The Effect Of Thermo-mechanical Treatment On Microstructure In 2205 Duplex Stainless Steel

Austenitic-ferritic duplex stainless steels have both austenite(γ) phase and ferrite(α) phase,in which the two-phase microstructure possessed higher toughness and good weldability of austenitic stainless steels and higher strength and high resistance to stress corrosion cracking of ferritic stainless steels,and therefore duplex stainless steels took on the combined advantages of austenitic stainless steels and ferritic stainless steels.Austenitic-ferritic duplex stainless steels presented an attractive combination of good mechanical properties and localized corrosion resistance and were successfully used in such industries as oil refining,petrochemistry and chemical,paper pulp and paper making and many other fields.In order to investigate volume fraction,configuration and grain size in austenitic phase and ferritic phase of austenitic-ferritic duplex stainless steels,it was required that etching samples to information of correlative microstructure.The chemical etchants used at room temperature,hot chemical etching agent and electrolytic etching solution were utilized to reveal the microstructure,the experimental results showed that,different chemical etchants revealed different the microstructure in the same material;hot chemical etching agent was able to present a striking contrast between ferrite phase and austenitic phase;while electrolytic etching in acid solution was able to relatively integrally reveal grain boundaries of ferrite phase and austenitic phase.To the refinement method of thermo-mechanical treatment in this paper,it was analyzed that the effect of re-crystallization annealing,different thickness reduction and pre-heat treatment on grain size,phase proportion and microstructure hardness. The microstructure and hardness of a thickness reduction of 40%by cold deformation of 2205 duplex stainless steel after different re-crystallization annealing and soaked time was studied,the result showed that,on the condition that the annealing temperature was 900℃and the time of constant temperature was 1 hour,theσphase was precipitated in the sample.With the time of constant temperature continued,the amount of o phase precipitation increased.When the annealing temperature was 950℃or higher,there wereαandγphases in the sample.With the annealing temperature increased,the proportion of the ferrite phase in sample increased.At the same time, there was a small amount of austenite annealing twins.Under conditions of a certain annealing temperature and holding time,the grain size grew smaller and smaller.So, the relationship was complex,that was the different re-crystallization annealing temperature,holding time and the grain size,micro-hardness of the sample.When the re-crystallization annealing temperature and holding time were a certain value,the effect of 20%,40%,60%,80%deformations on the grain size was studied, the results showed that with the increasing of deformation,the micro-harness of samples was improved.When the re-crystallization temperature was 1100℃;the holding time for 1h;the deflection of more than 40%,the phenomenon of re-crystallization appeared;and that the greater deformation,the smaller grain size.First the preheating treatment's temperature was 1300℃and the cold deformation and annealing treatment were carried on.After preheating treatment,it was found that the shape branch of austenite organization was precipitated on the matrix of ferrite, that the transformative compound twin appeared in the austenite organization by the different amount of cold deformation.By the cold deformation,re-crystallization was treated on the sample,which is 1100℃,which holding time of annealing is 1 hour. when the deflection was beyond 40 percent,the re-crystallization was appeared again. It was also found that the greater deformation,the smaller grain size after re-crystallization.