| Traditional austenitic stainless steels use nickel to stabilize austenite,which is expensive and has biocompatibility with the human body.This limits the application of austenitic stainless steels.It has been found through research that nitrogen is a strong austenitic stabilizing element that can replace nickel to stabilize austenite in stainless steel.Nowadays,stainless steel usually uses nitrogen instead of nickel to stabilize austenite.The nitrogen-containing austenitic stainless steel thus obtained has higher strength,toughness,and corrosion resistance than traditional austenitic stainless steel.Therefore,the development and application of nitrogen-containing stainless steel has become one of the focuses of current research in the field of materials.At present,the main nitrogen addition methods of stainless steel are solid-phase add nitrogen and liquid-phase add nitrogen,and they all have certain deficiencies in industrial production.Therefore,this study used a new type of process to add nitrogen to stainless steel.This study combined with solid-phase add nitrogen can effectively increase the nitrogen content and liquid-phase add nitrogen under normal pressure can achieve the characteristics of large-scale production.We will reduce the smelting temperature to the mushy zone(solid/liquid two-phase zone)and keep it in a nitrogen atmosphere.For a certain period of time,nitrogen is added to the stainless steel.The main research contents and results of this paper are as follows:(1)In this paper,the Mn18Cr18 N stainless steel as the research material,using the paste zone insulation process,to achieve nitrogen in the stainless steel.When the nitrogen pressure is 0.1 MPa,the stainless steel is retained at the mushy zone temperature of 1365°C for 0 min,5 min,10 min,and 20 min,respectively.The measured nitrogen contents are 0.161%,0.197%,0.279%,and 0.384%,respectively.As the holding time of the zone increases,the nitrogen content in the stainless steel increases.(2)The microstructure of stainless steel with different nitrogen contents was observed.The results showed that as the nitrogen content increased,the ferrite content in the stainless steel decreased,and the austenite content increased,which means that nitrogen can stabilize the austenite structure in the stainless steel.(3)The shrinkage pores and pores in stainless steel ingots after smelting were studied,and the mechanisms of shrinkage pores and pore formation were analyzed.The effect of the holding time of the mushy zone on shrinkage pores and stomata is studied.The result is that with the increase of the holding time of the mushy zone,the shrinkage rate decreases,while there is no obvious change in the porosity rate.(4)The size and position of the stomata in the tissue were studied.With the increase of the incubation time in the mushy zone,the size of the stomata decreased,the number increased,and the overall stomata rate changed little.The stomata in the tissue mainly concentrated in the austenite.(5)The nitrogen-containing stainless steel was subjected to a compression test.The compressive true stress-true strain curve shows that there are mainly elastic deformation stages and plastic deformation stages in the compression process.With the increase of nitrogen content,the yield strength of stainless steel increases,while the work hardening index does not remain basically unchanged.(6)The nitrogen-containing stainless steels were subjected to immersion and electrochemical tests to test their resistance to uniform corrosion and pitting corrosion,respectively.As a result,the resistance to uniform corrosion and pitting corrosion resistance of stainless steels increased with increasing nitrogen content. |
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