The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 14, 2021
Filed:
Oct. 30, 2018
Nippon Steel Corporation, Tokyo, JP;
NIPPON STEEL CORPORATION, Tokyo, JP;
Abstract
Provided is a hot rolled steel sheet comprising a predetermined composition wherein the hot rolled steel sheet comprises a dual structure of, by area fraction, a structural fraction of a martensite phase of 10 to 40% and a structural fraction of a ferrite phase of 60% or more, has an average grain size of ferrite grains of 5.0 μm or less, and has a coverage rate of martensite grains by ferrite grains of more than 60%. Also provided is a method for producing a hot rolled steel sheet comprising rolling a steel sheet wherein the respective rolling loads of the final three rolling stands are 80% or more of an immediately previous rolling stand and an average value of these rolling temperatures is 800 to 950° C., and forcibly cooling, then coiling the steel sheet wherein the forcibly cooling includes cooling started within 1.5 seconds after the rolling ends and cooling the steel sheet by a 30° C./second or more average cooling rate down to 600 to 750° C., natural cooling for 3 seconds or more and 10 seconds or less, and cooling by a 30° C./second or more average cooling rate down to 200° C. or less.