Thermodynamic analysis on tin precipitation behavior in Ti-bearing peritectic steel after magnesium treatment  

镁处理对含Ti包晶钢中TiN析出行为影响的热力学分析

作　　者：QU Tian-peng WANG De-yong WANG Hui-hua HOU Dong TIAN Jun 屈天鹏;王德永;王慧华;侯栋;田俊(Shagang School of Iron and Steel,Soochow University,Suzhou 215021,China)

机构地区：[1]Shagang School of Iron and Steel,Soochow University,Suzhou 215021,China

出　　处：《Journal of Central South University》2020年第12期3637-3651,共15页中南大学学报（英文版）

基　　金：Projects(51774208,52074186,U1860205)supported by the National Natural Science Foundation of China。

摘　　要：TiN,which is ubiquitous in Ti-bearing steel,has a critical influence on both the mechanical properties and the welding process of steel,and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance.In this paper,Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition.Furthermore,microsegregation models were used to analyze the precipitation process of TiN at solidification front,and the calculation results were finally verified by scanning electron microscope(SEM).Research showed that a multitude of dispersed particles of high melting oxide MgAl2O4 or MgO always existed in molten steel after magnesium treatment.In consideration of the segregation and enrichment of solute elements at the solidification front,the Ohnaka microsegregation model was employed to compute the precipitation during solidification.In the event of the solid fraction reaching 0.95 or more,the concentration product of[Ti][N]at the solidification front exceeded the equilibrium concentration product,then TiN began to precipitate.MgO or MgAl2O4 cores were generally found in TiN particles of peritectic steel after the magnesium treatment,which was consistent with the thermodynamic calculation results.Moreover,the average size of TiN particles was reduced by approximately 49%.This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment,by which the heterogeneous nucleation of TiN was promoted it;therefore,favorable nucleation sites were provided for further refining the high-temperature ferrite phase.含Ti钢中普遍存在的TiN对钢的力学性能和焊接过程有重要影响,研究TiN在冶金熔池中的析出行为有重要意义。本文以含Ti包晶钢为研究对象,采用FactSage计算了钢种成分对钢中典型夹杂物析出行为的影响规律。采用微观偏析模型对凝固前沿TiN的析出过程进行了分析,借助SEM对计算结果进行了验证。研究结果表明,镁处理后钢液中始终存在大量弥散分布的高熔点氧化物MgAl2O4或MgO,考虑溶质元素在凝固前沿的偏聚富集现象,利用Ohnaka微观偏析模型进行凝固析出计算,当固相率达到0.95时凝固前沿的[Ti][N]浓度积高于平衡浓度积,开始析出TiN。镁处理后包晶钢中TiN颗粒内部普遍存在MgO或MgAl2O4核心,与热力学计算结果相符,且TiN颗粒平均尺寸减小了62%左右,表明镁处理形成富镁高熔点夹杂物促使了TiN异质形核,为进一步细化高温铁素体相提供了有利的形核质点。

关 键 词：magnesium treatment peritectic steel TIN heterogeneous nucleation thermodynamic analysis 

分 类 号：TG142.1[一般工业技术—材料科学与工程]