Simulation Study On Melt Solidification With Bottom Argon Blowing During Ingot Casting

In this pepper,methods of physical simulation and mathematical simulation were used to study the effects of bottom Ar blowing during casting and solidification of liquid steel in an ingot mold on the bubble diameter,bubble motion,nucleation and growth behavior of NH4Cl crystal grains,and the change of temperature field under different conditions with NH4ClH2O solution simulating molten steel and air the argon gas.It was found that the average diameter of the bubbles is the largest when the bottom gas flow rate is q=166 ml/min,being 0.559mm?0.570mm,while that is the smallest when the bottom gas flow rate is q=76 ml/min,being 0.516mm?0.521mm.It was found that the primary crystal spacing and the secondary crystal spacing of the dendrites is larger without bottom gas blowing,and the average values of the primary crystal spacing and the secondary crystal spacing are 1.037 mm and 0.188 mm,respectively.The dendritic structure is not compact,and some porosity can be observed.With bottom gas blowing at gas flow rate from q=76ml/min to q=166ml/min,the primary and secondary crystal spaces tend to decrease gradually.Under experimental cooling conditions at L=60mm porous plug center distance and q=166 ml/min bottom air blowing flow rate,the primary crystal spacing and the secondary crystal spacing are the smallest,0.555mm and 0.136mm,respectively.It was shown that the bottom gas blowing can effectively improve the structure of dendrites,and as the gas flow rate increases,the structure of dendrites will be denser and denser,and the porosity between dendrites will also be weakened.When the bottom gas blowing is not performed,the columnar crystals are more developed,and the proportion of equiaxed crystals is small,being only 18.11%.Under the condition of bottom blowing with t=15 min blowing time,the proportion of the equiaxed crystal increases with the increase of the bottom blowing flow rate.When the bottom blowing flow rate reaches q=166 ml/min,the equiaxed crystal ratio reaches 37.80%.When the blowing flow rate is q=76ml/min,the proportion of equiaxed crystals increases with the increase of the blowing time.When the bottom gas blowing time is t=25min,the proportion of equiaxed crystals reaches 40.16%.The thickness of the solidified layer may change due to different gas blowing conditions.Appropriate increase of the porous plug center distance and the bottom blowing flow rate can effectively improve the thickness unevenness of the upper and the lower of the solidified layer.When the bottom blowing is not perfnrmed,the difference between the solidified layer thickness at height H=50 mm and H=300 mm is 4.1mm.When the bottom air blowing flow rate is q=76 ml/min and the blowing time is t=25 min,the difference between the solidified layer thickness at height H=50 mm and H=300 mm is only 1.5mm.When the bottom blowing flow rate is q=166 ml/min and the blowing time is t=15min,the difference between the solidified layer thickness at height H=50 mm and H=300 mm is only 1.4mm.In the mathematical simulation,a low velocity region in the flow field appears at the bottom corner region of the ingot mold model without bottom gas blowing.With the bottom gas blowing,due to the agitation of bubbles to the molten steel,the flow velocity of the flow field increases as the bottom blowing increases.As a result,such low flow velocity region of the flow field at the bottom corner region is reduced or even eliminated.By comparing the mathematical simulation with the physical simulation,the temperature curves of different positions in the ingot model are agreed to each other.In the mathematical simulation of bubble motion,it was found that the attraction of the liquid rising stream to the small bubble causes the bubble column to exhibit a tendency to shift or bend in the case of bottom gas blowing,and there is a phenomenon of dispersion of fine bubbles near liquid surface because the control ability of the rising liquid stream to the these bubbles becomes weak,As the flow rate of the bottom gas blowing increases,the floating velocity of the large bubbles is higher,and the degree of bending of the bubble column is lowered.The temperature field change in the ingot mold model is shown in the form of temperature contours.Without bottom gas blowing,the isotherm is "U" type when the solidification time reaches 995 s,and with the solidification time the bottom of the "U" type isotherm moves from bottom to top,and the sides of the "U"type isotherm move from the outside to the inside.When the bottom blowing is performed,the obvious temperature drop occurs in the bottom and surrounding areas of the model at 1995 s solidification time.As the solidification time advances,the temperature drop becomes more and more obvious,and the bottom of the "U" isotherm is wider and its movement is slower than those without bottom gas blowing,which indicates that the temperature gradient inside the mold with bottom gas blowing is smaller than that without bottom gas blowing.