# US 4,398,971 A · Method of heating, holding or heat treatment of metal material

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- Number: US 4,398,971 A
- Document ID: US4398971A
- Status: Granted
- Kind: A
- Application number: 06/337,087
- Filed: 1981-12-31
- Granted: 1983-08-16
- Earliest claimed: 1981-12-31
- Assignees: AGA Aktiebolag
- Inventors: Rune Peterson
- Web page: https://patentgrep.com/patent/US4398971A

## CPC

- C21D 1/763: {using a catalyst}
- 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

In an indirectly heated, gas-fired furnace (10) for the heat treatment of metal material in an atmosphere of processing gas consisting predominantly of nitrogen, the processing gas is produced using the heating exhaust gases as the principal raw material. The exhaust gases are cooled, filtered and freed of carbon monoxide and water vapor, whereupon a small amount of air is added to impart a predetermined value to the oxygen content and a controlled amount of liquefied petroleum gas or other hydrocarbon gas is added. A processing gas consisting predominantly of nitrogen, hydrogen and carbon monoxide is produced by thermal cracking of the liquefied petroleum gas in a catalytic reactor (25) and fed to the furnace (10). If a processing gas free of carbon and consisting predominantly of nitrogen and hydrogen is required, the reactor (25) may be replaced by a deoxo reactor into which the exhaust gases, after their oxygen content has been adjusted, are fed together with a controlled amount of hydrogen gas.

## Claims

### Claim 1

Method of heating, holding or heat treatment of metal material in an atmosphere of processing gas consisting predominantly of nitrogen and produced at, or in close vicinity to, the location where the heating, holding or heat treatment takes place, characterized in that the processing gas is produced using as the principal raw material exhaust gases from an installation generating heat by the complete combustion of hydrocarbon fuel, the exhaust gases being substantially free of carbon dioxide and water vapor and having a predetermined oxygen content of one or a few percent by volume, and hydrogen being then added in an amount having a predetermined relationship to the oxygen content.

### Claim 2 (depends on 1)

Method according to claim 1 in which the heating, holding or heat treatment takes place in a furnace having a furnace chamber heated indirectly by heating exhaust gases produced by the combustion of said hydrocarbon fuel, characterized in that said heating exhaust gases are used as the principal raw material for the processing gas.

### Claim 3 (depends on 1)

Method according to claim 1, characterized in that the hydrogen is added as hydrocarbon gas, and in that the hydrocarbon gas of the resulting gas mixture is subjected to thermal cracking and reacted with the oxygen to form carbon monoxide and hydrogen gas.

### Claim 4 (depends on 1)

Method according to claim 1, characterized in that the hydrogen is added as hydrogen gas in excess with respect to the oxygen of the exhaust gases and reacted with substantially all of the oxygen to form water, the excess of hydrogen being such that the resulting gas mixture has a predetermined content of hydrogen gas.

### Claim 5 (depends on 1)

A method according to claim 1, said hydrocarbon fuel being liquified petroleum gas.

### Claim 6 (depends on 1)

A method according to claim 1, the hydrocarbon fuel being natural gas.

### Claim 7 (depends on 3)

A method according to claim 3, said hydrocarbon gas being liquified petroleum gas.

### Claim 8 (depends on 3)

A method according to claim 3, said hydrocarbon gas being natural gas.