Research methods and influencing factors of interfacial heat transfer during sub-rapid solidification process of strip casting

Interfacial heat transfer behavior between the molten steel and twin-rolls is a key issue in the strip casting process,and it has already attracted wide attention from industrial and academic communities of steel.The research methods and influencing factors on the interfacial heat transfer were summarized.Numerical simulation models,semi-industrial scale,and laboratory equipment have been developed in this field,and these methods were also improved by worldwide researchers based on the development of computer,automatic,and visual technologies.Coating properties,naturally deposited film,and casting parameters are the main factors which affect the heat transfer significantly.Although lots of research has been carried out,the internal relations among these influencing factors,interfacial heat transfer,and the quality of the strip are still worth to be further explored.Keywords Strip casting Interfacial heat transfer Simulation method Coating property Naturally deposited film Casting parameter.

Effect of AI_(2)O_(3)and MgO on crystallization and structure of Ca0-Si0_(2)-B_(2)0_(3)-based fluorine-free mold flux

The crytallization behavior and melt structure of the CaO-Si0^(2-)B20_(3)-based fluorine-free mold fux were investigated.The results show that the crytallization of the mold fux was first inhibited and then promoted with the increase in Al_(2)0_(3) content from 4 to 12 wt.%.However,it was enhanced by MgO in the range of 2-10 wt.%.The results of Fourier transform infrared spectroscopy and Raman spectroscopy showed that Al_(2)0_(3) worked as a network former in the mold flux melt when its content was in the range of 4-8 wt.%,whereas it worked as the network breaker to provide 0^(2-)when its content was in the range of 8-12 wt.%.In addition,the combined efects from the charge compensation by Mg^(2+)and the network broken by 0^(2-)led to the increase in some typicalT-O-T(AI-O-A1,B-O-B,etc.,)and simpler structural units(Q^(2)(Si),B_^(O-)in the[B0_(2)0^(-)],.etc.)when the MgO content was in the range of 2-6 wt.%.The continuous increase in 0^(2-)provided by the addition of MgO from 6 to 10 wt.%further depolymerized the network of the melt and fnally caused fast crystallizationo.

Effect of Al2O3/SiO2 and CaO/Al2O3 ratios on wettability and structure of CaO-SiO2-Al2O3-based mold flux system

The effect of Al2O3/SiO2 and CaO/Al2O3 ratios on the molten structure of CaO-SiO2-Al2O3-based mold flux system was analyzed by Fourier transform infrared spectroscopy,Raman spectroscopy,and X-ray photoelectron spectroscopy.Also,the variation in the wettability between the mold flux system and an interstitial free(IF)steel substrate was investigated using the sessile drop method.The results indicate that the contact angle and interfacial tension between the molten slag and solid steel increase slightly with the increase in the Al2O3/SiO2 ratio,while they decrease with the increase in the CaO/Al2O3 ratio.The network structure for the designed mold flux system changes gradually from silicate to aluminosilicate and aluminate with the increase in the Al2O3/SiO2 ratio,and the network is simplified with the increase in the CaO/Al2O3 ratio.Besides,combining the results of sessile drop method and melt structure analyses,it suggests that the variation in interfacial properties of mold flux/IF steel substrate is mainly caused by the change in melt structure,especially the variation in free oxygen ions(O^2-)and non-bridged oxygen(O^-)at the interface.

Effect of Al_(2)O_(3)/Na_(2)O ratio and MnO on high-temperature properties of mold flux for casting peritectic steel

The influences of Al_(2)O_(3)/Na_(2)O ratio and MnO content on high-temperature properties,such as melting,crystallization,heat transfer,and viscosity of mold flux for casting peritectic steel,have been investigated.The results show that the melting temperatures of mold flux decrease,whereas the ratio of crystalline layers increases with the decrease in Al_(2)O_(3)/Na_(2)O ratio and increase in MnO content.The average response temperatures of the three mold fluxes decrease from 566,525,to 512℃,respectively,which indicates that the heat transfer controlling ability of mold flux is promoted due to the increase in crystallization ability and addition of transition metal oxide MnO.Furthermore,the viscosity-temperature curves suggest that the viscosity at 1300℃ decreases,but the break temperature increases with the reduction in Al_(2)O_(3)/Na_(2)O and addition of MnO.

Special issue on continuous casting

Continuous casting is considered to be one of the most important innovations in steel industry since it is first propagated by Henry Bessemer in 1846.It has many benefits,including(Ⅰ)increased yield,(Ⅱ)improved product quality,(Ⅲ)energy saving,(Ⅳ)less pollution,(Ⅴ)reduced costs,(Ⅵ)better working conditions,etc.Nowadays,more than 98% of crude steel output in the world is produced through the continuous casting process.