Industrial experiments were carried out to investigate the formation of CaS-bearing inclusion during Ca double modification in oil casting steels using polished cross sections and electrolytic extraction. Immediately ...Industrial experiments were carried out to investigate the formation of CaS-bearing inclusion during Ca double modification in oil casting steels using polished cross sections and electrolytic extraction. Immediately after Ca addition, the role of newly generated CaS as an intermediate reaction product, which modified the Al_2O_3 inclusion into a liquid calcium aluminate, was confirmed. The formation of transient CaS was attributed to the high surface segregation of S at the liquid steel-calcium vapor interface, where a simple site coverage model based upon the Langmuir adsorption equation was established. Moreover, a CaS outer layer surrounding the liquid calcium aluminate was attained mainly in the tundish, which was distributed unevenly on the surface of liquid particles according to the three-dimensional mapping results. The surface of a well-modified calcium aluminate with higher CaO activity and Al_2O_3 activity under bulk composition conditions in the tundish acted as a favorable site for the generation of CaS. Additionally, CaS could be precipitated directly onto existing inclusions during solidification of the steel, which led to various morphologies of CaS-bearing inclusions in slabs. Furthermore, the phase transformation of inclusions during solidification was strongly influenced both by the S content and the Ca/S ratio in the tundish via thermodynamics.展开更多
Overcasting is a new kind of dissimilar joining technique used to produce the aluminum（solid）/magnesium（liquid） bonding bi-metallic material in this study. For the Al/Mg（A390/AM60） bi-metallic samples, the inter...Overcasting is a new kind of dissimilar joining technique used to produce the aluminum（solid）/magnesium（liquid） bonding bi-metallic material in this study. For the Al/Mg（A390/AM60） bi-metallic samples, the interface microstructures are the research points, which directly influence the mechanical properties. It is, therefore, of vital importance to find a method to improve the interface microstructures. This research focused on the effect of the calcium（Ca） addition in the liquid Mg alloys and the heat treatment on the A390/AM60 interface microstructures of the bi-metallic samples. The testing results showed that, with Ca addition in AM60, owing to two possible reasons, the interface microstructure and the shear strength of the A390/AM60 bi-metallic samples could be improved. The heat treatment could further improve the interface microstructure and the mechanical properties by dissolving β-Mg_（17）Al_（12） into α-Mg and destroying the Mg_2Si layer structure.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51574026)
文摘Industrial experiments were carried out to investigate the formation of CaS-bearing inclusion during Ca double modification in oil casting steels using polished cross sections and electrolytic extraction. Immediately after Ca addition, the role of newly generated CaS as an intermediate reaction product, which modified the Al_2O_3 inclusion into a liquid calcium aluminate, was confirmed. The formation of transient CaS was attributed to the high surface segregation of S at the liquid steel-calcium vapor interface, where a simple site coverage model based upon the Langmuir adsorption equation was established. Moreover, a CaS outer layer surrounding the liquid calcium aluminate was attained mainly in the tundish, which was distributed unevenly on the surface of liquid particles according to the three-dimensional mapping results. The surface of a well-modified calcium aluminate with higher CaO activity and Al_2O_3 activity under bulk composition conditions in the tundish acted as a favorable site for the generation of CaS. Additionally, CaS could be precipitated directly onto existing inclusions during solidification of the steel, which led to various morphologies of CaS-bearing inclusions in slabs. Furthermore, the phase transformation of inclusions during solidification was strongly influenced both by the S content and the Ca/S ratio in the tundish via thermodynamics.
基金Funded by the National Natural Science Foundation of China(No.51571080)
文摘Overcasting is a new kind of dissimilar joining technique used to produce the aluminum（solid）/magnesium（liquid） bonding bi-metallic material in this study. For the Al/Mg（A390/AM60） bi-metallic samples, the interface microstructures are the research points, which directly influence the mechanical properties. It is, therefore, of vital importance to find a method to improve the interface microstructures. This research focused on the effect of the calcium（Ca） addition in the liquid Mg alloys and the heat treatment on the A390/AM60 interface microstructures of the bi-metallic samples. The testing results showed that, with Ca addition in AM60, owing to two possible reasons, the interface microstructure and the shear strength of the A390/AM60 bi-metallic samples could be improved. The heat treatment could further improve the interface microstructure and the mechanical properties by dissolving β-Mg_（17）Al_（12） into α-Mg and destroying the Mg_2Si layer structure.
