High toughness steel material and method of producing steel pipes using same

A steel material having high toughness comprising

• by mass %, C:
• 0.17-0.32%, Si:
• 0.1-0.5%, Mn:
• 0.30-2.0%, P:
• not more than 0.030%, S:
• not more than 0.010%, Cr:
• 0.10-1.50%, Mo:
• 0.01-0.80%, sol. Al:
• 0.001-0.100%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and
• a content of Mo [Mo] in the carbides satisfying the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.

A steel material having high toughness comprising

• by mass %, C:
• 0.17-0.32%, Si:
• 0.1-0.5%, Mn:
• 0.30-2.0%, P:
• not more than 0.030%, S:
• not more than 0.010%, Cr:
• 0.10-1.50%, Mo:
• 0.01-0.80%, sol. Al:
• 0.001-0.100%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070% and further containing one or more of Ti:
• 0.005-0.04%, Nb:
• 0.005-0.04% and V:
• 0.03-0.30%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and
• a content of Mo [Mo] in the carbides satisfying the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.

A steel material having high toughness comprising

• by mass %, C:
• 0.20-0.28%, Si:
• 0.1-0.5%, Mn:
• 0.35-1.4%, P:
• not more than 0.015%, S:
• not more than 0.005%, Cr:
• 0.15-1.20%, Mo:
• 0.10-0.80%, sol. Al:
• 0.001-0.050%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070% and further containing one or more of Ti:
• 0.005-0.04%, Nb:
• 0.005-0.04% and V:
• 0,03-0.30%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and
• a content of Mo [Mo] in the carbides satisfying the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.

A method of producing highly tough steel pipes for oil wells, comprising hot rolling a steel which contains, by mass %, C:

• 0.17-0.32%, Si:
• 0.1-0.5%, Mn:
• 0.30-2.0%, P:
• not more than 0.030%, S:
• not more than 0.010%, Cr:
• 0.10-1.50%, Mo:
• 0.01-0.80%, sol. Al:
• 0.001-0.100%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and quenching the hot rolled product from the austenite region, wherein, after the subsequent tempering, a content of Mo [Mo] in the carbides satisfies the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.

A method of producing highly tough steel pipes for oil wells, comprising hot rolling a steel which contains, by mass %, C:

• 0.17-0.32%, Si:
• 0.1-0.5%, Mn:
• 0.30-2.0%, P:
• not more than 0.030%, S:
• not more than 0.010%, Cr:
• 0.10-1.50%, Mo:
• 0.01-0.80%, sol. Al:
• 0.001-0.100%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070% and further containing one or more of Ti:
• 0.005-0.04%, Nb:
• 0.005-0.04% and V:
• 0.03-0.30%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and quenching the hot rolled product from the austenite region, wherein, after the subsequent tempering, a content of Mo [Mo] in the carbides satisfies the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.

A method of producing highly tough steel pipes for oil wells, comprising hot rolling a steel which contains, by mass %, C:

• 0.20-0.28%, Si:
• 0.1-0.5%, Mn:
• 0.35-1.4%, P:
• not more than 0.015%, S:
• not more than 0.005%, Cr:
• 0.15-1.20%, Mo:
• 0.10-0.80%, sol. Al:
• 0.001-0.050%, B:
• 0.0001-0.0020% and N:
• not more than 0.0070% and further containing one or more of Ti:
• 0.005-0.04%, Nb:
• 0.005-0.04% and V:
• 0.03-0.30%, the balance being Fe and unavoidable impurities, the steel including carbides precipitated at austenite grain boundaries;
• and quenching the hot rolled product from the austenite region, wherein, after the subsequent tempering, a content of Mo [Mo] in the carbides satisfies the formula (a) given below:
• [Mo]≦exp(G−5)+5 (a)
• where G is the austenite grain size number according to ASTM E 112.