Hot-rolled steel sheet for coiled tubing and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-11401594-B2
Application number	US-201916964630-A
Country	US
Kind code	B2
Filing date	Jan 16, 2019
Priority date	Jan 29, 2018
Publication date	Aug 2, 2022
Grant date	Aug 2, 2022

Abstract

Provided are a hot-rolled steel sheet for coiled tubing and a method for manufacturing the steel sheet. The steel sheet has a yield strength of 480 MPa or more, a tensile strength of 600 MPa or more, a yield-strength difference (ΔYS) of 100 MPa or more, where the yield-strength difference is defined as a difference in yield strength between before and after a prestrain-heat treatment performed for simulation of a tube-making process and a stress-relief annealing heat treatment which are currently implemented, and a yield strength of 620 MPa or more after the prestrain-heat treatment.

First claim

The invention claimed is:

1. A hot-rolled steel sheet for coiled tubing, the steel sheet having
a chemical composition containing, by mass %,
C: 0.10% or more and 0.16% or less,
Si: 0.1% or more and 0.5% or less,
Mn: 0.8% or more and 1.8% or less,
P: 0.001% or more and 0.020% or less,
S: 0.0050% or less,
Al: 0.01% or more and 0.08% or less,
Cu: 0.1% or more and 0.5% or less,
Ni: 0.1% or more and 0.5% or less,
Cr: 0.5% or more and 0.8% or less,
Mo: 0.10% or more and 0.5% or less,
Nb: 0.01% or more and 0.05% or less,
Ti: 0.01% or more and 0.03% or less,
N: 0.001% or more and 0.006% or less, and
a balance of Fe and inevitable impurities,
a microstructure at a position located at ½ of a thickness of the steel sheet including bainite and bainitic ferrite in a total amount of 80% or more in terms of area fraction, in which an amount of solid solution Nb is 20% or more of a total Nb mass content,
a yield strength of 480 MPa or more,
a tensile strength of 600 MPa or more and 800 MPa or less,
a yield-strength difference (ΔYS) of 100 MPa or more, where the yield-strength difference is defined as a difference in yield strength between before and after a prestrain-heat treatment, in which the steel sheet is subjected to a heat treatment at a temperature of 650° C. for 60 seconds after 5% pre-straining, and
a yield strength of 620 MPa or more after the prestrain-heat treatment.

2. The hot-rolled steel sheet for coiled tubing according to claim 1 , wherein the chemical composition further contains, by mass %, one or more selected from
B: 0.0005% or more and 0.0050% or less,
V: 0.01% or more and 0.10% or less,
Ca: 0.0005% or more and 0.0100% or less,
REM: 0.0005% or more and 0.0200% or less,
Zr: 0.0005% or more and 0.0300% or less, and
Mg: 0.0005% or more and 0.0100% or less.

3. A method for manufacturing the hot-rolled steel sheet for coiled tubing according to claim 2 , the method comprising heating a steel slab having the chemical composition to a temperature of 1100° C. or higher and 1250° C. or lower, performing rough rolling on the heated steel slab, performing finish rolling on the rough-rolled steel slab under a condition of a finish rolling temperature of 820° C. or higher and 920° C. or lower, cooling the finish-rolled steel sheet to a temperature of 600° C. or lower at an average cooling rate of 30° C./s or higher and 100° C./s or lower in terms of a temperature in a central portion in a thickness direction of the steel sheet, and coiling the cooled steel sheet at a temperature of 450° C. or higher and 600° C. or lower.

4. A method for manufacturing the hot-rolled steel sheet for coiled tubing according to claim 1 , the method comprising heating a steel slab having the chemical composition to a temperature of 1100° C. or higher and 1250° C. or lower, performing rough rolling on the heated steel slab, performing finish rolling on the rough-rolled steel slab under a condition of a finish rolling temperature of 820° C. or higher and 920° C. or lower, cooling the finish-rolled steel sheet to a temperature of 600° C. or lower at an average cooling rate of 30° C./s or higher and 100° C./s or lower in terms of a temperature in a central portion in a thickness direction of the steel sheet, and coiling the cooled steel sheet at a temperature of 450° C. or higher and 600° C. or lower.

Assignees

• Jfe Steel Corp

Inventors

• Kimura Hideyuki
• Kawamura Shuji
• Sugimoto Ichiro
• Asai Makoto
• Yokota Takeshi

Classifications

• C21D8/02 Primary

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

• C22C38/50

  with titanium or zirconium · CPC title

• C21D8/0226

  Hot rolling · CPC title

• C22C38/60

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/58 Primary

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