SEAMLESS PRECISION STEEL TUBES WITH IMPROVED ISOTROPIC TOUGHNESS AT LOW TEMPERATURE FOR HYDRAULIC CYLINDERS AND PROCESS FOR OBTAINING THE SAME

摘要

Process for manufacturing seamless precision steel tubes with improved isotropic toughness at low temperature for hydraulic cylinders comprising the following steps; -(i) providing a steel having a composition comprising 0.06 -0,15% by weight of carbon, 0.30 - 2.5% by weight of Mn, and 0.10 - 0.60% by weight of Si, -(ii) hot-rolling the said steel at a temperature higher than Ac3 such as to obtain a seamless steel tube, -(iii) heating the said seamless steel tube at a temperature in the range between Ac1 and Ac3, -(iv) quenching the said heated seamless steel tube, such as to establish a dual (or multi-) phase microstructure in the steel employed, composed of ferrite and martensite and optionally bainite and/or retained austenite, -(v) cold drawing the quenched seamless steel tube such as to provide a seamless precision steel tube of the desired dimensions, -(vi) subjecting the so-obtained seamless precision steel tube to stress relieving treatment to improve its isotropic toughness, and optionally -(vii) straightening the so-obtained seamless precision steel tube with improved toughness.