Nippon Steel Sumitomo Metal Corporation

Takafumi Sebayashi

Takuya Hara

Yoshio Terada

Shinya Sakamoto

Itsuroh Hiroshige

Electric resistance welded steel pipe excellent in deformability and fatigue properties after quenching which enables working into complicated shapes without spheroidization and which improves the fatigue properties after cold working and quenching without carburization are provided. The electric resistance welded steel pipe is characterized by containing, by mass %, C: 0.15 to 0.55%, Si: 0.01 to 0.30%, Mn: 0.5 to 1.5%, Ca: 0.0010 to 0.0030%, S: 0.0005 to 0.0050%, and O: 0.0005 to 0.0050%, having contents of Ca, O, and S satisfying 0.10&#x2266;[Ca](1&#x2212;124[O])/1.25[S]&#x2266;2.50, having Ca-based inclusions present at the base material and electric resistance weld zone with an average particle size of 1.0 to 10 &#x3bc;m and a density of 3 to 300/mm, and having a difference &#x394;Hv of the maximum hardness of the electric resistance weld zone and the average hardness of the base material part satisfying 100 to 500.

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Tokyo, Japan

Takafumi Sebayashi