| Duplex stainless steel owns the characteristics of both ferrite stainless steel and austenitic stainless steel with fine mechanical properties and corrosion resistance,so it is widely used in pollution control industry.However,the strain of austenite phase and ferrite phase are unevenly distributed in the hot rolling process of traditional duplex stainless steel,because of the difference of hardness of phases,and the crack generation will result in poor thermoplasticity and edge cracking.In this paper,a new resource-saving Fe-Cr-Mn-Al duplex stainless steel with better thermoplasticity was designed by using Mn instead of Ni and Al instead of part of Cr,in order to adjust the ratio of phases,thus it not only reduces the cost,but also has better thermoplasticity.And its manufacturing technique was studied,in order to obtain better mechanical and corrosion resistance properties.The main contents of this paper are as follows:(1)Designing two kinds of compositions by means of the equilibrium phase diagram calculated by Thermo-Calc,one was 1#Fe-19Cr-12Mn-0.6Al,the other was 2#Fe-19Cr12Mn-0.6Al-1Ni.There was only ferrite phase existed in 1#experimental steel above 1020?,and 2#experimental steel above 1085?,and sigma phase precipitation of two kinds of experimental steels existed under 760?.And when the final rolling temperature was 850?,almost 100%of the 1#microstructure was ferrite phase,and more than 90%of the 2#microstructure was ferrite phase,which ensured that the experimental steels owned better hot forming properties?(2)The 1#hot rolled plates were cold rolled at the reduction rate of 60%,70%and 80%,and then they were annealed at 800? for 4 h.The research showed that the serious reduction rate could promote the transformation speed of ferrite phase to austenite phase,so that the austenite phase was more evenly distributed and owned fine mechanical properties.(3)Experimental cold-rolled steel plates were annealed at different times.The results showed that there are two kinds of processes in the annealing process,one was the transformation of ferrite phase to austenite phase,because of strain energy from large cold rolling deformation,the other was the recrystallization process of ferrite,which were two kinds of competing relationship.When 1#steel was annealed at 800? for different times,the firstly occurred the ferrite recrystallization,the transformation of ferrite phase to austenite phase would be inhibited and delayed,and large ferrite grains would appear,with poor mechanical properties.And when 2#steel was annealed at 850? for different times,the firstly occurred the transformation of ferrite phase to austenite phase,the ferrite recrystallization would be inhibited and delayed,and the two-phase structure was evenly distributed,grain size was small,owning better mechanical properties and pitting corrosion resistance.(4)Experimental cold-rolled steel plates were annealed at different temperatures.The results showed that because the critical nucleation size of austenite phase was smaller at lower annealing temperature,the nucleation and growth would be in the grain boundary and inside of ferrite,the microstructure was evenly distributed,and the grain size was smaller,and the pitting corrosion resistance were better,however,because of the appearance of acicular austenite reduced plasticity.When 2#steel was annealed at lower temperature,sigma phase precipitation occurred,which improved the strength,decreased the ductility and reduced the pitting corrosion resistance.(5)Cr and Al were mainly enriched in the ferrite phase,while Mn and Ni were mainly enriched in the austenite phase,resulting in the Pitting Resistance Equivalent of the ferrite phase was higher than that of the austenite phase.So,pitting occurred in the boundary between the ferrite phase and austenite phase. |
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