CPC C23C 8/18 (2013.01) [C10G 9/16 (2013.01); C10G 9/203 (2013.01); C21D 1/72 (2013.01); C21D 6/004 (2013.01); C22C 19/05 (2013.01); C22C 19/053 (2013.01); C22C 19/058 (2013.01); C22C 30/00 (2013.01); C23C 8/02 (2013.01); C23C 8/14 (2013.01); F28F 1/12 (2013.01); F28F 1/26 (2013.01); F28F 1/40 (2013.01); F28F 19/06 (2013.01); F28F 21/083 (2013.01)] | 25 Claims |
1. A method to make a surface on a steel substrate, the method comprising:
in an oxidizing atmosphere:
in a first heating step, heating the steel substrate from room temperature to a first target temperature from 220 to 240° C.;
in a second heating step, heating the steel substrate to a second target temperature from 365 to 375° C.;
in a third heating step, heating the steel substrate to a third target temperature from 1000 to 1100° C.; and
in a cooling step, cooling the steel substrate to a fourth target temperature from 18 to 25° C.;
wherein the surface comprises:
an outer layer comprising a spinel of the formula MnxCr3-xO4, wherein x is from 0.5 to 2; and
an intermediate layer between the outer layer and the steel substrate comprising Cr2O3, wherein the outer layer and the intermediate layer covers at least 85% of the surface of the steel substrate; and
wherein the steel substrate comprises from 40 to 55 wt. % Ni, from 30 to 35 wt. % Cr, from 15 to 25 wt. % Fe, from 1.0 to 2.0 wt. % Mn, from 0.01 to 0.60 wt. % La, from 0.0 to 0.65 wt. % Ce, from 0.06 to 1.8 wt. % Nb, and up to 2.5 wt. % of one or more trace elements, carbon, and silicon.
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