5%Si高硅奥氏体不锈钢元素偏析及均匀化处理

 高硅奥氏体不锈钢由于高含量硅元素的加入使其具有优异的耐高温腐蚀性能和较低的成本,在制酸行业有着潜在的应用价值。然而,该合金中高含量硅元素的加入会促进凝固过程中溶质再分配,进而造成显著的元素偏析,最终导致合金内部产生枝晶组织和大量的有害相。对铸锭组织进行均匀化处理能够有效消除枝晶与元素偏析,促进析出相回溶和枝晶消融,从而改善材料的热塑性,有效应对热变形开裂问题。因此,采用金相显微镜(OM)、扫描电镜能谱分析(SEM/EDS)、电子探针(EPMA)、JMatPro软件计算等方法,研究了实验室条件下制备的5%Si高硅奥氏体不锈钢铸锭的显微组织和元素分布状态,通过残余偏析指数、扩散动力学计算并结合均匀化处理试验验证,最终确定了5%Si高硅奥氏体不锈钢合理的均匀化处理工艺。结果表明,5%Si高硅奥氏体不锈钢凝固过程中钼元素偏析最为严重,通过残余偏析指数模型计算得到的均匀化动力学方程可用来指导该成分合金的均匀化处理工艺;5%Si高硅奥氏体不锈钢经过1 150 ℃×12 h均匀化处理后,铸锭内枝晶消融,元素偏析基本消除,析出相与铁素体回溶到基体中,合金转变为全奥氏体组织,热塑性得到改善;当加热温度达到1 250 ℃时,合金出现过烧现象,晶界开始熔化。

Segregation and homogenization treatment of 5%Si high silicon austenitic stainless steel

High-silicon austenitic stainless steel has excellent high-temperature corrosion resistance properties and low cost due to the addition of high content silicon,and it has potential application value in the acid industry. However, the addition of high content Si will promote the redistribution of solute during solidification process, which will cause significant element segregation,and ultimately lead to the formation of dendritic structure and numerous harmful phases in the alloy. Homogenizing the ingot structure can effectively eliminate dendrites and element segregation,promote precipitation phase re-dissolution and dendrite ablation,thereby improving the thermoplasticity of material,and effectively coping with the problems of thermal deformation and cracking. Therefore,the work studied the microstructure and element distribution of 5%Si high-silicon austenitic stainless steel ingots prepared under laboratory conditions through metallographic microscope (OM), scanning electron microscope/energy spectrum analysis (SEM/EDS), Electronic probe (EPMA), JMatPro software calculation and other methods. Finally,a reasonable homogenization treatment process for 5%Si high-silicon austenitic stainless steel was confirmed using the calculation of residual segregation index and diffusion kinetics,combined with homogenization treatment experiments. The results show that Mo is the most serious segregation element during the solidification of 5%Si high-silicon austenitic stainless steel,the homogenization kinetic equation calculated by residual segregation index model can be used to guide the homogenization treatment process of this alloy. After homogenizing at 1 150 ℃×12 h,the dendrites in 5%Si high-silicon austenitic stainless steel ingot are ablated and element segregation is eliminated,the precipitated phase and ferrite are re-dissolved into the matrix,the alloy is transformed into full austenite structure and thermoplasticity is improved. When the temperature is increased to 1 250 ℃,the alloy is overheated and grain boundaries begin to melt.