Austenite Nucleation And Growth Behavior Of 2205 Duplex Stainless Steel Under Rapid Heat Treatment

Through preliminary experiments,it is found that the austenite with fine morphology which appeared in the welding thermal simulation experiment of 2205 duplex stainless steel can also be obtained by rapid heat treatment.And the effect of rapid heat treatment on the microstructure of 2205 duplex stainless steel was significant,it's peak temperature,temperature of dual phase zone,cooling rate and the holding time all had obvious effects on the morphology of austenite.Similarly,the morphology of the final austenite directly affects the properties and application of duplex stainless steel.Therefore,it has important theoretical significance and practical application value to study the effect of nucleation and growth behavior of austenite on the final austenite morphology under rapid heat treatment of 2205 duplex stainless steel.In this paper,the effect of rapid heat treatment process parameters on austenite morphology of 2205 duplex stainless steel was studied by means of rapid heat treatment.The nucleation and growth behaviors of acicular austenite and equiaxed austenite were compared and analyzed.At the same time,from the point of thermodynamic calculation,the influence of transformation temperature and alloying element concentration on the morphology of austenite was analyzed in detail.The main findings are as follows:1.The results of EBSD analysis show that the orientation distribution of austenite is concentrated,and the orientation angle of equiaxed morphology of austenite is in the range of 44°?45°.At 25°?26°and 60°,the distribution of orientation angle of austenite also shows a certain intensity peak.In acicular austenite,the orientation angle is between 44°and 45°.2.Combined with TEM observation results,the orientation relationship of adjacent acicular austenite was analyzed and the mechanism of induced nucleation of adjacent austenite was determined.The orientation relationship between austenite and parent ferrite and the similar orientation relationship between austenite and adjacent austenite determine that the length of acicular austenite is at an angle of about 60°in two directions.3.During the austenite growth process,austenitic forming elements diffuse from ferrite to austenite,and ferrite formation elements diffuse from austenite to ferrite.Both equiaxed austenite and acicular austenite have enrichment of carbon elements and alloying elements at the interface with ferrite.The difference is that the concentration of carbon at the interface of acicular austenite is higher than that at the interface of equiaxed austenite.Therefore,it once again transitioned to PLE growth model.4.Combined with KRC thermodynamic model,some parameters were modified to calculate the driving force of austenitic transformation in this experiment.The driving force of phase transition decreases with the increase of the holding temperature in the two-phase region,and decreases with the increase of carbon concentration at the ?/? phase boundary,and the resistance of phase transition gradually changes from interfacial energy to strain energy.5.Combined with the microstructure morphology of the sample and the results of electron probe analysis,the KRC model is verified.The results show that the temperature of the two-phase region varies from low to high to 850?,900?,950?,respectively.The driving force of austenite transformation decreases with the increase of temperature,and the morphology of austenite changes from equiaxed to acicular.