Patent ID: 8926771
Filing Date: 2015-01-06
Classification: C21D,C22C,Y10T

Abstract:
1. A method 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 steel at a temperature higher than Ac3 to obtain a seamless steel tube, (iii) holding the seamless steel tube at a temperature in the range between Ac1 and Ac3, (iv) quenching the heated seamless steel tube to establish a multi-phase microstructure in the steel comprising ferrite and non-tempered martensite, (v) cold drawing the quenched seamless steel tube comprising ferrite and non-tempered martensite to provide a seamless precision steel tube of desired dimensions, and (vi) subjecting the seamless precision steel tube to stress relieving treatment to improve isotropic toughness.