一种Cr-Ni-Mo-Ti-Al系高强度不锈钢的凝固偏析行为

Solidification segregation behavior of a Cr-Ni-Mo-Ti-Al high strength stainless steel

采用差示扫描量热分析、高温共聚焦显微镜原位观察和定向凝固的方法研究了冷却速率对一种Cr-Ni-Mo-Ti-Al系高强度不锈钢元素偏析的影响规律。结果表明:试验钢的凝固顺序为:L→L+δ→L+δ+γ→L+δ+γ+TiN→δ+γ+TiN→γ+TiN;随着冷却速率的提高,凝固组织的二次枝晶间距逐渐降低,枝晶组织得到细化,二次枝晶间距与冷却速率之间的函数关系为λ2=86.7(GLR)-1/3;铸态组织中Mo、Ni、Al和Ti元素属于正偏析,Cr元素属于负偏析,其中Ni和Ti元素偏析程度较大,主要富集于枝晶间,Mo、Cr和Al元素偏析程度较轻,在铸锭中分布较均匀。凝固末期残余液相中Ti元素的富集导致形成AlN夹杂的倾向增加。冷却速率增加,Ni和Ti等元素偏析现象显著降低。

The influence of cooling rate on element segregation in a Cr-Ni-Mo-Ti-Al high strength stainless steel was studied using differential scanning calorimetry,in-situ observation under high-temperature confocal laser scanning microscopy and directional solidification experiments.The results show that the solidification sequence of the experimental steel is:L→L+δ→L+δ+γ→L+δ+γ+TiN→δ+γ+TiN→γ+TiN.As the cooling rate increases,the secondary dendrite spacing of the solidified structure gradually decreases,and the dendrite structure is refined.The functional relationship between the secondary dendrite spacing and the cooling rate isλ2=86.7(GLR)-1/3.In the as-cast microstructure,Mo,Ni,Al and Ti elements belong to positive segregation,while Cr element belongs to negative segregation.Among them,Ni and Ti elements have a greater degree of segregation and are mainly enriched between dendrites.Mo,Cr,and Al elements have a lighter degree of segregation and are evenly distributed in the ingot.The enrichment of Ti element in the residual liquid phase at the end of solidification increases the tendency to form AlN inclusion.As the cooling rate increases,the segregation phenomenon of elements such as Ni and Ti is significantly reduced.