Method for chromium upgrading of ferritic steel interconnects for solid oxide cell stack applications
In a method for chromium upgrading of interconnects made of ferritic steel to be used in solid oxide cell stacks, comprising the steps of shaping the interconnect, depositing a coating comprising Cr on at least one surface of the shaped interconnect and performing one or more thermal treatments at a temperature below 1000° C., the resulting Cr concentration near the surface of the interconnect is higher than the Cr concentration in the ferritic steel before shaping. Specifically, the average Cr concentration of the shaped interconnect is increased to 26 wt % Cr or higher.
1. A method for chromium upgrading of interconnects made of ferritic steel to be used in solid oxide cell stacks, comprising the steps of:
shaping the interconnect,
depositing a coating comprising Cr on at least one surface of the shaped interconnect,
performing one or more thermal treatments at a temperature below 1000° C.,
whereby the resulting Cr concentration near the surface of the interconnect is higher than the Cr concentration in the ferritic steel before shaping.
2. The method according to claim 1 , wherein the average Cr concentration of the shaped interconnect is increased to 26 wt % Cr or higher.
3. The method according to claim 1 , wherein the ferritic steel is a group 1 ferritic steel, group 2 ferritic steel, group 3 ferritic steel, group 4 ferritic steel or one of the following steels: Crofer22APU, Crofer22H, ZMG G10.
4. The method according to claim 3 , wherein the ferritic steel is a group 2 ferritic steel.
5. The method according to claim 1 , wherein the deposition step can be characterized as hard chromium plating.
6. The method according to claim 5 , wherein the thickness of the deposited coating is at least 1 micron and less than 1 millimeter.
7. The method according to claim 1 , wherein the deposition step is a chromizing process.
8. The method according to claim 1 , wherein the shaping of the interconnect is carried out by forming.
9. The method according to claim 8 , wherein the forming is carried out by stamping, pressing, forging, rolling, coining, embossing, extrusion, roll-forming, hydroforming or deep-drawing.
10. The method according to claim 8 , wherein the pressing power used for forming of the interconnect is less than 500 bar.
11. The method according to claim 1 , wherein the shaping of the interconnect is carried out by machining.
12. The method according to claim 11 , wherein the machining is carried out by drilling, milling, photochemical etching, electrochemical etching, dry etching, or laser cutting.
13. The method according to claim 1 , wherein the coefficient of thermal expansion of the interconnect after chromium upgrading is higher than 12 ppm/K, but lower than 13 ppm/K.
14. An interconnect of ferritic steel to be used in solid oxide cell stacks wherein the interconnects are prepared by the method according to claim 1 .
15. The method according to claim 3 , wherein the ferritic steel is AISI 430.
16. The method according to claim 8 , wherein the pressing power used for forming of the interconnect is less than 200 bar.