Hot-rolled steel sheet and manufacturing method thereof, and manufacturing method of cold-rolled steel sheet

Patent metadata

Field	Value
Publication number	US-11066720-B2
Application number	US-201615540855-A
Country	US
Kind code	B2
Filing date	Mar 22, 2016
Priority date	Mar 23, 2015
Publication date	Jul 20, 2021
Grant date	Jul 20, 2021

Abstract

A Si/Mn ratio of steel material components of a base material is not less than 0.27 nor more than 0.90 in mass ratio, an internal oxide layer having a thickness of not less than 1 μm nor more than 30 μm is provided right below an oxide scale of a steel sheet surface layer portion, and regarding the internal oxide layer, an internal oxide in a crystal grain of the internal oxide layer is an oxide containing Si and having a thickness of not less than 10 nm nor more than 200 nm in a crystal grain in a range of greater than 0% and 30% or less of a thickness of the internal oxide layer from an interface between the internal oxide layer and base iron toward a direction of the surface layer oxide scale, one or more branches of the internal oxide exist in a cross section of 1 μm×1 μm square, and in any crystal grain boundary having a length of 1 μm, one or more of the internal oxides in the crystal grain are connected to an internal oxide of the crystal grain boundary to form a net-like structure.

First claim

The invention claimed is:

1. A hot-rolled steel sheet, comprising:
C: 0.05 mass % to 0.45 mass %;
Si: 0.5 mass % to 3.0 mass %;
Mn: 0.50 mass % to 3.60 mass %;
P: 0.030 mass % or less;
S: 0.010 mass % or less;
Al: 0 mass % to 1.5 mass %;
N: 0.010 mass % or less;
O: 0.010 mass % or less;
Ti: 0 mass % to 0.150 mass %;
Nb: 0 mass % to 0.150 mass %;
V: 0 mass % to 0.150 mass %;
B: 0 mass % to 0.010 mass %;
Mo: 0 mass % to 1.00 mass %;
W: 0 mass % to 1.00 mass %;
Cr: 0 mass % to 2.00 mass %;
Ni: 0 mass % to 2.00 mass %;
Cu: 0 mass % to 2.00 mass %;
a total of one kind or two kinds or more selected from a group consisting of Ca, Ce, Zr, Hf, and REM: 0 mass % to 0.500 mass %; and
the balance: iron and impurities, wherein:
a Si/Mn ratio of steel material components of a base material of the steel sheet is not less than 0.27 nor more than 0.90 in mass ratio;
an internal oxide layer having a thickness of not less than 1 um nor more than 30 um is provided right below an oxide scale of a steel sheet surface layer portion; and
an internal oxide in a crystal grain existing in a region of greater than 0% and 30% or less of a thickness of the internal oxide layer from an interface between the internal oxide layer and base iron toward the surface layer oxide scale:
contains Si and has a thickness of not less than 10 mu nor more than 200 nm; and
forms a net-like structure in which one or more branches of the internal oxide exist in any 1 μm×1 μm square region of a cross section and an internal oxide at any crystal grain boundary with a length of 1 μm is connected to one or more of the internal oxides, and
wherein the net-like structure is formed in a manner that e internal oxides are dispersed in substantially the entire area in the crystal grain.

2. The hot-rolled steel sheet according to claim 1 , wherein
the Si/Mn ratio of the steel material components of the base material is 0.70 or less in mass ratio.

3. The hot-rolled steel sheet according to claim 1 , wherein
in the internal oxide layer, an oxide (Fe x , Mn 1-x ) 2 SiO 4 (0≤x<1) whose x value decreases toward a center of the steel sheet, and an amorphous SiO 2 exist.

4. The hot-rolled steel sheet according to claim 2 , wherein
in the internal oxide layer, an oxide (Fe x , Mn 1-x ) 2 SiO 4 (0≤x<1) whose x value decreases toward a center of the steel sheet, and an amorphous SiO 2 exist.

5. The hot-rolled steel sheet according to claim 1 , wherein
in the internal oxide layer, the oxide containing Si and having the net-like structure exists in a range of greater than 0% and 50% or less of the thickness of the internal oxide layer from the interface between the internal oxide layer and the base iron toward the direction of the surface layer oxide scale.

6. The hot-rolled steel sheet according to claim 2 , wherein
in the internal oxide layer, the oxide containing Si and having the net-like structure exists in a range of greater than 0% and 50% or less of the thickness of the internal oxide layer from the interface between the internal oxide layer and the base iron toward the direction of the surface layer oxide scale.

7. The hot-rolled steel sheet according to claim 3 , wherein
in the internal oxide layer, the oxide containing Si and having the net-like structure exists in a range of greater than 0% and 50% or less of the thickness of the internal oxide layer from the interface between the internal oxide layer and the base iron toward the direction of the surface layer oxide scale.

8. The hot-rolled steel sheet according to claim 4 , wherein
in the internal oxide layer, the oxide containing Si and having the net-like structure exists in a range of greater than 0% and 50% or less of the thickness of the internal oxide layer from the interface between the internal oxide layer and the base iron toward the direction of the surface layer oxide scale.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Fujii Takashi
• Date Hiromitsu
• Taniyama Akira
• Nishimoto Takumi
• Tadokoro Kenichiro

Classifications

• C21D8/02

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D8/0463

  following hot rolling · CPC title

• C22C38/58

  with more than 1.5% by weight of manganese · CPC title

• C22C38/00

  Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title