纯δ-铁素体低密度钢热变形模型及再结晶特征

Thermal deformation model and recrystallization characteristics of low-density steel containing solely δ-ferrite

Fe-Al低密度钢作为一类新兴的钢铁材料,凭借其低密度、高塑性、优异耐蚀性、成本效益和批量生产的可行性引起广泛的关注和研究。与其他具有竞争力的结构材料相比,高铝Fe-Al低密度钢组织为粗大δ-铁素体,在无相变发生的情况下如何细化Fe-Al铁素体钢的晶粒成为一个难题。利用热模拟试验机和微观组织分析等手段,对高铝Fe-7.5Al铁素体低密度钢在变形温度为850~1100℃及应变速率为0.01~10 s^(-1)条件下的热变形过程中的组织演化和再结晶行为进行分析,提供动态再结晶实现晶粒细化以达到强度和塑性的良好配合的可行性。基于压缩真应力-应变曲线,构建了预测峰值应力的本构方程,并根据动态材料模型绘制了Fe-7.5Al钢的热加工图。结果表明,Fe-7.5Al钢的热变形行为符合具有中等层错能的合金材料的一般规律,由位错的滑移和攀移控制;Fe-7.5Al钢的动态软化机制以动态回复为主。提高变形温度和应变速率有利于不连续动态再结晶行为的发生,这种不连续再结晶形核是由应变诱导晶界迁移产生的,其热变形激活能约为368.5 kJ/mol。在变形温度较低(<950℃)以及高应变速率(>1 s^(-1))下将出现不稳定塑性变形区,此时Fe-7.5Al钢将沿δ/δ-铁素体晶界形成微带,并且在三叉晶界处产生楔形开裂。

As a novel steel material,Fe-Al low-density steel has attracted extensive attention and research interest due to its low density,high plasticity,excellent corrosion resistance,cost-effectiveness and feasibility for mass production.In comparison to other competitive structural materials,the microstructure of high-aluminum Fe-Al low-density steel exhibits coarse δ-ferrite.In the absence of phase transformation,the challenge lies in how to refine the grain size of Fe-Al ferrite steel.A comprehensive investigation was conducted into the microstructural evolution and recrystallization behavior of high-aluminum Fe-7.5Al ferritic low-density steel under conditions of deformation temperature range of 850-1100℃ and strain rates of 0.01-10 s^(-1).This investigation was performed using a combination of hot simulation testing equipment and microscopic organizational analysis.The aim was to provide the feasibility of achieving a favorable balance between strength and plasticity through dynamic recrystallization for refining grain size.Based on the true stress-strain curves of Fe-7.5Al steel,constitutive equations predicting peak stress was established,and the processing maps of Fe-7.5Al steel were generated using a dynamic materials model.The result indicated that the hot-working behavior of Fe-7.5Al steel conformed to that of alloy materials with moderate stacking fault energy.The deformation mechanism was governed by the dislocation slip and climb.The dynamic restoration mechanism of Fe-7.5Al steel was primarily dominated by dynamic recovery.Increasing deformation temperature and strain rate facilitated the occurrence of discontinuous dynamic recrystallization behavior.This discontinuous recrystallization nucleation was generated by strain-induced grain boundary migration,and the deformation activation energy of Fe-7.5Al steel was calculated as approximately 368.5 kJ/mol.At lower deformation(<950℃)and higher strain rate(>1 s^(-1))unstable domain,microband arrays were formed along the δ/δ-ferrite grain boundaries,and wedge-shaped cracking occurs at the triple junctions.