HOT COIL FOR LINE PIPE USE AND METHOD OF PRODUCTION OF SAME

摘要

The present invention provides a hot coil for line pipe use which can reduce deviation in ordinary temperature strength and improve low temperature toughness despite the numerous restrictions in production conditions due to the coiling step and provides a method of production of the same, specifically makes the steel plate stop for a predetermined time between rolling passes in the recrystallization temperature range and performs cooling by two stages after hot rolling so as to thereby make the steel structure at the center part of plate thickness and effective crystal grain size of 3 to 10 μm, make the total of the area ratios of bainite and acicular ferrite 60 to 99%, and make the absolute value of A-B 0 to 30% when the totals of the area ratios of bainite and acicular ferrite at any two portions are designated as respectively A and B.

主权项

1. Hot coil for line pipe use which has a chemical composition which contains, by mass %,
C: 0.03 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.5 to 2.5%, P: 0.001 to 0.03%, S: 0.0001 to 0.0030%, Nb: 0.0001 to 0.2%, Al: 0.0001 to 0.05%, Ti: 0.0001 to 0.030% and B: 0.0001 to 0.0005% and has a balance of iron and unavoidable impurities, which has a steel structure at a center of plate thickness with an effective crystal grain size of 2 to 10 μm, which has a total of the area ratios of bainite and acicular ferrite of 60 to 99%, which has an absolute value of A-B of 0 to 30% when designating the totals of the area ratios of bainite and acicular ferrite at any two portions as respectively A and B, which has a plate thickness of 7 to 25 mm, and which has a tensile strength TS in the width direction of 400 to 700 MPa.