Study On The Hot Deformation Behavior Of 304 Stainless Steel And The Application In Complicated Forging Part

304 austenite stainless steel owns strong corrosion resistance and beautiful appearance,which make it widely used in automobile industry.Combined with the advantages of forging process that could keep the metal flow line and the compact structure,the forging parts of 304 stainless steel have excellent mechanical properties and nice appearance.Based on the defects of surface coarse grain and?-ferrite that exist in 304 stainless steel forging part,the hot deformation behavior and the evolution of grain size and?-ferrite phase of the material under different forming conditions was studied.According to the research achievement,the forging process of common rail was designed,besides,the influence of different process parameters was analyzed by the finite element(FE)simulation,which could be used to improve the forging process.The main conclusions are shown as follows:1)Thermal simulation experiments of 304 stainless steel at the temperature range of 800 ^oC?1200 ^oC and strain rate range of 0.1 s^-1?10 s^-1were carried out.The Arrhenius and Hensel-Spittel equation of 304 stainless steel were modeled and the comparison of the error between predicted value and testing value of these two equations were conducted,the results show the Hensel-Spittel equation can give a more accurate prediction to the whole deformation process and a smaller error can be achieved.According to the processing map and microstructure analysis,the power dissipation coefficient is larger at higher deformation temperature and smaller strain rate,where the plastic deformation is stable as well.As the decrease of temperature and the increase of strain rate,power dissipation coefficient becomes smaller,and deformation instability may occur.The best forming range of temperature and strain is 1070 ^oC?1170 ^oC and 0.1 s^-1?1 s^-1.2)The main factors that result in the surface coarse grain of 304stainless steel part are heating rate and temperature.Recrystallization happened as the soaking and forming temperature increased to 1150 ^oC,at which temperature the grain size increased rapidly as the increase of soaking time and deformation temperature.There is no coarse grain when the heating rate is 20s for each billet and the temperature is 1100 ^oC.Plastic deformation would fine the grain,and the grain size became smaller as the increase of strain rate.The increase of strain rate and deformation temperature will increase the storage energy of microstructure and then shorten the incubation period for recrystallization.3)The microstructure of deformed material consists of austenite phase and?-ferrite phase.The amount of?-ferrite phase increased first and then decreased as the increase of heating temperature,it also increases uniformly to 8%and then stops as the increase of soaking time.The microstructure contains largest proportion of?-ferrite during the strain rate range of 0.16 s^-1?2.5 s^-1,and the peak values exist at the temperature of 975 ^oC and 1115 ^oC.Less than 5%?-ferrite was found in the microstructure at the deformation temperature range of 800 ^oC?900 ^oC and strain rate range of 4 s^-1?10 s^-1.4)According to the material behavior and the FE simulation results,the design and modification of the forging process of common rail was conducted,which reduced the forming force and improved the material utilization.