Patent ID: 6051081
Filing Date: 2000-04-18
Classification: C22C

Abstract:
Superduplex austenitic-ferritic steel applicable for making seamless tubes with a high mechanical strength, high pitting resistance, a good intergranular corrosion behavior and a high hot-formability, in a process comprising the following steps: meltdown in an electric-arc furnace, refining in an AOD converter, ascensional ingot casting and Gothic section billet rolling, and then transforming the billet obtained into seamless tubes by upsetting the gothic billet into a round followed by hot piercing in a vertical press, tube extrusion in a horizontal press, reduction in a stretch reduction mill and Pilger cold-rolling, essentially characterized in that the alloy is added standard elements such as C, Mn, Si, Cr, Ni, Mo, N, P, S with no Cu and W, and with the inclusion of significant quantities of B and Ca wherein the alloy has a weight percentage of C less than or equal to 0.02%, a weight percentage of Mn between 0.65% to 0.85%, a weight percentage of Si between 0.40% to 0.60%, a weight percentage of Cr between 25.2% to 25.6%, a weight percentage of Ni between 6.2% to 6.6%, a weight percentage of Mo between 3.6% to 3.8%, a weight percentage of N between 0.24% to 0.30%, a weight percentage of P less than or equal to 0.025%, a weight percentage of S less than or equal to 0.002%, a weight percentage of B between 0.0015% to 0.0030%, and a weight percentage of Ca between 0.0010to 0.005%.