Ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment, and method of producing the same

Patent metadata

Field	Value
Publication number	US-2016017451-A1
Application number	US-201414773988-A
Country	US
Kind code	A1
Filing date	Mar 14, 2014
Priority date	Mar 14, 2013
Publication date	Jan 21, 2016
Grant date	—

Abstract

A ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment in the present invention contains, by mass %, C: 0.020% or less, Cr: 10.0% to 25.0%, N: 0.020% or less, Sn: 0.010% to 0.50%, and one or more of Ti: 0.60% or less, Nb: 0.60% or less, V: 0.60% or less, and Zr: 0.60% or less so as to satisfy the following Equation (1), in which the difference between stress σ1 (N/mm 2 ) after prestrain imparting tensile deformation with 7.5% of strain, and upper yield stress σ2 (N/mm 2 ) when the steel sheet is subjected to heat treatment at 200° C. for 30 minutes and then to tension again after the tensile deformation is 8 or less.
(Ti/48+V/51+Zr/91+Nb/93)/(C/12+N/14)≧1.0  (1)

First claim

1 . A ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment, comprising, as a steel composition, by mass %:
C: 0.020% or less; Si: 0.01% to 2.0%; Mn: 2.0% or less; P: less than 0.050%; S: less than 0.010%; Cr: 10.0% to 25.0%; N: 0.020% or less; Sn: 0.010% to 0.50%; one or more of Ti: 0.60% or less, Nb: 0.60% or less, V: 0.60% or less, and Zr: 0.60% or less so as to satisfy the following Equation (1); and a balance substantially consisting of Fe and inevitable impurities, wherein stress σ1 (N/mm 2 ) after prestrain imparting tensile deformation with 7.5% of strain and upper yield stress σ2 (N/mm 2 ) when the steel sheet is subjected to a heat treatment at 200° C. for 30 minutes and then to tension again after the prestrain imparting tensile deformation satisfy the following Equation (2):
(Ti/48+V/51+Zr/91+Nb/93)/(C/12+N/14)≧1.0  (1)

σ2−σ1≦8  (2)

(in Equation (1), each element name represents the amount (mass %) thereof and the amount of an element not contained in the steel is substituted by 0).

2 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 1 , further comprising, by mass %,
Al: 0.003% to 1.0%.

3 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 1 , further comprising, by mass %, one or more of,
Ni: 0.01% to 2.0%, Cu: 0.01% to 2.0%, and Mo: 0.01% to 2.0%.

4 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 1 , further comprising, by mass %, one or more of,
B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50%.

5 . A method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment, comprising:
a hot rolling process of performing finish rolling, which is performed subsequent to rough rolling and includes plural passes, at a total rolling reduction of 40% or more of the last three passes in the finish rolling and rolling temperature of 950° C. or lower of the last pass in the finish rolling, and performing coiling treatment at 500° C. or lower after the finish rolling; and a hot-rolled sheet annealing process of heating the steel sheet to 850° C. to 1,100° C. at a heating rate of 3° C./s or more in a range from 500° C. to 700° C., and then performing heat treatment at a cooling rate of 50° C./s or less in a range from 850° C. to 550° C. after the hot rolling process, wherein the method is used when a ferritic stainless steel sheet comprises, as a steel composition, by mass %, C: 0.020% or less, Si: 0.01% to 2.0%, Mn: 2.0% or less, P: less than 0.050%, S: less than 0.010%, Cr: 10.0% to 25.0%, N: 0.020% or less, Sn: 0.010% to 0.50%, one or more of Ti: 0.60% or less, Nb: 0.60% or less, V: 0.60% or less, and Zr: 0.60% or less so as to satisfy the following Equation (3), and a balance substantially consisting of Fe and inevitable impurities, is produced:
(Ti/48+V/51+Zr/91+Nb/93)/(C/12+N/14)≧1.0  (3)

(in Equation (3), each element name represents the amount (mass %) thereof and the amount of an element not contained in the steel is substituted by 0).

6 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 5 ,
wherein the reheating temperature of a slab having the steel composition before the hot rolling process is set to 1,100° C. or higher.

7 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 5 ,
wherein the steel sheet further comprises, by mass %, Al: 0.003% to 1.0% as the steel composition.

8 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 5 ,
wherein the steel sheet further comprises, by mass %, one or more of Ni: 0.01% to 2.0%, Cu: 0.01% to 2.0%, and Mo: 0.01% to 2.0% as the steel composition.

9 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 5 ,
wherein the steel sheet further comprises, by mass %, one or more of B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50% as the steel composition.

10 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 2 , further comprising, by mass %, one or more of,
Ni: 0.01% to 2.0%, Cu: 0.01% to 2.0%, and Mo: 0.01% to 2.0%.

11 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 2 , further comprising, by mass %, one or more of,
B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50%.

12 . The ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 3 , further comprising, by mass %, one or more of,
B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50%.

13 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 6 ,
wherein the steel sheet further comprises, by mass %, Al: 0.003% to 1.0% as the steel composition.

14 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 6 ,
wherein the steel sheet further comprises, by mass %, one or more of Ni: 0.01% to 2.0%, Cu: 0.01% to 2.0%, and Mo: 0.01% to 2.0% as the steel composition.

15 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 7 ,
wherein the steel sheet further comprises, by mass %, one or more of Ni: 0.01% to 2.0%, Cu: 0.01% to 2.0%, and Mo: 0.01% to 2.0% as the steel composition.

16 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 6 ,
wherein the steel sheet further comprises, by mass %, one or more of B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50% as the steel composition.

17 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 7 ,
wherein the steel sheet further comprises, by mass %, one or more of B: 0.0003% to 0.0025%, Mg: 0.0001% to 0.0030%, Ca: 0.0003% to 0.0030%, Sb: 0.001% to 0.50%, Ga: 0.0003% to 0.1%, REM (rare earth metal): 0.002% to 0.2%, and Ta: 0.005% to 0.50% as the steel composition.

18 . The method of producing a ferritic stainless steel sheet exhibiting small increase in strength after aging heat treatment according to claim 8 ,
wherein the steel sheet further comprises, by mass %, one or more of B: 0.0003% to 0.00

Assignees

• Nippon Steel & Sumikin Sst

Inventors

• Kimura Ken
• Hamada Junichi
• Ishimaru Eiichiro
• Yamagishi Akihito
• Hansaki Naoto

Classifications

• C21D8/00 Primary

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/001

  containing N · CPC title

• C22C38/50

  with titanium or zirconium · CPC title