DOUBLE-PHASE STAINLESS STEEL AND DOUBLE-PHASE STAINLESS STEEL SEAMLESS PIPE Russian patent published in 2023 - IPC C21C7/06 C21D9/08 C22C38/44 C22C38/60 

FIELD: metallurgy.

SUBSTANCE: invention relates to two-phase stainless steel and a seamless pipe made from it, which can be used as an oil field pipe. Two-phase stainless steel having a composition, in wt.%: C 0.002 - 0.03, Si 0.05 - 1.0, Mn 0.10 - 1.5, P 0.040 or less, S 0.0005 - 0.020, Cr 20.0 - 28.0, Ni 4.0 - 10.0, Mo 2.0 - 5.0, Al 0.001 - 0.05 and N 0.06 - 0.35, optionally at least one element selected from groups A to E. Group A: W 1.5 or less and/or Cu 2.0 or less, Group B: V 0.20 or less, group C at least one element selected from Zr 0.50 or less, B 0.010 or less and Nb 0.50 or less, group D: at least one element selected from REM 0.005 or less, Ca 0.010 or less, Sn: 0.20 or less and Mg 0.01 or less, Group E: at least one element selected from Ta 0.10 or less, Co 1.0 or less, and Sb 1.0 or less, and the rest is Fe and incidental impurities. Dual-phase stainless steel has a microstructure containing 20 to 70% by volume of the austenite phase and 30 to 80% by volume of the ferritic phase, and comprises oxide inclusions, of which oxide inclusions with an average particle diameter of 1 mcm or more have a number density of 15/mm² or less than and not more than 50% of the oxide inclusions having an average particle diameter of 1 mcm or more are aluminium-containing oxide inclusions.

EFFECT: steel has high resistance to sulphide stress cracking, as well as high strength and toughness.

4 cl, 2 tbl, 66 ex