AUSTENITIC STAINLESS STEEL FOR POLYMER FUEL CELL SEPARATOR WITH IMPROVED CONTACT RESISTANCE AND MANUFACTURING METHOD THEREOF

Abstract

Disclosed is an austenitic stainless steel for a fuel cell separator with improved contact resistance. The austenitic stainless steel for a fuel cell separator with improved contact resistance according to an embodiment of the present disclosure includes, in percent by weight (wt %), at most of C (excluding 0), at most 3.0% of Si (excluding 0), at most 3.0% of Mn (excluding 0), 20 to 30% of Cr, 8 to 20% of Ni, at most 0.003% of S, at most 0.03% of P, at most 0.6% of Mo (excluding 0), at most 0.8% of Cu (excluding 0), 0.1 to 0.3% of N, at most 2.0% of W (excluding and the remainder being Fe and other inevitable impurities.

Claims

1. An austenitic stainless steel for a fuel cell separator with improved contact resistance comprising, in percent by weight (wt %), at most 0.1% of C (excluding 0), at most 3.0% of Si (excluding 0), at most 3.0% of Mn (excluding 0), 20 to 30% of Cr, 8 to 20% of Ni, at most 0.003% of S, at most 0.03% of P, at most 0.6% of Mo (excluding 0), at most 0.8% of Cu (excluding 0), 0.1 to 0.3% of N, at most 2.0% of W (excluding 0), and the remainder being Fe and other inevitable impurities.

2. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel comprises, in percent by weight (wt %), 0.01 to 0.5% of W.

3. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel has an interfacial contact resistance of at most 10 m.Math.cm.sup.2 (100 N/cm.sup.2).

4. A method of manufacturing an austenitic stainless steel for a fuel cell separator with improved corrosion resistance, the method comprising: bright annealing a cold-rolled austenitic stainless steel comprising, in percent by weight (wt %), at most 0.1% of C (excluding 0), at most 3.0% of Si (excluding 0), at most 3.0% of Mn (excluding 0), 20 to 30% of Cr, 8 to 20% of Ni, at most 0.003% of S, at most 0.03% of P, at most 0.6% of Mo (excluding 0), at most 0.8% of Cu (excluding 0), 0.1 to 0.3% of N, at most 2.0% of W (excluding 0), and the remainder being Fe and other inevitable impurities; and performing alternating current electrolysis on the bright-annealed material in a sulfuric acid solution, wherein the alternating current electrolysis is performed by applying a current density of 15 to 30 A/dm.sup.2 for 7 seconds to 10 seconds.

5. The method according to claim 4, wherein the austenitic stainless steel comprises, in percent by weight (wt %), 0.01 to 0.5% of W.

6. The method according to claim 4, wherein the bright annealing is performed at a temperature of 1050 C. to 1150 C.

7. The method according to claim 4, wherein a temperature of the sulfuric acid solution is from 40 to 80 C.

8. The method according to claim 4, wherein a concentration of the sulfuric acid solution is from 50 to 300 g/L.

9. The method according to claim 4, wherein a frequency of the alternating current is from 10 to 120 Hz.

Description

EXAMPLES

[0072] Slabs having the compositions of alloying elements shown in Table 1, which were prepared by continuous casting, were heated at 1,250 C. for 2 hours and hot-rolled, followed by hot annealing at 1,100 C. for 90 seconds. Subsequently, the resultant was cold-rolled with a reduction ratio of 70% and bright-annealed at 1,050 C. after the cold rolling.

TABLE-US-00001 TABLE 1 Steel Type C Si Mn Cr Ni Mo Cu N W Steel Type A 0.025 0.4 0.8 21.3 10.5 0.6 0.8 0.2 0.01 Steel Type B 0.02 0.2 3 22 11 0.1 0.1 0.15 0.01 Steel Type C 0.03 2 0.5 22 12.5 0.1 0.1 0.2 0.5

[0073] Subsequently, electrolysis was performed under the conditions of Table 2 below, and interfacial contact resistance values under the conditions were measured. Evaluation of the interfacial contact resistance was performed as follows. Two pieces of the prepared material each having an area of 50 cm.sup.2 were prepared, and one piece of carbon paper (SGL-10BA) having an area of 4 cm.sup.2 and used as a gas diffusion layer was interposed therebetween, and then interfacial contact resistance was evaluated 5 times under a contact pressure of 100 N/cm.sup.2.

TABLE-US-00002 TABLE 2 Electrolysis Concentration Temperature Applied Current Frequency Interfacial of of current application of contact Steel sulfuric sulfuric density time current resistance Example Type acid (g/L) acid ( C.) (A/dm.sup.2) (s) (Hz) (mcm.sup.2) Example 1 A 200 60 15 7 60 5.8 Example 2 B 200 60 15 7 60 6.8 Example 3 C 200 60 15 7 60 7.9 Example 4 C 200 60 15 7 30 9.2 Example 5 C 200 60 15 7 120 7.6 Example 6 C 200 60 30 7 60 8 Example 7 C 200 80 15 7 60 8.3 Comparative C 200 60 20 7 5 25.5 Example 1 Comparative C 200 60 15 7 DC 52.5 Example 2 Comparative C 200 60 5 7 10 18.3 Example 3 Comparative C 200 60 10 7 60 53.1 Example 4 Comparative C 200 30 15 7 60 31.7 Example 5

[0074] Referring to Table 2, in the case where electrolysis was performed under the conditions of sulfuric acid and current suggested by the present disclosure, an interfacial contact resistance of at most 10 m.Math.cm.sup.2 was able to be obtained.

[0075] On the contrary, in Comparative Example 1, the surface reforming effect decreased due to the frequency of 5 Hz, so that a slightly high interfacial contact resistance of 25.5 m.Math.cm.sup.2 was obtained.

[0076] In Comparative Example 2, DC electrolysis was performed instead of AC electrolysis, so that a high interfacial contact resistance of 52.5 m.Math.cm.sup.2 was obtained.

[0077] In Comparative Examples 3 and 4, current densities lower than 15 A/dm.sup.2 were applied, and thus the layer formed by bright annealing was not removed and a high interfacial contact resistance exceeding 10 m.Math.cm.sup.2 was obtained. In Comparative Example 5, a temperature of the sulfuric acid solution was below 40 C., and thus removal of the layer formed by bright annealing is not sufficient, resulting in a high interfacial contact resistance of 31.7 m.Math.cm.sup.2.

[0078] According to the disclosed embodiment, the contact resistance may be 10 m.Math.cm.sup.2 or less by optimizing the conditions of current density and frequency during an electrolysis process, without additional surface treatment such as coating, and thus the austenitic stainless steel according to the present disclosure may be applied to a material of polymer fuel cell separators.

[0079] While the present disclosure has been particularly described with reference to exemplary embodiments, it should be understood by those of skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure.

INDUSTRIAL APPLICABILITY

[0080] The austenitic stainless steel for fuel cell separators according to the present disclosure may be industrially used by reducing manufacturing costs and manufacturing time because contact resistance is improved by optimizing electrolysis conditions, and accordingly an additional post-processing step is not required.