退火温度对转向架用低密度钢组织性能的影响

Effect of annealing temperature on microstructure and mechanical properties of low⁃density steel for bogie frame

通过Thermo-Calc热力学计算、扫描电镜(SEM)、电子背散射衍射(EBSD)、拉伸试验和机器学习,从相转变、几何必需位错密度、晶界类型以及晶界密度的角度,设计并研究了退火温度对转向架用中Mn低密度中厚板组织性能的影响。结果表明,室温下低密度钢的热轧组织为δ铁素体、奥氏体和马氏体;退火时,基体会发生逆转变以及原奥氏体的长大,且在退火过程中产生的奥氏体的稳定性会随着退火温度的升高而降低;随退火温度的增加,试验钢的几何必需位错密度不断减小;退火过程中晶粒的长大和马氏体板条合并会导致组织中的原奥氏体界面(PAG boundaries)和马氏体板条界面(Lath boundaries)密度下降;退火后,试验钢的断后伸长率相比热轧态有显著提升,其屈服强度随退火温度的增加而降低;热轧态及退火后的试验钢在拉伸测试中均表现为均匀变形,并发生了解理断裂;在820和880℃退火后,试验钢的屈服强度分别达到了491和413 MPa。

Effect of annealing temperature on the microstructure and mechanical properties of a medium⁃Mn low density medium thick plate for bogie was designed and investigated by means of Thermo⁃Calc calculations,scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),tensile tests and machine learning from the perspectives of phase transformation,densities of geometrically necessary dislocations,grain boundary types and grain boundary density.The results show that the hot⁃rolled microstructure of the low⁃density steel at room temperature consists ofδ⁃ferrite,austenite,and martensite.The matrix undergoes reverse transformation and the growth of prior austenite during annealing treatment,and the stability of austenite decreases with the increase of annealing temperature.The densities of geometrically necessary dislocations of the tested steel decrease with the increase of annealing temperature.The growth of the grains and the merging of martensite laths during annealing lead to a decrease in the density of prior austenite grain boundaries and martensite lath boundaries.The annealed tested steel shows significantly higher elongation than that of the hot⁃rolled state,with yield strength decreasing as the annealing temperature increasing.The tested steel under both hot⁃rolled and annealed states shows uniform deformation and cleavage fracture during tensile test.After annealing at 820 and 880℃,the yield strength of the tested steel reaches 491 and 413 MPa,respectively.