Study On Multi-layer Cladding Progressive Solidification Path Of Large Ingot

As the core components of major equipment,the high-quality production of large forgings is one of the signs to measure the level of the country’s manufacturing industry.At present,the development trend of large forgings is large-scaled and integrated,and the required ingot size and tonnage are getting larger and larger.However,problems such as uneven structure,macrosegregation,and shrinkage/porosity during the production and manufacture of large ingots have seriously affected the high-level development of large forgings.For this reason,this paper draws on the idea of layered casting forming technology,and conducts layer-by-layer cladding and layer-by-layer solidification research on large steel ingots.Through the combination of numerical simulation and thermal experiment,the change law of the heat transfer coefficient from ingot to ingot mold interface was obtained,and the changes of the temperature field and solidification field of the clad ingot under different ingot core preheating temperatures and molten steel casting temperatures were simulated.According to the law,the cladding paths of metallurgical bonding of ingot cores with different diameters under different conditions are determined.The thermal scaling experiments were carried out on the cladding path under the condition that the diameter of the ingot core was 100mm,the molten steel casting temperature was 1560℃,and the ingot core was not preheated.The following research results were obtained:(1)The relationship between the interface heat transfer coefficient and time between the ingot and the ingot mold conforms to the change law of the exponential function,and has a linear relationship with the diameter of the steel ingot.After W/(m~2·℃),it basically does not change with the increase of heat transfer time.(2)When the molten steel casting temperature is 1560℃ and the ingot core is not preheated,the thickness of the coating layer and the liquid-solid ratio increase with the increment of the diameter of the ingot core,and the solid-liquid coexistence area on the surface of the ingot core becomes wider.The melting rate decreases accordingly;when the casting temperature is 1560℃,the liquid-solid ratio of the ingot core preheating temperature of 400℃ is reduced by 2.0 on average compared with the liquid-solid ratio without preheating,and when the preheating temperature is 800℃,the liquid-solid ratio is lower than that when the preheating temperature is 400℃.The average decrease is 2.5,and the higher the preheating temperature of the ingot core is,the higher the melting rate of the surface of the ingot core becomes.When the diameter of the ingot core is below 200 mm without preheating,and the casting temperature is 1590℃and 1560℃,the simulation results are not much different.The liquid-solid ratio and the thickness of the coating layer remain unchanged.When the diameter of the ingot core is above 250 mm,with the increment of the casting temperature,the liquid-solid ratio and the thickness of the coating layer decrease significantly with the growth rate of the ingot core diameter.(3)The experimental results of thermal scaling verify the accuracy of realizing the interface metallurgical bonding cladding path.Under the preset cladding path,the interface between the ingot core and the cladding layer is in good condition.The microstructure at the interface is mainly martensite and ferrite.There is no obvious composition segregation on both sides of the interface,and the interface hardness is between that of the ingot core and the coating.