AUSTENITIC-FERRITIC STEEL OF THE SUPERDUPLEX TYPE APPLICABLE TO THE FABRICATION OF SEAMLESS TUBES

摘要

The disclosed steel is applicable to the fabrication of seamless tubes having a high mechanical resistance, high resistance to corrosion by bitting and a high heat deformation capacity, by a process which comprises the melting in an electric arc furnace, refining in AOD converter, ascensional ingot casting and lamination to a billet of gothic profile and the subsequent transformation of said billet to seamless tubes by upsetting of the gothic billet to a tube in a horizontal press, reduction in a reductor-stretcher and Pilger cold rolling. Its composition is: a maximum 0.02 % of C, between 0.65 and 0.85 % of Mn, between 0.40 and 0.60 % of Si, between 25.2 and 25.6 % of Cr, between 6.2 and 6.6 % of Ni, between 3.6 and 3.8 % of Mo, between 0.24 and 0.30 % of N, a maximum 0.025 % of P, a maximum 0.002 % of S, absence of Cu and W and with the inclusion of B in a percentage comprised between 0.0015 and 0.0030 % and between 0.0010 and 0.0050 % of Ca.