# US 10,246,766 B2 · Concurrent flow of activating gas in low temperature carburization

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 10,246,766 B2
- Document ID: US10246766B2
- Status: Granted
- Kind: B2
- Application number: 15/409,074
- Filed: 2017-01-18
- Published: 2017-05-11
- Granted: 2019-04-02
- Earliest claimed: 2012-01-20
- Assignees: Swagelok Company
- Applicants: Swagelok Company
- Inventors: Sunniva R. Collins; Gerhard H. Schiroky; Steven V. Marx; Peter C. Williams
- Web page: https://patentgrep.com/patent/US10246766B2

## CPC

- C23C 8/22: of ferrous surfaces
- C21D 1/06: Surface hardening
- C21D 1/74: Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- C21D 1/773: under reduced pressure or vacuum
- C21D 6/00: Heat treatment of ferrous alloys
- C21D 6/001: {containing Ni (C21D6/004 takes precedence)}
- C21D 6/002: {containing Cr (C21D6/004 takes precedence)}
- C21D 6/004: {containing Cr and Ni}
- C21D 6/005: {containing Mn}
- C21D 6/008: {containing Si}
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)

## Abstract

Low temperature gas carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. Carburization is made to go faster by including HCl or other carbon-free, halogen-containing activating compound in the carburizing gas being fed to the carburization reactor.

## Claims

### Claim 1

A process for surface hardening a workpiece made from an iron, nickel and/or chromium based alloy by gas carburization in which an unsaturated hydrocarbon is contacted with the workpiece inside a carburization reactor under a pressure of about 3.5 to 100 torr and at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer which is essentially free of carbide precipitates as well as a thermal oxide film, the process further comprising increasing the rate at which carburization occurs by feeding a carbon-free, halogen-containing activating compound to the carburization reactor simultaneously with feeding the unsaturated hydrocarbon to the carburization reactor, wherein the unsaturated hydrocarbon is acetylene, the concentration of the of the unsaturated hydrocarbon inside the carburization reactor is about 8 to 35 vol. % and the concentration of the carbon-free, halogen-containing activating compound inside the carburization reactor is about 0.5 to 3 vol. %.

### Claim 2 (depends on 1)

The process of claim 1, wherein the carbon-free, halogen-containing activating compound is HF, HCl, NF3, F2, Cl2 or a mixture thereof.

### Claim 3 (depends on 2)

The process of claim 2, wherein the workpiece is made from stainless steel and further wherein, prior to contact of the workpiece with the unsaturated hydrocarbon, the workpiece is not activated to remove the coherent, impervious layer of chromium oxide which inherently forms on the surface of the steel.

### Claim 4 (depends on 3)

The process of claim 3, wherein the workpiece is made from an AISI 300 or 400 series stainless steel.

### Claim 5 (depends on 4)

The process of claim 4, further comprising feeding a companion gas to the carburization reactor, the companion gas being a gas which is not an unsaturated hydrocarbon and further which is capable of reacting with oxygen under the conditions encountered during the carburization reaction.

### Claim 6 (depends on 5)

The process of claim 5, wherein the companion gas is hydrogen.

### Claim 7 (depends on 3)

The process of claim 3, wherein the carburization potential of the gas mixture inside the carburization reactor is changed over the course of carburization by at least one of (1) lowering the carburization temperature, (2) lowering the concentration of unsaturated hydrocarbon in the carburizing gas, (3) interrupting the carburization process by terminating the flow of unsaturated hydrocarbon to the carburization reactor while maintaining the workpiece at elevated temperature, and (4) interrupting the carburization process by terminating the flow of unsaturated hydrocarbon to the carburization reactor while maintaining the workpiece at elevated temperature and, during this interruption, reactivating the workpiece by contact with a carbon-free, halogen containing gas.

### Claim 8 (depends on 1)

The process of claim 1, comprising
(a) contacting the workpiece inside a carburization reactor with a halogen containing activating compound to at least partially activate the workpiece for low temperature carburization,
(b) thereafter feeding an unsaturated hydrocarbon to the carburization reactor under a pressure of about 3.5 to 100 torr and at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer which is essentially free of carbide precipitates as well as a thermal oxide film, and
(c) simultaneously with step (b) feeding additional amounts of a halogen containing activating compound to the carburization reactor for ˜0.5 minutes to ˜2 hours, after which the feeding of this carbon-free, halogen-containing activating compound to the carburization reactor is terminated while the feeding of the unsaturated hydrocarbon to the carburization reactor is continued.

### Claim 9 (depends on 8)

The process of claim 8, wherein steps (b) and (c) start at the same time.

### Claim 10 (depends on 8)

The process of claim 8, wherein additional amounts of a halogen containing activating compound are fed to the carburization reactor in step (c) for ˜1 minute to ˜1 hour.

### Claim 11 (depends on 10)

The process of claim 10, wherein additional amounts of a halogen containing activating compound are fed to the carburization reactor in step (c) for ˜2 minutes to ˜40 minutes.

### Claim 12 (depends on 8)

The process of claim 8, wherein the feeding of additional amounts of halogen containing activating compound to the carburization reactor in step (c) is terminated early enough to avoid substantial formation of by-product soot.

### Claim 13 (depends on 8)

The process of claim 8, wherein the carburization potential of the gas mixture inside the carburization reactor is changed over the course of carburization by at least one of (1) lowering the carburization temperature, (2) lowering the concentration of unsaturated hydrocarbon in the carburizing gas, (3) interrupting the carburization process by terminating the flow of unsaturated hydrocarbon to the carburization reactor while maintaining the workpiece at elevated temperature, and (4) interrupting the carburization process by terminating the flow of unsaturated hydrocarbon to the carburization reactor while maintaining the workpiece at elevated temperature and, during this interruption, reactivating the workpiece by contact with a carbon-free, halogen containing gas.

### Claim 14 (depends on 8)

The process of claim 8, wherein the carbon-free, halogen-containing activating compound is HF, HCl, NF3, F2, Cl2 or a mixture thereof.