Ferrite-martensite dual-phase stainless steel and method of manufacturing the same

Patent metadata

Field	Value
Publication number	US-2016289786-A1
Application number	US-201415033291-A
Country	US
Kind code	A1
Filing date	Oct 27, 2014
Priority date	Oct 31, 2013
Publication date	Oct 6, 2016
Grant date	—

Abstract

A ferrite-martensite dual-phase stainless steel has satisfactory corrosion resistance and workability for a material for the body of a freight car and excellent low-temperature toughness. The ferrite-martensite dual-phase stainless steel has a specified chemical composition, in which inequalities (I) and (II) below are satisfied, and a steel microstructure including a dual phase of a ferrite phase and a martensite phase, in which the content of the martensite phase is 5% or more and 95% or less in terms of vol. %:
10.5≦Cr+1.5×Si≦13.5  (I)

1.5≦30×(C+N)+Ni+0.5×Mn≦6.0  (II),
where Cr and Si in inequality (I) above and C, N, Ni, and Mn in inequality (II) above respectively represent the contents (mass %) of the corresponding chemical elements.

First claim

1 - 8 . (canceled)

9 . A ferrite-martensite dual-phase stainless steel, the steel having a chemical composition containing, by mass %,
C: 0.005% or more and 0.030% or less, N: 0.005% or more and 0.030% or less, Si: 0.05% or more and 1.00% or less, Mn: 0.05% or more and 2.5% or less, P: 0.04% or less, S: 0.02% or less, Al: 0.01% or more and 0.15% or less, Cr: 10.0% or more and 13.0% or less, Ni: 0.3% or more and 5.0% or less, V: 0.005% or more and 0.10% or less, Nb: 0.05% or more and 0.4% or less, Ti: 0.1% or less, and the balance being Fe and inevitable impurities, wherein inequalities (I) and (II) below are satisfied and a steel microstructure including a dual phase of a ferrite phase and a martensite phase, the content of the martensite phase being 5% or more and 95% or less in terms of vol. %:
10.5≦Cr+1.5×Si≦13.5  (I)

1.5≦30×(C+N)+Ni+0.5×Mn≦6.0  (II),

where Cr and Si in inequality (I) above and C, N, Ni, and Mn in inequality (II) above respectively represent the contents (mass %) of the corresponding chemical elements.

10 . The ferrite-martensite dual-phase stainless steel according to claim 9 , comprising a composition of the steel further containing at least one group selected from the groups A to B consisting of:
Group A: one, two, or more of Cu: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, and Co: 0.5% or less, by mass % Group B: one, two, or more of Ca: 0.01% or less, B: 0.01% or less, Mg: 0.01% or less, and REM: 0.05% or less, by mass %.

11 . The ferrite-martensite dual-phase stainless steel according to claim 9 wherein, by mass %,
the N content is 0.005% or more and 0.015% or less,
the Si content is 0.05% or more and 0.50% or less,
the Mn content is more than 1.0% and 2.5% or less,
the Ni content is 0.3% or more and less than 1.0%,
the Nb content is 0.05% or more and 0.25% or less, and
the Ti content is 0.02% or less and
wherein relational expression (III) below is satisfied:
2600C+1700N−20Si+20Mn−40Cr+50Ni+1660≧1270  (III),

where, C, N, Si, Mn, Cr, and Ni in relational expression (III) respectively represent the contents (mass %) of the corresponding chemical elements.

12 . The ferrite-martensite dual-phase stainless steel according to claim 11 , wherein, by mass %, the P content is less than 0.02%.

13 . The ferrite-martensite dual-phase stainless steel according to claim 11 , comprising a composition of the steel further containing at least one group selected from the groups C to D consisting of:
Group C: one, two, or more of Cu: 1.0% or less, Mo: less than 0.5%, W: 1.0% or less, and Co: 0.5% or less, by mass % Group D: one, two, or more of Ca: 0.01% or less, B: 0.01% or less, Mg: 0.01% or less, and REM: 0.05% or less, by mass %.

14 . The ferrite-martensite dual-phase stainless steel according to claim 12 , comprising a composition of the steel further containing at least one group selected from the groups C to D consisting of:
Group C: one, two, or more of Cu: 1.0% or less, Mo: less than 0.5%, W: 1.0% or less, and Co: 0.5% or less, by mass % Group D: one, two, or more of Ca: 0.01% or less, B: 0.01% or less, Mg: 0.01% or less, and REM: 0.05% or less, by mass %.

15 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 9 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

16 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 10 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

17 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 11 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

18 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 12 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

19 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 13 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

20 . A method of manufacturing the ferrite-martensite dual-phase stainless steel according to claim 15 , comprising:
heating a steel slab to a temperature of 1100° C. or higher and 1300° C. or lower; performing hot rolling including hot rough rolling in which at least one rolling pass is performed with a rolling reduction of 30% or more in a temperature range higher than 900° C.; and performing annealing at a temperature of 700° C. or higher and 900° C. or lower for one hour or more.

Assignees

• Jfe Steel Corp

Inventors

• Ishii Tomohiro
• Ota Hiroki
• Kami Chikara
• Murata Saiichi
• Fujisawa Mitsuyuki
• Ishibashi Genichi

Classifications

• C22C38/24

  with vanadium · CPC title

• C22C38/52

  with cobalt · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title

• C22C38/54

  with boron · CPC title