Nippon Steel Corporation

Shinichi Omiya

Manabu Hoshino

Takayuki Kagaya

Tetsuya Namegawa

A Ni steel has a chemical composition within a predetermined range, in which a metallographic structure of a thickness middle portion contains 2.0 vol % to 20.0 vol % of an austenite phase, an average grain size of prior austenite grains is 3.0 &#x3bc;m to 12.0 &#x3bc;m, an average aspect ratio of the prior austenite grains is 2.6 to 10.0, a plate thickness is 4.5 mm to 20 mm, a yield stress at room temperature is 590 MPa to 710 MPa, and a tensile strength at the room temperature is 690 MPa to 810 MPa, when the plate thickness is more than 16 mm, the Ni steel contains Ni: 11.5% or more, and when the plate thickness is 16 mm or less and the Ni steel contains Ni: less than 11.5%, the average grain size of the prior austenite grains is 6.0 &#x3bc;m or less.

Nickel-containing steel for low temperature

A nickel-containing steel for low temperature according to an aspect of the present invention has a chemical composition within a predetermined range, in which a metallographic structure of a thickness middle portion contains 2.0 vol % to 20.0 vol % of an austenite phase, an average grain size of prior austenite grains is 3.0 &#x3bc;m to 15.0 &#x3bc;m, an average aspect ratio of the prior austenite grains is 1.0 to 2.4, a plate thickness is 4.5 mm to 30 mm, the chemical composition and the average grain size of the prior austenite grains are further limited depending on the plate thickness, a yield stress at room temperature is 460 MPa to 710 MPa, and a tensile strength at the room temperature is 560 MPa to 810 MPa.

This nickel-containing steel for low temperature includes, as a chemical composition, by mass %: C: 0.020% to 0.070%; Si: 0.03% to 0.30%; Mn: 0.20% to 0.80%; Ni: 12.5% to 17.4%; Al: 0.010% to 0.060%; N: 0.0015% to 0.0060%; and O: 0.0007% to 0.0030%, in which a metallographic structure contains 2.0% to 30.0% of an austenite phase by volume fraction %, in a thickness middle portion of a section parallel to a rolling direction and a thickness direction, an average grain size of prior austenite grains is 3.0 &#x3bc;m to 20.0 &#x3bc;m, and an average aspect ratio of the prior austenite grains is 1.0 to 2.9.

This nickel-containing steel for low temperature includes, as a chemical composition, by mass %: C: 0.030% to 0.070%; Si: 0.03% to 0.30%; Mn: 0.10% to 0.80%; Ni: 12.5% to 17.4%; Mo: 0.03% to 0.60%; Al: 0.010% to 0.060%; N: 0.0015% to 0.0060%; and O: 0.0007% to 0.0030%, in which a metallographic structure contains 2.0% to 30.0% of an austenite phase by volume fraction %, in a thickness middle portion of a section parallel to a rolling direction and a thickness direction, an average grain size of prior austenite grains is 3.0 &#x3bc;m to 20.0 &#x3bc;m, and an average aspect ratio of the prior austenite grains is 3.1 to 10.0.

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Tokyo, Japan

Shinichi Omiya