.316 Ln Stainless Steel Recrystallization And Thermal Processing

316LN austenitic stainless steels, as the main channel materials of the3rd-generation nuclear power plants, have the good mechanical properties and resistance to intergranular corrosion. However, the deformation and temperature distribution of the large forgings is uneven in the forging process, and the forgings require longstanding heat preservation among different fire forging, which will occur dynamically recrystallization, the meta-dynamic recrystallization, static recrystallization and grain growth, resulting in grain structures and grain sizes of the different regions are different, thus the phenomenon of mixed grains and coarse grains can be observed. In this paper, the316LN stainless steels were processed the heat treatment, thermal simulation to study the processing parameters and heat treatment temperature effect on the recrystallized grain evolving regulars during the hot deformation of the large forgings, which plays a guiding role for the actual production.In this paper, the Gleeble thermal simulation compressive experiments, as well as the solution heat treatment experiments in different temperatures were carried out, the high temperature deformation behavior and the recrystallized microstructure evolving regulars in the solution treatment of the316LN stainless steel was studied, the hot deformation equation of the steel was established. According to the theory of dissipative structure, the processing map of the316LN stainless steel was established on the basis of the dynamic material model, and its characteristics of high temperature deformation were analyzed. The following main conclusions were acquired:(1)Through the metallographic observation, in the longstanding heat preservation case, the critical temperature of grain growth of the forging sample of the316LN stainless steel at a high temperature solution treatment for2h is1175℃.(2)After the Gleeble-1500D single channel axial compression immediately water quenching, and then solution heat treatment and observed metallography. The results show that, solution treatment in the1075℃, the critical deformation degree of the occurrence of static recrystallization is between5%and10%, at40%deformation degree the static recrystallization is basically completive. Under the conditions of30%deformation degree is and0.03/s strain rate, the dynamic recrystallization occurs only when the deformation temperature is higher than1000℃; under the conditions of the deformation temperature of1000℃and the deformation degree of30%, the dynamic recrystallization occurs when strain rate is lower than0.03/s; when solution treatment, the sample of occuring dynamic recrystallization would occur meta-dynamic recrystallization, the grain would grow rapidly, the size was larger than the static recrystallization grain size, which may lead to the phenomenon of mixed crystal. Deformed specimens would occur abnormal growth at1175℃solution temperature. The lower or the higher heating rate all would lead to recrystallization temperature increasing.(3) The samples were made the single channel axial compression experiments on the Gleeble-1500D by changing the deformation parameters, and immediately water quenched to retain the high temperature microstructure, and to acquire the flow curve and the diagram of microstructure. The results show that the316LN stainless steel flow curve is not particularly evident in the performance peak, but metallographic observation showed that the dynamic recrystallization had occurred. The flow stress and peak strain increased with the increase of the strain rate and the decrease of deformation temperature. By means of the analysis and calculation of the flow curve, the critical strain value (εc) of the dynamic recrystallization and the hot deformation activation energy (Q=478.6KJ/mol) of the316LN stainless steel would be known. Moreover, the thermal deformation constitutive equations was obtained:(4)According to the theory of hot working, the hot working maps of the316LN stainless steel were established by basing on the dynamic material model. The results show that:the strain variable has little effect on the distribution of the power dissipation map, the power dissipation values increase with the rise of deformation temperature and the drop of strain rate. At the high strain rate and the low strain temperature, Such as (800℃,10/s),(950℃,10/s) and (1000℃,1/s), the deformation concentration zone would appear, which may develop into the adiabatic shear band, and then caused the machining instability. When strain temperature was1050℃～1200℃and the strain rate was0.01/s～1/s, the dissipation efficiency could reach30%, peak efficiency of38%corresponded to the strain temperature of1200℃and the strain rate of1s-1, and the area is fully dynamic recrystallization.