Patent ID: 11965253
Assignee: MANNESMANN PRECISION TUBES FRANCE
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  F  Y | IPC C  F

Claim 0:
1. A method for forming a layer of single-phase oxide (Fe, Cr)2O3 with a rhombohedral structure on a steel or super alloy substrate, the method comprising:
(a) removing a surface layer of a substrate of steel or super alloy covered by the surface layer, the steel or super alloy comprising iron and at least 2% by weight of chromium, to reach the substrate, in a subtraction, under an atmosphere containing at least 0.2 atm of dioxygen, the subtraction generating a level of microstrains in a steel or super alloy crystalline lattice of the substrate larger than 1.0×10−3 and locally heating at a rate of more than 400° C./s, so as to form a single-phase rhombohedral oxide (Fe, Cr)2O3 layer; and
(b) heat treating, under air at a partial water pressure of less than 10,000 ppm, and at a temperature in a range of from 400° C. to 1000° C., so as to grow the single-phase rhombohedral oxide (Fe, Cr)2O3 layer formed in the removing (a) to a thickness in a range of from 70 nm to 150 nm.