The Fine Homogenization Craft And Performance Investigation Of Duplex Stainless Steel Based On Thermomechanical Treatment

The duplex stainless steel is a stainless steel whose α and γ each about half so that it owns excellent mechanical and welding properties and good corrosion resistance in the complex corrosive environments. The mechanical properties depends primarily γ / α phase ratio and the shape and distribution of two-phase etc. The microstructure of rolled surface appears that stretched γ austenite phase is distributed at the ferrite matrix when it’s rolled at the(α+γ) duplex region. It limits the application scope severely because of the significant anisotropy. The specimen is solution-treated at higher temperature in α single-phase region, then treated in(α+γ) duplex region, very coarse two-phase structure is formed and γ phases precipitate along coarse α boundaries and within α grains. It leads to low elongation and bad ductility. Therefore, the elimination of(α+γ) duplex stainless steel anisotropy to increase its plasticity and toughness has become an important requirement for its application.In case of microstructure, the refinement of γ phase(includes phase within the grains) is effective in improving plastic deformation. One of the typical chemical compositions is Fe-22%Cr-5%Ni-0.18%N and this steel is investigated in the paper. Based on thermomechanical treatment process(α single-phase + severe cold deformation + solution treatment), much finer and uniform structure can be obtained. The formation mechanism of fine-grain microstructure is discussed with EBSD. Compared with mechanical properties and corrosion resistance, we can get the law between fine-grained microstructure and performance. The results show that:(1)The cold deformation is larger, the refining effect of the(α + γ) two-phase structure is better. Fine-uniform microstructure can eliminate the anisotropy clear.(2) The fine-uniform degree of γ phase is influenced especially with the solution treat. The γ phase size is larger at higher temperature and longer holding time. Besides, it is the linear relationship between grain size and solution temperature.(3)Small γ particles are mainly located at the trigeminal α subgrains boundaries. It maintains the typical K-S orientation relationship between γ particles and α matrix.(4) Fine-uniform microstructure can improve the strength and hardness for the material. And the relationship between the tensile strength and hardness meet values: σb≈3Hv. Besides, the fine-uniform duplex structure of duplex stainless steel still has the good corrosion resistance.