Electric resistance welded steel pipe and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-12498059-B2
Application number	US-202017777115-A
Country	US
Kind code	B2
Filing date	Nov 11, 2020
Priority date	Nov 29, 2019
Publication date	Dec 16, 2025
Grant date	Dec 16, 2025

Abstract

An electric resistance welded steel pipe, and a method for manufacturing the same are provided. An electric resistance welded steel pipe has a welded portion that includes a heat-affected zone having a steel microstructure principally including a bainitic ferrite phase and/or a bainite phase. The steel microstructure at half the wall thickness includes a bainitic ferrite phase and/or a bainite phase in a total area ratio of 90% or more. In the steel microstructure located 1 mm in the wall thickness direction, the bainitic ferrite phase and/or the bainite phase has an average grain size of 20 μm or less. The average grain size of the bainitic ferrite phase and/or the bainite phase located 1 mm in the wall thickness direction is 0.5 times or more and 2 times or less the average grain size of the bainitic ferrite phase and/or the bainite phase at half the wall thickness.

First claim

The invention claimed is:

1 . An electric resistance welded steel pipe, wherein
the electric resistance welded steel pipe is a thick-walled electric resistance welded steel pipe and comprises a welded portion comprising a heat-affected zone having a steel microstructure principally including a bainitic ferrite phase and/or a bainite phase, the steel microstructure at half the wall thickness of the heat-affected zone of the welded portion includes a bainitic ferrite phase and/or a bainite phase in a total area ratio of 90% or more relative to the entire microstructure at half the wall thickness of the heat-affected zone of the welded portion, in the steel microstructure located 1 mm in the wall thickness direction below the outer surface of the heat-affected zone of the welded portion, the bainitic ferrite phase and/or the bainite phase has an average grain size of 20 μm or less, and the average grain size of the bainitic ferrite phase and/or the bainite phase located 1 mm in the wall thickness direction below the outer surface of the heat-affected zone of the welded portion is 0.5 times or more and 2 times or less the average grain size of the bainitic ferrite phase and/or the bainite phase at half the wall thickness of the heat-affected zone of the welded portion.

2 . The electric resistance welded steel pipe according to claim 1 , wherein the absorbed energy in a Charpy impact test at 0° C. is 100 J or more as measured with respect to a region extending from a location 1 mm in the wall thickness direction below the outer surface of the welded portion to a location 11 mm in the wall thickness direction below the outer surface of the welded portion.

3 . The electric resistance welded steel pipe according to claim 1 , wherein the chemical composition of a base steel portion comprises, on mass % basis, C: 0.02 to 0.10%, Si: 0.05 to 0.30%, Mn: 0.80 to 2.00%, P: 0.030% or less, S: 0.0050% or less, Nb: 0.010 to 0.100%, Ti: 0.001 to 0.025%, and Al: 0.01 to 0.08%, the balance being Fe and incidental impurities.

4 . The electric resistance welded steel pipe according to claim 2 , wherein the chemical composition of a base steel portion comprises, on mass % basis, C: 0.02 to 0.10%, Si: 0.05 to 0.30%, Mn: 0.80 to 2.00%, P: 0.030% or less, S: 0.0050% or less, Nb: 0.010 to 0.100%, Ti: 0.001 to 0.025%, and Al: 0.01 to 0.08%, the balance being Fe and incidental impurities.

5 . The electric resistance welded steel pipe according to claim 3 , wherein the chemical composition further comprises one, or two or more selected from, on mass % basis, Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.10% or less, and Ca: 0.0050% or less.

6 . The electric resistance welded steel pipe according to claim 4 , wherein the chemical composition further comprises one, or two or more selected from, on mass % basis, Cu: 0.50% or less, Ni: 0.50% or less, Cr: 0.50% or less, Mo: 0.50% or less, V: 0.10% or less, and Ca: 0.0050% or less.

7 . A method for manufacturing the electric resistance welded steel pipe of claim 1 , comprising:
forming and electric resistance welding a steel material, heating the outer surface of a welded portion to a temperature of 1000° C. or above and 1400° C. or below, cooling the outer surface of the welded portion to Ac 1 transformation temperature or below at an average cooling rate of 20° C./sec or more and 200° C./sec or less, and reheating the outer surface of the welded portion to a temperature of 900° C. or above and 1120° C. or below.

8 . The method for manufacturing an electric resistance welded steel pipe according to claim 7 , wherein the reheating is performed to bring the temperature of the inner surface of the welded portion to Ac 3 transformation temperature or above.

9 . The method for manufacturing an electric resistance welded steel pipe according to claim 7 , wherein the reheating is followed by quenching of the outer surface of the welded portion under conditions in which average cooling rate: 20° C./sec or more and 70° C./sec or less, and cooling stop temperature: 300° C. or above and 550° C. or below.

10 . The method for manufacturing an electric resistance welded steel pipe according to claim 8 , wherein the reheating is followed by quenching of the outer surface of the welded portion under conditions in which average cooling rate: 20° C./sec or more and 70° C./sec or less, and cooling stop temperature: 300° C. or above and 550° C. or below.

Assignees

• Jfe Steel Corp

Inventors

• Matsumoto Atsushi
• Nakazawa Ryo
• Yasuda Jun
• Urahata Eiichi

Classifications

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• C21D9/08 Primary

  for tubular bodies or pipes · CPC title

• B23K11/066

  of tube sections · CPC title

• C22C38/58

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

• C22C38/06

  containing aluminium · CPC title