镁铝尖晶石固溶体成分对TiN析出行为的影响

摘要

Through the experiment of slag/steel reaction equilibrium on 2205 duplex stainless steel, inclusions in MgO-Al2O3 binary solid solution were obtained with different slag compositions.When the reaction reached the equilibrium, the new complex inclusion of MgO-Al2O3 solid solution combined with TiN would further form if adding 0.05% Ti to the steel.After water quenching, the inclusions were analyzed by SEM, and samples were electrolyzed by oxalic acid with content of 10%.And then grain morphology and size of δ ferrite was compared to that of as-cast microstructure without Ti.The experiment results showed that the precipitation quantity increased with the increase of Al2O3 proportion in MgO-Al2O3 solid solution while the grain of as-cast δ ferrite was obviously refined.It was found that TiN precipitated rarely out of MgO-rich MgO-Al2O3 solid solution and MgO-Al2O3, and the grain refining effect of δ ferrite was not obvious.By thermodynamic calculation, heterogeneous nucleation theory and experimental result analysis, it was concluded that inclusion composition of MgO-Al2O3 binary solid solution was jointly determined by slag composition and activity of Mg and Al.The increase of Al2O3 content in MgO-Al2O3 solid solution contributed to the lattice distortion of MgO-Al2O3, which is closely associated with vacancy in the lattice.Because of the enrichment of vacancies, lattice constant e was uneven.And vacancies had changed the crystal field and caused the movement or transfer of O2-, which led to omission solid solution of spinel.It was the energy state changes of lattice that promoted the precipitation of Ti and N atoms on the surface of MgO-Al2O3 inclusion.%通过2205双相不锈钢渣-钢反应平衡实验,得到不同炉渣配比下的MgO-Al2O3二元系固溶体夹杂,当反应达到平衡后,向钢中添加了0.05%的Ti,进而得到了"MgO-Al2O3固溶体+TiN"的复合夹杂.试样经水淬后,通过电镜分析夹杂物,然后采用10%的草酸进行电解,与不加Ti的铸态组织δ铁素体晶粒形貌、尺寸进行了对比.实验结果发现:TiN析出量随MgO-Al2O3固溶体中Al2O3比例的增加而增加,铸态δ铁素体晶粒可得到明显细化,实验结果发现富MgO的MgO-Al2O3固溶体以及MgO·Al2O3析出TiN很少,δ铁素体细化效果不明显.通过热力学计算、异质形核理论以及实验结果证明,MgO-Al2O3二元系固溶体夹杂物成分由炉渣成分及钢中Mg、Al活度共同决定,MgO-Al2O3固溶体中Al2O3含量增加,使MgO·Al2O3晶格发生畸变,这与点阵中存在着空位密切相关.由于空位富集,使得点阵常数e不均匀,也由于空位改变晶格场,引起O2-的移动或转移,形成缺位尖晶石固溶体.晶格的能量状态发生变化促进了Ti原子和N原子在MgO-Al2O3夹杂物表面析出.