Jfe Steel Corporation

Jfe Steel Corporatin

Yusuke Terazawa

Kazukuni Hase

Kenji Hayashi

Katsuyuki Ichimiya

Naoki Takayama

Shigeru Endo

Shigeki Kitsuya

Masao Yuga

Naoki Matsunaga

Yoshiaki Murakami

Minoru Suwa

Masayuki Horie

Yusaku Takemura

Yasuhiro Murota

Teruhisa Kinugawa

An abrasion-resistant steel plate comprises: a chemical composition containing, in mass %, C: 0.20% to 0.45%, Si: 0.01% to 1.0%, Mn: 0.3% to 2.5%, P: 0.020% or less, S: 0.01% or less, Cr: 0.01% to 2.0%, Ti: 0.10% to 1.00%, B: 0.0001% to 0.0100%, Al: 0.1% or less, N: 0.01% or less, and a balance consisting of Fe and inevitable impurities; and a microstructure in which a volume fraction of martensite is 90% or more, and a prior austenite grain size is 80 &#x3bc;m or less, wherein a number density of TiC precipitate having a size of 0.5 &#x3bc;m or more is 400 particles/mmor more, and a Mn content [Mn] and a P content [P] in a plate thickness central segregation area satisfy 0.04[Mn]+[P]&#x3c;0.50.

Abrasion-resistant steel plate and method of producing abrasion-resistant steel plate

An abrasion-resistant steel plate comprises: a specific chemical composition; and a microstructure in which a volume fraction of martensite at a depth of 1 mm from a surface of the abrasion-resistant steel plate is 90% or more, and a prior austenite grain size in a plate thickness central part at the mid-thickness of the abrasion-resistant steel plate is 80 &#x3bc;m or less, wherein hardness at a depth of 1 mm from the surface of the abrasion-resistant steel plate is 460 to 590 HBW 10/3000 in Brinell hardness, and a concentration [Mn] of Mn in mass % and a concentration [P] of P in mass % in a plate thickness central segregation area satisfy 0.04[Mn]+[P]&#x3c;0.50.

Provided is an abrasion-resistant steel plate which has high hardness up to the mid-thickness part thereof although the steel plate is 50 mm or more, and can be manufactured at low cost. The abrasion-resistant steel plate has a specific chemical composition having DI* of 120 or more, where DI* is defined by the following Formula (1): DI*=33.85&#xd7;(0.1&#xd7;C)&#xd7;(0.7&#xd7;Si+1)&#xd7;(3.33&#xd7;Mn+1)&#xd7;(0.35&#xd7;Cu+1)&#xd7;(0.36&#xd7;Ni+1)&#xd7;(2.16&#xd7;Cr+1)&#xd7;(3&#xd7;Mo+1)&#xd7;(1.75&#xd7;V+1)&#xd7;(1.5&#xd7;W+1) . . . (1), has HBof 360 HBW10/3000 to 490 HBW10/3000, HBbeing a Brinell hardness at a depth of 1 mm from a surface, has a hardness ratio, HBto HB, of 75% or more, HBbeing a Brinell hardness at a mid-thickness position, and has a plate thickness of 50 mm or more.

Abrasion-resistant steel plate and method of manufacturing same

An abrasion-resistant steel plate that can achieve both gas cutting cracking resistance and abrasion resistance at low cost is provided. An abrasion-resistant steel plate comprises: a chemical composition containing, in mass %, C: more than 0.34% and 0.50% or less, Si: 0.01% to 1.0%, Mn: 0.30% to 2.00%, P: 0.015% or less, S: 0.005% or less, Cr: 0.01% to 2.00%, Al: 0.001% to 0.100%, N: 0.01% or less, and a balance consisting of Fe and inevitable impurities; and a microstructure in which a volume fraction of martensite at a depth of 1 mm from a surface of the abrasion-resistant steel plate is 90% or more, and a prior austenite grain size at the mid-thickness of the abrasion-resistant steel plate is 80 &#x3bc;m or less, wherein hardness at a depth of 1 mm from the surface of the abrasion-resistant steel plate is 560 HBW 10/3000 or more in Brinell hardness, and a concentration [Mn] of Mn in mass % and a concentration [P] of P in mass % in a plate thickness central segregation area satisfy 0.04[Mn]+[P]&#x3c;0.45.

An abrasion-resistant steel plate comprises: a specific chemical composition; and a microstructure in which a volume fraction of martensite at a depth of 1 mm from a surface of the abrasion-resistant steel plate is 90% or more, and a prior austenite grain size at the mid-thickness of the abrasion-resistant steel plate is 80 &#x3bc;m or less, wherein hardness at a depth of 1 mm from the surface of the abrasion-resistant steel plate is 360 to 490 HBW 10/3000 in Brinell hardness, and a concentration [Mn] of Mn in mass % and a concentration [P] of P in mass % in a plate thickness central segregation area satisfy 0.04[Mn]+[P]&#x3c;0.55.

A steel plate comprising, by mass %: C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and optionally one or two or more of Cu and the like. Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base metal of the plate has an effective grain size of 20 &#x3bc;m or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at &#xbc; and &#xbd; of the thickness of the plate. The complex inclusions comprise a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 &#x3bc;m or more.

Thick steel plate having good multipass weld joint CTOD characteristics and method for manufacturing the same

A high toughness and high tensile strength thick steel plate has a plate thickness of 100 mm or more, wherein a reduction of area in a center of the plate thickness by tension in a plate thickness direction is 40% or more. Thus, a high tensile strength thick steel plate with excellent strength and toughness in a center of the plate thickness can be obtained with no need for a larger production line, even in the case of producing a high strength thick steel plate for which the addition amount of alloying element needs to be increased.

High toughness and high tensile strength thick steel plate and production method therefor

Provided are a steel plate having high tensile strength, high yield strength, and excellent low-temperature toughness and a method for manufacturing the steel plate. A steel plate contains 0.04% to 0.15% C, 0.1% to 2.0% Si, 0.8% to 2.0% Mn, 0.025% or less P, 0.020% or less S, 0.001% to 0.100% Al, 0.010% to 0.050% Nb, and 0.005% to 0.050% Ti and further contains Cu, Ni, Cr, Mo, and N on a mass basis such that 0.5%&#x2264;Cu+Ni+Cr+Mo&#x2264;3.0% and 1.8&#x2264;Ti/N&#x2264;4.5 are satisfied, the remainder being Fe and inevitable impurities. The area fraction of polygonal ferrite is less than 10%. The effective grain size at the through-thickness center is 15 &#x3bc;m or less. The standard deviation of the effective grain size is 10 &#x3bc;m or less.

Thick steel plate and production method for thick steel plate

There is provided a thick steel plate having good multipass weld joint CTOD characteristics for low to medium heat input and a method for manufacturing the thick steel plate. A steel plate containing, on a mass percent basis, C: 0.03% to 0.12%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and optionally one or two or more of Cu and the like, wherein Ti/N, Ceq, Pcm, and ACR are in particular ranges, a base material of the plate has an effective grain size of 20 &#x3bc;m or less at half the thickness of the plate, and the plate contains a particular number of complex inclusions at &#xbc; and &#xbd; of the thickness of the plate, the complex inclusions being composed of a sulfide containing Ca and Mn and an oxide containing Al and having an equivalent circular diameter of 0.1 &#x3bc;m or more. Steel having the composition described above is heated at a particular temperature, is then hot-rolled, and is cooled.

Thick steel sheet having excellent CTOD properties in multilayer welded joints, and manufacturing method for thick steel sheet

Provided are a thick steel plate with which a welded joint having good CTOD property is formed by low-to-medium heat input multipass welding and a method for producing the thick steel plate. The steel plate has a composition containing, by mass, C: 0.03% to 0.10%, Si: 0.5% or less, Mn: 1.0% to 2.0%, P: 0.015% or less, S: 0.0005% to 0.0050%, Al: 0.005% to 0.060%, Ni: 0.5% to 2.0%, Ti: 0.005% to 0.030%, N: 0.0015% to 0.0065%, O: 0.0010% to 0.0050%, Ca: 0.0005% to 0.0060%, and, as needed, one or more elements such as Cu. Ti/N, Ceq, Pcm, and ACR each fall within the specific range. The effective crystal grain size of the base metal at the center of the plate in the thickness direction is 20 &#x3bc;m or less. A specific amount of a composite inclusion including a sulfide containing Ca and Mn and an oxide containing Al having an equivalent circular diameter of 0.1 &#x3bc;m or more is present at the &#xbc;-thickness position and the &#xbd;-thickness position of the plate. The steel having the above-described composition is heated to a specific temperature, hot rolled, and cooled.

The present invention provides a high tensile strength steel plate having a chemical composition containing, in percent by mass, 0.03% to 0.12% of C, 0.01% to 0.30% of Si, 0.5% to 1.95% of Mn, 0.008% or less of P, 0.005% or less of S, 0.015% to 0.06% of Al, 0.011% to 0.05% of Nb, 0.005% to 0.02% of Ti, 0.001% to 0.006% of N, 0.0005% to 0.003% of Ca, optionally, one or two or more of Cr, Mo, V, Cu, and Ni, in which Ceq is 0.44 or less, Ti/N is 1.5 to 3.5, and parameter formulas composed of specific elements for controlling the sulfide morphology and the degree of center segregation in the steel are satisfied, and the balance being Fe and incidental impurities, in which the hardness of the center segregation area of the steel sheet is further specified.

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Tokyo, Japan

Yusuke Terazawa