Stainless steel having superior surface quality and moldability for fuel cell divider sheet, and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-9777344-B2
Application number	US-201214368689-A
Country	US
Kind code	B2
Filing date	Dec 26, 2012
Priority date	Dec 26, 2011
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

Provided is a ferrite-based stainless steel having superior moldability when molding a fuel cell divider sheet from a material by controlling yield point elongation in accordance with alloy components. The ferrite-based stainless steel comprises, in weight percentages: no more than 0.02% of C; no more than 0.02% of N; no more than 0.4% of Si; no more than 0.2% of Mn; no more than 0.04% of P; no more than 0.02% of S; 25.0-32.0% of Cr; 0-1.0% of Cu; no more than 0.8% of Ni; no more than 0.01-0.5% of Ti; no more than 0.01-0.5% of Nb; no more than 0.01-1.5% of V; and residual Fe and inevitable elements, wherein the content of Ti, Nb, V, C, and N in terms of weight % of steel uses Formula (1) to render a yield point elongation of the material of no more than 1.1%, and wherein a steel material has superior moldability.

9.1C−1.76V+5.37(C+N)/Ti−1.22Nb≦0.7.  Formula (1)

First claim

The invention claimed is:

1. A stainless steel having superior surface quality and moldability, comprising:
in weight %, more than 0 to no more than 0.02% of C; more than 0 to no more than 0.02% of N; more than 0 to no more than 0.4% of Si; more than 0 to no more than 0.2% of Mn; more than 0 to no more than 0.04% of P; more than 0 to no more than 0.02% of S; 25.0 to 32.0% of Cr, 0 to 1.0% of Cu; more than 0 to no more than 0.8% of Ni; 0.01 to 0.5% of Ti; 0.01 to 0.05% of Nb, 0.01 to 1.5% of V; residual Fe; and inevitably contained elements,
wherein the stainless steel meets Formula (1) below, and has yield point elongation of no more than 1.1%,
9.1C−1.76V+5.37(C+N)/Ti−1.22Nb≦0.7  Formula (1)

and wherein the stainless steel further comprises (Ti,Nb) (C,N) precipitates, wherein an area fraction (%) of the entire precipitates per unit area in the stainless steel is no more than 3.5%, and an area fraction (%) of (Ti,Nb) (C,N) precipitates/entire precipitates is 62% or more.

2. The stainless steel of claim 1 , further comprising: one or two elements selected from the group consisting of 0 to 4% of Mo and 0 to 1% of W in weight %.

3. The stainless steel of claim 1 , wherein the yield point elongation of the stainless steel is measured for a cold rolled sheet having a thickness of no more than 0.2 mm.

4. The stainless steel of claim 1 , comprising: more than 0 to no more than 0.3% of Ni in weight %.

5. The stainless steel of claim 1 , wherein C+N is no more than 0.032% in weight %.

6. A method of manfuacturing a stainless steel having superior surface quality and moldability, comprising: in weight %, more than 0 to no more than 0.02% of C; more than 0 to no more than 0.02% of N; more than 0 to no more than 0.4% of Si; more than 0 to no more than 0.2% of Mn; more than 0 to no more than 0.04% of P; more than 0 to no more than 0.02% of S; 25.0 to 32.0% of Cr; 0 to 1.0% of Cu; more than 0 to no more than 0.8% of Ni; 0.01 to 0.5% of Ti; 0.01 to 0.5% of Nb; 0.01 to 1.5% of V; residual Fe, and inevitably contained elements,
wherein the stainless steel having a composition meeting Formula (1) is subjected to a casting process, a hot rolling process, and a cold rolling process, and then a cold-rolling annealing heat treatment, and yield point elongation is controlled to be no more than 1.1%, and a temperature of the cold-rolling annealing heat treatment after the cold rolling process is controlled at a temperature of 900 to 1100° C., and wherein, after cold-rolling annealing heat treatment, the stainless steel includes (Ti,Nb)(C,N) precipitates, and an area fraction (%) of the entire precipitates per unit area in the stainless steel is no more than 3.5%, and an area fraction (%) of (Ti,Nb)(C,N) precipitates/entire precipitates is 62% or more
9.1C−1.76V+5.37(C+N)/Ti−1.22Nb≦0.7  Formula (1).

7. The method of claim 6 , wherein the stainless steel further includes one or two elements selected from the group consisting of 0 to 4% of Mo and 0 to 1% of W in weight %.

8. The method of claim 6 , further comprising molding the stainless steel into a thin plate for the fuel cell divider sheet.

9. The method of claim 6 , wherein the stainless steel includes more than 0 to no more than 0.3% of Ni in weight %, and no more than 0.032% of C+N.

Assignees

• Posco

Inventors

• Kim Jong Hee
• Jo Ki-Hoon
• Chung Yang Jin
• Lee Yun Yong
• Lee Sang Woo

Classifications

• Y02P70/50

  Manufacturing or production processes characterised by the final manufactured product · CPC title

• C22C38/24

  with vanadium · CPC title

• C21D6/002

  containing Cr (C21D6/004 takes precedence) · CPC title

• C22C38/28

  with titanium or zirconium · CPC title

• C22C38/02

  containing silicon · CPC title