# US 6,294,131 B1 · Heat resistant steel

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- Number: US 6,294,131 B1
- Document ID: US6294131B1
- Status: Granted
- Kind: B1
- Application number: 09/554,709
- Filed: 2000-07-14
- Granted: 2001-09-25
- Earliest claimed: 1997-11-17
- Assignees: Ceramic Fuel Cells Limited
- Inventors: Donald Jaffrey
- Web page: https://patentgrep.com/patent/US6294131B1

## CPC

- H01M 8/0208: Alloys
- H01M 8/021: Alloys based on iron
- H01M 2008/1293: {Fuel cells with solid oxide electrolytes}
- H01M 2300/0074: Ion conductive at high temperature
- Y02E 60/50: Fuel cells
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A steel composition particularly useful for components of solid oxide fuel cells, for example a connector plate for collecting electrical current from a solid oxide fuel cell, consisting of, in weight percent, 18-28.5 Cr, 0.001-0.20 C, <0.1 Si, 0.005-0.10 Mn, <1.0 Ni, <0.25 N, <0.05 S, <0.08 P, <0.06 Al, <0.25 Additional Defined Metals, and 0.005-0.50 REM, wit the residue iron, excluding incidental impurities, where Additional Defined Metals is the sum of titanium, niobium, vanadium, molybdenum and copper, and REM is one or more of the rare earth metal elements in the group of the lanthanide elements 57 to 71, scandium and yttrium.

## Claims

### Claim 1

A steel composition consisting of, in weight percent,
Chromium 20-27.5 Carbon 0.001-0.20 Silicon <0.1 Manganese 0.005-0.10 Nickel <1.0 Nitrogen <0.25 Sulphur <0.05 Phosphorus <0.08 Aluminium <0.06 Additional Defined Metals <0.25 (total amount) REM 0.005-0.50 (total amount)
with the residue iron, excluding incidental impurities, where Additional Defined Metals is any titanium, niobium, vanadium, molybdenum and copper present in the steel composition, and REM is any rare earth metal element or elements in the group of the lanthanide elements 57 to 71, scandium and yttrium, said steel having a stable, adherent and very thin layer of chromium oxide which protects the underlying metal from further oxygen induced degradation and provides a superior level of electrical conductivity for use in components of solid oxide fuel cells.

### Claim 2 (depends on 1)

A steel composition according to claim 1 consisting of, in weight percent,
Chromium 20-27.5 Carbon 0.01-0.08 Silicon <0.1 Manganese 0.005-0.05 Nickel <0.1 Nitrogen <0.20 Sulphur <0.03 Phosphorus <0.04 Aluminium <0.05 Additional Defined Metals up to 0.10 REM 0.01-0.25
with the residue iron, excluding incidental impurities.

### Claim 3 (depends on 2)

A steel composition according to claim 2 consisting of, in weight percent,
Chromium 23-25 Carbon 0.03-0.06 Silicon <0.09 Manganese 0.005-0.05 Nickel <0.02 Nitrogen <0.10 Sulphur <0.01 Phosphorus <0.04 Aluminium <0.05 Additional Defined Metals <0.10 REM 0.01-0.10
with the residue iron, excluding incidental impurities.

### Claim 4 (depends on 1, 2)

A steel composition according to claims 1, 2, or 3 wherein the total level of any Additional Defined Metals is <0.04 weight percent.

### Claim 5 (depends on 1, 2)

In a solid oxide fuel cell stack, a component adapted to be exposed to a temperature in excess of 750° C. and an oxidising atmosphere, said component being formed of a steel composition according to claims 1, 2, or 3.

### Claim 6 (depends on 1, 2)

A connector plate for collecting electrical current from a solid oxide fuel cell, said plate being formed of a steel composition according to claims 1, 2, or 3.

### Claim 7 (depends on 6)

A connector plate according to claim 6 wherein at least one surface thereof is subjected to a calorising treatment.