Electric resistance welded steel pipe or tube
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.
1. An electric resistance welded steel pipe or tube comprising:
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;
a microstructure composed of ferrite and pearlite, or a microstructure composed of ferrite, pearlite, and bainite; 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.
2. The electric resistance welded steel pipe or tube according to claim 1 , wherein the chemical composition further contains, in mass %, one or both of
Cu: 1.0% or less, and
Ni: 1.0% or less.
3. The electric resistance welded steel pipe or tube according to claim 1 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
Nb: 0.05% or less,
W: 0.5% or less,
V: 0.50% or less, and
Mo: 2.0% or less.
4. The electric resistance welded steel pipe or tube according to claim 1 , wherein the chemical composition further contains, in mass %,
Rare Earth Metal (REM): 0.020% or less.
5. The electric resistance welded steel pipe or tube according to claim 2 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
Nb: 0.05% or less,
W: 0.5% or less,
V: 0.50% or less, and
Mo: 2.0% or less.
6. The electric resistance welded steel pipe or tube according to claim 2 , wherein the chemical composition further contains, in mass %,
Rare Earth Metal (REM): 0.020% or less.
7. The electric resistance welded steel pipe or tube according to claim 3 , wherein the chemical composition further contains, in mass %,
Rare Earth Metal (REM): 0.020% or less.
8. The electric resistance welded steel pipe or tube according to claim 5 , wherein the chemical composition further contains, in mass %,
Rare Earth Metal (REM): 0.020% or less.