| At present,under the background of increasing global demand for power supply and reducing environmental pollution,ultra-supercritical coal-fired power generation is gradually becoming the main mode of power supply in China.Research shows that improving the energy conversion efficiency of thermal power units and reducing the emission of pollutants such as CO2and SO2,it is necessary to improve the operating parameters of the unit,which puts forward new requirements for the service performance of key components such as superheater and reheater tube heat-resistant materials for thermal power boilers.But at present,China mainly relies on foreign imports of such heat-resistant materials,the degree of localization is not high,limiting the pace of Chinese ultra-supercritical power generation technology.Therefore,the development of a new generation of heat-resistant materials and their manufacturing technology that can meet the requirements of Chinese units is of great practical significance for the development of China's industry.By Shanxi TISCO and the General Research Institute of Iron and Steel jointly developed a new generation of austenitic heat-resistant stainless steel C-HRA-5 still has good performance in harsh service environment,to meet the needs of actual applications.At present,C-HRA-5 heat-resistant steel is in the trial stage,in the material hot-rolled production process may be cracked,uneven deformation and other defects,for the material processing and forming process the best range of process parameters are not yet fully understood.Therefore,it is important to study the thermal deformation behavior and workability of C-HRA-5 heat-resistant steel and determine the optimal thermal processing process window for the mass production application of the material and product quality.In this paper,a Gleeble-3800 thermal simulation tester was used to perform a double-hit hot compression test on the new austenitic heat resistant stainless steel C-HRA-5.In the experiment,the stress-strain curves of C-HRA-5 heat-resistant steel under the conditions that the deformation temperature range is 900?1100?,the strain rate range is 0.01?1 s-1,and the interval time is 1 s,5 s,15 s,and 30 s,respectively,to explore the flow stress change regularity of C-HRA-5 heat-resistant steel under different deformation parameters;the softening mechanism and the change regularity during the channel interval were determined,meanwhile,the kinetic equations were established;the microstructure after deformation is observed,and the evolution of the microstructure under different deformation parameters is studied;the dynamic material model were used as theoretical guide to draw power dissipation,instability and hot processing maps of C-HRA-5 heat-resistant steel to determine the optimal hot processing range.The main research results are as follows:(1)The stress-strain curves of C-HRA-5 heat-resistant steel in double-hit hot compression show the typical feature that the flow stress gradually decreases as the deformation temperature increases and the strain rate decreases.This change is mainly the result of the difference in the mobility of atoms and dislocations under different deformation parameters.The stress-strain curves of C-HRA-5 heat-resistant steel deformed at high strain rates show wave-shaped characteristics,which is a reflection of the discontinuous dynamic recrystallization during the material deformation process.(2)The softening mechanism of C-HRA-5 heat-resistant steel during the channel period is metadynamic recrystallization.The metadynamic recrystallization fraction at different deformation parameters was calculated by the 0.2%offset method,and it was found that the metadynamic recrystallization fraction increased with the increase of deformation temperature,strain rate and interval time.Under the deformation parameters of this paper,the activation energy of C-HRA-5 heat-resistant steel is 311.775 KJ/mol,and its metadynamic recrystallization kinetic equation is(?)(3)The microstructure evolution of C-HRA-5 heat-resistant steel after deformation under different deformation parameters has a pattern:increasing deformation temperature and decreasing strain rate are conducive to the occurrence of dynamic recrystallization,and the appearance of necklace structure in the microstructure is a significant sign of dynamic recrystallization.(4)Based on the dynamic material model(DMM),the power dissipation and instability maps of C-HRA-5 heat-resistant steel were plotted for different strains and channel interval times,and then superimposed to obtain the hot processing maps.It is found that under different deformation parameters,the stable process parameter ranges in the hot working diagram of C-HRA-5 heat-resistant steel are similar.Within the research scope of this paper,and taking into account the actual production situation,the suitable process parameters range for C-HRA-5 heat-resistant steel is:the deformation temperature is 1000?1100°C,strain rate is 0.01?0.1 s-1,and channel interval time is15 s. |
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