Cr对Fe-28Mn-12Al-1.6C钢κ-碳化物析出行为的影响

Effect of Cr onκ-carbide precipitation behavior in Fe-28Mn-12Al-1.6C steel

随着可持续发展战略的要求,Fe-Mn-Al-C轻质钢逐渐成为汽车工业的主要发展目标之一。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、热力学计算和第一性原理研究了Cr元素对Fe-28Mn-12Al-1.6C奥氏体低密度钢κ-碳化物析出行为的影响。结果表明,不同温度固溶处理后,0Cr钢在室温下随着时间延长硬度逐渐增大且增值达到10HRC,通过TEM分析确认0Cr钢室温下析出的为κ-碳化物,并计算其室温析出的吉布斯自由能为-19.5806 kJ/mol,从而验证了0Cr钢可以在室温下析出κ-碳化物;随着Cr含量的增加,轧制后快速凝固试样中κ-碳化物的质量分数逐渐降低,室温时效的硬度增值减小。Cr含量的增加也显著减小了κ-碳化物的生长速度,κ-碳化物的粒径从60~200 nm细化到20~40 nm和5~27 nm。同时第一性原理计算结果表明,κ-碳化物结构中掺杂Cr原子后,增大了κ-碳化物的形成能,使其形成变得困难。此外,随着Cr含量的增加,γ-奥氏体与κ-碳化物的晶格失配度增加,两相间的弹性应变能增大,导致κ-碳化物的生长速度减慢。研究结果可为后续更高Al含量的Fe-Mn-Al-C钢的成分设计和性能调控提供理论依据。

With the requirements of sustainable development strategy,Fe-Mn-Al-C lightweight steel has gradually become one of the main development goals of the automotive industry.The effect of chromium on the precipitation behavior ofκ-carbide in Fe-28Mn-12Al-1.6C austenitic low density steel was investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),thermodynamic calculation and first principles.The results show that after solution treatment at different temperatures,the hardness of 0Cr steel increases gradually with time at room temperature and the increment reaches 10HRC.Theκ-carbide precipitated at room temperature is confirmed by TEM analysis.The Gibbs free energy of precipitated at room temperature is-19.5806 kJ/mol.It has been verified that 0Cr steel can precipitateκ-carbide at room temperature.With the increase of Cr content,the mass fraction ofκ-carbide in the rapidly solidified sample after rolling decreases gradually,and the hardness increment decreases at room temperature aging.The increase of Cr content also significantly slows down the growth rate forκ-carbide,whose particle size is refined from 60-200 nm to 20-40 nm and 5-27 nm.At the same time,the first-principles calculation results show that the formation energy ofκ-carbide is increased by doping Cr atom in theκ-carbide structure,which makes the formation ofκ-carbide difficult.In addition,with the increase of Cr content,the lattice mismatch betweenγ-austenite andκ-carbide increases,and the elastic strain energy between the two phases increases,which leads to the slowing down of the growth rate forκ-carbide.The result provides theoretical basis for the composition design and performance control of Fe-Mn-Al-C steel with higher Al content in the future.