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US 7,442,268 B2Granted
Method of manufacturing cold rolled dual-phase steel sheet
AssigneeNucor Corporation
InventorWeiping Sun
Life of this patent
Estimating the term…
Abstract
A steel sheet having (a) a dual phase microstructure with a martensite phase and a ferrite phase and (b) a composition containing by percent weight: 0.01% to 0.2% C; 0.3% to 3% Mn; 0.05% to 2% Si; 0.1% to 2% Cr; 0.01% to 0.10 Al; and 0.0005% to 0.01% Ca, with the balance of the composition being iron and incidental ingredients. Also, the steel sheet is made by a batch annealing method, and has a tensile strength of at least approximately 400 MPa and an n-value of at least approximately 0.175.
Claims14
A batch annealing method of making a dual phase 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 0.2% by weight,
- manganese in a range from about 0.3% by weight to about 3% by weight,
- silicon in a range from about 0.05% by weight to about 2% by weight,
- chromium in a range from about 0.1% by weight to about 2% by weight,
- aluminum in a range from about 0.01% by weight to about 0.10% by weight, and
- calcium in a range from about 0.0005% by weight to about 0.01% by weight,
- with the balance of said 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) to a temperature not higher than about 750° C. (about 1382° F.) obtaining a steel sheet comprising a dual phase microstructure comprising a martensite phase no more than about 35% by volume embedded in a ferrite matrix phase;
- (III) coiling the cooled band to form a coil;
- (IV) cold rolling the coil to a desired steel sheet thickness, with a total reduction of at least about 35%;
- (V) annealing the cold rolled steel sheet in a batch furnace at a temperature higher than about 500° C. (about 932° F.) and lower than about the Ac1 temperature for longer than about 60 minutes;
- (VI) cooling the annealed steel sheet to a temperature lower than about 400° C. (about 752° F.) obtaining a steel sheet comprising (a) a dual phase microstructure comprising a martensite phase and a ferrite phase, (b) said composition, and (c) properties comprising a tensile strength of at least about 400 MPa and an n-value of at least about 0.175.
10 more elements
A batch annealing method of making a steel sheet, comprising:
- (I) at a temperature in a range between about (Ar3-30)° C. and about 950° C., (about 1742° 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 0.2% by weight,
- manganese in a range from about 0.3% by weight to about 3% by weight,
- silicon in a range from about 0.05% by weight to about 2% by weight,
- chromium in a range from about 0.1% by weight to about 2% by weight,
- aluminum in a range from about 0.01% by weight to about 0.10% by weight, and
- calcium in a range from about 0.0005% by weight to about 0.01% by weight,
- with the balance of said composition comprising iron and incidental ingredients;
- (II) cooling the hot band at a mean rate of at least about 10° C./s (about 18° F./s) to a temperature not higher than about 6500 C. (about 1202° 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) cold rolling the coil at about ambient temperature to a desired steel sheet thickness, with a total reduction ranging from about 45% to about 85%;
- (V) annealing the cold rolled steel sheet in a batch furnace at a temperature higher than about 650° C. (about 1202° F.) and lower than about the Ac1 temperature for longer than about 60 minutes;
- (VI) cooling the annealed steel sheet to a temperature lower than about 300° C. (about 572° F.), and
- (VII) obtaining a steel sheet comprising (a) a dual phase microstructure comprising a martensite phase embedded in a ferrite matrix 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 comprising a tensile strength of at least about 400 MPa, and an n-value of at least about 0.175 after cold rolling and batch annealing.
11 more elements
Dependencies are inferred from the claim text.