High-strength thick-walled electric resistance welded steel pipe having excellent low-temperature toughness and method of manufacturing the same

Patent metadata

Field	Value
Publication number	US-9841124-B2
Application number	US-201314394163-A
Country	US
Kind code	B2
Filing date	Apr 11, 2013
Priority date	Apr 13, 2012
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

A high-strength thick-walled electric resistance welded steel pipe has excellent low-temperature toughness and excellent HIC resistance and a yield strength of 400 MPa or more.
The steel has a chemical composition consisting of C: 0.025% to 0.084%, Si: 0.10% to 0.30%, Mn: 0.70% to 1.80%, controlled amounts of P, S, Al, N, and O, Nb: 0.001% to 0.065%, V: 0.001% to 0.065%, Ti: 0.001% to 0.033%, and Ca: 0.0001% to 0.0035% on a mass percent basis and the remainder being Fe and incidental impurities, and satisfies Pcm of 0.20 or less.

First claim

The invention claimed is:

1. A high-strength thick-walled electric resistance welded steel pipe having excellent low-temperature toughness and excellent HIC resistance comprising:
a base metal composition consisting of, on a mass percent basis,
C: 0.025% to 0.084%, Si: 0.10% to 0.30%,
Mn: 0.70% to 1.80%, P: 0.001% to 0.018%,
S: 0.0001% to 0.0029%, Al: 0.01% to 0.10%,
Nb: 0.001% to 0.065%, V: 0.001% to 0.065%,
Ti: 0.001% to 0.033%, Ca: 0.0001% to 0.0035%,
N: 0.0050% or less, O: 0.0030% or less, and
optionally, one or more selected from the group consisting of B: 0.0030% or less, Cu: 0.001% to 0.350%, Ni: 0.001% to 0.350%, Mo: 0.001% to 0.350%, and Cr: 0.001% to 0.700% and the remainder being Fe and incidental impurities,

wherein Pcm defined by formula (1) is 0.20 or less,
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B  (1)

wherein C, Si, Mn, Cu, Ni, Cr, Mo, V, and B denote amounts (mass %) of corresponding elements,

a microstructure which includes 90% by area or more of quasi-polygonal ferrite having a grain size of 10 μm or less in each of a base steel portion and an electric resistance welded portion of the steel pipe,
a yield strength YS of 400 MPa or more,
and
an absorbed energy vE −50 of 150 J or more at −50° C. in a Charpy impact test,
wherein the electric resistance welded steel pipe is formed by rounding a steel strip having the base metal composition to form a butt joined seam by electronic resistance welding.

2. The welded steel pipe according to claim 1 , wherein the total amount of Si, Mn, Al, Ca, and Cr in inclusions having an equivalent circular diameter of 2 μM or more contained in the electric resistance welded portion is 0.0089% or less on a mass percent basis.

3. A method of manufacturing a high-strength thick-walled electric resistance welded steel pipe having excellent low-temperature toughness and excellent HIC resistance, comprising:
a hot-rolling step of producing a hot-rolled steel strip from steel by heating, hot-rolling, cooling, and coiling,
a pipe-forming step of continuously roll-forming the hot-rolled steel strip after the hot-rolling step to form a tubular product having a substantially circular cross section and
butt-welding circumferential ends of the tubular product by electric resistance welding to produce an electric resistance welded steel pipe, wherein

the steel has a chemical composition consisting of C: 0.025% to 0.084%, Si: 0.10% to 0.30%,
Mn: 0.70% to 1.80%, P: 0.001% to 0.018%,
S: 0.0001% to 0.0029%, Al: 0.01% to 0.10%,
Nb: 0.001% to 0.065%, V: 0.001% to 0.065%,
Ti: 0.001% to 0.033%, Ca: 0.0001% to 0.0035%,
N: 0.0050% or less, O: 0.0030% or less on a mass percent basis, and
optionally, one or more selected from the group consisting of B: 0.0030% or less, Cu: 0.001% to 0.350%, Ni: 0.001% to 0.350%, Mo: 0.001% to 0.350%, and Cr: 0.001% to 0.700% and the remainder being Fe and incidental impurities,
wherein Pcm defined by formula (1) is 0.20 or less,
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B  (1)

wherein C, Si, Mn, Cu, Ni, Cr, Mo, V, and B denote the amounts (mass %) of the corresponding elements,

the hot-rolling step is performed by heating the steel to a temperature of 1200° C. to 1280° C., maintaining the temperature for 90 min or more, hot-rolling the steel at a hot-rolling reduction of 20% or more in an unrecrystallized austenite region, after completion of the hot-rolling, cooling the steel to a finish cooling temperature of 630° C. or less at a cooling rate of 7° C./s to 49° C./s, the cooling rate being an average cooling rate at a temperature from 780° C. to 630° C. at a central portion in the thickness direction, and coiling the steel at a coiling temperature of 400° C. or more and less than 600° C.,
the pipe-forming step is followed by a heat treatment that includes heating the electric resistance welded portion of the electric resistance welded steel pipe on a production line such that the electric resistance welded portion has a temperature of 800° C. to 1150° C. over the total wall thickness, then cooling the electric resistance welded portion to a finish cooling temperature of 630° C. or less at a cooling rate of 7° C./s to 49° C./s, the cooling rate being the average cooling rate at a temperature from 780° C. to 630° C. at the central portion in the thickness direction, and then allowing the electric resistance welded portion to air-cool,
and
the base steel portion and the electric resistance welded portion of the electric resistance welded steel pipe have a yield strength YS of 400 MPa or more and an absorbed energy vE —50 of 150 J or more at −50° C. in a Charpy impact test.

4. The method according to claim 3 , further comprising forming a tapered groove in end faces of the hot-rolled steel strip in the width direction by fin pass forming during the roll-forming in the pipe-forming step, a distance between a taper starting position of the tapered groove and a surface that will become a pipe outer surface or a surface that will become a pipe inner surface in the steel strip thickness direction is 2% to 60% of the hot-rolled steel strip thickness.

5. The method according to claim 4 , wherein atmospheric oxygen partial pressure in the electric resistance welding in the pipe-forming step is adjusted at 900/f oxy mass ppm or less, and the f oxy represents a degree of oxidizability of molten steel defined by formula (2),
f oxy =Mn+10(Si+Cr)+100Al+1000Ca  (2)

wherein Mn, Si, Cr, Al, and Ca denote the amounts (mass %) of the corresponding elements.

6. The method according to claim 3 , wherein atmospheric oxygen partial pressure in the electric resistance welding in the pipe-forming step is adjusted at 900/f oxy mass ppm or less, and the f oxy represents a degree of oxidizability of molten steel defined by formula (2),
f oxy =Mn+10(Si+Cr)+100Al+1000Ca  (2)

wherein Mn, Si, Cr, Al, and Ca denote the amounts (mass %) of the corresponding elements.

7. The method according to claim 3 , wherein the cooling in the heat treatment includes installing at least two lines of cooling headers in a conveying direction above the electric resistance welded portion, the cooling headers being coupled to a nozzle through which a rod-like flow of cooling water can be ejected at a water flow rate of 1 m 3 /m 2 ·min or more, and ejecting the rod-like flow of cooling water through the nozzle at a rate of 1 m/s or more.

8. The method according to claim 7 , wherein the plurality of cooling headers are configured to independently control the ejection of cooling water.

Assignees

• Jfe Steel Corp

Inventors

• Toyoda Shunsuke
• Goto Sota
• Okabe Takatoshi
• Inoue Tomohiro
• Egi Motoharu
• Yonemoto Atsushi

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• B21B3/00

  Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences {; Rolling of aluminium, copper, zinc or other non-ferrous metals}(altering special metallurgical properties of alloys, other than structure consolidation or mechanical properties resulting therefrom C21D, C22F) · CPC title

• C21D9/08

  for tubular bodies or pipes · CPC title

• C21D9/085

  Cooling or quenching · CPC title

• B23K11/0873

  of the longitudinal seam of tubes · CPC title