experimental steel is U71MnG produced in Bao steel. Various grade microstructures of the steel will be got by various heat treatment systems and then the weight loss, appearance of corrosion pit, electric current of self-corrosion and electric potential of corrosion of heavy rail steel will be measured by the method of cyclic wet-dry test of corrosion and electrochemical test after it is corroded under the simulating condition of atmosphere. Then how the size of microstructure of steel effecting on property of corrosion resistance to atmosphere will be studied. Various content of Cr will be added into U71MnG smelting in vacuum induction furnace. The C curve of U71MnG will shift to right caused by the addition of Cr, from which various grade microstructure of heavy rail steel will be got in the same heat treatment system. Then how component adjustment effecting on mechanical property and property of corrosion resistance to atmosphere of heavy rail steel will be studied. Comparing the property of corrosion resistance to atmosphere of heavy rail steel of various microstructures got by the two different methods, the relation will be studied between microstructure, component and property of corrosion resistance to atmosphere of heavy rail steel. Result of the project can provide theory direction on improving the property of corrosion resistance to atmosphere of pearlite steel.

包钢是我国重要的重轨生产企业，其有自己的品牌重轨钢，据包钢技术人员反应，包钢重轨在南方潮湿气候下腐蚀相对较重，目前对重轨在大气条件下腐蚀的相关研究较少，而其组织与腐蚀间关系更是很少涉及。项目选用包钢生产的U71MnG为实验钢种，采用不同的热处理制度得到不同等级的组织，采用周浸腐蚀，结合电化学实验，测试重轨模拟大气环境腐蚀时的失重率、腐蚀坑形貌、自腐蚀电流、腐蚀电位等；研究组织细小程度对抗大气腐蚀的性能的影响；用真空感应炉冶炼，在U71MnG中添加不同量的Cr，由于Cr的添加使U71MnG的“C”曲线右移，可使相同的热处理制度获取不同等级的重轨组织，研究通过成分调整对重轨钢机械性能的影响和其对抗大气腐蚀性能的影响；将两种方法获得的不同组织的重轨钢抗大气腐蚀性能进行对比，研究组织和成分与重轨钢抗大气腐蚀间关系。项目研究成果可以为珠光体钢提高抗大气腐蚀性能提供理论指导。

金属腐蚀是金属失效的一个重要原因，每年造成巨大的经济损失和安全隐患，国内外相关科技工作者很早就开始在钢轨腐蚀机理、锈层成分、腐蚀电化学等进行了多方面的理论研究与技术探索。. 无CrU71Mn重轨在大气环境中经历加速腐蚀阶段到减速腐蚀阶段的过渡，珠光体组织片层间降低，腐蚀速率也降低。试样锈层成分均含有α-FeOOH、γ-FeOOH、Fe3O4，随珠光体片层间距减小，α-FeOOH物质量增多，珠光体片层距越小锈层越致密。无Cr重轨U71Mn钢腐蚀行为与珠光体平均片层间距有直接的影响，片层距降低，钢基体表面以点腐蚀为主转变以均匀腐蚀为主。. 含Cr 重轨钢U71Mn在120 h腐蚀速度最快，在240 h形成具有一定保护作用的锈层其腐蚀速度最慢，360 h后耐蚀性趋于平缓，含Cr重轨钢U71Mn珠光体组织片层间距越小，腐蚀失重率越小，锈层中α/γ*的比值增大，极化阻抗增加。. 含Cr和不含Cr珠光体重轨钢腐蚀机理一致，都为电化学腐蚀。随珠光体片层距降低，腐蚀微电池数量越多，初期腐蚀速率较快，产生的腐蚀产物量越大，最先生成的腐蚀产物为Fe(OH)2¬，之后转变为FeOOH和Fe3O4，进一步生成γ-FeOOH，最后转变为较为致密的抗腐蚀能力较强的α-FeOOH，珠光体片层距较小的实验钢，在腐蚀60分钟后就产生了抗腐蚀能力较强的α-FeOOH，而片层距较大的实验钢则需要更长的时间。. 珠光体片层距越小的重轨钢腐蚀微电池数量愈多，趋向于形成整个表明的均匀腐蚀，而片层距大的重轨实验钢则由初期的均匀腐蚀转变为点腐蚀。.通过热处理和合金化元素两种方法均可提高重轨钢的腐蚀性，合金化的方式获得的珠光体组织单位微米的失重率是热处理获得的珠光体组织的3～5倍，通过热处理的方式细化重轨钢的珠光体组织能够获得较有的抗大气腐蚀性能。. 本研究为提高钢的抗大气腐蚀能力提供了一种新的途径，具有一定的应用前景。