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

Patent metadata

Field	Value
Publication number	US-10745774-B2
Application number	US-201415033291-A
Country	US
Kind code	B2
Filing date	Oct 27, 2014
Priority date	Oct 31, 2013
Publication date	Aug 18, 2020
Grant date	Aug 18, 2020

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

The invention claimed is:

1. A ferrite-martensite dual-phase hot rolled and annealed 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 0.026% 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 less than 1.0%,
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 microstructure of the hot rolled and annealed stainless steel includes 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, and
wherein an absorbed energy at a temperature of −50° C. on a Charpy test is 25 J or more, a corrosion area ratio is 15% or less and an elongation is 15.0% or more.

2. The ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 1 , 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 %.

3. The ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 1 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.

4. The ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 3 , wherein, by mass %, the P content is less than 0.02%.

5. The ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 3 , 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 %.

6. The ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 4 , 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 %.

7. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 1 , 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.

8. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 2 , 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.

9. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 3 , 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.

10. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 4 , 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.

11. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 5 , 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.

12. A method of manufacturing the ferrite-martensite dual-phase hot rolled and annealed stainless steel according to claim 6 , 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

• C22C38/26

  with niobium or tantalum · CPC title

• C22C38/58 Primary

  with more than 1.5% by weight of manganese · CPC title

• C22C38/24

  with vanadium · CPC title

• C22C38/004

  Very low carbon steels, i.e. having a carbon content of less than 0,01% · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title