| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel tube for machine structural member having high strength, high toughness and sufficient weldability, and to provide a method for producing the steel tube inexpensively by means of proper accelerated cooling and holding after the stop of the cooling. SOLUTION: In the method for producing the high-strength steel tube for machine structure, when a steel tube is subjected to accelerated cooling from the outer surface of the steel tube from≥750°C to a cooling stopping temperature T [°C] of≤400°C at a cooling velocity V [°C/s] of 5 to 50°C/s while being rotated to the circumferential direction, and is thereafter held to the temperature range of 350 to 600°C for a holding time of t [s], the cooling stopping temperature T [°C] and the cooling velocity V [°C] satisfy inequality; 150<T<821.34×V<SP>-0.3112</SP>, and the cooling stopping temperature T [°C] and the holding time t [s] satisfy inequality; 1<t<-3.6×T+3240. COPYRIGHT: (C)2009,JPO&INPIT
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