An apparatus (100) for cooling long products is provided, the apparatus (100) having a coolant supply line (42) for supplying a coolant and a plurality of cooling devices (70), each connected to the coolant supply line (42) via an individually adjustable control valve (90), whose coolant delivery depends is each case on a degree of opening of the respective control valve (90), so that distribution of the coolant delivery along the travel direction can be flexibly adjusted by individually setting the degrees of opening of the control valves (90).

The steel material according to the present disclosure contains a chemical composition consisting of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.20 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.0100% or less and O: 0.0100% or less, with the balance being Fe and impurities. The steel material contains an amount of dissolved C within a range of 0.010 to 0.050 mass %. The steel material also has a yield strength within a range of 965 to 1069 MPa, and a yield ratio of the steel material is 90% or more.

The seamless steel pipe according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.070%, Cr: 0.30 to 1.50%, Mo: 0.25 to 2.00%, Ti: 0.002 to 0.020%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, rare earth metal: 0.0001 to 0.0015%, Ca: 0.0001 to 0.0100%, N: 0.0100% or less and O: 0.0020% or less, with the balance being Fe and impurities, and satisfying Formula (1) described in the description. A predicted maximum major axis of inclusions is 150 μm or less, the predicted maximum major axis being predicted by means of extreme value statistical processing. The yield strength is within a range of 758 to 862 MPa.

The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 5.00 to 6.50%, Cr: more than 10.00 to 13.40%, Cu: more than 1.50 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), wherein a depassivation pH of an inner surface is 3.00 or less.

Cr+2.0Mo+0.5Ni+2.0Cu+0.5Co≥20.0  (1)

Provided is an electric resistance welded steel pipe or tube that develops no quench cracks despite having carbon content of 0.40% or more and has excellent fatigue strength. An electric resistance welded steel pipe or tube comprises: a chemical composition containing, in mass %, C: 0.40% to 0.55%, Si: 0.10% to 1.0%, Mn: 0.10% to 2.0%, P: 0.10% or less, S: 0.010% or less, Al: 0.010% to 0.100%, Cr: 0.05% to 0.30%, Ti: 0.010% to 0.050%, B: 0.0005% to 0.0030%, Ca: 0.0001% to 0.0050%, and N: 0.0005% to 0.0050%, with a balance consisting of Fe and inevitable impurities; and a ferrite decarburized layer at each of an outer surface and an inner surface, the ferrite decarburized layer having a depth of 20 μm to 50 μm from the surface.

The steel material according to the present disclosure contains a chemical composition consisting of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.030% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.10 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, N: 0.0100% or less and O: 0.0100% or less, with the balance being Fe and impurities. The steel material contains an amount of dissolved C within a range of 0.010 to 0.050 mass %. The steel material also has a yield strength within a range of 655 to less than 862 MPa, and a yield ratio of the steel material is 85% or more.

A method for manufacturing an electric resistance welded steel tube for high-strength thin hollow stabilizers is provided. A steel with a certain chemical composition is heated to a temperature of 1000 to 1300° C., hot rolled under conditions where the rolling finish temperature is 750 to 950° C., cooled, coiled into a coil at 500 to 650° C., and skin pass rolled with a rolling reduction ratio of not less than 0.3%. The resultant hot rolled sheet is electric resistance welded into an electric resistance welded steel tube, which is then reheated to a temperature of 800 to 1100° C. and hot stretch-reducing rolled under conditions where the rolling finish temperature is not more than 850° C. and the cumulative diameter reduction is not more than 75%. Consequently, a thin electric resistance welded steel tube is produced.

The chemical composition of the seamless steel pipe contains Cr 15.00 to 18.00% in mass % and satisfies Formulae (1) and (2). Furthermore, in the microstructure, (I) a total volume ratio of ferrite and martensite is 80% or more, with the balance being retained austenite of a volume ratio of 20% or less, (II) the number of intersections NT.sub.L in the L-direction observation field of view is 38 or more and NT.sub.L/NL is 1.80 or more, and further (III) the number of intersections NT.sub.C in the C-direction observation field of view is 30 or more and NT.sub.C/NC is 1.70 or more.

156Al+18Ti+12Nb+11Mn+5V+328.125N+243.75C+12.5S≤12.5  (1)

Ca/S≥≥4.0  (2)

A method of manufacturing a stainless steel pipe includes preparing a hollow shell having a composition (mass %): up to 0.05% C; up to 1.0% Si; 0.01 to 1.0% Mn; up to 0.05% P; below 0.002% S; 0.001 to 0.1% Al; 16.0 to 18.0% Cr; 3.0 to 5.5% Ni; 1.8 to 3.0% Mo; 1.0 to 3.5% Cu; up to 0.05% N; up to 0.05% O; 0 to 0.3% Ti; 0 to 0.3% Nb; 0 to 0.3% V; 0 to 2.0% W; 0 to 0.01% Ca; 0 to 0.01% B; the balance Fe and impurities, holding the shell in a temperature range of 420 to 460° C. for 60 to 180 minutes; and then holding the shell in a temperature range of 550 to 600° C. for 5 to 300 minutes.

The steel material according to the present invention contains a chemical composition consisting of, in mass %, C: 0.25 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010% and O: 0.0100% or less, with the balance being Fe and impurities. The steel material also contains an amount of dissolved C within a range of 0.010 to 0.050 mass%. The steel material also contains an yield strength is in a range of 862 to less than 965 MPa, and an yield ratio is 90% or more.