Method of making quenched and tempered steel pipe with high fatigue life
A method for producing a high fatigue life quenched/tempered steel pipe comprises a quenching treatment of keeping an unquenched starting steel pipe having a composition that comprises, % by mass, C: 0.1 to 0.4%, Si: 0.5 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02%, S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1%, B: 0.0005 to 0.01%, and N: at most 0.01%, with a balance of Fe and inevitable impurities, at 900 to 1100° C. for 10 to 60 seconds and then rapidly cooling it. The cooled pipe is subjected to a tempering treatment of keeping the pipe at 280 to 380° C. for 10 to 60 minutes.
1. A method for producing a high fatigue life quenched/tempered steel pipe, comprising quenching treatment: of keeping an unquenched starting steel pipe having a composition that comprises, % by mass, C: 0.1 to 0.4%, Si: 0.65 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02% S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1% B: 0.0005 to 0.01%, and N: at most 0.01%, with a balance of Fe and inevitable impurities, at 900 to 1100° C. for 10 to 60 seconds and then cooling the pipe such that the pipe undergoes martensitic transformation, followed by tempering treatment of keeping it at 280 to 380° C. for 10 to 60 minutes.
2. The method for producing a high fatigue life quenched/tempered steel pipe as claimed in claim 1 , wherein the starting steel pipe further contains at least one of Ni: at most 0.5%, Ca: at most 0.02%, Mo: at most 0.5% and V: at most 0.5%.
3. The method for producing a high fatigue life quenched/tempered steel pipe as claimed in claim 1 , wherein the starting steel pipe is formed by welding a steel plate having a wall thickness t of from 1 to 7 mm into a pipe having an outer diameter D of from 10 to 45 mm and satisfying D/t≧4.