Numerical Simulation Of Solidification Process Of Large Steel Ingot In ZYSCO

With upsizing of equipment forging in heavy industry, which needs large-scaleingots as well, the quality of large-scale ingots can directly affect performance offorging. However, the solidification of steel ingots is processed in ingot mold underhigh temperature, which makes difficulty to observe and control, the numericalsimulation has become an important research method. There still has many problemsthough the numerical simulation of ingot solidification process has made greatprogress. The main shortcomings include the accuracy of calculated results,determination of boundary conditions and generalization degree of model for practicalproblem.In this paper, the solidification of25t large-scale ingots of ZYSCO (ZhongyuanSpecial Steel Co.Ltd) is researched through3-D numerical simulation of temperatureof process. The study takes the simulation of temperature field in large-scale ingotssolidification process as initial target. Then the exact boundary conditions, thermalparameters and reasonable mathematical model are determined by combination withfield data analysis. By the calculation of temperature field in ingot pouring andsolidification process, the rule of ingots solidification is studied. The existing problemsin the process are evaluated along with simulation results and field conditions. Foringot defects, cap heat preservation conditions and pouring temperature are chosen tooptimize current production process through simulation method.The main findings are as follows:(1) By changing the temperature field of ingot solidification process, the timeconsumption from pour-completed ingots to fully solidification is about6.9h while thestripping time of actual production is8h. Stripping in advance will accelerate the pace of production based on the needs of production.(2) Under the cooling effect of the chassis in initial solidification process, thesolidification direction of ingots goes upward from the bottom of the ingots. Thesurface of ingots in radial direction is formed solidified shell firstly. As the weakeningof cooling effect of chassis in the middle and later periods of solidification, thesolidification rate slows in axial direction. While advancing in radial direction, the Vshape becomes long and narrow in the solidification front which is not conducive toliquid steel feeding and may produce shrinkage or porosity in the axis.(3) The porosity of the ingots on the axis is calculated with usage of Nyiamacriterion. The results show that the cap contracts towards more regular concave surfacewith feeding and solidification progresses. The shrink depth is about130mm. Theshrinkage cavity of approximately40mm is formed under the lower part of the concavesurface center. More serious porosity presents in the upper axis of the ingot.(4) Comparing the depth and angle of V-shaped liquid phase region in cap areaunder different pouring temperature, the results show that increasing of pouringtemperature will lead to the longer and narrower V-shaped liquid phase region in laterperiod of solidification and aggravate porosity of ingots axis. The possible axisporosity of ingots is predicted using Nyiama criterion. The results shows that with thedecrease of pouring temperature, the length of the porosity area on ingot axis graduallyreduced. Comparing the depth of concave surface in cap top area under differentpouring temperature. It is found that lower pouring temperature will help reduce theingot contraction in solidification process, provide favorable conditions for lower capcapacity and avoid primary shrinkage in ingots. Therefore, the pouring temperature canbe reduced further under the proper degree of superheat.(5) The solidification process of ingots is analyzed after improve the cap heatpreservation conditions and compared with the numerical simulation results of theoriginal process conditions. It is found that cap heat preservation get better as thermalconductivity decreases. The cap area can maintain liquid state at long time as the temperature of steel liquid drops slowly. The macroscopic shrinkage in the lower partof ingot in cap disappeared. The porosity of1%porosity distribute in small region. Theporosity in ingots axis still exists but reduces in certain extent. The solidification timeconsuming of the ingot without cap percentage of the whole solidification processreduces from80.4%to76.6%. The feeding time of ingots from cap liquid steelextends greatly which helps to improve density of ingots top and cap. The quality ofingots is improved as well.