Device for continuous casting metal strip and its roller and its produced steel-casting strip

Abstract

Twin roll casting has been applied with some success to non-ferrous metals, which solidify rapidly on cooling. The same, however, is not true for ferrous metals, as it has not been possible to achieve sufficiently rapid and even cooling of metal over the casting surfaces of the rolls. This problem has been overcome by utilising a metallic surface for the rolls, which has a high affinity for the molten steel of the casting pool and a melting temperature greater than the temperature of the casting surface. The molten steel produces extremely good wetting of the casting surface of the roll, resulting in a wetting angle of the molten steel on the casting surface of less than 40 DEG . Preferably, this wetting angle is less than 20 DEG and the casting surface has an Arithmetic Mean Roughness Value (Ra) of less than 10 microns. These desirable properties on the roll surface are achieved by selecting an at least partially amorphous alloy of two constituents. Preferably, the alloy is a fully amorphous alloy of the nickel-phosphorus systemcontaining about 10 % phosphorus and the balance nickel, which may be applied by eletroless coating. This roll surface prevents the build-up of iron oxide on the casting surfaces of the rolls, which build-up interferes with the uniform conduction of heat away from the molten steel, resulting in simultaneous solidification of the delta and gamma iron phases (0.01-0.18 %C), which causes a surface defect, known as "crocodile-skin". The net effect of utilising this amorphous alloy for the surface of the casting roll is a superior and uniform conduction of heat away from the molten steel, rapid transformation of the steel's microstructure into the wholly austenitic ( gamma ) region, exhibited by fine prior austenite grain boundaries conforming to dendritic grain boundaries and absence of "crocodile-skin" surface defects on the cast strip.

Description

[0001] The application number is Chinese national application number 98805502.3, the international application number is PCT / AU98 / 00412, the international application date is June 2, 1998, and the title of the invention is "amorphous or glassy A divisional application of the invention patent application for alloy-coated rollers. technical field [0002] This invention relates to metal strip casting. It is used particularly, but not exclusively, in the casting of iron-based metal strip. In particular, the invention relates to an apparatus for continuously casting metal strip and the rolls therein and the cast steel strip produced therein. Background technique [0003] It is known to cast metal strips by means of twin-roll continuous casting machines. In this technique molten metal is directed between a pair of counter-rotating horizontal casting rolls, which are cooled so that they solidify on the surface of the moving r...

AI Technical Summary

Problems solved by technology

However, if too much oxide is deposited, the melting of the oxide produces a high initial heat flux, but the heat flux decreases rapidly as the oxide resolidifies

Variations in heat flux in the solidified shell produce local deformations leading to surface defects in alligator skin

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