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

• US 10,745,774 B2
• Filed: 10/27/2014
• Issued: 08/18/2020
• Est. Priority Date: 10/31/2013
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Ishii, Tomohiro, Ota, Hiroki, Kami, Chikara, Murata, Saiichi, Fujisawa, Mitsuyuki, Ishibashi, Genichi
• Primary Examiner(s): Hevey, John A
• Application Number:
  US15/033,291
• Publication Number:
  US 20160289786A1
• Time in Patent Office: 2,122 Days
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 6/004 containing Cr and Ni
• CPC Class Codes: C21D 6/005 containing Mn
• CPC Class Codes: C21D 6/008 containing Si
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 9/46 for sheet metals
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/004 Very low carbon steels, i.e. having a carbon content of less than 0,01%
• CPC Class Codes: C22C 38/005 containing rare earths, i.e. Sc, Y, Lanthanides
• CPC Class Codes: C22C 38/008 containing tin
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/24 with vanadium
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: C22C 38/28 : with titanium or zirconium
• CPC Class Codes: C22C 38/42 : with copper
• CPC Class Codes: C22C 38/44 : with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 : with vanadium
• CPC Class Codes: C22C 38/48 : with niobium or tantalum
• CPC Class Codes: C22C 38/50 : with titanium or zirconium
• CPC Class Codes: C22C 38/52 : with cobalt
• CPC Class Codes: C22C 38/54 : with boron
• CPC Class Codes: C22C 38/58 : with more than 1.5% by weight of manganese

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.

Claims

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.