| In the last few years a few companies have announced the final stage of the commercial development of strip casting of steels.; In strip casting heat extraction and productivity are limited by the thermal resistance at the interface between processed material and moving mold (rolls for twin-roll strip casters). Among many factors influencing interfacial heat transfer, films of various composition, either formed during casting or deposited before casting on the surface of the rolls, melt superheat and gas atmosphere composition can have a significantly positive or negative effect on the achieved heat transfer rate.; From an industrial point view, methods to improve interfacial heat transfer rates must be found, in order to increase productivity.; The objective of this research project is to assess if it is feasible to improve heat transfer rates during solidification of steel in direct contact with a copper mold: (1) by the application of thin coatings on the mold surface; (2) by adding a reactive gas species containing sulfur in the gas shrouding where casting is performed.; To address the former, solidification experiments were performed with the mold surface either kept uncoated or coated with coatings of different compositions. To address the latter, the experiments were performed in gas shrouding atmospheres with or without sulphydric acid. It was observed that the resulting heat extraction rates were improved by the application of certain coatings and by the addition of H2S to the gas atmosphere. These findings prove that the application of coatings and the use of small amounts of reactive gaseous species containing sulfur may be methods to increase productivity in strip casting.; The effect of superheat and the effect of naturally deposited oxides (Mn-oxide) were also evaluated experimentally.; A numerical study of the effect of the critical undercooling on the productivity of a twin-roll strip caster showed that the maximum allowable casting speed can be increased by increasing the critical undercooling, which in turns can be changed by changing the composition of the coating applied on the roll surface; this increase is significant when casting thicknesses are small (less than 1 mm).; Finally, a procedure, based on Scheill's method, vaporization and liquation, to predict the composition of films depositing naturally during solidification, starting from the steel composition, is proposed. |
