| With the continuous breakthroughs in nuclear power technology and increasing production capacity,the production of nuclear pressure vessels requires increasingly high performance of nuclear power materials.Advanced SA508 Gr.4N steel for nuclear pressure vessels has gradually attracted the attention of researchers,which has better mechanical properties than SA508 Gr.3 steel,and is considered to be a candidate RPV steel for the next generation of nuclear reactors.Because the preparation of large forgings has the shortcomings of "long production cycle,easy to produce defects",so it is not appropriate to use the trial and error method to analyze and establish reasonable thermal processing parameters.Therefore,based on the single pass hot compression experiment data of SA508 Gr.4N steel,the paper uses DEFORM software to simulate the thermal deformation process of large forgings to provide scientific guidance for optimizing the production process of large nuclear power tube sheet forgings by analysis multi-physics simulation results.Main research work and conclusions are as follows:(1)Establishment of flow stress constitutive model and dynamic recrystallization model.The new generation of nuclear power candidate material SA508 Gr.4N steel was selected as the research object.By using the existing single-pass thermal compression flow stress data,a two-stage flow stress constitutive model was established,and correlation coefficients and average relative errors were introduced to measure the model.The stress value of flow stress curve in the range of 0?1.0 was predicted.The results show that the correlation coefficient and average relative error between the calculated value and the actual value are 0.9915 and5.06%,respectively.At the same time,the microstructure of the hot compression sample was characterized,and the dynamic recrystallization microstructure evolution model was established and input into the deform software to simulate the thermal compression process.It has been verified that through the thermal simulation compression experiment under various deformation conditions,the correlation coefficient R of the simulated value and measured value of the grain size is 0.9524.(2)Secondary development of flow stress subroutine.The Absoft Fortran compiler was adopted to further develop the DEFORM software,and the established two-stage flow stressconstitutive model was written into the USRMTR subroutine included in DEFORM to simulate the thermal deformation process of SA508 Gr.4N steel.(3)Non-uniform thermal compression experiment and its numerical simulation.The non-uniform thermal compression experiment of SA508 Gr.4N steel was conducted with a200-ton hydraulic press and a tube heating furnace.The average grain size of the designated area after deformation by metallographic experiment was measured.The non-uniform thermal compression experiment was simulated,and the experimental value of the average grain size at a specific location was compared with the simulated value.It is verified that the experimental value of the average grain size is basically the same as the simulated value.The average deviation is 16.78%,and the minimum and the maximum value of the deviation is7.28% and 25.62% respectively.(4)Numerical simulation of large nuclear power tube sheet forgings.Based on the forging process of large-scale nuclear power tube sheet forgings,with the DEFORM software after secondary development,the WHF method and flat hammer head rotation widening in the process plan was simulated,and reasonable parameters of the WHF method and flat hammer head rotation widening were obtained.And finally,the simulation of the whole production process of large nuclear power tube sheet forgings was presented,and the multi-physics state of the forgings under each fire and process was given to provide scientific guidance for actual production. |
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