Simulation Study On Hot Working Process Of 2.25Cr1Mo Large Forgings

With the increasingly prominent problems of environmental pollution and energy depletion,nuclear energy,considered both clean and efficient,which meets the requirements of green development in the current era,has gradually attracted people's attention.Known as the "nuclear lung",steam generator is one of the most critical component of the nuclear power plant,in which plays a vital role,since the steam generator needs to serve in an environment of high temperature,high pressure and liquid sodium for a long time,higher requirements have been proposed towards the generator steel.As one of the typical representatives of large forgings,steam generators impose higher restrictions on forging and heat treatment processes.In a background of the research and development of steam generator experiment,the research was based on the processing of 2.25Cr1 Mo steel(SA-336 F22)large forgings for fast reactor steam generator,the actual forging and heat treatment process of large forgings is simulated based on Simufact-forming finite element software.And the conclusions are listed below.According to the finite element simulation,the finite element models of 2.25Cr1 Mo steel were constructed,including physical metallurgy model and microstructure phase transformation model.The mathematical model of constitutive equation,critical strain and dynamic recrystallization fraction were also established,which provides a solid foundation for the subsequent large forging simulation.Based on the Simufact-forming forging process module,the influence of the blanking process on the grain size was investigated,and the particle position of the blank was tracked.It was found that the two-two extraction process is more conducive to the grain refinement than the one-and-one extraction process.The steam generator forging process was simulated by pre-bending and forging,and the influence of different temperatures,different reductions and different reduction rates on the grain size of large forgings was investigated.According to the simulation results,under the condition of high temperature(1250?),large strain rate(400 mm/s),large reduction(1220 mm),the 2.25Cr1 Mo steel steam generator large forgings are more conducive to core grain refinement,which improves the performance of large forgings.Under the heat treatment process,microstructure patterns of large forgings under different cooling media were simulated.According to the results,the large forgings are limited by size and hardenability,and it is difficult to to lower temperature in an area away from the "nozzle" and one-half the thickness from the bottom wall.The area is less affected by the cooling medium.For large forgings of steam generators,it is difficult to obtain bainite-based structures under water-cooling process.In actual production,cooling efficiency should be improved to ensure uniformity of the structure.According to the Larsen-Miller formula,the post-weld heat treatment time can be adjusted from 16 h to 21.5h~26h to meet the design requirements.The simulation results are consistent with the actual test results,and the simulation results are true and reliable.