GB770906A - Improvements in or relating to the heat treatment of metals and alloys - Google Patents

Abstract

770,906. Furnace atmospheres. GENERAL ELECTRIC CO., Ltd., DOVEY, D. M., and RANDLE, K. C. May 16, 1955 [May 14, 1954], No. 14217/54. Class 51 (2). In the heat treatment of a metal or alloy in a reducing atmosphere, in which the metal or a constituent metal of the alloy is readily oxidizable at the treatment temperature, the atmosphere gas is given a preliminary deoxidizing and drying treatment, and then a small amount of a halide or a hydride capable of reacting at a high temperature to produce either carbon monoxide or a refractory oxide is added either before or after the gas enters the treatment chamber. Among the additives used are chlorides and fluorides of titanium, zirconium, silicon and boron, e.g. the tetrachloride of silicon, titanium or zirconium, and the lower aliphatic hydrocarbons, particularly methane. A typical example is in the bright annealing of an alloy containing: 20 per cent chromium, 20 per cent cobalt, 2 per cent titanium, 1 per cent aluminium, 1 per cent silicon, 1 per cent manganese, 5 per cent iron and balance nickel-at 900-1000‹ C. in an atmosphere of hydrogen flowing through the annealing chamber at 90 litres/hour. A proportion of the hydrogen stream amounting to a flow of 10 litres/hour is bubbled through liquid titanium tetrachloride at 5‹ C., and mixed with the main flow before passing into the annealing chamber. The preliminary deoxidation and drying of the atmosphere gas is carried out in a known manner, e.g. by treating with a de-oxidizing catalyst, such as palladinized asbestos or copper heated to 800‹ C., and then passing through a tower filled with activated alumina. The additive combines with traces of oxygen or water vapour remaining in the atmosphere gas or taken up from the annealing furnace walls.