晶粒尺寸对超低碳IF钢耐大气腐蚀性能的影响

采用不同轧制及热处理工艺制备了化学成分相同而晶粒尺寸不同的3种超低碳IF钢试样.采用浸泡腐蚀、周浸腐蚀、原子力显微镜(AFM)及扫描电镜(SEM)微观分析、电化学阻抗测试等手段对晶粒尺寸与IF钢耐大气腐蚀性能之间的规律进行了研究.AFM及SEM微观分析结果表明,随着晶粒尺寸从15μm增加到220μm,超低碳IF钢浸泡腐蚀后晶界处的局部腐蚀更加严重,腐蚀裂纹处的深度加深,裂纹宽度变宽.超低碳IF钢晶粒尺寸从15μm增加到46μm,周浸腐蚀实验后锈层中空洞和裂纹增多,锈层电阻下降,耐候性下降;晶粒尺寸进一步增大到220μm后,锈层整体致密性得到增加,锈层电阻上升,耐候性得到增加.对晶粒尺寸影响耐大气腐蚀性能的机理进行了讨论.晶粒尺寸增大后晶界能的减少使得腐蚀表面的宏观总体缺陷数量有所减少,耐候性有所提高;但是晶粒尺寸增大后晶界处因局部腐蚀电流密度增大将会在局部造成更深的腐蚀坑槽并降低耐候性;晶粒尺寸的变化对钢铁材料耐大气腐蚀性能的影响不仅要考虑其对晶界局部腐蚀电流密度的影响,而且还必须考虑对基体整体晶界能所造成的影响.

EFFECT OF GRAIN SIZE ON ATMOSPHERIC CORROSION RESISTANCE OF ULTRALOW CARBON IF STEEL

Three kinds of ultra-low carbon IF steel with different grain sizes,and same chemical composition were prepared by different rolling and heat treat process.The relationship between grain size and atmospheric corrosion resistance of IF steel was investigated by immersion corrosion test,cyclic immersion corrosion test,AFM/SEM micro-analysis and electrochemical test. The results show that the local corrosion in grain boundary increases after immersion corrosion test,the depth of crack in grain boundary becomes deeper and the width of crack becomes wider with grain sizes of IF steel increase from 15μm to 220μm.The crack and cavity in the rust after cycle immersion corrosion test are increased and the atmospheric corrosion resistance is decreased with IF steel grain size coarsing from 15μm to 46μm.As grain size increase from 15μm to 220μm,the whole compactness of rust are increased,the rust resistance and the atmospheric corrosion resistance are increased.The effect of grain size on the corrosion current density of local grain boundary was analysed and the mechanics of corrosion was discussed.The total quantity of corrosion surface defect is decreased due to the decrease of grain boundary energy with the increase of grain size and the atmospheric corrosion resistance is increased.Meanwhile,the local corrosion near the grain boundary is increased duo to the increase of local corrosion current density with the increase of grain size and the atmospheric corrosion resistance is decreased.The atmospheric corrosion resistance is influenced by the two factors simultaneously.