Grain Boundary Engineering And Its Effect On Corrosion Resistance Of Cr20Mn18Ni2Mo2 High Nitrogen Steel

High nitrogen austenitic stainless steels have good mechanical properties such as high strength and toughness,as well as excellent corrosion resistance,non-magnetism and biocompatibility,etc.It has broad application prospects in chemical production,marine engineering and petroleum exploitation.In this paper,Cr20Mn18Ni2Mo2 high nitrogen steel smelted in medium frequency induction furnace is taken as the research object.Through optical microscope,EBSD test and electrochemical experiment,the effects of electroslag remelting,forging,cold deformation and GBE treatment on the microstructure and properties of the high nitrogen steel are studied,the influence of grain boundary characteristic distribution on the corrosion resistance was emphatically studied.The results show that:After electroslag remelting,the loss of alloying elements of Cr20Mn18Ni2Mo2 high nitrogen steel is less,and the nitrogen content is slightly increased.Compared with the medium frequency induction smelting,the tensile strength is increased by 31.2% and the elongation is increased by 1.3 times.The microstructure of Cr20Mn18Ni2Mo2 high nitrogen steel is single-phase austenite after forging,and the grain size is about 75 ?m,which is obviously refined.There are a few twins in some grains.The tensile strength,elongation and impact energy are increased by 52.7%,3 times and nearly 60 times compared with the medium frequency induction smelting samples.Cr20Mn18Ni2Mo2 high nitrogen steel has a large strain hardening index,which is up to 0.55.The austenite structure is single before and after cold deformation,and there are two main deformation mechanisms of slip and twinning in the process of cold deformation.Twins and slippage are involved in deformation at the initial stage.As the amount of deformation increases,the twinning mechanism plays a major role.Cr20Mn18Ni2Mo2 high nitrogen steel has good corrosion resistance after cold deformation.The self-corrosion potential of 22% sample is the highest,which is-1.068 V.The self-corrosion potential of62% sample is the lowest,which is-1.096 V.Compared with the undeformed specimens(-1.087 V),the self-corrosion potential of the cold-deformed Cr20Mn18Ni2Mo2 high nitrogen steel changes little.The special grain boundary length and the special grain boundary volume fraction per unit area of Cr20Mn18Ni2Mo2 high nitrogen steel can be increased by GBE(Grain boundary engineering)treatment.After single-step strain recrystallization,the volume fraction of special grain boundary per unit area of Cr20Mn18Ni2Mo2 high nitrogen steel with 40% deformation increases greatly,and the highest value is 41.8% under 1050?-1min annealing.After repeated strain recrystallization,the volume fraction of special grain boundary per unit area of Cr20Mn18Ni2Mo2 high nitrogen steel with 20% and 30%deformation is also increased.The volume fraction of special grain boundary per unit area of the deformed 20% sample increased from 20.4% to 33.2%,and the deformation 30%sample increased from 20.4% to 64.2%.Increasing the special grain boundary volume fraction per unit area is beneficial to reduce the corrosion tendency of Cr20Mn18Ni2Mo2 high nitrogen steel.At the same time,higher special grain boundary volume fraction is beneficial to improve the intergranular corrosion resistance of the material.