Abstract：Delta ferrite is a common harmful precipitated phase in martensitic heat-resistant steel. Its existence will adversely affect the mechanical properties and corrosion resistance of the material,and it is difficult to be removed by conventional heat treatment. Therefore,how to remove delta ferrite is the focus of research in this field. C-Cr-Ni-Mo martensitic heat-resistant steel is taken as the main research object,and three kinds of experimental steels with different compositions of C-Cr-Ni-Mo,C-Cr-Ni-Mo-Nb and C-Cr-Ni-Mo-Ti are designed. By means of OM,SEM and EDS,the effects of Nb and Ti microalloying on the dissolution behavior of delta ferrite in martensitic heat-resistant steel are studied and the mechanism is revealed by comparing the volume percent of delta ferrite,the dissolution rate of delta ferrite and the austenite grain size in the as-cast microstructure of three different composition experimental steels,which provides a new method for the rapid dissolution of delta ferrite in martensitic heat-resistant steel. The experimental results show that Nb and Ti microalloying elements,as ferrite forming elements,will aggravate the segregation of alloy composition and fail to fully transform during the cooling process,resulting in an increase in the volume percent of delta ferrite in the as-cast structure at room temperature,but the size of the generated delta ferrite is relatively small. The dissolution rate of delta ferrite is related to its morphology and position. Nb and Ti microalloying can increase the dissolution rate of delta ferrite. On the one hand,Nb and Ti microalloying will refine the delta ferrite in the as-cast structure and increase the specific surface area of delta ferrite. On the other hand,by forming precipitates containing Nb and Ti,pinning grain boundaries,inhibiting austenite grain growth,delaying the transformation of delta ferrite from irregular shape to spherical shape during dissolution,more delta ferrite is maintained at austenite grain boundaries for a longer time during heating and maintain a large specific surface area,thereby increasing the dissolution rate of delta ferrite.
李奇, 张旭, 李晓晴, 李俊儒, 张鹏飞, 张玉馨. Nb、Ti对耐热钢中δ铁素体固溶行为的影响[J]. 钢铁, 2023, 58(10): 131-139.
LI Qi, ZHANG Xu, LI Xiaoqing, LI Junru, ZHANG Pengfei, ZHANG Yuxin. Effect of Nb and Ti on dissolution behavior of delta ferrite in heat-resistant steel[J]. Iron and Steel, 2023, 58(10): 131-139.
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