GB1082613A

GB1082613A - Ferrous metal articles

Info

Publication number: GB1082613A
Application number: GB39025/64A
Authority: GB
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1963-09-24
Filing date: 1964-09-24
Publication date: 1967-09-06
Also published as: NL6410994A; DE1496952B1; US3294498A; BE653276A

Abstract

A ferrous metal substrate is electro-plated with at least three alternating layers of Cr and Fe of which the first layer is Cr and the plated substrate is then heated to at least 800 DEG C. for a time such as to produce a diffusion coating comprising layers each made up of Cr-Fe alloy, the dimensions of substantially all the grains normal to the coating being at most equal to the thickness of the layer in which they occur and the boundaries of the grains forming tortuous paths between the substrate and the surface of the coating. The substrate may be cleaned prior to plating. The Fe plating bath may be operated at a pH below 1 and be vigorously stirred during plating. At the beginning of each cycle of a Cr and an Fe deposition, the substrate may be immersed in the Cr plating bath at least momentarily in the absence of current flow. A Cu strike may be deposited before the laminate plating of Cr and Fe. Ni or Co may be introduced into the coating e.g. by plating Cr-Ni or Fe-Ni alloy layers rather than the pure elements themselves. Alternatively, layers of an additional alloying element such as Al may be introduced between the alternate layers of Cr and Fe. The heat treatment, e.g. at 800 to 1100 DEG C., may be in the atmosphere in A, H2 or in a molten salt or molten metal bath, e.g. a bath containing Ca and Cr as disclosed in Specification 964,323 which bath itself serves as a Cr diffusion medium. Heated articles may be quenched, subjected to surface passivation, buffing and cold working. The examples relate to coating aluminium billed steel strip using the following baths and conditions. .Cr Bath.Fe Bath .250 g/l of CrO3.300 g/l of FeCl2.H2O .2.5 g/l of H2SO4.335 g/l of CaCl2 .30 to 35 DEG C..pH < 1 .500 amps/ft2.85 to 90 DEG C ..120 amps/ft2 The plated article in Examples 1 and 2 is heated in a molten Ca-Cr bath, quenched in an oil bath, cleaned in bath containing trichlorethylene and dried. In Example 3, it is heated in an H2 furnace and quenched in a blast of cool H2 gas. The process is also applied to mild steel, Ti containing steel and low carbon content irons. In Example 4, the plated article is heated in an A furnace and quenched in a cool blast of He.