The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and ...The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and carbide morphology. With increasing melt superheating temperature (below 2023 K),the grain size increases obviously and the carbide morphology is changed from a blocky to a script-like shape. However,when the melt superheating temperature is between 2023 K and 2123 K,the grain size decreases gradually,and the morphology of the MC carbide changes back to the blocky appearance. The content of W is also influenced by melt superheating treatment.展开更多
Melt-spun Nd7Fe90B3 ribbons were prepared under different melt treatment conditions,i.e.,the melt temperature was varied prior to ejection onto the quenching wheel.The microstructure characteristics,crystallization be...Melt-spun Nd7Fe90B3 ribbons were prepared under different melt treatment conditions,i.e.,the melt temperature was varied prior to ejection onto the quenching wheel.The microstructure characteristics,crystallization behavior,and subsequent magnetic properties of α-Fe/Nd2Fe14B-based exchange-spring magnets were investigated using X-ray diffraction,differential scanning calorimeter,transmission electron microscopy,and vibrating sample magnetometer.It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior.Under high quenching temperature,precipitation of TbCu7 type phase was inhibited during crystallization,resulting in remarkable reduction of grain size.This led to strengthening of exchange coupling effect between the magnetically hard and soft phase and improvement of magnetic properties of annealed ribbons.展开更多
The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide ir...The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide iron foundry industry.High power,medium frequency coreless induction furnaces are commonly used in electric melting grey iron foundries.This has resulted in low sulphur(<0.05wt.%)and aluminium(<0.005wt.%)contents in the iron,with a potential for higher superheating(>1,500°C),contributing to unfavourable conditions for graphite nucleation.Thin wall castings are increasingly produced by these electric melt shops with a risk of greater eutectic undercooling during solidification.The paper focused on two groups of grey cast irons and their specific problems:carbides and graphite morphology control in lower carbon equivalent high strength irons(CE=3.4%-3.8%),and austenite dendrite promotion in eutectic and slightly hypereutectic irons(CE=4.1%-4.5%),in order to increase their strength characteristics.There are 3 stages and 3 steps involving graphite formation,iron chemistry and iron processing that appear to be important.The concept in the present paper sustains a threestage model for nucleating flake graphite[(Mn,X)S type nuclei].There are three important groups of elements(deoxidizer,Mn/S,and inoculant)and three technological stages in electric melting of iron(superheat,pre-conditioning of base iron,final inoculation).Attention is drawn to a control factor(%Mn)x(%S)ensuring it equals to 0.03–0.06,accompanied by 0.005wt.%–0.010wt.%Al and/or Zr content in inoculated irons.It was found that iron powder addition promotes austenite dendrite formation in eutectic and slightly eutectic,acting as reinforcement for the eutectic cells.But,there is an accompanying possible negative influence on the characteristics of the(Mn,X)S type graphite nuclei(change the morphology of nuclei from polygonal compact to irregular polygonal,and therefore promote chill tendency in treated irons).A double addition(iron powder+inoculant)appears to be an effective treatment to benefit both austenite and graphite nucleation,with positive effects on the final structure and chill tendency.展开更多
文摘The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and carbide morphology. With increasing melt superheating temperature (below 2023 K),the grain size increases obviously and the carbide morphology is changed from a blocky to a script-like shape. However,when the melt superheating temperature is between 2023 K and 2123 K,the grain size decreases gradually,and the morphology of the MC carbide changes back to the blocky appearance. The content of W is also influenced by melt superheating treatment.
基金supported by the Science and Technology Foundation of Shenzhen,China (200605)
文摘Melt-spun Nd7Fe90B3 ribbons were prepared under different melt treatment conditions,i.e.,the melt temperature was varied prior to ejection onto the quenching wheel.The microstructure characteristics,crystallization behavior,and subsequent magnetic properties of α-Fe/Nd2Fe14B-based exchange-spring magnets were investigated using X-ray diffraction,differential scanning calorimeter,transmission electron microscopy,and vibrating sample magnetometer.It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior.Under high quenching temperature,precipitation of TbCu7 type phase was inhibited during crystallization,resulting in remarkable reduction of grain size.This led to strengthening of exchange coupling effect between the magnetically hard and soft phase and improvement of magnetic properties of annealed ribbons.
文摘The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide iron foundry industry.High power,medium frequency coreless induction furnaces are commonly used in electric melting grey iron foundries.This has resulted in low sulphur(<0.05wt.%)and aluminium(<0.005wt.%)contents in the iron,with a potential for higher superheating(>1,500°C),contributing to unfavourable conditions for graphite nucleation.Thin wall castings are increasingly produced by these electric melt shops with a risk of greater eutectic undercooling during solidification.The paper focused on two groups of grey cast irons and their specific problems:carbides and graphite morphology control in lower carbon equivalent high strength irons(CE=3.4%-3.8%),and austenite dendrite promotion in eutectic and slightly hypereutectic irons(CE=4.1%-4.5%),in order to increase their strength characteristics.There are 3 stages and 3 steps involving graphite formation,iron chemistry and iron processing that appear to be important.The concept in the present paper sustains a threestage model for nucleating flake graphite[(Mn,X)S type nuclei].There are three important groups of elements(deoxidizer,Mn/S,and inoculant)and three technological stages in electric melting of iron(superheat,pre-conditioning of base iron,final inoculation).Attention is drawn to a control factor(%Mn)x(%S)ensuring it equals to 0.03–0.06,accompanied by 0.005wt.%–0.010wt.%Al and/or Zr content in inoculated irons.It was found that iron powder addition promotes austenite dendrite formation in eutectic and slightly eutectic,acting as reinforcement for the eutectic cells.But,there is an accompanying possible negative influence on the characteristics of the(Mn,X)S type graphite nuclei(change the morphology of nuclei from polygonal compact to irregular polygonal,and therefore promote chill tendency in treated irons).A double addition(iron powder+inoculant)appears to be an effective treatment to benefit both austenite and graphite nucleation,with positive effects on the final structure and chill tendency.
