Oil country tubular goods excellent in collapse characteristics after expansion and method of production thereof

Oil country tubular goods excellent in collapse characteristics after expansion consisting essentially of, by wt %:

• C:
• 0.03 to 0.3%,
• Si:
• 0.8% or less,
• Mn:
• 0.3 to 2.5%,
• P:
• 0.03% or less,
• S:
• 0.01% or less,
• Nb:
• 0.01 to 0.3%,
• Ti:
• 0.005 to 0.03%,
• Al:
• 0.1% or less, and
• N:
• 0.001 to 0.01%,
• further containing one or more of:
• Ni:
• 1% or less,
• Mo:
• 0.6% or less,
• Cr:
• 1% or less,
• Cu:
• 1% or less,
• V:
• 0.3% or less,
• B:
• 0.0003 to 0.003%,
• Ca:
• 0.01% or less, and
• REM:
• 0.02% or less, and
• a balance of Fe and unavoidable impurities, characterized in that a ratio of collapse pressure after expansion and collapse pressure before expansion is in the range of a/b:
• 0.85 to less than 1.0, where
• a:
• collapse strength (MPa) after expansion 10 to 20% and b:
• collapse strength (MPa) of unexpanded steel pipe of same dimensions as steel pipe measured for a,
• said oil country tubular goods has a hot rolled structure having a low temperature transformation phase of only bainitic ferrite or bainite alone or combined.

Oil country tubular goods excellent in collapse characteristics after expansion consisting essentially of, by wt %:

• C:
• 0.03 to 0.3%,
• Si:
• 0.8% or less,
• Mn:
• 0.3 to 2.5%,
• P:
• 0.03% or less,
• S:
• 0.01% or less,
• Nb:
• 0.01 to 0.3%,
• Ti:
• 0.005 to 0.03%,
• Al:
• 0.1% or less, and
• N:
• 0.001 to 0.01% and
• a balance of Fe and unavoidable impurities, characterized in that a ratio c/d of collapse pressure after expansion and ageing and collapse pressure before expansion is in the range of 1 to 1.2, where
• c:
• collapse strength (MPa) after expansion 10 to 20% and ageing at 80 to 200° C. and d:
• collapse strength (MPa) of unexpanded steel pipe of same dimensions as steel pipe measured for c,
• said oil country tubular goods has a hot rolled structure having a low temperature transformation phase of only bainitic ferrite or bainite alone or combined.

Oil country tubular goods excellent in collapse characteristics after expansion consisting essentially of, by wt %:

• C:
• 0.03 to 0.3%,
• Si:
• 0.8% or less,
• Mn:
• 0.3 to 2.5%,
• P:
• 0.03% or less,
• S:
• 0.01% or less,
• Nb:
• 0.01 to 0.3%,
• Ti:
• 0.005 to 0.03%,
• Al:
• 0.1% or less, and
• N:
• 0.001 to 0.01%,
• further containing one or more of:
• Ni:
• 1% or less,
• Mo:
• 0.6% or less,
• Cr:
• 1% or less,
• Cu:
• 1% or less,
• V:
• 0.3% or less,
• B:
• 0.0003 to 0.003%,
• Ca:
• 0.01% or less, and
• REM:
• 0.02% or less, and
• a balance of Fe and unavoidable impurities, characterized in that a ratio c/d of collapse pressure after expansion and ageing and collapse pressure before expansion is in the range of 1 to 1.2, where
• c:
• collapse strength (MPa) after expansion 10 to 20% and ageing at 80 to 200° C. and d:
• collapse strength (MPa) of unexpanded steel pipe of same dimensions as steel pipe measured for c,
• said oil country tubular goods has a hot rolled structure having a low temperature transformation phase of only bainitic ferrite or bainite alone or combined.