轧制变形及再结晶00Cr12铁素体不锈钢中的{011}/{011}近奇异晶界

The{011}/{011}near singular boundaries in 00Cr12 ferritic stainless steel after rolling and recrystallization

不同于低层错能面心立方结构的奥氏体不锈钢,高层错能体心立方结构的铁素体不锈钢在形变及再结晶等组织重构过程中很难形成结构稳定且十分耐蚀的奇异晶界(共格孪晶界).研究{011}/{011}近奇异晶界的影响因素和形成机理,将有可能为改善铁素体不锈钢,特别是低Cr铁素体不锈钢晶间腐蚀性能提供晶界工程新思路.本文选用经固溶处理和组织均匀化处理的00Cr12低Cr铁素体不锈钢为实验材料,5个平行试样分别在350℃,500℃,580℃,650℃和690℃进行厚度减缩量为70%的单向轧制变形后,立即进行750℃、2 h再结晶退火处理.使用基于电子背散射衍射和五参数分析的晶界界面匹配表征方法对上述样品进行测试和分析发现,轧制温度对00Cr12铁素体不锈钢再结晶{011}/{011}近奇异晶界比例有显著影响,再结晶后的{011}/{011}近奇异晶界比例随再结晶退火前轧制温度的升高先上升再下降,其中经650℃轧制的样品,其再结晶后{011}/{011}近奇异晶界比例达到极大值6.82%.取向分布函数(ODF)和重叠极图晶界迹线分析表明,经650℃轧制的样品,其再结晶组织中形成了强的{011}<0-11>织构;具有{011}<0-11>及其漫散取向的晶粒之间较多地存在<011>/θ取向差关系(θ为绕<011>的旋转角),其关联晶界为{011}/{011}近奇异晶界,这是经650℃轧制的样品,其再结晶后{011}/{011}近奇异晶界比例达到极大值的原因.离线原位表面侵蚀实验表明,{011}/{011}近奇异晶界的腐蚀抗力显著高于一般晶界.因此,基于本文研究结果,进一步调控并提高{011}/{011}近奇异晶界的比例将有助于从根本上显著改善00Cr12铁素体不锈钢晶间腐蚀性能.

Different from the low stacking fault energy(SFE)face-centered cubic(FCC)austenitic stainless steels,high SFE body-centered cubic(BCC)ferritic stainless steels are hardly to produce structure-stable and corrosion-resistant singular boundaries or namely the coherent twin boundaries during recrystallization after deformation.To investigate the so-called{011}/{011}near singular boundaries will be significant to the grain boundary engineering(GBE)approach to better the performance against intergranular corrosion(IGC)in the ferritic stainless steels,especially in the low Cr ferritic stainless steels.In the current work,the solid-solutiontreated and microstructure-uniformed 00Cr12 low Cr ferritic steel were chosen as experimental materials.Five parallel samples were rolled respectively at 350°C,500°C,580°C,650°C and 690°C followed by 2 h recrystallization annealing at 750°C.The method of grain boundary inter-connection(GBIC)characterization based on electron backscatter diffraction(EBSD)and five parameter analysis(FPA)was used to determine the content of{011}/{011}near singular boundaries in the processed samples.It is found that the preceding rolling temperature has a significant impact on the formation of{011}/{011}near singular boundaries during subsequent annealing at 750°C.The fraction of{011}/{011}near singular boundaries after recrystallization is increasing at first and then decreasing when the preceding rolling temperature increasing from 350°C to 690°C.The sample rolled at 650°C followed by annealing at 750°C has a peak content of{011}/{011}near singular boundaries and the fraction reaches 6.82%,which is about 10 times higher compared to that of the singular boundaries.Orientation distribution function(ODF)and over-lapped pole-figure boundary trace analysis indicate that a strong{011}<0−11>texture is developed in the sample rolled at 650°C followed by annealing 750°C.Quite a few grains of{011}<0−11>orientation,including its diffuse orientation,have<011>/θmisorientation(θis a rotation angle around<011>)with each other,and the relevant grain boundaries are{011}/{011}near singular boundaries.This is the reason why the sample rolled at 650°C followed by annealing 750°C has a peak content of{011}/{011}near singular boundaries.Off-line in-situ surface etching test demonstrates that the{011}/{011}near singular boundaries are much more resistant to corrosion compared to random boundaries.Based on the present results,to regulate the{011}/{011}near singular boundaries will be promised for bettering the performance against IGC in 00Cr12 ferritic stainless steel.