含Ti不锈钢冶金工艺进展

Metallurgy development of Ti-stabilized stainless steel

  • 摘要: 围绕含Ti不锈钢冶金工艺的研究进展,从冶金物理化学基础、氧化物和TiN夹杂的形成与控制、凝固过程TiN复合核心和Ti元素对不锈钢铸件力学性能的影响等方面进行了总结和讨论。主要的研究进展为:含Ti不锈钢在冶炼过程生成的Al2O3、镁铝尖晶石、(MgO−Al2O3)rich−CaO−TiOx等高熔点氧化物夹杂是导致含钛不锈钢连铸水口堵塞的主要原因;优化的Al、Ca、Ti的添加方式和炉渣控制工艺是夹杂物减少和低熔点化的重要手段;TiN夹杂的析出、扩散长大和碰撞聚合的基本规律是关注的热点,钢液中大尺寸氧化物夹杂会促进TiN团簇的形成;通过严格控制凝固过程TiN或氧化物-TiN复合核心能够促进δ-Fe异质形核,提高连铸坯等轴晶率;固溶Ti元素能提高奥氏体或双相不锈钢中铁素体含量,提升不锈钢铸件的拉伸性能。

     

    Abstract: Titanium is widely used in the manufacture of stainless steel due to its stabilizing ability of carbon and nitrogen, the pinning effect on grain growth, and strengthening effect, which are contributed by the formation of Ti(C, N) with different compositions, sizes, and distributions. Due to the excellent corrosion resistance, formability, and mechanical properties, Ti-bearing stainless steel is widely applied to daily life and priority industries, including petroleum, aerospace, nuclear power, and transportation. However, complex inclusions can be formed after Ti addition in the metallurgy process. Moreover, those inclusions have adverse effects on the metallurgy and the quality of stainless steel, including the clogging of the submerged entry nozzle, layered defects, and surface defects. Therefore, it is important to develop the metallurgy of Ti-stabilized stainless steel. This paper discussed and concluded the investigation development of Ti-bearing stainless steel regarding the fundamentals of metallurgy, the formation and control of oxides and TiN, heterogeneous nucleation, and the influence of Ti on the mechanical properties of stainless steel. First, oxides with high melting points, including Al2O3, spinel, and (MgO−Al2O3)rich−CaO−TiOx, generally cause the clogging of the submerged entry nozzle in the Ti-bearing stainless steel. The optimized addition of Al, Ca, and Ti, as well as the control of slag, can decrease the amount of oxides with a high melting point. Second, the formation and growth of TiN and complex TiN inclusions happen during the cooling and the solidification of the titanium-stabilized stainless steel, which can collide and aggregate to form TiN clusters. Moreover, macro-oxides can promote the formation of TiN clusters. However, TiN or complex TiN inclusions can also work as heterogeneous nuclei for δ-Fe during the solidification of stainless steel and promote the generation of an equiaxed fine-grain structure. In addition to forming compounds, titanium can present as a solid solution state in steel and promote the formation of ferrite in austenitic stainless steel or increase the ferrite fraction in duplex stainless steel with its strong ferrite forming ability, which is beneficial to the improvement of the mechanical properties of stainless steel casting.

     

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