含Cr重轨钢珠光体组织对抗大气腐蚀的影响

Effect of Pearlite Structure of Cr-containing Heavy Rail Steel on Atmospheric Corrosion

目的通过向重轨钢中添加Cr来改变重轨钢组织,研究其组织对抗大气腐蚀的影响。方法用中频感应炉冶炼实验用U71Mn,轧制后空冷。用SEM测量了实验钢的珠光体片层距,在(1.0±0.05)×10^-2 mol/L的NaHSO3溶液中,模拟了工业大气环境下实验钢的腐蚀,利用失重率、SEM、XRD和电化学方法研究了珠光体组织对抗大气腐蚀的影响。结果随着腐蚀时间的增加,试样的平均腐蚀速率呈先增大后减小最后趋于稳定的变化趋势,在120 h时腐蚀速度最快,在240 h时试样表面形成具有一定保护作用的锈层,使其腐蚀速度最慢,360 h后耐蚀性趋于平缓。重轨钢U71Mn珠光体组织的片间距分别为0.2910、0.2500、0.2238μm时,实验钢的腐蚀失重逐渐增大,且平均腐蚀失重率分别为1.572、1.387、1.190 g/(m^2·h),其锈层中α/γ^*的比值依次增大,分别为0.717、0.868、0.997;极化阻抗依次增大,分别为3.715、8.604、13.739Ω·cm^2;而锈层等效电容依次减小,分别为8.434´10-6、0.411´10-6、0.081´10^-6 F/cm^2。结论珠光体片间距越小,腐蚀失重率越小,锈层α/γ^*的比值和极化阻抗越大,腐蚀速度越慢,锈层孔洞和厚度明显变小,缝隙越细,锈层与基体的结合能力越好,其抗大气腐蚀性能越好。

The work aims to change the structure of heavy rail steel by adding Cr to it,and study the resistance of the structure to atmospheric corrosion.U71Mn was smelted in an intermediate frequency induction furnace and then air cooled after rolled.The pearlite layer spacing of the experimental steel was measured by SEM.The corrosion of the experimental steel in the industrial atmosphere was simulated in NaHSO3 solution with a concentration of(1.0±0.05)×10^-2 mol/L.The weight loss rate,SEM,XRD and Electrochemical methods were used to study the resistance of pearlite structure to atmospheric corrosion.The average corrosion rate increased firstly and then decreased with the increase of corrosion time and finally tended to be steady.The corrosion rate was the fastest at 120 h,and the rust layer with a certain protective effect formed at 240 h had the slowest corrosion rate.After 360 h,the corrosion resistance tended to be gentle.When the sheet spacing of U71Mn pearlite structure of heavy rail steel was 0.2910μm,0.2500μm and 0.2238μm,the corrosion loss of the experimental steel gradually increased,and the average corrosion weight loss rate was 1.572 g/(m^2·h),1.387 g/(m^2·h)and 1.190 g/(m^2·h),the ratio ofα/γ^*in the rust layer increased by 0.717,0.868,and 0.997,respectively,and the polarization resistance increased by 3.715Ω·cm^2,8.604Ω·cm^2 and 13.739Ω·cm^2,and the equivalent capacitance of the rust layer was sequentially decreased to 8.434×10^-6 F/cm^2,0.411×10^-6 F/cm^2 and 0.081×10^-6 F/cm^2,respectively.Therefore,as the spacing of the pearlite sheets and the corrosion weight loss rate become smaller,the ratio of the rust layerα/γ^*and the polarization resistance become larger and the corrosion rate slows down,which leads to smaller pores and thickness of the rust layer as well as finer gap,thus achieving good bonding ability between rust layer and substrate and improving the resistance to atmospheric corrosion.