The Effect Of N On The Structure And Properties Of Super Duplex Stainless Steel UNS S32750

Super duplex stainless steel UNS S32750 is one of the typical representatives of the third duplex stainless steel s,which has been widely used.It has high strength,excellent welding property and outstanding corrosion resistance.On the other hand,both of the microstructure stability and hot plasticity of alloy are poor due to its high level of alloys element,as N,Mo and Cr.Among them,N is the key eleme nt during the development of the second and the third generation of the duplex stainless steels.Therefore,it can make a significant sense by conducting systemative investigat ion on the influence of N on mi crostructure and properties of UNS S32750.The effect of N content on the microstructure and properties of UNS S32750 was investigated by means of solution treatment testing,impact testing,tensile testing,pitting corrosion resistance testing and hot compression test ing.The results obtained were analysed by optical microscopy,scanning electron microscopy_SEM,transmission electron microscopy_TEMand physicochemical phase analysis.The results of solution treatment testing show that with increasing solution treatment temperature from 950? to 1060?,the content of ? phase was decreased from 11.031% to 0%.When the specimens was treated at 1100?,the alloy can get excellent intergrated mechanical performances and pitting corrosion resistance with the phase ratio being closed to 1:1.With increasing the temperature from 1050 ? to 1250?,the content of Cr and Mo within ferrite decreased and the content of Mo within austenite decreased,while the content of Ni within ferrite and the content of Cr within austenite increased,the content of Ni within austenite slightly decreased.The influence of the content of N on the microstructure and properties of UNS S32750 was investigated by the solution treatment.The results revealed that with increasing the content of N,the content of austenite increased,the content of ferrite decreased,the content and complete dissolution temperature of ? phase decreased,the solution temperature where phase ratio close to 1:1 increased.When the alloy was treated at temperature of 110 0?,with increasing the content of N,the strength and pitting corrosion resistance increased,while the reduction of area decreased.The toughness is enhanced when the content of N is increased from 0.25% to 0.28% and then decreased with further increasin g the content of N.The hot deformation behaviors of UNS S32750 with different content of N was investigated by hot compression testing.The results show that with increasing the content of N,the hot deformation apparent activation energy for UNS S32750 was increased from 560 KJ/mol to 647 KJ/mol,the optimal temperature range for the hot deformation shifted from 1030 ? ¹100? to 1130? ¹200?.