Due to the nature of the solute redistribution,the reduction in the solidification rate with time in a square root relationship,and the multiphase melt flow during the solidification,casting defects such as macrosegre...Due to the nature of the solute redistribution,the reduction in the solidification rate with time in a square root relationship,and the multiphase melt flow during the solidification,casting defects such as macrosegregation,shrinkage cavity,and porosity will inevitably occur in the steel ingot and intensify with the increase in ingot size.These defects directly affect the performance of the final product and severely restrict the choice of subsequent thermal processing methods and process windows.Therefore,the solidification defects including macrosegregation,shrinkage/porosity,and inclusions encountered in the preparation of large steel ingots and their formation mechanisms were reviewed.The development progress and the latest development of the macrosegregation model for steel ingots were introduced in detail,especially the latest progress in the coupling prediction of macrosegregation and shrinkage as well as macrosegregation and inclusions.Some methods to reduce macrosegregation of ingots were discussed as well.Finally,a new casting method called layered casting was introduced in detail.This method can effectively improve the uniformity of the macrostructure and reduce the macrosegregation of the large ingots and therefore is a promising method for preparing large ingots with high homogeneity.展开更多
Flywheel shells with a complex structure and large wall-thickness difference,as key components in heavy trucks,serve to connect the engine and transmission.Formability and mechanical performance control of such compon...Flywheel shells with a complex structure and large wall-thickness difference,as key components in heavy trucks,serve to connect the engine and transmission.Formability and mechanical performance control of such components should be taken into consideration.In this work,an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting.The role of local loading on microstructure and mechanical property at thick-walled positions was investigated.Furthermore,the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed.The results showed that at the thickwalled positions,local loading not only helped eliminate the solidification defects,but also refined the microstructure includingα-Al grains and secondary dendrite arm spacing.With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa,microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained.After T6 heat treatment,the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa,respectively,owing to the formation of spherical eutectic Si phases and nano-sizedβ’’,Q and S precipitates.展开更多
Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and ...Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and 20 h)in different casting zones(casting center and transition zone)on the microstructure and mechanical properties of non-standard heavy-section ferritic ductile iron(EN-GJS-400-15)castings.The different solidification conditions significantly influenced the microstructure(graphite and ferrous matrix).The extent of phenomena such as degenerate graphite,solidification defects,hard carbides,and intergranular pearlitic areas and the microstructural coarsening were proportional to the solidification time and attributable to the combined effect of limited undercooling,solid solution diffusion mechanisms,and segregation phenomena.For comparable solidification time,the transition zone was characterized by larger nodules,comparable nodularity,and lower nodule count than the casting center due to more effective diffusion phenomena during cooling.Moreover,the lower segregation phenomena in the transition zone reduced the amount of pearlite and carbides in the intercellular zones.Hardness was only slightly influenced by the different solidification conditions and did not represent a reliable indicator of the microstructural inhomogeneities.These results are essential to refine casting simulations for producing large ferritic ductile iron castings,considering the wide microstructural variability within non-standard heavy-section castings caused by significantly different solidification conditions.展开更多
基金This work is sponsored by the National Natural Science Foundation of China(Grant No.52074182)Natural Science Foundation of Shanghai(Grant No.22ZR1430700).
文摘Due to the nature of the solute redistribution,the reduction in the solidification rate with time in a square root relationship,and the multiphase melt flow during the solidification,casting defects such as macrosegregation,shrinkage cavity,and porosity will inevitably occur in the steel ingot and intensify with the increase in ingot size.These defects directly affect the performance of the final product and severely restrict the choice of subsequent thermal processing methods and process windows.Therefore,the solidification defects including macrosegregation,shrinkage/porosity,and inclusions encountered in the preparation of large steel ingots and their formation mechanisms were reviewed.The development progress and the latest development of the macrosegregation model for steel ingots were introduced in detail,especially the latest progress in the coupling prediction of macrosegregation and shrinkage as well as macrosegregation and inclusions.Some methods to reduce macrosegregation of ingots were discussed as well.Finally,a new casting method called layered casting was introduced in detail.This method can effectively improve the uniformity of the macrostructure and reduce the macrosegregation of the large ingots and therefore is a promising method for preparing large ingots with high homogeneity.
基金supported by the National Key Re-search and Development Program of China(No.2022YFE0137900)National Natural Science Foundation of China(Nos.U2341253,U2241232,52371019 and 52301034)+2 种基金Natural Science Foundation of Liaoning Province(No.2023-BS-170)Dalian High-level Talents Innovation Support Program(No.2021RD06)Applied Basic Research Program of Liaoning Province(No.2022JH2/101300003).
文摘Flywheel shells with a complex structure and large wall-thickness difference,as key components in heavy trucks,serve to connect the engine and transmission.Formability and mechanical performance control of such components should be taken into consideration.In this work,an Al–Si–Fe–Mn–Mg–Cu alloy was used to manufacture the flywheel shell via squeeze casting.The role of local loading on microstructure and mechanical property at thick-walled positions was investigated.Furthermore,the effect of the squeeze casting specific pressure and heat treatment on the microstructure and mechanical property of the Al–Si–Fe–Mn–Mg–Cu alloy flywheel shells was also analyzed.The results showed that at the thickwalled positions,local loading not only helped eliminate the solidification defects,but also refined the microstructure includingα-Al grains and secondary dendrite arm spacing.With increasing the squeeze casting specific pressure from 24 MPa to 32 MPa,microstructure refinement and mechanical property enhancement of squeeze casting flywheel shells were obtained.After T6 heat treatment,the yield strength and ultimate tensile strength of flywheel shells were further increased to 261.8 and 318.4 MPa,respectively,owing to the formation of spherical eutectic Si phases and nano-sizedβ’’,Q and S precipitates.
文摘Ductile iron represents an optimal solution for saving material and costs in producing large heavy-section castings in the energy sector.It aimed to investigate the influence of very long solidification time(3,10 and 20 h)in different casting zones(casting center and transition zone)on the microstructure and mechanical properties of non-standard heavy-section ferritic ductile iron(EN-GJS-400-15)castings.The different solidification conditions significantly influenced the microstructure(graphite and ferrous matrix).The extent of phenomena such as degenerate graphite,solidification defects,hard carbides,and intergranular pearlitic areas and the microstructural coarsening were proportional to the solidification time and attributable to the combined effect of limited undercooling,solid solution diffusion mechanisms,and segregation phenomena.For comparable solidification time,the transition zone was characterized by larger nodules,comparable nodularity,and lower nodule count than the casting center due to more effective diffusion phenomena during cooling.Moreover,the lower segregation phenomena in the transition zone reduced the amount of pearlite and carbides in the intercellular zones.Hardness was only slightly influenced by the different solidification conditions and did not represent a reliable indicator of the microstructural inhomogeneities.These results are essential to refine casting simulations for producing large ferritic ductile iron castings,considering the wide microstructural variability within non-standard heavy-section castings caused by significantly different solidification conditions.
