Nano-crystal austenitic steel bulk material having ultra-hardness and toughness and excellent corrosion resistance, and method for production thereof

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid-solution wherein said austenite nano-crystal grains are obtained by mechanical alloying (MA) using a ball mill or the like, and wherein some amount of a metal oxide or a semi-metal oxide is inevitably formed on the surface of MA powder products during MA processing, acting as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano crystal grains,

• wherein said bulk material comprising an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution comprises a nitrogen-affinity metal element that has a stronger chemical affinity for nitrogen than iron, said nitrogen-affinity metal element selected from the group consisting of niobium, tantalum, manganese, and chromium, so as to prevent denitrification during a forming-by-sintering process thereof, and
• wherein said bulk material comprising an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution has a steel forming and blending composition comprising 4 to 40% (by mass) of Mn, 0.1 to 2.0% (by mass) of N, 0.1 to 2.0% (by mass) of C and 3 to 10% (by mass) of Cr with the rest being substantially Fe.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing of 0.1 to 2.0% (by mass) of nitrogen in solid solution, wherein said austenite nano-crystal grains are obtained by mechanical alloying (MA) using a ball mill or the like, and wherein an amount of a metal oxide or a semi-metal oxide is inevitably formed on the surface of MA powder products during MA processing, acting as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano crystal grains, and wherein at least one or two selected from the group consisting of (1) a metal oxide or a semimetal oxide, (2) a metal silicide or a semimetal silicide and (3) a metal boride or a semimetal boride exist as a crystal grain growth inhibitor between and/or in said nano-crystal grains,

• wherein said austenite steel bulk material comprising an aggregate of austenite nanocrystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution contains in a structure thereof an amount of ferrite nano-crystal grains, and
• wherein said bulk material comprising an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution has a steel forming and blending composition comprising 4 to 40% (by mass) of Mn, 0.1 to 2.0% (by mass) of N, 0.1 to 2.0% (by mass) of C and 3 to 10% (by mass) of Cr with the rest being substantially Fe.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing of 0.1 to 2.0% (by mass) of nitrogen in solid solution, wherein said austenite nanocrystal grains are obtained by mechanical alloying (MA) using a ball mill or the like, and wherein an amount of a metal oxide or a semimetal oxide is inevitably formed on the surface of MA powder products during MA processing, acting as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano crystal grains, and wherein at least one or two selected from the group consisting of (1) a metal oxide or a semimetal oxide, (2) a metal silicide or a semimetal silicide and (3) a metal boride or a semimetal boride exist as a crystal grain growth inhibitor between and/or in said nano-crystal grains, wherein said bulk material comprising an aggregate of austenite nanocrystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution comprises a nitrogen-affinity metal element that has a stronger chemical affinity for nitrogen than iron, said nitrogen-affinity metal element selected from the group consisting of niobium, tantalum, manganese, and chromium, so as to prevent denitrification during a forming-by-sintering process thereof, and

• wherein said bulk material comprising an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of nitrogen in solid solution has a steel forming and blending composition comprising 4 to 40% (by mass) of Mn, 0.1 to 2.0% (by mass) of N, 0.1 to 2.0% (by mass) of C and 3 to 10% (by mass) of Cr with the rest being substantially Fe.