The Numerical Simulation Of Macrosegregation And Stress Field During Solidification Of Super Large Steel Ingot

With the rapid development of nuclear power and shipbuilding industry in recentyears, the requirement to the production of heavy forgings is increasing and to theperformance of heavy forgings is more and more high. And, the heavy forgings aremade of large ingots directly in industrial production, so the quality of large ingotsdetermines the quality of heavy forgings. Macrosegregation, crack and deformation arethe common defects in the large ingots, and these defects will seriously downgrade theperformance and service life of the ingots，and it is difficult to be diminished eventhrough the subsequent processes, such as forging, heat treatment and so on. Hence,these defects must be predicted and alleviated the defects during the castingsolidification process to get large ingots with high quality, and lay the foundation forproducing high quality forging for nuclear power and shipbuilding industry.In this paper, the600T super large ingot used by China First Heavy Industry istaken as research subject. And, the temperature field and stress field of the super largeingot during the solidification process are simulated and analyzed by casting processsimulation software ProCAST. Then, the temperature field data is taken as knownconditions and a prediction algorithm of macrosegregation and negative segregationdeposit cone programmed by C++is presented, based on the formation theory ofmacrosegregation and negative segregation deposit cone. The macrosegregation andnegative segregation deposit cone formed in the solidification process of the super largeingot are simulated and calculated using the prediction algorithm. At last, according tothe calculation results of the temperature field and stress field, the effects of the size andshape of the ingot moulds on the temperature field and stress field are studied, and thestudy provides a theoretical basis for the optimal design of ingot moulds. The maincontent and research results of this thesis are as follows.①The calculation of temperature field during the solidification process of thesuper large ingot. The600T super large ingot is taken as research subject, and themathematical model of the temperature field during the solidification process is createdand the temperature field during the solidification process is simulated and calculated.The result is, the complete solidifying time of the600T super large ingot is140.14h, andthe solidification rate in initial solidification is greater than that of in the latersolidification. ②The simulation of macrosegregation and negative segregation deposit cone. Aprediction algorithm of macrosegregation and negative segregation deposit coneprogrammed by C++is presented, based on the formation theory of macrosegregationand negative segregation deposit cone. The macrosegregation and negative segregationdeposit cone formed in the solidification process of the super large ingot are simulatedand calculated using the prediction algorithm. The result is, the obviousmacrosegregation can be found in the simulated ingot and there is a negativesegregation deposit cone in the bottom of the ingot, it is proved that themacrosegregation and negative segregation deposit cone can be predicted by thisalgorithm.③The calculation of stress field during the solidification process of the super largeingot. Based on the calculation of temperature field, the stress field during thesolidification process of the super large ingot is calculated and simulated. The result is,there is tensile stress on the exterior of the ingot and press stress on the interior of theingot in the initial stage of solidification. And, with the solidification going on, thestress in the ingot is changing, the press stress acts on the exterior of the ingot and thetensile stress acts on the interior of the ingot. The crack is most likely to appear on theexterior of the ingot.④The design improvements to the super large ingot moulds. Based on thecalculation to the macrosegregation and stress field, the effects of structure parametersof the super large ingot moulds on the results of macrosegregation and stress field arestudied. The result is the solidification time and macrosegregation during solidificationis reduced with the increase of height-to-diameter, the height of the negative segregationdeposit cone decreased from2300mm to1200mm with the increase ofheight-to-diameter，the stress is minimum value when the height-to-diameter value is1.15, and the effect of taper on the solidification time and macrosegregation is notobvious, the stress is minimum value when the taper value is1.15. And, the optimumvalue of the height-to-diameter ratio and taper of ingot mold is1.30and4.25%, basedon the simulation results of stress field and macrosegregation.