SEAMLESS PRECISION STEEL TUBES FOR HYDRAULIC VESSELS WITH RAISED ISOTROPIC RIGIDITY AT LOW TEMPERATURE AND PROCEDURE FOR FABRICATION OF THESE TUBES Russian patent published in 2011 - IPC C21D8/10 C22C38/18 

FIELD: metallurgy.

SUBSTANCE: production of seamless precision steel tubes for hydraulic vessels of increased low temperature isotropic rigidity consists of following stages: - (i) production of steel containing wt %: 0.06-0.15 C, 0.30-2.5 Mn and 0.10-0.60 Si, - (ii) produced steel hot rolling at temperature exceeding Ac₃ and production of seamless steel tube, - (iii) heating produced seamless steel tube at temperature within range Ac₁-Ac₃, - (iv) quenching heated steel tube for production of two-phase or multi-phase microstructure of steel consisting of ferrite, martensite and, by choice, bainite and/ or residual austenite, - (v) cold drawing quenched seamless steel tube for production of seamless precision steel tube of required size, - (vi) treatment of seamless steel tube fabricated by this procedure by stress relief to increase its isotropic rigidity and optionally, - (vii) shaping produced seamless precision steel tube of raised rigidity. Yield point of the pipe is not less, than 520 MPa, longitudinal and lateral stiffness at -40°C is not less, than 27 J, deviation of value of internal diametre is not more, than 0.6 % at internal diametre not more, than 100 mm and deviation of value of internal diametre is not more, than 0.45 % at internal diametre over 100 mm.

EFFECT: increased low temperature operational characteristics of tubes.

27 cl, 3 dwg, 7 tbl