| 摘要 |
PURPOSE:To obtain a seamless steel pipe having high toughness and good weldability by making a steel contg. a decreased amt. of C and Mn and a specified amt. of Ni, Cu and carbide forming element into a pipe by a seamless method and subjecting the pipe to reheating, cooling, heating and tempering treatments under specific conditions. CONSTITUTION:A steel consisting of 0.02-0.10wt% C, 0.02-0.50% Si, 0.70- 1.80% Mn, <=2.0% Mn + 10C, 0.10-1.00% Cu, 0.05-0.70% Ni, 0.15<=Ni+Cu<= 1.00% and further >=1 kind of 0.010-0.050% Ti and 0.020-0.070% Nb and the balance Fe with inevitable impurities is melted. Such steel is made into a pipe at a finishing temp. of >=700 deg.C by a Mannesmann plug mill hot seamless steel pipe making method. The pipe is heated to the Ac3 point or above after cooling and is cooled at a cooling rate of 20-70 deg.C/sec down to a temp. region of <=300 deg.C. The pipe is further heated to a temp. region of 550- Ac1 transformation point and is subjected to a tempering treatment. The seamless steel pipe having high toughness and good weldability is thus obtd. with less alloy components. |
