# US 11,993,823 B2 · High strength annealed steel products and annealing processes for making the same

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- Number: US 11,993,823 B2
- Document ID: US11993823B2
- Status: Granted
- Kind: B2
- Application number: 16/544,127
- Filed: 2019-08-19
- Published: 2020-02-06
- Granted: 2024-05-28
- Earliest claimed: 2016-05-10
- Assignees: United States Steel Corporation
- Applicants: United States Steel Corporation
- Inventors: David Paul Hoydick; Eduardo Augusto Silva; Matthew Michael McCosby
- Web page: https://patentgrep.com/patent/US11993823B2

## CPC

- C21D 9/46: for sheet metals
- 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}
- B32B 15/043: {of metal (B32B15/01 takes precedence)}
- B32B 15/18: comprising iron or steel {(B32B15/011, B32B15/012 and B32B15/013 take precedence)}
- C21D 1/20: Isothermal quenching, e.g. bainitic hardening
- C21D 1/22: Martempering
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 1/26: Methods of annealing
- C21D 1/78: Combined heat-treatments not provided for above
- C21D 8/0247: characterised by the heat treatment
- 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 38/008: {containing tin}
- 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 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium
- C22C 38/14: containing titanium or zirconium
- C22C 38/16: containing copper
- C22C 38/18: containing chromium
- C22C 38/40: with nickel
- C22C 38/54: with boron
- C23C 2/0224: {Two or more thermal pretreatments}
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath
- C23C 2/40: Plates; Strips
- C23C 28/021: {including at least one metal alloy layer}
- C23C 28/025: {with at least one zinc-based layer}
- C25D 3/22: of zinc
- C25D 5/36: of iron or steel
- C25D 7/0614: {Strips or foils}
- C21D 8/0236: {Cold rolling}
- C21D 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence)
- C21D 2211/001: Austenite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- 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)
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR

## Abstract

The present invention provides steel sheet products having controlled compositions that are subjected to two-step annealing processes to produce sheet products having desirable microstructures and favorable mechanical properties such as high strength and ultra-high formability. The steel sheet products may be cold rolled or hot rolled. Steels processed in accordance with the present invention exhibit favorable combined ultimate tensile strength and total elongation (UTS•TE) properties, and may fall into the category of Generation 3 advanced high strength steels, desirable in various industries including automobile manufacturers.

## Claims

### Claim 1

A high strength rolled steel sheet product comprising from 0.12 to 0.5 weight percent C, from 1 to 3 weight percent Mn, from 0.8 to 3 weight percent of a combination of Si and Al, balance Fe wherein the steel sheet product has been subjected to a two-step annealing process, comprises ferrite, substantially equiaxed retained austenite grains having an average aspect ratio of less than 2.0:1, and less than 15 volume percent of fresh, untempered martensite, is substantially free of tempered martensite, and has a combination of ultimate tensile strength and total elongation UTS•TE of greater than 25,000 MPa % and a hole expansion ratio of at least 30 percent.

### Claim 2 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the Si comprises up to 2 weight percent, the Al comprises up to 2 weight percent, and the rolled steel sheet product further comprises up to 0.05 weight percent Ti, and up to 0.05 weight percent Nb.

### Claim 3 (depends on 2)

The high strength rolled steel sheet product of claim 2, wherein the C comprises from 0.15 to 0.4 weight percent, the Mn comprises from 1.3 to 2.5 weight percent, the Si comprises from 0.2 to 1.8 weight percent, the Al comprises up to 1.5 weight percent, the Ti comprises up to 0.03 weight percent, and the Nb comprises up to 0.03 weight percent.

### Claim 4 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the ferrite comprises at least 50 volume percent, and the retained austenite comprises from 5 to 25 volume percent.

### Claim 5 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the retained austenite has an average grain size of less than 10 microns.

### Claim 6 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the retained austenite has an average grain size of less than 1 micron.

### Claim 7 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the rolled steel sheet product has an ultimate tensile strength of from 720 to 1,100 MPa and has a total elongation of at least 20 percent.

### Claim 8 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the UTS TE is at least 27,000 MPa %.

### Claim 9 (depends on 1)

The high strength rolled steel sheet product of claim 1, further comprising a zinc-based coating on the rolled steel sheet product.

### Claim 10 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the rolled steel sheet product is hot rolled.

### Claim 11 (depends on 1)

The high strength rolled steel sheet product of claim 1, wherein the retained austenite has an average grain size of less than 0.5 micron.