热处理对固态304不锈钢中氧化物夹杂的影响研究

Control of oxide inclusions is one of the main tasks of steelmakers during the production of high grade stainless steels. Previous investigations mainly focus on the modification and removal of inclusions in the liquid steel during the ladle refining and continuous casting process. However, oxide inclusions may react with alloying elements within the matrix of solid 304 stainless steel during the heat treatment process. The variation of oxide inclusions during the heat treatment process directly affacts the performance of 304 stainless steels. The laboratory experiment, thermodynamic calculation, kinetic modeling and plant trial will be employed in the current project. Firstly, the mechanism of thermodynamic formation and transformation of inclusions during the heat treatment is determined. Secondly, the transformation rate of inclusions with various sizes will be kinetically predicted. Thirdly, the mechanism and influence factors of fine oxide particles pining the austenite grain boundary would be revealed. It is aimed to achieve precisely control of oxide inclusions and the refinement of grain size during the heat treatment process, which is crucial to improve the quality and performance of 304 stainless steels.

氧化物夹杂的控制是生产高品质不锈钢的重中之重。此前对于304不锈钢中氧化物夹杂的研究主要集中在钢铁生产中精炼、浇铸工艺阶段的液态钢水中夹杂物变性或去除的方面，却忽视了后续的热处理过程铸坯中的氧化物夹杂仍然会与304不锈钢基体中的合金元素发生高温反应，氧化物夹杂在该过程的变化直接影响最终产品304不锈钢的质量和性能。本研究拟用实验室实验、热力学计算、动力学计算和工业试验的方法，揭示304不锈钢中氧化物夹杂在热处理过程的生成和转变机理，明确氧化物夹杂在热处理过程中生成和转变的热力学条件，预测不同尺寸的氧化物夹杂在不同热处理温度下的动力学转变速率，确定热处理过程中304不锈钢中氧化物夹杂变化对奥氏体晶粒长大的抑制机理及其影响因素。研究成果能够实现对热处理过程中304不锈钢中氧化物夹杂的有效控制，达到细化304不锈钢晶粒组织的目的，从而为304不锈钢产品质量和性能的提升提供理论基础。

研究了热处理对304不锈钢中夹杂物的影响。研究发现在1373 K下的氩气保护气氛的热处理过程中，304不锈钢夹杂物的演变机理为：在热处理之前，钢中的夹杂物主要为球形液态MnO-SiO2夹杂物。热处理过程中，钢中的[Cr]元素逐渐向钢/MnO-SiO2夹杂物界面传质，随后[Cr]还原MnO-SiO2夹杂物中的SiO2和MnO，在MnO-SiO2夹杂物表面生成MnO·Cr2O3尖晶石夹杂物，同时生成的[Si]和[Mn]从反应界面传质回钢中。最终，MnO-SiO2夹杂物被完全变性为纯MnO·Cr2O3尖晶石夹杂物。将热处理温度从1273 K增加至1473 K可以有效地加快夹杂物的转变速率。此外，建立了一个热处理过程夹杂物转变动力学模型，可以有效预测不同温度下的热处理过程中夹杂物的转变率。通过激光高温共聚焦显微镜直接原位揭示了铝脱氧钙处理钢中夹杂物的转变过程，在热处理过程中，铝、镁、硫、氧、钙等元素在反应边界层与钢基体之间扩散传质，与CaO-Al2O3夹杂物反应形成Al2O3-MgO-CaS。