A high-strength, high-toughness seamless steel pipe used for a line pipe contains 0.03 to 0.06% of C, 0.05 to 0.15% of Si, 1.6 to 2.0% of Mn, 0.010 to 0.10% of Al, 0.3 to 0.7% of Ni, 0.10 to 0.40% of Mo, 0.01 to 0.06% of V, 0.003 to 0.03% of Nb, 0.003 to 0.020% of Ti, and 0.0010 to 0.0100% of N, the relationships Mo+5V.gtoreq.0.4% and 2Nb-V.ltoreq.0% being satisfied, and the balance being Fe and incidental impurities. Consequently, it is possible to provide the high-strength, high-toughness seamless steel pipe used for a line pipe in which grade X80 strength and toughness are stably ensured, and the target strength can be easily attained regardless of the size.

Uma high-strength, tubulação de aço sem emenda do elevado-high-toughness usada para uma linha tubulação contem 0.03 a 0.06% de C, 0.05 a 0.15% do silicone, 1.6 a 2.0% do manganês, 0.010 a 0.10% do al, 0.3 a 0.7% do Ni, 0.10 a 0.40% do Mo, 0.01 a 0.06% de V, 0.003 a 0.03% do Nb, 0.003 a 0.020% do ti, e 0.0010 a 0.0100% de N, dos relacionamentos Mo+5V.gtoreq.0.4% e 2Nb-V.ltoreq.0% que estão sendo satisfeitos, e do contrapeso que é Fe e impurezas incidentais. Conseqüentemente, é possível fornecer a high-strength, tubulação de aço sem emenda do elevado-high-toughness usada para uma linha tubulação em que a força e o toughness da classe X80 são assegurados estàvel, e a força do alvo pode fàcilmente ser alcançada não obstante o tamanho.

 
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