Technological Development Of Multi Core Compound Casting Large Ingot

A multi-core composite casting process is proposed and simulated using Na2SO3 ?5H2O as melt to solve the problem of segregation,porosity and shrinkage in the traditional ingot.On the one hand,the solidification percentage of sodium thiosulfate melt was determined and the effect of core number on solidification was discussed in this paper.On the other hand,the two-core and four-core composite ingot were cast in the protective atmosphere,and the temperature change value of the core in the mold was measured during the casting process.The temperature change curve and the macro section of the ingot were discussed.After the optimized process,the five-core composite ingot was cast,and then the five-core composite ingot was cut and sampled.The macroscopic cross sections of the ingots were compared and analyzed.At the same time,the composite interface and the microstructure of the ingots were compared and analyzed.The sodium thiosulfate simulated experimental results show that the preset cores in the mould can improve the nucleation on the surface of cores,increase the dendrite rain in melt,raise the proportion of fine equiaxed grains and decrease greatly the solidification time of the melt.With an increase of core number,the dendrite rain rises significantly,solidification rate is faster and the solidification structure is finer and more compact.The actual casting experimental results show that the defects such as shrinkage cavity and looseness inevitably exist in the coreless ingot because the molten steel gradually cools only from the outside to the inside and the molten steel in the ingot core is slow to be cooled and the shrinkage is not good.What's more,the internal microstructure is coarse.Because of the large amount of heat absorbed by the steel mold in the double-core and four-core billet composite ingot,the shrinkage of the composite ingot during solidification is not good and the pores and shrinkage cavities are generated.At the same time,the crack is localized at the interface.Due to the large cooling rate,large undercooling and high nucleation rate,the solidified microstructure at the interface near the surface of the core blank is extremely small.The farther the solidified microstructure is from the surface of the core blank,the coarser the solidified structure.The five core composite ingot is casted by brick mould,which ensures the better feeding condition of molten steel solidification,and provides enough heat for the combination of core and molten steel,so the interface of five core billet is better.On the one hand,the five-core billets allow the melt inside and outside to be cooled at the same time,reducing the solidification distance and the temperature difference of the molten steel,increasing the cooling rate and the nucleation rate of the melt,increasing the steel liquid undercooling,uniforming liquid steel temperature field.Finally,the solidification structure is refined;On the other hand,the geometric space occupied by the intermediate core in the five-core billet composite ingot completely replaces the shrinkage cavity and the loose geometric space in the coreless billet,so the composite ingot avoids the Shrinkage,loose and other defects.It is shown that the simulation results are consistent with the actual test results.And the process of multi-core composite casting large steel ingot can solve the quality problems such as segregation,loose and shrinkage in the traditional cast ingot.