METHOD OF MANUFACTURING OF HIGH-STRENGTH SEAMLESS STEEL TUBES

摘要

A method of manufacturing high-strength seamless steel tubes by hot-rolling followed b accelerated cooling in which feed ingots of a steel annealed with aluminum and/or silicon of the following composition in weight per cent: 0.08 - 0.13 % C 1.40 - 1.90 % Mn 0.20 - 0.50 % Cr 0 - 0.50 % Mo 0 - 0.70 % Ni 0 - 0.40 % Cu 0.04 - 0.13 % V max. 0.020 % P max. 0.010 % S wherein the balance comprises iron and ordinary impurities, the sum of the contents of Cr and Mo is within the range of about 0.20 to about 0.70% and the Cu/Ni quantity ration in case of the presence of both elements is limited to at most 1, are heated to a temperature of about 1150 to about 1280.degree.C and hot-rolled into tubes in multiple stages and, after leaving the last hot-rolling stage, the tubes which have a temperature above AC3 are quenched directly from the rolling heating in about 5 to about 50 seconds, substantially avoiding formation of ferrite, down to a temperature range of about 340-560.degree.C and thereafter the tubes are further cooled in air.