GB1352944A - Surface treatment of iron or steel - Google Patents

Abstract

1352944 Halide diffusion coating; heat treatment; carburizing KITO K K 19 April 1971 [4 March 1970 5 March 1970 24 March 1970] 23133/71 Heading C7F, N and U Iron or steel is coated by a halide diffusion process in which the substrate is passed through a non oxidizing gas curtain extending across the open door 4 of the furnace 1, is heated in the presence of metal or metallized vapours in the furnace, is then passed into cooling or quenching chamber 10 or 18 and then discharged through a non oxidizing gas curtain extending across the open door 16 of the chamber. The halide vapour may be the chloride iodide or fluoride of Cr, Ti or Si and may be supplied either by heating a source 5 in the furnace or by introducing the vapour via inlet 7<SP>1</SP>. The substrate is fed into the furnace on sliding plate 6 and the gas curtain of nitrogen, argon or hydrocarbon is supplied from perforated pipes 3 and 15. Furnace 1 is evacuated and maintained at 1000‹C for 5 hours while the substrate contacts the halide vapour. Carbon powder or 0À1-5% volume of methane or propane may then be introduced to form a carbide coating. The furnace and chamber 10 or 18 are then purged with nitrogen, argon or hydrocarbon, partition 13 is raised and the coated substrate passed into chamber 10 where it is cooled or into chamber 18 where it is quenched in oil bath 17. The coated substrate is then discharged through the gas curtain formed at 15. Partition 13 may be replaced by a gas curtain and a feed chamber 21 with gas curtain at 19 may also be connected to the inlet of furnace 10. The substrate may be carburized or carbonitrided prior to diffusion coating. The coated substrate may be tempered at 180-600‹C.