Protective surface on stainless steel

Patent metadata

Field	Value
Publication number	US-11859291-B2
Application number	US-202117214652-A
Country	US
Kind code	B2
Filing date	Mar 26, 2021
Priority date	Oct 4, 2017
Publication date	Jan 2, 2024
Grant date	Jan 2, 2024

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.

First claim

What is claimed is:

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 Mn x Cr 3-x O 4 , wherein x is from 0.5 to 2; and
an intermediate layer between the outer layer and the steel substrate comprising Cr 2 O 3 , 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.

2. The method of claim 1 , wherein the first target temperature is from 225 to 235° C.

3. The method of claim 1 , wherein the first heating step comprises heating the steel substrate at a first rate from 10 to 15° C./min.

4. The method of claim 3 , wherein the first rate is from 12 to 14° C./min.

5. The method of claim 1 , wherein the first heating step further comprises holding the steel substrate at the first target temperature from 1.5 to 3 hours.

6. The method of claim 1 , wherein the first heating step further comprises holding the steel substrate at the first target temperature from 2 to 2.5 hours.

7. The method of claim 1 , wherein the second target temperature is from 370 to 374° C.

8. The method of claim 1 , wherein the second heating step comprises heating the steel substrate at a second rate from 1 to 5° C./min.

9. The method of claim 8 , wherein the second rate is from 2 to 3° C./min.

10. The method of claim 1 , wherein the second heating step further comprises holding the steel substrate at the second target temperature from 1 to 3 hours.

11. The method of claim 1 , wherein the second heating step further comprises holding the steel substrate at the second target temperature from 1 to 2 hours.

12. The method of claim 1 , wherein the third target temperature is from 1050 to 1090° C.

13. The method of claim 1 , wherein the third heating step comprises heating the steel substrate at a third rate from 1 to 5° C./min.

14. The method of claim 13 , wherein the third rate is from 2 to 3° C./min.

15. The method of claim 1 , wherein the third heating step further comprises holding the steel substrate at the third target temperature for 4 to 8 hours.

16. The method of claim 1 , wherein the third heating step further comprises holding the steel substrate at the third target temperature for 5 to 7 hours.

17. The method of claim 1 , wherein the cooling step comprises cooling the steel substrate at a fourth rate from 1 to 2.5° C./min.

18. The method of claim 1 , wherein the oxidizing atmosphere comprises:
40 to 50 wt. % air; and
one or more inert gases, wherein the one or more inert gases comprise nitrogen, argon, or mixtures thereof.

19. The method of claim 1 , wherein the intermediate layer has a thickness from 1 to 1.7 microns, and the outer layer has a thickness from 1.5 to 4.0 microns.

20. The method of claim 1 , wherein the outer layer of the surface comprises not less than 85 wt. % of the compound of Mn x Cr 3-x O 4 , wherein x is from 0.5 to 2.

21. The method of claim 1 , wherein the surface comprises oxides of Mn or Si selected from the group consisting of MnO, MnSiO 3 , Mn 2 SiO 4 , and mixtures thereof.

22. The method of claim 21 , wherein the oxides are present in amounts of less than 5 wt. %.

23. The method of claim 1 , wherein the steel substrate comprises from 40 to 50 wt. % Ni, from 33 to 35 wt. % Cr, from 20 to 25 wt. % Fe, and from 0.20 to 0.60 wt. % La.

24. The method of claim 1 , wherein the steel substrate comprises from 0.4 to 0.6 wt. % C, less than 1.5 wt. % Si, from 0.01 to 0.20 wt. % Ti, from 0.05 to 0.25 wt. % Mo, and less than 0.25 wt. % Cu.

25. The method of claim 1 , wherein the total weight percent of the trace elements, carbon, and silicon ranges from 0.6 to 2.20 wt. %.

Assignees

• Nova Chemicals Corp
• Kubota Kk
• Nova Chem Int Sa

Inventors

• Simanzhenkov Vasily
• Farag Hany
• Benum Leslie
• Santos Billy
• Donnelly Kathleen
• Sakamoto Nobuyuki
• Hashimoto Kunihide
• Gyorffy Michael

Classifications

• C23C8/18 Primary

  Oxidising of ferrous surfaces · CPC title

• C10G9/16 Primary

  Preventing or removing incrustation · CPC title

• C10G9/203

  chemical composition of the tubes · CPC title

• C21D1/72

  during chemical change of surfaces · CPC title

• C21D6/004

  containing Cr and Ni · CPC title