Grain Refinement Of 2205 Duplex Stainless Steel Based On σ Phase

The duplex stainless steel(DSS) is one of high performance structural material as its excellent corrosion resistance and mechanical properties.It became the main stainless steel of the 21'st centry.Now,more and more DSSs have been applied in chemical,petrochemical,paper and petroleum industries.2205 duplex stainless steel is normally the most usefull.However,the high performance of the duplex stainless steel is relative,in the manufacturing and welding process,because unwarrantable heat treatments cause the Coarseδferrite,make the property go to the bad,and directly affect the material quality and safe reliable application.Therefore,the research of grain refining will become a key direction in the the duplex stainless steel.The method to refine the grain size of 2205 duplex stainless steel was investigated throughσtreatment and anti-σtreatment.The follow is the the principle of refining the grain size:σtreatmentδ→γ+σand anti-σtreatmentγ+σ→δ.The microstructures and mechanical properties of 2205 duplex stainless steel after different heat reatments were investigated by optical microscope,transmission electron microscope,scanning electron microscope,X-ray diffraction analyzer,the tension test and impact test.(1) The results after solution treatment are as follow:with the heat treatment temperature high,the constituent content of the ferrite phase increase;The strip-shaped austenite phase gradually decomposes,spheroidizes,then distributes in the ferrite phases;When the heating temperature is quite higher,the organization has the recrystallization,then the crystal grows.According to the tension test and the impact test's results,when the the heat treatment temperature was 1000～1100℃,the mechanical properties of the 2205 duplex stainless steel are quite stable.After solution treatments from 900℃to 1200℃,the principal character of the fracture was the dimple,the specimen has the good resilience,the ballistic work is above 270J,the specimen is curving,but not broken,the microscopic fracture presents the elongated dimple,the snake-shaped glide characteristic or the ripple,the non-characteristic areas.(2) Afterσ-ageing treatment,when the aging temperature is high,σ-phase atδ/γphase boundary andδ-phase will nucleate,grow,and easily form massive texture.When temperature is low,σphase will form segregation at theδ/γphase boundary for nucleation,then grow in theδ-phase,andσ-phase will easily form lamellar structures;meanwhile,as the ageing time is longer,the quantity ofσ-phase will increase.Ageing at the temperature of 475℃and 600℃makes remarkable rise of the strength,but less decrease of the plasticity.The dimples are found on the fracture surface of specimens.Aging at 750℃makes rise of the strength,but leads the significant decrease of the impact properties,the facet exists on the fracture surface.(3) After ati-σtreatment,the samples are heated at 1200℃for a minute to make coarseδferrite refining.Through solution treatment at 1050℃for 1h,and ageing at 750℃for 38h,then 1200℃rapid heating anti-σtreatment for 2 minutes,the results of grain refining is best;the strength and plasticity is better;and mechanical properties the samples are perfect;the size,shape,and distribution of the dimple is uniform.