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Yan W.,University of Science and Technology Beijing | Yan W.,University of Toronto | Chen W.,University of Science and Technology Beijing | Yang Y.,University of Toronto | And 2 more authors.
Ironmaking and Steelmaking | Year: 2015

In order to facilitate the development of CaO-AI2O3 based mould flux for casting high aluminium, non-magnetic steel, the effect of CaO/AI2O3 ratios from 0.6 to 3.2 on viscosity and crystallisation characteristics were investigated with the aid of a rotational viscometer, Fourier transform infrared spectroscopy, a single hot thermocouple technique and X-ray diffraction analysis. The results showed that, at temperatures above 1543 K (1270°C), the viscosity first decreased and then became stable with increase in the CaO/AI2O3 ratio. At temperatures below 1543 K (1270°C), the viscosity again first decreased but then increased, with the CaO/AI2O3 ratio. This viscosity behaviour can be attributed to changes in the network structure characteristics and the precipitation of solid particles within the liquid flux. Increase in the CaO/AI2O3 ratio also first inhibited and then enhanced crystallisation as demonstrated by the changes in initial crystallisation temperatures and incubation times. The X-ray diffraction results confirmed that, at both low and high CaO/AI2O3 ratios, the dominant precipitates were compounds with highmelting points.On the other hand, with CaO/AI2O3 ratios in themidrange, the dominant precipitates were compounds with relatively low melting temperatures. It is concluded that mould flux with a CaO/AI2O3 ratio in the range 1.1-1.6 is the most appropriate for casting high aluminium, non-magnetic steels. © 2015 Institute of Materials, Minerals and Mining.


Hao Z.,University of Science and Technology Beijing | Chen W.,University of Science and Technology Beijing | Lippold C.,Qingdao Stollberg and Samil Co.
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2010

The heat transfer behavior between mold and slab changes when titania is absorbed into the mold flux during the continuous casting of titanium-stabilized stainless steel. The trend and the extent of this effect were investigated in the laboratory. Furthermore, to investigate the effect of titania on heat transfer, the effect of titania on the crystallization properties of the mold flux was studied. The results showed that with an increasing titania content of mold fluxes, the heat transfer coefficient and the heat flux of the slag film increases, whereas the heat transfer resistance decreases; the effect is that the growth and crystallization temperature of the cuspidine crystallites in the slag are suppressed by the absorption of titania. © 2010 The Minerals, Metals & Materials Society and ASM International.


Yan W.,University of Science and Technology Beijing | Chen W.,University of Science and Technology Beijing | Lippold C.,Qingdao Stollberg and Samil Co. | Xu H.,University of Science and Technology Beijing
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2013

The heat-transfer behavior across mold fluxes for Invar alloy Fe-36Ni would introduce significant influence on the slab surface quality. A study on the heat-transfer property of mold flux film for Invar alloy Fe-36Ni was carried out by an interaction between laboratory simulation and field trial. The study results indicate that great effect on heat transfer across flux film is caused by chemical compositions of mold fluxes. An increase of basicity and CaF 2 content suppresses heat transfer across flux film; heat transfer across flux film increases when the Al2O3 content increases from 4 pct to 8 pct but decreases when Al2O3 content is above 8 pct. The crystalline phases of both the conventional mold fluxes and the improved mold fluxes are all cuspidine phases. However, crystallization capability of the improved mold fluxes decreases as the result of the increase of basicity and CaF2 content as well as the decrease of Al2O3 content. The average thickness of flux film taken from mold is about 1.6 mm, and the crystalline fraction is only 21.4 pct. All these promote heat transfer across the flux film. The field trial of the improved mold fluxes shows that the properties of liquid slag are steady during continuous casting; comprehensive heat transfer across flux film meets the needs of continuous casting of Fe-36Ni. Border solidification structures of solidified shell are refined remarkably, and hot cracking gets avoidance eventually. © 2013 The Minerals, Metals & Materials Society and ASM International.


Yan W.,University of Science and Technology Beijing | Yan W.,University of Toronto | Chen W.,University of Science and Technology Beijing | Yang Y.,University of Toronto | And 2 more authors.
ISIJ International | Year: 2015

Intense reaction between silica in mold fluxes and aluminium in liquid steel during casting of high-Al non-magnetic steel 20Mn23AlV (1.5-2.5 Al in mass percent) would significantly alter both chemical compositions and properties of mold fluxes. This would subsequently lead to severe casting problems such as lots of slag rims, breakout and poor surface quality. Investigation carried out in this paper started with plant sampling, followed by a look at how the variation of Al2O3/SiO2 ratio with reaction time can affect the casting process and product quality. Thus, this work focuses on the study of increasing Al2O3/SiO2 and partial substitution of CaO with BaO in CaO-SiO2 system mold fluxes in terms of heat transfer and crystallization behavior. The techniques implemented are heat flux simulator and single hot thermocouple technique (SHTT). The results showed that an increase in Al2O3/SiO2 inhibits heat transfer, increases crystallization temperature and critical cooling rate while shortens incubation time, additionally, accelerates precipitation of phase with high melting temperature. However, greater substitution of CaO with BaO accelerates heat transfer, reduces crystallization temperature and critical cooling rate at the cost of longer incubation time even at elevated Al2O3/SiO2. Eventually, partial substitution of CaO with BaO, to some extent, counteracts the effect of increasing Al2O3/SiO2 on heat transfer and crystallization properties of mold fluxes for casting of high-Al steels. © 2015 ISIJ.


Yan W.,University of Science and Technology Beijing | Yan W.,University of Toronto | Chen W.,University of Science and Technology Beijing | Yang Y.,University of Toronto | And 2 more authors.
Steel Research International | Year: 2016

When continuous casting was used to replace electro-slag remelting for the production of heat-resistant alloy Incoloy 800 containing Al and Ti, there were a number of quality problems associated with the cast product which were attributed to the use of an inappropriate mold flux. The aim of the current investigation was to develop and evaluate an improved mold flux by combining data derived from laboratory experiments with results obtained from plant-trials. The effects of composition on viscosity and heat transfer properties were investigated and a new mold flux was designed with improved casting behavior. By decreasing the characteristic melting temperatures, selecting an appropriate viscosity and enhancing the heat transfer properties, slab quality was improved. Chemical analysis combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) evaluation of liquid flux and flux film samples indicated that changes in composition, characteristic temperatures, and viscosity during the casting operation were negligibly small. The flux film with a thickness of 1.1 mm, a crystalline ratio of 30%, and cuspidine as the main crystalline phase was beneficial for improving heat transfer thus strengthening the initial shell and improving the quality of the cast product. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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