| 摘要 |
A method is disclosed for forming a billet [B1-B23] comprising a core body [C, 51, 53, 55, 57, 63] of solid steel housed in a tube [J, 12, 52, 54, 58, 62] of stainless steel, nickel-chrome, nickel-copper and copper-nickel alloys. The billet can be square or round and can be hot rolled in a conventional rolling mill to form a corrosion resistant product [R, F]. Machinery [29-30, 36-40, 42-45] is disclosed for inserting the core in the tube and stretching the tube so as to exceed the elastic limit of the alloy, thereby reducing the clearance gap at the interface [Z] between the core and the tube. After the tube has been stretched, briquettes [Ea, Et, Em] of finely divided aluminium, titanium and/or magnesium are placed adjacent the interface in the tube. The tube may be closed to prevent gases outside the billet from penetrating to the interface. Before the tube reaches a temperature at the interface at which oxidation starts, the ends of the billet are heated up causing the briquettes to scavenge oxygen from the residual air at the interface. Alternatively, reliance may be placed on the briquettes to scavenge oxygen from the residual air and also from atmospheric air and furnace gases before they can penetrate to the interface. The briquettes of aluminium or magnesium [Ea, Em] melt before the billet reaches its rolling temperature and a further element [Ea] of finely divided carbon steel may then be inserted between these briquettes and the steel body to prevent the molten metal from penetrating to the interface. In an open tube, an additional element [Eu] composed of ammonium chloride or urea may be inserted between the carbon steel briquette and steel body. The additional element disassociates at a low temperature to scour residual gases out of the interface. The elements can be placed directly in the tube or in a cartridge [20, 30] which is subsequently welded to the tube.
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