Method of casting steel strip in which molten steel solidifies as a shell on a chilled casting surface (100). The casting surface (100) has a texture (101) formed by a regular pattern of surface projections (103) and depressions (102) and the steel chemistry is selected to generate in the casting pool deoxidation products which form on the casting surface (100) a layer of less than 5 microns thickness a major proportion of which is liquid during cooling of the steel to below its liquidus temperature in the formation of said solidified shell. The substantially liquid layer suppresses the formation of surface defects in the solidifying metal surface due to early deposition of solid oxides on the casting surface.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. application Ser. No. 08/845,027, filed Apr. 21, 1997, now U.S. Pat. No. 5,934,359.
A method of producing strip comprising the steps of assembling a pair of casting rolls with a nip between them, introducing between the casting rolls to form a casting pool of molten carbon steel having a total oxygen content of at least 70 ppm usually less than 250 ppm, and a free oxygen content 20 and 60 ppm, counter rotating the casting rolls, solidifying the molten steel on the rolls to form metal shells with levels of oxide inclusions reflected by the total oxygen content of the molten steel, and forming thin steel strip through the nip between the casting rolls from the solidified shells. The molten steel may have a total oxygen content is at least 100 ppm and the free oxygen content may be between 30 and 50 ppm. A unique steel strip may be obtained using the method having ductile properties.
In twin roll casting of steel strip, molten steel is introduced into the nip between parallel casting rolls to create a casting pool supported on casting surfaces of the rolls and the rolls are rotated to deliver solidified strip downwardly from the nip. Casting surfaces are textured by a random pattern of discrete projections at least some of which include peaks having a surface distribution of between 5 and 200 projections per mm.sup.2 and an average height of at least 10 microns. The random texture may be produced by grit blasting the casting surfaces on a substrate covered by a protective coating. Alternatively the texture may be produced by chemical deposition or electrodeposition of a coating onto a substrate to form the casting surfaces.
A wrought aluminum sheet product having a textured surface for improved heat transfer properties. A plurality of textured features having dimensions of about 1-50 microns is roll textured onto one or both sides of the sheet. The aluminum sheet may be used as the fins or tubing of a heat exchanger.
In twin roll casting of steel strip, molten steel is introduced into the nip 16B between parallel casting rolls to create casting pool supported on casting surfaces of the rolls and the rolls are rotated to deliver solidified strip downwardly from the nip. Casting surfaces are textured by a random pattern of discrete projections, which may have an average surface distribution of between 5 and 200 peaks per mm.sup.2 and an average height of at least 10 microns. In order to suppress chatter defects, the molten steel also has manganese content of at least 0.55% by weight and a silicon content in the range of 0.1 to 0.35% by weight. The strip is thus capable of moving away from the casting pool at a speed of more than 60 meters per minute without substantial high speed chattering defects.
A wrought aluminum sheet product having a textured surface for improved heat transfer properties. A plurality of textured features having dimensions of about 1-50 microns is roll textured onto one or both sides of the sheet. The aluminum sheet may be used as the fins or tubing of a heat exchanger.
