Manufacturing method of seamless steel pipe for mechanical structural parts

Abstract

The present invention provides a manufacturing method of seamless steel pipe for mechanical structural parts. According to this manufacturing method, production process is simplified and production cost is reduced by employing inline quenching, and simultaneously, the toughness of steel pipe is guaranteed by controlling Ti/N to be 3.5 or lower. A manufacturing method of seamless steel pipe, in which steel having the chemical composition: by weight percent, 0.10 to 0.25% of C, not greater than 1.00% of Si, 0.20 to 2.00% of Mn, not greater than 0.03% of P, not greater than 0.020% of S, 0.10 to 1.5% of Cr, not greater than 0.5% of Mo, 0.005 to 0.030% of Ti, 0.01 to 0.10% of V, and the balance being Fe and incidental impurities, and Ti/N being 3.5 or lower, is subjected to finish rolling at temperature of 900° C. or higher and the section-decrease rate of 40% or greater; then subjected to soaking directly at temperature of 900 to 1000° C. without cooling, and then quenching and tempering.

1 . A manufacturing method of seamless steel pipe, in which steel having the chemical composition: by weight percent, 0.10 to 0.25% of C, not greater than 1.00% of Si, 0.20 to 2.00% of Mn, not greater than 0.03% of P, not greater than 0.020% of S, 0.10 to 1.5% of Cr, not greater than 0.5% of Mo, 0.005 to 0.030% of Ti, 0.01 to 0.10% of V, and the balance being Fe and incidental impurities, and Ti/N being 3.5 or lower, is subjected to finish rolling at temperature of 900° C. or higher and a section-decrease rate of 40% or greater; then subjected to soaking directly at temperature of 900 to 1000° C. without cooling, and then quenching and tempering.  
   
   
       2 . A manufacturing method of seamless steel pipe according to  claim 1 , wherein said steel further comprises one or more components selected from C: not greater than 0.5%, Ni: not greater than 1.0% and Nb: not greater than 0.01%.