# US 5,702,540 A · Vacuum carburizing method and device, and carburized products

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- Number: US 5,702,540 A
- Document ID: US5702540A
- Status: Granted
- Kind: A
- Application number: 08/623,129
- Filed: 1996-03-28
- Granted: 1997-12-30
- Earliest claimed: 1995-03-29
- Assignees: JH Corporation
- Inventors: Ken Kubota
- Web page: https://patentgrep.com/patent/US5702540A

## CPC

- C23C 8/22: of ferrous surfaces
- 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)

## Abstract

In order to keep down soot production and to enable every part of the workpiece, including deep concavities to be uniformly carburized by vacuum carburizing, and to enable decreases in the quantities of gas and heat employed, carburizing treatment is performed in the heating chamber 2 of a vacuum carburizing furnace 1 with workpieces M being heated while acetylene gas is supplied from a carburizing gas source C inside the heating chamber 2, and the inside of the heating chamber 2 being evacuated by a vacuum evacuation source V to give a vacuum of .ltoreq.1 kPa.

## Claims

### Claim 1

A vacuum carburizing method which is a vacuum carburizing method in which carburizing treatment is performed by vacuum heating workpieces from steel material in the heating chamber of a vacuum carburizing furnace, and supplying a carburizing gas to the heating chamber, comprising employing a gaseous unsaturated aliphatic hydrocarbon comprising an acetylenic gas as said carburizing gas, and performing said carburizing treatment with the heating chamber at a vacuum of not more than 1 kPa.

### Claim 2 (depends on 1)

A vacuum carburizing method according to claim 1, wherein said acetylenic gas comprises acetylene gas.

### Claim 3 (depends on 1)

A vacuum carburizing method according to claim 1, further comprising performing a carbonitriding treatment by adding a gaseous nitrogen source to said carburizing gas.

### Claim 4

A vacuum carburizing device comprising a vacuum carburizing furnace provided with a heating chamber for heating workpieces comprising steel material, a carburizing gas source which supplies an acetylenic gas into said heating chamber, and a vacuum evacuation source which evacuates said heating chamber to a pressure of not more than 1 kPa, wherein said vacuum carburizing is performed at not more than 1 kPa.

### Claim 5

A carburized steel product which is a steel product provided with closed concavities in which the inside walls of said concavities are carburized having an inner diameter D and a depth L of a region over which the carburized case depth in the inner walls of the aforementioned closed holes is almost uniform characterized in that a ratio of L/D is in the range of 12-50.

### Claim 6 (depends on 5)

A carburized steel product according to claim 5 wherein said ratio L/D is in the range 12-36.

### Claim 7

A vacuum carburizing method which is a vacuum carburizing method in which carburizing treatment is performed by vacuum heating workpieces from steel material in the heating chamber of a vacuum carburizing furnace, and supplying a carburizing gas to the heating chamber, comprising employing a gaseous unsaturated aliphatic hydrocarbon comprising an acetylenic gas as said carburizing gas, and performing said carburizing treatment with the heating chamber at a vacuum of not more than 0.5 kPa.

### Claim 8

A vacuum carburizing device comprising a vacuum carburizing furnace provided with a heating chamber for heating workpieces comprising steel material, a a carburizing gas source which supplies an acetylenic gas into said heating chamber, and a vacuum evacuation source which evacuates said heating chamber to a pressure of not more than 0.5 kPa, wherein said vacuum carburizing is performed at not more than 0.5 kPa.