镁铝复合夹杂物细化晶粒途径、机制的协同研究

The technology of oxide metallurgy was proposed to utilize the positive effect of the fine oxide inclusions to refine the grain. According to this method, the fine oxide inclusions can not only inhibit austenitic grain growth through the pinning effect, but also induce nucleation of intragranular acicular ferrite (IAF) during the phase transformation from austenite to ferrite. Although its mechanism is still controversial, various kinds of non-metallic inclusions have been proposed as the potential catalysts for nucleation of IAF. Recently, Mg-bearing oxides have attracted much attention in the new generation of oxide metallurgy. However, its approach and mechanism to achieve grain refinement is still under discussion.According to earlier studies, the proposer found that the Mg-Al complex oxides can act as nucleation sites for acicular ferrite. Moreover, line scanning analysis of EDS hints that Mn-depletion zone (MDZ) exists adjacent to the complex inclusion, which means that the manganese-depleted zone mechanism may be used to explain the mechanism of inclusions on the nucleation of IAF. Thus, the objective of this proposal is to carry out systemic study by adjusting the contents of Mg and Al. On the one hand, the relationship between the evolution of complex inclusions and power of grain refinement is elucidated through the coordination between pinning effect and inducing nucleation. This matching is realized by the suitable size of austenite grain based on the adjustment of heat-treatment process. On the other hand, the probability distribution characteristics of inducing nucleation will be derived through the regression theory and experimetal results from the SEM measurements (line scanning analysis of EDS and EBSD). Based on the upper analyses, the existence and function of MDZ will be well discussed, and the nature of inducing nucleation will be revealed. These results will be helpful to clarify the approach and mechanism of grain refinement by Mg-Al complex inclusions, and promote the application of oxide metallurgy.

氧化物冶金技术利用钢中的氧化物钉扎奥氏体晶界和诱导晶内针状铁素体形核，以优化组织。镁氧化物作为新一代氧化物冶金技术的代表，引起了人们的广泛关注，但对于其细化晶粒的途径、机制等问题依然存在争论。在预研中，申请人在低碳钢中利用镁铝复合夹杂物获得了针状铁素体组织，验证了其诱导形核能力，提出贫锰区是解释该现象的可能机制。本项目拟进一步开展系统研究，通过调节低碳钢中的镁铝含量，一方面基于热模拟工艺的调整，以原奥氏体晶粒尺寸为纽带，协同匹配镁铝复合夹杂物的钉扎效应和诱导形核作用，解析夹杂物性质演变进程与其晶粒细化能力之间的内在关联性，另一方面运用统计回归理论和扫描电镜平台(能谱的线扫描和电子背散射衍射技术)，刻画镁铝复合夹杂物诱导形核能力的概率分布特征，验证贫锰区的存在与作用，确定诱导形核的强关联因素与物理机制，从而澄清镁铝复合夹杂物细化晶粒途径、机制的争论，并为其实用化奠定坚实的理论和工艺基础。

氧化物冶金技术利用钢中的氧化物夹杂诱导晶内铁素体形核，以优化组织。镁氧化物作为新一代氧化物冶金技术的代表，引起了人们的广泛关注，但对于其细化晶粒的途径、机制等问题依然存在争论。.本项目对镁铝复合夹杂物诱导晶内铁素体形核的机制进行了系统研究。通过系统调节低碳钢中的镁铝元素含量、调整热模拟工艺，探索夹杂物与组织性能之间的演变关系，一方面通过与不能诱导形核氧化物、单纯硫化锰的对比，进一步验证了含镁复合夹杂物诱导形核的贫锰区机制，另一方面探讨了夹杂物中的镁铝含量变化、硫化锰吸附与诱导形核现象之间的关联性，表明单纯氧化镁和硫化锰均不能诱导形核，需要控制复合夹杂物中的镁铝含量以优化其细化晶粒效果。.本项目还以诱导的铁素体条数作为夹杂物诱导形核能力的定性指标，探讨不同类型夹杂物(镁铝、钛铝复合夹杂物)的诱导形核能力与其尺寸、成分之间的关联性。一方面发现随着尺寸的增加，夹杂物的诱导形核能力逐渐增强，具有尺寸效应，另一方面发现夹杂物中的成分(镁铝尖晶石、三氧化二钛)与诱导形核能力之间呈现一定的概率特征。分析认为前者是由于夹杂物尺寸的增加降低了铁素体形核能，后者则与氧化物中的阳离子空位浓度、锰元素在其中的扩散系数以及晶内/晶界铁素体之间的能量差异有关。.最后，本项目通过不同含镁氧化物（钛酸镁、氧化镁）的引入，探索外部加入法在氧化物冶金中的应用。结果表明，相对于二氧化钛，氧化镁由于其润湿性、反应性的差异，难以通过简单方式引入到钢液中。而通过钛镁复合处理或二氧化钛加镁处理，均可获得钛镁复合夹杂物，从而优化组织。.以上结果有助于澄清镁铝复合夹杂物诱导晶内铁素体形核的机制，从而为氧化物冶金的实用化提供数据参考和理论支持。.截至目前，本项目在SCI 收录期刊上共发表论文8篇，国内核心期刊上发表论文3篇。