US 7,608,155 B2Granted

High strength, hot dip coated, dual phase, steel sheet and method of manufacturing same

AssigneeNucor Corporation

InventorWeiping Sun

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Abstract

A galvanized steel sheet having (a) a dual phase microstructure with a martensite phase and a ferrite phase and (b) a composition containing by percent weight: carbon in a range from about 0.01% to about 0.18%; manganese in a range from about 0.2% to about 3%; silicon ≦ about 1.2%; aluminum in a range from about 0.01% to about 0.1%; one or both of chromium and nickel in a range from about 0.1% to about 3.5%; calcium in a range from about 0.0003% to about 0.01%; phosphorus ≦ about 0.01%; sulfur ≦ about 0.03%; nitrogen ≦ about 0.02%; molybdenum ≦ about 1%; copper ≦ about 0.8%; one or more of niobium, titanium, and vanadium ≦ about 1%; and boron ≦ about 0.006% by weight; and with the balance of the composition being iron and incidental ingredients. In one embodiment, the steel sheet is both galvanized and galvannealed.

Claims18

Dependent claims

A method of making a galvanized steel sheet, comprising:

(I) at a temperature in a range between about (Ar3-60)° C. and about 980° C. (about 1796° F.), hot rolling a steel slab into a hot band, wherein the steel slab comprises a composition comprising:
carbon in a range from about 0.01% by weight to about 0.18% by weight,
manganese in a range from about 0.2% by weight to about 3% by weight,
silicon ≦ about 1.2% by weight,
aluminum in a range from about 0.01% by weight to about 0.1% by weight,
chromium or nickel or a combination thereof in a range from about 0.1% by weight to about 3.5% by weight,
calcium in a range from about 0.0003% by weight to about 0.01% by weight,
phosphorus ≦ about 0.01% by weight,
sulfur ≦ about 0.03% by weight,
nitrogen ≦ about 0.02% by weight,
molybdenum ≦ about 1% by weight,
copper ≦ about 0.8% by weight,
niobium or titanium or vanadium or a combination thereof ≦ about 1% by weight, and
boron ≦ about 0.006% by weight, and
with the balance of said composition comprising iron and incidental ingredients;
(II) cooling the hot band at a mean rate of at least about 3° C./s (about 5.4° F./s) to a temperature not higher than about 800° C. (about 1472° F.) obtaining a steel sheet comprising a dual phase microstructure comprising a martensite phase at least 3% by volume embedded in a ferrite matrix phase;
(III) coiling the cooled band to form a coil;
(IV) galvanizing the steel sheet by heating to a temperature higher than about 600° C. (1112° F.), holding the temperature in a soaking zone of a galvanizing line while using a line speed or process speed faster than about 30 m/min, cooling the steel sheet to a temperature close to the temperature in the galvanizing bath in a range between about 400° C. (about 752° F.) and about 550° C. (about 1022° F.), passing the steel sheet through the galvanizing bath to coat the steel sheet with a zinc coating or a zinc alloy coating, and cooling the galvanized steel sheet;
and
(V) obtaining a galvanized steel sheet comprising (a) a dual phase microstructure comprising a martensite phase and a ferrite phase, (b) said composition, and (c) one or more of a property chosen from (i) a weldability superior to that of known galvanized steel sheet having a dual phase microstructure of a martensite phase and a ferrite phase, (ii) an impact energy ≧ about 1200 g-m, measured on a V-notch Charpy specimen of about 1.5 mm thickness, or (iii) a yield strength/tensile strength ratio ≦ about 70%.

17 more elements

A method of making a galvanized steel sheet, comprising:

(I) at a temperature in a range between about (Ar3-30)° C. and about 930° C. (about 1706° F.), hot rolling a steel slab having said composition into a hot band, wherein the steel slab comprises a composition comprising:
carbon in a range from about 0.02% by weight to about 0.12% by weight,
manganese in a range from about 0.3% by weight to about 2.8% by weight,
silicon ≦ about 1% by weight,
aluminum in a range from about 0.0 15% by weight to about 0.09% by weight,
chromium or nickel or a combination thereof in a range from about 0.2% by weight to about 3% by weight,
calcium in a range from about 0.0005% by weight to about 0.009% by weight,
phosphorus ≦ about 0.08% by weight,
sulfur ≦ about 0.02% by weight,
nitrogen ≦ about 0.015% by weight,
molybdenum ≦ about 0.8% by weight,
copper ≦ about 0.6% by weight,
niobium or titanium or vanadium or a combination thereof ≦ about 0.8% by weight, and
boron ≦ about 0.003% by weight, and
with the balance of the composition comprising iron and incidental ingredients;
(II) cooling the hot band at a mean rate of at least about 5° C./s (about 9° F./s) obtaining a steel sheet comprising a dual phase microstructure comprising a martensite phase from about 3% to about 35% by volume embedded in a ferrite matrix phase;
(III) coiling the cooled band at a temperature in a range between 400° C. (about 752° F.) and about 750° C. (about 1382° F.) to form a coil of the steel sheet;
(IV) pickling the coil;
(V) cold rolling the pickled coil to a desired steel sheet thickness, with a total reduction of at least about 30%;
(VI) galvanizing the steel sheet by heating to a temperature in a range between about 650° C. (1202° F.) and about 950° C. (about 1742° F.), holding the temperature in a soaking zone of a galvanizing line while using a line speed or process speed in a range from about 50 m/min to about 150 m/min, and cooling the steel sheet to a temperature close to the temperature in the galvanizing bath in a range between about 425° C. (about 797° F.) and about 500° C. (about 932° F.),
passing the steel sheet through the galvanizing bath to coat the steel sheet with a zinc coating or a zinc alloy coating, and cooling the galvanized steel sheet;
and
(VII) obtaining a galvanized steel sheet comprising (a) a dual phase microstructure comprising a martensite phase and a ferrite phase, wherein the martensite phase comprises from about 3% by volume to about 35% by volume of the microstructure (b) said composition, and (c) properties of (i) a weldability superior to that of known galvanized steel sheet having a dual phase microstructure of a martensite phase and a ferrite phase, (ii) a yield strength/tensile strength ratio ≦ about 70%, (iii) an impact energy ≧ about 1200 g-m, measured on a V-notch Charpy specimen of about 1.5 mm thickness, (iv) an elongation ≧ about 20%, and (vii) an excellent n-value.

20 more elements

A method of making a galvanized and galvannealed steel sheet, comprising:

(I) at a temperature in a range between about (Ar3-60)° C. and about 980° C. (about 1796° F.), hot rolling a steel slab into a hot band, wherein the steel slab comprises a composition comprising:
carbon in a range from about 0.01% by weight to about 0.18% by weight,
manganese in a range from about 0.2% by weight to about 3% by weight,
silicon ≦ about 1.2% by weight,
aluminum in a range from about 0.01% by weight to about 0.1% by weight,
chromium or nickel or a combination thereof in a range from about 0.1% by weight to about 3.5% by weight,
calcium in a range from about 0.0003% by weight to about 0.01% by weight,
phosphorus ≦ about 0.01% by weight,
sulfur ≦ about 0.03% by weight,
nitrogen ≦ about 0.02% by weight,
molybdenum ≦ about 1% by weight,
copper ≦ about 0.8% by weight,
niobium or titanium or vanadium or a combination thereof ≦ about 1% by weight, and
boron ≦ about 0.006% by weight, and
with the balance of said composition comprising iron and incidental ingredients;
(II) cooling the hot band at a mean rate of at least about 3° C./s (about 5.4° F./s) to a temperature not higher than about 800° C. (about 1472° F.) obtaining a steel sheet comprising a dual phase microstructure comprising a martensite phase from about 3% to about 35% by volume embedded in a ferrite matrix phase;
(III) coiling the cooled band to form a coil;
(IV) galvanizing the steel sheet by heating to a temperature higher than about 600° C. (about 1112° F.), holding the temperature in a soaking zone of a galvanizing line while using a line speed or process speed faster than about 30 m/min, cooling the steel sheet to a temperature close to the temperature in the galvanizing bath in a range between about 400° C. (about 752° F.) and about 550° C. (about 1022° F.), passing the steel sheet through the galvanizing bath to coat the steel sheet with a zinc coating or a zinc alloy coating, and cooling the galvanized steel sheet;
(V) galvannealing the steel sheet by reheating to a temperature in a range from about 450° C. (about 842° F.) to about 650° C. (about 1202° F.) and cooling the steel sheet;
and
(VI) obtaining a galvanized and galvannealed steel sheet comprising (a) a dual phase microstructure comprising a martensite phase and a ferrite phase, wherein the martensite phase comprises from about 3% by volume to about 35% by volume of the microstructure, (b) said composition, and (c) one or more of a property chosen from (i) a weldability superior to that of known galvanized and galvannealed steel sheet having a dual phase microstructure of a martensite phase and a ferrite phase, (ii) an impact energy ≧ about 1200 g-m, measured on a V-notch Charpy specimen of about 1.5 mm thickness, or (iii) a yield strength/tensile strength ratio ≦ about 70%.

18 more elements

A method of making a galvanized and galvannealed steel sheet, comprising:

(I) at a temperature in a range between about (Ar3-30)° C. and about 930° C. (about 1706° F.), hot rolling a steel slab having said composition into a hot band, wherein the steel slab comprises a composition comprising:
carbon in a range from about 0.02% by weight to about 0.12% by weight,
manganese in a range from about 0.3% by weight to about 2.8% by weight,
silicon ≦ about 1% by weight,
aluminum in a range from about 0.0015% by weight to about 0.09% by weight,
chromium or nickel or a combination thereof in a range from about 0.2% by weight to about 3% by weight,
calcium in a range from about 0.0005% by weight to about 0.009% by weight, phosphorus ≦ about 0.08% by weight,
sulfur ≦ about 0.02% by weight,
nitrogen ≦ about 0.015% by weight,
molybdenum ≦ about 0.8% by weight,
copper ≦ about 0.6% by weight,
niobium or titanium or vanadium or a combination thereof ≦ about 0.8% by weight, and
boron ≦ about 0.003% by weight, and with the balance of the composition comprising iron and incidental ingredients;
(II) cooling the hot band at a mean rate of at least about 5° C./s (about 9° F./s) obtaining a steel sheet comprising a dual phase microstructure comprising a martensite phase from about 3% to about 35% by volume embedded in a ferrite matrix phase;
(III) coiling the cooled band at a temperature in a range between 400° C. (about 752° F.) and about 750° C. (about 1382° F.) to form a coil of the steel sheet;
(IV) pickling the coil;
(V) cold rolling the pickled coil to a desired steel sheet thickness, with a total reduction of at least about 30%;
(VI) galvanizing the steel sheet by heating to a temperature in a range between about 650° C. (1202° F.) and about 950° C. (about 1742° F.), holding the temperature in a soaking zone of a galvanizing line while using a line speed or process speed in a range from about 50 m/min to about 150 m/min, and cooling the steel sheet to a temperature close to the temperature in the galvanizing bath in a range between about 425° C. (about 797° F.) and about 500° C. (about 932° F.),
passing the steel sheet through the galvanizing bath to coat the steel sheet with a zinc coating or a zinc alloy coating, and cooling the galvanized steel sheet;
(VII) galvannealing the steel sheet by reheating to a temperature in a range from about 500° C. (about 932° F.) to about 600° C. (about 1112° F.) and cooling the steel sheet;
and
(VIII) obtaining a galvanized and galvannealed steel sheet comprising (a) a dual phase microstructure comprising a martensite phase and a ferrite phase, wherein the martensite phase comprises from about 3% by volume to about 35% by volume of the microstructure (b) said composition, and (c) properties of (i) a weldability superior to that of known galvanized steel sheet having a dual phase microstructure of a martensite phase and a ferrite phase, (ii) a yield strength/tensile strength ratio ≦ about 70%, (iii) an impact energy ≧ about 1200 g-m, measured on a V-notch Charpy specimen of about 1.5 mm thickness, (iv) an elongation ≦ about 20%, and (vii) an excellent n-value.

19 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/527,918Filed 27 Sep 2006
Published: US 2008/0075971 A127 Mar 2008
Granted: 27 Oct 2009
Term ends: Not estimatedThe source records don’t support an estimate.

Classification17 codes

C22C 38/002
Ferrous alloys, e.g. steel alloys: containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
C22C 38/02
Ferrous alloys, e.g. steel alloys: containing silicon
C22C 38/04
Ferrous alloys, e.g. steel alloys: containing manganese
C22C 38/06
Ferrous alloys, e.g. steel alloys: containing aluminium

Family

US 2008/0075971 A1Pre-grant publication · published 27 Mar 2008
US 7,608,155 B2This patent

From the US filing history. Foreign family members aren’t listed.

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