Transition metal nitride, separator for fuel cells, fuel cell stack, fuel cell vehicle, method of manufacturing transition metal nitride, and method of manufacturing separator for fuel cells

A method of manufacturing a transition metal nitride to be formed by nitriding by a plasma nitriding method comprising using a pulse plasma power supply adapted configured to repeat a discharge and an interruption having a duration of discharge of plasma and a duration of interruption of plasma within 1 to 1,000 μsec and the plasma nitriding method is performed under a condition that the base material has a temperature between 400° C. or more and 450° C. or less, a base material including an austenitic stainless steel, the manufacturing method comprising:

• forming, on a base layer formed by the base material, a first layer having a stacked crystal structure of a nano-level including a nitride having a cubic crystal structure of M4N type, and a nitride having a hexagonal crystal structure of M2-3N type;
• and having a second layer formed continuously on the first layer, including a nitride having at least one kind of crystal structure out of hexagonal crystal structures of Cr2N, CrN, and M2-3N type, and a cubic crystal structure of M4N type, and being formed as a surface-nitriding-processed portion of the base material continuously in a depth direction from a surface of the base material.

A method of manufacturing a separator for fuel cells, comprising:

• press-forming a passage for a fuel or an oxidizer to a work comprising a base material including an austenitic stainless steel;
• and applying a nitriding process to the work wherein the nitriding process comprises a plasma nitriding method comprising using a pulse plasma power supply adapted to repeat a discharge and an interruption having a duration of discharge of plasma and a duration of interruption of plasma within 1 to 1,000 μsec and the plasma nitriding method is performed under a condition that the base material has a temperature between 400° C. or more and 450° C. or less, thereby forming, on a base layer formed by the base material, a first layer having a stacked crystal structure of a nano-level including a nitride having a cubic crystal structure of M4N type, and a nitride having a hexagonal crystal structure of M2-3N type, and having a second layer formed continuously on the first layer, including a nitride having at least one kind of crystal structure out of hexagonal crystal structures of Cr2N, CrN, and M2-3N type, and a cubic crystal structure of M4N type, and being formed as a surface-nitriding-processed portion of the base material continuously in a depth direction from a surface of the base material.