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 a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass), wherein a metal nitride or a semimetal nitride exists as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano-crystal grains.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass), wherein a metal carbide or a semimetal carbide exists as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano-crystal grains.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass), wherein a metal silicide or a semimetal silicide exists as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano-crystal grains.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass), wherein a metal boride or a semimetal boride exists as a crystal grain growth inhibitor between or in said nano-crystal grains, or between and in said nano-crystal grains.

A super hard and tough austenite steel bulk material with an improved corrosion resistance, comprising an aggregate of austenite nano-crystal grains containing a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass), wherein at least two selected from the group consisting of (1) a metal oxide or a semimetal oxide, (2) a metal nitride or a semimetal nitride, (3) a metal carbide or a semimetal carbide, (4) a metal silicide or a semimetal silicide and (5) a metal boride or a semimetal boride exist as a crystal grain growth inhibitor between and/or in said nano-crystal grains.

A process for preparing a nano-crystal austenite steel bulk material, which involves steps of:

• mixing fine powders of respective austenite steel forming components such as iron and chromium, nickel, manganese, carbon or the like together with a substance that becomes a nitrogen source,
• applying mechanical alloying (MA) to a mixture, using a ball mill or the like, thereby preparing fine powders of nano-crystal austenite steel having a high nitrogen concentration, and
• applying to said fine powders of said nano-crystal austenite steel forming-by-sintering treatment such as forming-by-sintering using one means selected from the group consisting of (1) rolling, (2) spark plasma sintering, (3) extrusion, (4) hot isostatic press sintering (HIP), (5) cold isostaticc pressing (CIP), (6) cold pressing, (7) hot pressing, (8) forging, and (9) swaging or two or more thereof in combination or explosive forming, thereby obtaining a super hard and tough austenite steel bulk material with an improved corrosion resistance, which comprises an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of a solid-solution type nitrogen.

A process for preparing a nano-crystal austenite steel bulk material, which involves steps of:

• mixing fine powders of respective austenite steel forming components such as iron and chromium, nickel, manganese, carbon or the like together with a substance that becomes a nitrogen source,
• applying mechanical alloying (MA) to a mixture, using a ball mill or the like, thereby preparing fine powders of nano-crystal austenite steel having a high nitrogen concentration, and
• applying to said fine powders of said nano-crystal austenite steel forming-by-sintering treatment in air, an oxidation-inhibition atmosphere or a vacuum such as at least one means selected from the group consisting of (1) rolling, (2) spark plasma sintering, (3) extrusion, (4) hot isostatic press sintering (HIP), (5) hot pressing, (6) forging, and (7) swaging or two or more thereof in combination, or explosive forming, followed by quenching, thereby obtaining a super hard and tough austenite steel bulk material with an improved corrosion resistance, which comprises an aggregate of austenite nano-crystal grains containing 0.1 to 2.0% (by mass) of a solid-solution type nitrogen.

A process for preparing a nano-crystal austenite steel bulk material, which involves steps of:

• mixing fine powders of respective austenite steel forming components such as iron and chromium, nickel, manganese, carbon or the like together with a substance that becomes a nitrogen source,
• applying mechanical alloying (MA) to a mixture, using a ball mill or the like, thereby preparing fine powders of nano-crystal austenite steel having a high nitrogen concentration, and
• applying spark plasma sintering to said fine powders of said nano-crystal austenite steel in a vacuum or an oxidization-inhibition atmosphere for forming-by-sintering, thereby obtaining a super hard and tough austenite steel bulk material with an improved corrosion resistance, which comprises an aggregate of austenite nano-crystal grains containing 0.3 to 1.0% (by mass)of a solid-solution type nitrogen, and having a crystal grain diameter of 50 to 1,000 nm.

A process for preparing a nano-crystal austenite steel bulk material, which involves steps of:

• mixing fine powders of respective austenite steel forming components such as iron and chromium, nickel, manganese, carbon or the like together with a substance that becomes a nitrogen source,
• applying mechanical alloying (MA) to a mixture, using a ball mill or the like, thereby preparing fine powders of nano-crystal austenite steel having a high nitrogen concentration, and
• applying spark plasma sintering to said fine powders of said nano-crystal austenite steel in a vacuum or an oxidization-inhibition atmosphere for forming-by-sintering, followed by rolling and quenching, thereby obtaining a super hard and tough austenite steel bulk material with an improved corrosion resistance, which comprises an aggregate of austenite nano-crystal grains containing 0.3 to 1.0% (by mass) of a solid-solution type nitrogen, and having a crystal grain diameter of 50 to 1,000 nm.