Nippon Yakin Kogyo Co., Ltd.

Fugao Wei

Takayuki Watanabe

Takafumi Kikutake

Taiki Maeda

A Ni—Cr—Mo—Nb alloy consists of, in mass %, C: not more than 0.020%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, P: not more than 0.03%, S: not more than 0.005%, Cr: 18.0 to 24.0%, Mo: 8.0 to 10.0%, Al: 0.005 to 0.4%, Ti: 0.1 to 1.0%, Fe: not more than 5.0%, Nb: 2.5 to 5.0%, N: 0.002 to 0.02%, and at least one of W: 0.02 to 0.3% and V: 0.02 to 0.3%, and Ni as a remainder and inevitable impurities, in which an freely selected cross section of alloy, sum of number of particles of NbC carbide and (Ti, Nb)N nitride is 100 to 1000 particles/mm, number of particles of the NbC carbide is not more than 40 particles/mm, and number of particles of the (Ti, Nb)N nitride is 100 to 1000 particles/mm.

Ni—Cr—Mo—Nb alloy

A duplex stainless steel has reduced precipitation risks of Al nitride and Cr nitride which are undesirable precipitates, and has superior low temperature toughness. The duplex stainless steel has in mass %, indicated as '%', C: 0.001 to 0.030%, Si: 0.05 to 0.5%, S: not more than 0.002%, Ni: 6 to 7.5%, Cr: 23 to 26%, Mo: 2 to 4.0%, N: 0.20 to 0.40%, Al: 0.005 to 0.03%, Mn: 0.05 to 0.3%, B: 0.0001 to 0.0050% and Fe, and the remainder being inevitable impurities. The duplex stainless steel has an impact value of not less than 87.5 J/cmat &#x2212;46&#xb1;2&#xb0; C. as defined in Japanese Industrial Standards Z2242.

Duplex stainless steel having superior low temperature toughness

The Ni-based alloy exhibits superior grain boundary corrosion resistance including C: 0.005 to 0.03 mass %, Si: 0.02 to 1 mass %, Mn: 0.02 to 1 mass %, P: not more than 0.03 mass %, S: not more than 0.005 mass %, Cr: 18 to 24 mass %, Mo: 8 to 10 mass %, Nb: 2.5 to 5.0 mass %, Al: 0.05 to 0.4 mass %, Ti: not more than 1 mass %, Fe: not more than 5 mass %, N: not more than 0.02 mass %, and Ni as a remainder and inevitable impurities. The C concentration range, the ratio of (Nb, Ti) C carbides to all carbides is not less than 90%, and the number of (Nb, Ti) C carbides satisfies the following formula: &#x2212;30&#xd7;T+37220=&#x3c;number of (Nb, Ti) C carbides (number/mm)=&#x3c;&#x2212;7.7&#xd7;T+15700&#xd7;T&#x2212;7866000 under a condition of 2000&#xd7;% C+890=&#x3c;T(temperature &#xb0; C.)=&#x3c;1150.

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Kawasaki, Japan

Fugao Wei