氧化物冶金过程中晶内铁素体优先竞争析出机理及控制的研究

In oxide metallurgy, inclusions which are suitable for heterogeneous nucleation in steel can not completely guarantee the preferential precipitation of intragranular ferrite,and the preferential precipitation of the grain boundary ferrite causes the failure of oxide metallurgy functions, the key link of oxide metallurgy technology is whether the intragranular ferrite could preferentially precipitate.In this study, in order to solve the problem of poor representativeness and poor controllability caused by inclusions in situ precipitation, the intragranular ferrite is induced by artificially prepared inclusions, the relationship between the crystal interface and the nucleation mechanism are tudied, and the theory of ferrite nucleation induced by inclusions is further improved and developed; the influence of the system environment on the preferential precipitation of intragranular ferrite in solid phase transformation is studied, the crystallographic relationships under different factors is analyzed, and the thermodynamics and kinetic mechanism of the preferential precipitation is clarified, master the rule of intragranular ferrite precipitation; the structural relationship between different phases in the composite inclusions and the preferred growth orientation of acicular ferrite on inclusions are studied, and the crystallographic relationship among ferrite/inclusions/austenite is Cleared.Based on the research, the mechanism and control method of the preferential precipitation of intragranular ferrite are obtained, which provides the theoretical basis and technical basis for the development of new steel material with high toughness and excellent welding performance.

在氧化物冶金中，钢液中适合异质形核的夹杂物并不能完全保证晶内铁素体优先析出，而晶界上铁素体的优先析出则使氧化物冶金作用失效，夹杂物诱发的晶内铁素体能否优先竞争析出是氧化物冶金技术的关键环节。本课题利用人工制备的可控夹杂物诱发晶内铁素体形核，排除将原位析出的单一夹杂物作为研究对象时代表性差、可控性差的问题，深入稳定解析各晶体界面关系，研究形核机理，完善和发展夹杂物诱发铁素体形核理论；研究固态相变时系统环境状态对晶内铁素体优先析出的影响，解析不同影响因素下的相变晶体学关系，明确优先析出的热力学、动力学机制，掌握控制晶内铁素体优先析出规律；研究原位析出的复合夹杂物中各物相间的结构关系及针状铁素体在夹杂物上的优势生长取向，明确铁素体/夹杂物/奥氏体三者间的晶体学关系。通过研究，掌握晶内铁素体优先竞争析出的机理和控制方法，为开发高强度、高韧性与优良焊接性能良好匹配的钢铁材料提供理论依据和技术基础。

氧化物冶金技术的核心思想是在奥氏体粗化的条件下，利用在钢中析出的夹杂物及第二相粒子作为晶内铁素体转变的形核源，诱发晶内铁素体特别是晶内针状铁素体的产生，在钉扎细化晶粒的同时形成交织互锁的组织结构，极大提高材料性能，特别是低温冲击韧性。对晶内铁素体特别是晶内针状铁素体较晶界铁素体优先析出的研究是推动氧化物冶金技术进一步发展的重心。.本课题通过熔盐电解制备了可控的夹杂物，将其合理添加至钢液中形成复合夹杂物，解析了人工制备的夹杂物诱发晶内铁素体的形核机理，进一步完善和发展夹杂物诱发晶内铁素体的形核机制理论，特别是完善和发展晶格低错配度诱发机理的理论和应力应变诱发机理的理论。.研究阐明了晶内铁素体优先于晶界铁素体竞争析出的热力学、动力学条件，研究表明，复合夹杂物各相间的热膨胀系数的差异导致凝固过程中夹杂物内部的热失配应力，形成α-MnS中位错缠结和Mn3Al2Si3O12中孪晶等晶体结构缺陷。复合夹杂物内部位错和孪晶等晶体结构缺陷中储存的晶格畸变能提供了IAF形核驱动力，是促进IAF相变的动力。这对于控制氧化物冶金过程中晶内铁素体优先析出细化中低碳钢的组织提供理论基础。.通过相变晶体学研究，解构了晶内针状铁素体的晶体学特征，明确晶内针状铁素体在形核及长大过程中与原奥氏体间保持的晶体学关系，解明了晶内针状铁素体的形核及长大机制。本研究对IAF三维形态及其母相奥氏体的取向进行了重构，阐明了IAF的各板条间的空间位置、晶体取向关系以及沿优势方向长大机制。结果表明，IAF以包裹的形式在夹杂物上呈放射状形核长大，其母相奥氏体间保持着K-S关系。在奥氏体向铁素体转变过程中，随温度降低，铁素体生长速率各向异性趋势逐渐增加，沿铁素体最大长大速率方向，即<111>α，定向长大趋势明显，最终导致其呈针状形态。.该课题的研究成果为开发高强度、 高韧性与优良焊接性能良好匹配的钢铁材料提供理论依据和技术基础。