# US 2015/0147589 A1 · Rolled steel that hardens by means of precipitation after hot-forming and/or quenching with a tool having very high strength and ductility, and method for manufacturing same

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- Number: US 2015/0147589 A1
- Document ID: US20150147589A1
- Status: Published application
- Kind: A1
- Application number: 14/343,331
- Filed: 2011-09-06
- Published: 2015-05-28
- Earliest claimed: 2011-09-06
- Assignees: Arcelormittal Investigacion Y Desarrollo, S.L.
- Inventors: Olivier Bouaziz; David Barbier; Coralie Jung
- Web page: https://patentgrep.com/patent/US20150147589A1

## CPC

- C21D 8/0247: characterised by the heat treatment
- B32B 15/012: {one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy}
- B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium}
- C21D 1/22: Martempering
- C21D 1/673: for die quenching
- C21D 6/02: Hardening by precipitation
- C21D 7/13: by hot working
- C21D 9/46: for sheet metals
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/08: containing nickel {(C22C38/105 takes precedence)}
- C22C 38/14: containing titanium or zirconium
- C22C 38/34: with more than 1.5% by weight of silicon
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/52: with cobalt
- C22C 38/54: with boron
- C22C 38/58: with more than 1.5% by weight of manganese
- C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence)
- C23C 2/0224: {Two or more thermal pretreatments}
- C23C 2/024: {by cleaning or etching}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/12: Aluminium or alloys based thereon
- C21D 2211/004: Dispersions; Precipitations
- C21D 2211/008: Martensite
- Y10T 428/12757: Fe
- Y10T 428/12799: Next to Fe-base component [e.g., galvanized]
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A rolled steel sheet or blank is provided, the composition of which comprises the elements listed below in per cent by weight: C≦0.1%; 0.5%≦Mn≦7%; 0.5%≦Si≦3.5%; 0.5%<Ti≦2%; 2%<Ni≦7%; Al≦0.10%; Cr≦2%; Cu≦2%; Co≦2%; Mo≦2%; S≦0.005%; P≦0.03%; Nb≦0.1%; V≦0.1%; B<0.005%; N≦0.008%, and the silicon and titanium contents are such that: Si + Ti ≥ 2.5  % , Ti Si ≥ 0.3 the remainder of the composition consisting of iron and unavoidable impurities resulting from processing. A method for the fabrication of a part for a land motor vehicle from the sheet or blank by hot stamping is also provided. The microstructure of the part consisting essentially of martensite and intermetallic precipitates of type Fe2TiSi with an area percentage between 1 and 5% intermetallic precipitates.

## Claims

### Claim at position 1

1-16. (canceled)

### Claim 17

A rolled steel sheet or blank having a chemical composition comprising, expressed in percent by weight:
C≦0.1%;
0.5%≦Mn≦7%;
0.5%≦Si≦3.5%;
0.5% Ti≦2%;
2%≦Ni≦7%;
Al≦0.10%;
Cr≦2%;
Cu≦2%;
Co≦2%;
Mo≦2%;
S≦0.005%;
P≦0.03%;
Nb≦0.1%;
V≦0.1%;
B<0.005%; and
N≦0.008%,
the levels of silicon and titanium being such that:
Si
+
Ti
≥
2.5

%
,
and
Ti
Si
≥
0.3
,
a remainder of the composition consisting of iron and unavoidable impurities resulting from processing.

### Claim 18 (depends on 17)

The rolled steel sheet or blank as recited in claim 17 wherein the chemical composition comprises, expressed in percent by weight:
C≦0.050%;
3≦Mn≦5%;
1.0≦Si≦3.0%;
0.5≦Ti≦1.5%;
2.5≦Ni≦3.5%;
Al≦0.10%;
Cr≦1%;
Cu≦0.05%;
Co≦1%;
Mo≦2%;
S≦0.005%;
P≦0.03%;
Nb≦0.1%;
V≦0.1%;
B<0.005%; and
N≦0.008%,
the levels of silicon and titanium being such that:
Si
+
Ti
≥
2.5

%
Ti
Si
≥
0.3
the remainder of the composition consisting of iron and the unavoidable impurities resulting from processing.

### Claim 19 (depends on 17)

A steel part fabricated from the rolled steel sheet or blank as recited in claim 17 having a microstructure comprising at least 95% martensite and intermetallic precipitates of type Fe2TiSi.

### Claim 20 (depends on 19)

The steel part as recited in claim 19 wherein an area percentage of said intermetallic precipitates is between 1 and 5%.

### Claim 21 (depends on 19)

The steel part as recited in claim 19 wherein an average radius of said intermetallic precipitates is between 1 and 10 nm.

### Claim 22 (depends on 19)

The steel part as recited in claim 19 wherein an elastic limit of the steel part is greater than or equal to 1300 MPa and an elongation at fracture of the steel part is greater than or equal to 4%.

### Claim 23 (depends on 19)

The steel part as recited in claim 19 further comprising a coating containing zinc, a zinc-based alloy or a zinc alloy.

### Claim 24 (depends on 19)

The steel part as recited in claim 19 further comprising a coating containing aluminum, an aluminum-based alloy or an aluminum alloy.

### Claim 25 (depends on 17)

A method for fabricating a steel part comprising:
procuring the rolled steel sheet as recited in claim 17, a microstructure of the rolled sheet comprising at least 1% surface percentage of intermetallic precipitates of type Fe2TiSi;
cutting the rolled steel sheet to obtain a blank;
heating the blank to a first temperature Tγ for a first length of time tγ in a furnace to give the blank a fully austenitic structure;
stamping the blank in a tool at a second temperature to obtain a part, the second temperature being greater than a martensitic transformation temperature Ms; then
cooling the part at an average cooling rate Vref1 to a third temperature to form a martensitic matrix, the third temperature being below the martensitic transformation temperature Ms; and then
heating the steel part to a hold temperature TOA for a hold time tOA to give the steel part specified mechanical characteristics by precipitation of intermetallics of type Fe2TiSi between 1% and 5% surface percentage.

### Claim 26 (depends on 25)

The method as recited in claim 25 wherein the first temperature Tγ is between 700 and 1200° C.

### Claim 27 (depends on 25)

The method as recited in claim 25 wherein the first temperature Tγ is between 880 and 980° C.

### Claim 28 (depends on 25)

The method as recited in claim 25 wherein the first length of time tγ is between 60 and 360 seconds.

### Claim 29 (depends on 25)

The method as recited in claim 25 wherein the average cooling rate Vref1 is between 10 and 70° C./s.

### Claim 30 (depends on 25)

The method as recited in claim 25 wherein the hold temperature TOA is between 400 and 600° C.

### Claim 31 (depends on 25)

The method as recited in claim 25 wherein the hold time tOA is between 30 and 600 minutes.

### Claim 32 (depends on 25)

The method as recited in claim 25 further comprising coating the part with zinc, a zinc alloy or a zinc-based alloy after the part is heated to the hold temperature TOA for the hold time tOA.

### Claim 33 (depends on 25)

The method as recited in claim 25 further comprising coating the part with aluminum, an aluminum alloy or an aluminum-based alloy after the part is heated to the hold temperature TOA for the hold time tOA.

### Claim 34 (depends on 17)

A method for fabricating a steel part comprising:
procuring the rolled steel sheet as recited in claim 17, a microstructure of the rolled sheet comprising at least 1% surface percentage of intermetallic precipitates of type Fe2TiSi;
cutting the rolled steel sheet to obtain a blank;
stamping the blank;
heating the blank to a first temperature Tγ for a first length of time tγ in a furnace to give the blank a fully austenitic structure;
removing the blank from the furnace;
stamping the blank in a tool at a second temperature to obtain a part, the second temperature being above a martensitic transformation temperature Ms;
cooling the part at an average cooling rate Vref1 to a third temperature below the martensitic transformation temperature Ms; and
heating the part to a hold temperature TOA for a hold time tOA to give the part specified mechanical characteristics by precipitation of intermetallics of type Fe2TiSi between 1% and 5% surface percentage.

### Claim 35 (depends on 34)

The method as recited in claim 34 wherein the first temperature Tγ is between 700 and 1200° C.

### Claim 36 (depends on 34)

The method as recited in claim 34 wherein the first temperature Tγ is between 880 and 980° C.

### Claim 37 (depends on 34)

The method as recited in claim 34 wherein the first length of time tγ is between 60 and 360 seconds.

### Claim 38 (depends on 34)

The method as recited in claim 34 wherein the average cooling rate Vref1 is between 10 and 70° C./s.

### Claim 39 (depends on 34)

The method as recited in claim 34 wherein the hold temperature TOA is between 400 and 600° C.

### Claim 40 (depends on 34)

The method as recited in claim 34 wherein the hold time tOA is between 30 and 600 minutes.

### Claim 41 (depends on 34)

The method as recited in claim 34 further comprising coating the part with zinc, a zinc alloy or a zinc-based alloy after the part is heated to the hold temperature TOA for the hold time tOA.

### Claim 42 (depends on 34)

The method as recited in claim 34 further comprising coating the part with aluminum, an aluminum alloy or an aluminum-based alloy after the part is heated to the hold temperature TOA for the hold time tOA.

### Claim 43 (depends on 19)

A structural or safety part for a land motor vehicle comprising:
the steel part as recited in claim 19.

### Claim 44

A rolled steel sheet or blank having a chemical composition comprising, expressed in percent by weight:
C≦0.1%;
0.5%≦Mn≦7%;
0.5%≦Si≦3.5%;
0.5% Ti≦2%;
2%≦Ni≦7%;
Al≦0.10%;
Cr≦2%;
Cu≦2%;
Co≦2%;
Mo≦2%;
S≦0.005%;
P≦0.03%;
Nb≦0.1%;
V≦0.1%;
B<0.005%; and
N≦0.008%,
the levels of silicon and titanium being such that:
Si
+
Ti
≥
2.5

%
,
and
Ti
Si
≥
0.3
,
a remainder of the composition including iron and unavoidable impurities resulting from processing.