PURPOSE:High-Cr low-Ni two phase cast stainless steel is added with an adequate amount of Nb, and an equivalent ratio of Cr/Ni is specified, to thereby enhance toghness and corrosion resistance to acid. CONSTITUTION:A stainless steel includes, C0.10%, Si1.5%, Mn1.5%, P 0.04%, S0.04%, Cr: 22 to 30%, Ni: 3 to 6%, Mo: 0.5 to 1.5%, Cu: 0.4 to 1.0%, N0.10%, Nb: 0.10 to 0.24%, additionally including less than 0.1% of single or both of Al and Ca, with equivalent ratio of Cr/Ni being in the range of 3 to 4.5. The structure consists of 50 to 80% of ferrite as base and austenite as mixed remainder, constituting two phase stainless steel. This steel has only a little of sensitizing degree that degrades toughness and corrosion resistance at 600 to 900 deg.C in a short period of time, and in addition provided with excellent toughness.
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