公开(公告)号：US20210062289A1

公开(公告)日：2021-03-04

申请号：US17048430

申请日：2019-04-26

Applicant: NIPPON STEEL CORPORATION

Inventor： Tetsuya HIRASHIMA ,  Takeshi TOYODA

IPC: C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C22C38/08

Abstract: In a hot-rolled steel sheet having a predetermined chemical composition and having a metallographic structure including 90 vol % or greater of martensite and 0 vol % to 10 vol % of a residual structure, the residual structure includes one or both of bainite and ferrite, the average prior austenite grain size in an L-section parallel to a rolling direction and an average prior austenite grain size in a C-section parallel to a direction orthogonal to the rolling direction are 1.0 μm to 10.0 μm the aspect ratio associated with the prior austenite grain size is 1.8 or less, the average grain size of the residual structure in the L-section and the average grain size of the residual structure in the C-section are 5.0 μm or less, and the aspect ratio associated with the average grain size of the residual structure is 2.0 or less.

公开(公告)号：US20210025019A1

公开(公告)日：2021-01-28

申请号：US16648976

申请日：2018-11-22

Applicant: NIPPON STEEL CORPORATION

Inventor： Tetsuya HIRASHIMA ,  Takeshi TOYODA

IPC: C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/12 ,  C22C38/08 ,  C22C38/14 ,  C22C38/16

Abstract: Provided is a hot rolled steel sheet comprising a predetermined composition wherein the hot rolled steel sheet comprises ferrite with an average orientation difference in the same grain of 0.5 to 5.0° in 30 to 70 vol %, the ferrite and martensite in a total of 90 vol % or more, and a balance microstructure of 10 vol % or less, has an average grain size of the ferrite of 0.5 to 5.0 μm, and has an average grain size of the martensite and the balance microstructure of 1.0 to 10 μm. Provided is a method for producing a hot rolled steel sheet comprising rolling where two or more consecutive passes of rolling including a final pass are performed under conditions of a rolling temperature: A point or more and less than Ae3 point, a strain rate: 1.0 to 50/sec, and a time between passes: within 10 seconds and where a total strain amount of all passes satisfying the conditions is 1.4 to 4.0, cooling by a 20° C./sec or more average cooling rate, and coiling the steel sheet at room temperature or more and less than 300° C.

公开(公告)号：US20210040589A1

公开(公告)日：2021-02-11

申请号：US17044693

申请日：2019-04-17

Applicant: NIPPON STEEL CORPORATION

Inventor： Takeshi TOYODA ,  Tetsuya HIRASHIMA ,  Riki OKAMOTO

IPC: C22C38/34 ,  C22C38/28 ,  C22C38/26 ,  C22C38/22 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D9/46 ,  C21D8/02

Abstract: The hot-rolled steel sheet includes, in % by mass, 0.10% or more and 0.50% or less of C; 0.10% or more and 3.0% or less of Si; 0.5% or more and 3.0% or less of Mn; 0.10% or less of P; 0.010% or less of S; 1.00% or less of Al; 0.010% or less of N; 0% or more and 0.20% or less of Ti; 0% or more and 0.100% or less of Nb; 0% or more and 0.0060% or less of Ca; 0% or more and 0.50% or less of Mo; and 0% or more and 1.00% or less of Cr; with the balance comprising Fe and impurities, and an average grain size of prior austenite in a structure is 0.1 μm or larger and 3.0 μm or smaller, and a sheet crown quantity corresponding to a thickness difference between a width center portion and a portion away, by 10 mm, from a width edge portion in the widthwise direction toward the width center portion is 80 μm or smaller.

公开(公告)号：US20200224294A1

公开(公告)日：2020-07-16

申请号：US16626469

申请日：2018-08-09

Applicant: NIPPON STEEL CORPORATION

Inventor： Tetsuya HIRASHIMA ,  Takeshi TOYODA

IPC: C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/04 ,  C22C38/02 ,  C22C38/06 ,  C22C38/00 ,  C21D8/02

Abstract: A hot rolled steel sheet according to an aspect of the present invention has a predetermined chemical composition, and a metallographic structure in which martensite is the major structure, wherein an average length of grains in an L direction parallel to a rolling direction is 0.2 μm or more and 5.0 μm or less, an average length of grains in a C direction parallel to a transverse direction is 0.1 μm or more and 5.0 μm or less, the ratio of the average length in the C direction to the average length in the L direction is 0.2 or more and 5.0 or less, and the tensile strength is 1180 MPa or more.

公开(公告)号：US20190390294A1

公开(公告)日：2019-12-26

申请号：US16481765

申请日：2018-02-16

Applicant: NIPPON STEEL CORPORATION

Inventor： Takeshi TOYODA ,  Riki OKAMOTO ,  Natsuko SUGIURA ,  Tetsuya HIRASHIMA

IPC: C21D9/46 ,  C22C38/28 ,  C22C38/26 ,  C22C38/22 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00 ,  B21B3/02 ,  B21B45/00

Abstract: A hot rolled steel sheet is provided, which is excellent in collision characteristics, excellent in anisotropy of toughness, and high in strength. The hot rolled steel sheet is characterized by containing, by mass %, C: 0.10% to 0.50%, Si: 0.10% to 3.00%, Mn: 0.5% to 3.0%, P: 0.100% or less, S: 0.010% or less, Al: 1.00% or less, N: 0.010% or less and a balance of Fe and impurities, wherein a metal structure at position of ¼ thickness from surface in L-cross-section of the steel sheet comprises prior austenite grains of average value of aspect ratios of 2.0 or less, average grain size of 0.1 μm to 3.0 μm, and coefficient of variation of a standard deviation of grain size distribution/average grain size of 0.40 or more, and a texture with X-ray diffraction intensity ratio of {001} orientation for random samples of 2.0 or more, and the steel sheet has tensile strength of 1180 MPa or more.