Annealing processes for making high strength steel products
AssigneeUnited States Steel Corporation
InventorsDavid Paul Hoydick, Eduardo Augusto Silva, Matthew Michael McCosby
Life of this patent
Estimating the term…
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. Steels processed in accordance with the present invention exhibit combined ultimate tensile strength and total elongation (UTS·TE) properties of greater than 25,000 MPa %. Steels with these properties fall into the category of Generation 3 advanced high strength steels, and are highly desired by various industries including automobile manufacturers.
Claims24
A method of producing a high strength rolled steel sheet product comprising from 0.12 to 0.5 weight percent C, from 1 to 3 weight percent manganese, from 0.8 to 3 weight percent of a combination of Si and Al, balance Fe, the method comprising:
- subjecting the steel sheet product to a first step annealing process to achieve a predominantly martensitic microstructure;
- and
- subjecting the steel sheet product to a second step process comprising soaking the sheet product in an intercritical regime at a temperature of from 720 to 850° C., cooling the steel sheet product to a temperature above 370° C., followed by holding the sheet product at a temperature of from 370 to 430° C., wherein the steel sheet product comprises ferrite, less than 15 volume percent of fresh, untempered martensite, retained austenite grains having an average aspect ratio of less than 2.0:1, is substantially free of tempered martensite, and has a combination of ultimate tensile strength and total elongation UTS·TE of greater than 27,000 MPa % and a hole expansion ratio of at least 30 percent.
A method of producing a high strength rolled steel sheet product comprising from 0.12 to 0.5 weight percent C, from 1 to 3 weight percent manganese, from 0.8 to 3 weight percent of a combination of Si and Al, balance Fe, the method comprising:
- subjecting the steel sheet product to a first step annealing process to achieve a predominantly martensitic microstructure;
- and
- subjecting the steel sheet product to a second step process comprising soaking the sheet product in an intercritical regime at a temperature of from 720 to 850° C., cooling the steel sheet product to a temperature above 370° C., followed by holding the sheet product at a temperature of from 370 to 430° C., wherein the steel sheet product comprises ferrite, less than 15 volume percent of fresh, untempered martensite, and retained austenite grains having an average aspect ratio of less than 2.0:1, is substantially free of tempered martensite, and has a total elongation of greater than 27 percent % and a hole expansion ratio of at least 30 percent.
Dependencies are inferred from the claim text.