Protective surface on stainless steel
AssigneesNOVA Chemicals Inc., Kubota Corporation, Kubota Materials Canada Corporation
InventorsVasily Simanzhenkov, Hany Farag, Leslie Benum, Billy Santos, Kathleen Donnelly, Nobuyuki Sakamoto, Kunihide Hashimoto, Michael Gyorffy
Life of this patent
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Abstract
A substrate steel of the comprising from 0.01 to 0.60 wt. % of La, from 0.0 to 0.65 wt. % of Ce; from 0.06 to 1.8 wt. % of Nb up to 2.5 wt. % of one or more trace elements and carbon and silicon may be treated in an oxidizing atmosphere to product a coke resistant surface coating of MnCr2O4 having a thickness up to 5 microns.
Claims19
A steel substrate comprising from 40 to 55 wt. % Ni, from 30 to 35 wt. % of Cr, from 15 to 25 wt. % Fe, from 1.0 to 2.0 wt. % of Mn, from 0.01 to 0.60 wt. % of La, from 0.0 to 0.65 wt. % of Ce;
- from 0.06 to 1.8 wt. % of Nb and one or more trace elements and carbon and silicon having on its surface an outer layer comprising a spinel of the formula:
- MnxCr3−xO4
- wherein x is from 0.5 to 2 having a thickness from 1.5 to 4.0 microns thick and an intermediate layer between the surface layer and the substrate comprising Cr2O3 having a thickness from 1 to 1.7 microns.
A method to make a surface comprising an outer layer comprising a spinel of the formula:
- MnxCr3−xO4wherein x is from 0.5 to 2 having a thickness from 1.5 to 4.0 microns thick and
- an intermediate layer between the surface layer and the substrate comprising Cr2O3 having a thickness from 1 to 1.7 microns covering at least 85% of a surface of a steel substrate comprising from 40 to 55 wt. % Ni, from 30 to 35 wt. % of Cr, from 15 to 25 wt. % Fe, from 1.0 to 2.0 wt. % of Mn, from 0.01 to 0.60 wt. % of La, from 0.0 to 0.65 wt. % of Ce;
- from 0.06 to 1.8 wt. % of Nb up to 2.5 wt. % of one or more trace elements and carbon and silicon comprising in an oxidizing atmosphere:
- 1) heating the steel from room temperature at a rate from 10 to 15° C./min to a temperature from 220° C. to 240° C. and holding the steel at this temperature from 1.5 to 3 hours;
- 2) heating the steel a rate from 1 to 5° C./min to a temperature from 365 to 375° C. and holding the steel at this temperature from 1 to 3 hours;
- 3) heating the steel at a rate from 1 to 5° C./min to 1000° C. to 1100° C. and holding the steel at this temperature for from 4 to 8 hours;
- 4) cooling the steel at a rate from 1° C. to 2.5° C. to a temperature from 18 to 25° C.
Dependencies are inferred from the claim text.