Enhanced activation of self-passivating metals

Patent metadata

Field	Value
Publication number	US-12371774-B2
Application number	US-202217941081-A
Country	US
Kind code	B2
Filing date	Sep 9, 2022
Priority date	Jul 31, 2014
Publication date	Jul 29, 2025
Grant date	Jul 29, 2025

Abstract

A workpiece made from a self passivating metal and having one or more surface regions defining a Beilby layer as a result of a previous metal shaping operation is activated for subsequent low temperature gas hardening by exposing the workpiece to the vapors produced by heating an oxygen-free nitrogen halide salt.

First claim

The invention claimed is:

1. A process comprising:
heating an oxygen-free nitrogen halide salt to produce vapors;
exposing to the vapors a workpiece made from a self-passivating metal and having a Beilby layer on at least a portion of a surface of the workpiece so that:
a temperature of the exposing is below a temperature at which nitride and/or carbide precipitates form in the workpiece;
the exposing activates the workpiece for carbonitriding; and

carbonitriding the workpiece while the workpiece is activated.

2. The process of claim 1 , wherein the oxygen-free nitrogen halide salt is an ionic compound that:
(1) comprises a halide anion;
(2) has a room temperature solubility in water of at least 5 moles/liter;
(3) comprises nitrogen;
(4) is substantially free of oxygen; and
(5) vaporizes when heated to a temperature of 350° C. at atmospheric pressure.

3. The process of claim 1 , wherein the carbonitriding utilizes gas derived exclusively from the oxygen-free nitrogen halide salt.

4. The process of claim 1 , wherein the carbonitriding comprises contacting the workpiece with a gas derived from a nitrogen containing compound different than the oxygen-free nitrogen halide salt.

5. The process of claim 4 , wherein the contacting the workpiece with the gas derived from the nitrogen containing compound occurs during the activation.

6. The process of claim 4 , wherein the contacting the workpiece with the gas derived from the nitrogen containing compound occurs as the activation begins.

7. The process of claim 4 , wherein the exposing occurs simultaneously with the contacting the workpiece with the gas derived from the nitrogen containing compound.

8. The process of claim 4 , wherein the contacting the workpiece with the gas derived from the nitrogen containing compound occurs after the exposing.

9. The process of claim 4 , wherein the nitrogen containing compound comprises:
one or more compounds comprising:
an N/C compound,
at least one nitrogen to carbon bond,
at least four carbon atoms, and

the one or more compounds are solid or liquid at 25° C. and under a pressure of 1 atmosphere.

10. The process of claim 9 , wherein the one or more compounds comprise at least one of urea, acetamide and formamide.

11. The process of claim 1 , wherein the carbonitriding further comprises:
contacting the workpiece with an additional gas different from the vapors, the additional gas comprising at least one of:
nitrogen derived from the decomposition of a compound during the carbonitriding;
carbon derived from the decomposition of a compound during the carbonitriding; and
nitrogen and carbon derived from the decomposition of a compound during the carbonitriding.

12. The process of claim 11 , wherein the additional gas comprises vapors from the decomposition of an N/C compound.

13. The process of claim 1 , wherein the exposing occurs for at least about 15 minutes.

14. The process of claim 13 , wherein the exposing occurs for at least about 30 minutes.

15. The process of claim 1 , wherein the oxygen-free nitrogen halide salt is a particulate solid and wherein the exposing further comprises:
encapsulating the workpiece with the particulate solid; and
heating the workpiece to a temperature high enough to vaporize the particulate solid.

16. The process of claim 1 , wherein the oxygen-free nitrogen halide salt comprises at least one of ammonium chloride, ammonium fluoride, guanidinium chloride, guanidinium fluoride, pyridinium chloride, and pyridinium fluoride.

17. The process of claim 16 , wherein the oxygen-free nitrogen halide salt comprises at least one of ammonium chloride and guanidinium chloride.

18. The process of claim 1 , wherein the self-passivating metal is a stainless steel.

19. The process of claim 18 , wherein the self-passivating metal includes 10 to 40 wt. % Ni and 10 to 35 wt. % Cr.

20. The process of claim 1 , wherein the carbonitriding comprises:
a first carbonitriding step during the exposing; and
a second carbonitriding step after the exposing.

21. The process of claim 1 , wherein the self-passivating metal comprises one of: a nickel-based alloy, a cobalt-based alloy, a manganese-based alloy, and a titanium-based alloy.

22. A process comprising:
heating an oxygen-free nitrogen halide salt to produce vapors;
exposing to the vapors a workpiece made from a self-passivating metal and having a Beilby layer on at least a portion of a surface of the workpiece so that:
a temperature of the exposing is below a temperature at which nitride and/or carbide precipitates form in the workpiece;
the exposing activates the workpiece for carbonitriding; and

carbonitriding the workpiece concurrently with the activating.

Assignees

• Swagelok Co
• Univ Case Western Reserve

Inventors

• Williams Peter C
• Marx Steven V
• Ernst Frank
• Agaponova Anna V

Classifications

• C23C8/26

  of ferrous surfaces · CPC title

• C23C8/32

  of ferrous surfaces · CPC title

• C23C8/22

  of ferrous surfaces · CPC title

• C23C8/24

  Nitriding · CPC title

• C23C8/02 Primary

  Pretreatment of the material to be coated (C23C8/04 takes precedence) · CPC title