JP6843119B2 - High hardness steel sheet and its manufacturing method - Google Patents

High hardness steel sheet and its manufacturing method Download PDF

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JP6843119B2
JP6843119B2 JP2018509544A JP2018509544A JP6843119B2 JP 6843119 B2 JP6843119 B2 JP 6843119B2 JP 2018509544 A JP2018509544 A JP 2018509544A JP 2018509544 A JP2018509544 A JP 2018509544A JP 6843119 B2 JP6843119 B2 JP 6843119B2
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ヨン−ロク イム、
ヨン−ロク イム、
ジュン−サン チャン、
ジュン−サン チャン、
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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    • C21D1/18—Hardening; Quenching with or without subsequent tempering
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C—CHEMISTRY; METALLURGY
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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Description

本発明は、様々な分野に使用される高硬度鋼板及びその製造方法に関する。 The present invention relates to a high hardness steel sheet used in various fields and a method for producing the same.

高い硬度を有する鋼板は、耐摩耗性と荷重支持能力に優れるため、長い使用寿命と耐久性を保証することができ、様々な部品に使用されている。 A steel sheet having high hardness has excellent wear resistance and load bearing capacity, so that a long service life and durability can be guaranteed, and it is used for various parts.

特に、耐摩耗鋼の場合、ブリネル硬度を基準としてその等級が規定されているが、通常、ＨＢ（ブリネル硬度）３５０級から、上はＨＢ６００級までの多様な硬度レベルで製造されている。 In particular, in the case of wear-resistant steel, the grade is defined based on the Brinell hardness, but it is usually manufactured at various hardness levels from HB (Brinell hardness) 350 grade to HB600 grade.

また、高い硬度を有する鋼板は、高い強度も同時に有するようになるため、衝突部材、補強材のように、高強度の構造を活用する部門においても使用することができ、部品軽量化と効率化の側面から高い経済的価値を有する。 In addition, since a steel plate having high hardness also has high strength at the same time, it can be used in departments that utilize high-strength structures such as collision members and reinforcing materials, and parts can be made lighter and more efficient. Has high economic value from the aspect of.

このような高硬度鋼板は、通常、オーステナイト温度領域から常温への冷却過程において鋼板をマルテンサイトあるいはベイナイト組織に相変態させ、このような低温変態組織 が有する高い硬度と強度を活用している。 Such a high-hardness steel sheet usually undergoes phase transformation of the steel sheet into a martensite or bainite structure in the cooling process from the austenite temperature region to room temperature, and utilizes the high hardness and strength of such a low-temperature transformation structure.

しかしながら、従来技術では、部品により要求される硬度を得るために、様々な成分及び工程を制御する方案が考案されているものの、一元化した硬度を得るための基準については提示されていない。 However, in the prior art, although a method for controlling various components and processes has been devised in order to obtain the hardness required by the component, a standard for obtaining a unified hardness has not been presented.

本発明の一側面は、５００ＨＢ以上のブリネル硬度を得るために、最小炭素含量の関係式を用いて鋼組成が設定された５００ＨＢ以上のブリネル硬度を有する高硬度鋼板を提供しようとするものである。 One aspect of the present invention is to provide a high-hardness steel sheet having a Brinell hardness of 500 HB or more in which a steel composition is set by using a relational expression of a minimum carbon content in order to obtain a Brinell hardness of 500 HB or more. ..

本発明の他の一側面は、５００ＨＢ以上のブリネル硬度を得るために、最小炭素含量の関係式に従って鋼組成を設定して５００ＨＢ以上のブリネル硬度を有する高硬度鋼板を製造する方法を提供しようとするものである。 Another aspect of the present invention is to provide a method for producing a high hardness steel sheet having a Brinell hardness of 500 HB or more by setting the steel composition according to the relational expression of the minimum carbon content in order to obtain a Brinell hardness of 500 HB or more. To do.

本発明の好ましい一側面は、熱間圧延された熱延鋼板を冷却する工程を含んで製造される鋼板であって、
重量％で、炭素（Ｃ）：０．０５〜０．３％、ケイ素（Ｓｉ）：０．５％以下（０％を除く）、マンガン（Ｍｎ）：２．５％以下（０％を除く）、クロム（Ｃｒ）：１．５％以下（０％を除く）、モリブデン（Ｍｏ）：１．０％以下（０％を除く）、ニッケル（Ｎｉ）：１．０％以下（０％を除く）、ニオブ（Ｎｂ）：０．１％以下（０％を除く）、チタン（Ｔｉ）：０．１％以下（０％を除く）、バナジウム（Ｖ）：０．１％以下（０％を除く）、ホウ素（Ｂ）：０．０１％以下（０％を除く）、アルミニウム（Ａｌ）：０．１％以下（０％を除く）、残部鉄（Ｆｅ）、及びその他不可避な不純物からなり；
上記炭素（Ｃ）の最小含量が下記関係式（１）を満たし、
［関係式１］
Ｃ（炭素（Ｃ）の最小含量）≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］
９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織を有し、並びに
５００ＨＢ以上のブリネル硬度を有する高硬度鋼板に関する。 A preferred aspect of the present invention is a steel sheet manufactured including a step of cooling a hot-rolled hot-rolled steel sheet.
By weight%, carbon (C): 0.05 to 0.3%, silicon (Si): 0.5% or less (excluding 0%), manganese (Mn): 2.5% or less (excluding 0%) ), Chromium (Cr): 1.5% or less (excluding 0%), Molybdenum (Mo): 1.0% or less (excluding 0%), Nickel (Ni): 1.0% or less (0%) (Excluding), Niobium (Nb): 0.1% or less (excluding 0%), Titanium (Ti): 0.1% or less (excluding 0%), Vanadium (V): 0.1% or less (0%) (Excluding), boron (B): 0.01% or less (excluding 0%), aluminum (Al): 0.1% or less (excluding 0%), residual iron (Fe), and other unavoidable impurities Nari;
The minimum content of carbon (C) satisfies the following relational expression (1),
[Relationship formula 1]
C (minimum content of carbon (C)) ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, Mn, Si, Cr, Ni, and Mo are values in which the content of each element is expressed in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]
95 vol. With respect to a high hardness steel sheet having a microstructure containing% or more of the martensite phase and having a Brinell hardness of 500 HB or more.

本発明の好ましい他の一側面は、重量％で、炭素（Ｃ）：０．０５〜０．３％、ケイ素（Ｓｉ）：０．５％以下（０％を除く）、マンガン（Ｍｎ）：２．５％以下（０％を除く）、クロム（Ｃｒ）：１．５％以下（０％を除く）、モリブデン（Ｍｏ）：１．０％以下（０％を除く）、ニッケル（Ｎｉ）：１．０％以下（０％を除く）、ニオブ（Ｎｂ）：０．１％以下（０％を除く）、チタン（Ｔｉ）：０．１％以下（０％を除く）、バナジウム（Ｖ）：０．１％以下（０％を除く）、ホウ素（Ｂ）：０．０１％以下（０％を除く）、アルミニウム（Ａｌ）：０．１％以下（０％を除く）、残部鉄（Ｆｅ）、及びその他不可避な不純物からなる鋼スラブを熱延鋼板として熱間圧延した後、冷却して、９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織、及び５００ＨＢ以上のブリネル硬度を有する鋼板を製造する方法であって、上記炭素（Ｃ）の最小含量が下記関係式（１）を満たす高硬度鋼板の製造方法に関する。
［関係式１］
Ｃ（炭素（Ｃ）の最小含量）≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］ Another preferred aspect of the present invention is by weight%, carbon (C): 0.05-0.3%, silicon (Si): 0.5% or less (excluding 0%), manganese (Mn) :. 2.5% or less (excluding 0%), chromium (Cr): 1.5% or less (excluding 0%), molybdenum (Mo): 1.0% or less (excluding 0%), nickel (Ni) : 1.0% or less (excluding 0%), niobium (Nb): 0.1% or less (excluding 0%), titanium (Ti): 0.1% or less (excluding 0%), vanadium (V) ): 0.1% or less (excluding 0%), boron (B): 0.01% or less (excluding 0%), aluminum (Al): 0.1% or less (excluding 0%), residual steel A steel slab composed of (Fe) and other unavoidable impurities is hot-rolled as a hot-rolled steel plate and then cooled to obtain 95 vol. A method for producing a steel sheet having a fine structure containing a martensite phase of% or more and a Brinell hardness of 500 HB or more, wherein the minimum content of carbon (C) satisfies the following relational expression (1). Regarding the method.
[Relationship formula 1]
C (minimum content of carbon (C)) ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, Mn, Si, Cr, Ni, and Mo are values in which the content of each element is expressed in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]

本発明の一側面によると、９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織、及び５００ＨＢ以上のブリネル硬度を有する鋼板を製造するために、より経済的で、一元化した鋼板成分設計を可能にする効果がある。 According to one aspect of the invention, 95 vol. In order to produce a steel sheet having a microstructure containing% or more of the martensite phase and a Brinell hardness of 500 HB or more, there is an effect of enabling more economical and unified steel sheet component design.

高硬度鋼板に関する従来技術は、部品により要求される硬度を得るために様々な成分及び工程を制御する方案が提案されているが、一元化した硬度を得るための成分基準などについては提示されていない。 In the prior art regarding high hardness steel sheets, a method of controlling various components and processes in order to obtain the hardness required by a part has been proposed, but a component standard for obtaining a unified hardness has not been presented. ..

そこで、本発明者らは、高い硬度と強度を確保するために、鋼板の微細組織を９５ｖｏｌ．％以上のマルテンサイト組織として形成するとき、必要な硬度レベルを確保するための成分設計の条件などについて研究及び実験を行い、その結果に基づいて本発明を完成するに至った。 Therefore, in order to secure high hardness and strength, the present inventors have made the fine structure of the steel sheet 95 vol. When forming as a martensite structure of% or more, research and experiments were conducted on the conditions of component design for ensuring the required hardness level, and the present invention was completed based on the results.

即ち、本発明の主な技術的思想の一つは、高い硬度と強度を確保するために、鋼板の微細組織を９５ｖｏｌ．％以上のマルテンサイト組織として形成するに際して、必要な硬度レベルを確保するための成分設計の条件を提示することであり、それに従って、９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織、及び５００ＨＢ以上のブリネル硬度を有する鋼板をより経済的に製造することができ、さらに、一元化した硬度を得ることができる。 That is, one of the main technical ideas of the present invention is to make the fine structure of the steel sheet 95 vol. In forming as a martensite structure of% or more, it is to present the conditions of the component design for ensuring the required hardness level, and accordingly, 95 vol. A fine structure containing% or more of the martensite phase and a steel sheet having a Brinell hardness of 500 HB or more can be produced more economically, and a unified hardness can be obtained.

以下、本発明の好ましい一側面による鋼板について説明する。 Hereinafter, a steel sheet according to a preferable aspect of the present invention will be described.

炭素（Ｃ）：０．０５〜０．３重量％（以下、「％」という。）
炭素（Ｃ）の含量は、０．０５〜０．３％であることができる。 Carbon (C): 0.05 to 0.3% by weight (hereinafter referred to as "%")
The content of carbon (C) can be 0.05-0.3%.

炭素の含量が０．０５％未満であると、オーステナイト領域からの冷却時に、マルテンサイト変態が生じ難くなることがあり、また、炭素の含量が０．３％を超えると、鋼材の脆弱性が増加し、部品の安定性を保証できなくなることがある。 If the carbon content is less than 0.05%, martensitic transformation may be less likely to occur when cooling from the austenite region, and if the carbon content exceeds 0.3%, the steel material may become fragile. It may increase and the stability of parts cannot be guaranteed.

上記炭素（Ｃ）の含量は、０．１９〜０．３％であることができる。 The content of the carbon (C) can be 0.19 to 0.3%.

ケイ素（Ｓｉ）：０．５％以下（０％を除く）
ケイ素（Ｓｉ）の含量は０．５％以下（０％を除く）であることができる。 Silicon (Si): 0.5% or less (excluding 0%)
The content of silicon (Si) can be 0.5% or less (excluding 0%).

ケイ素は、鋼材の耐摩耗性を増加させることから、硬度を活用する用途で好まれる合金元素である。但し、Ｓｉの添加量が過度に多いと、鋼材の表面特性及びめっき性が悪化し、再加熱時に完全なオーステナイト化が進行しない可能性がある。 Silicon is an alloying element preferred for applications that utilize hardness because it increases the wear resistance of steel materials. However, if the amount of Si added is excessively large, the surface characteristics and plating properties of the steel material deteriorate, and complete austenitization may not proceed during reheating.

上記ケイ素（Ｓｉ）の含量は０．２１〜０．５％であることができる。さらに、上記ケイ素（Ｓｉ）の含量は０．２５３〜０．３４％であることができる。 The content of the silicon (Si) can be 0.21 to 0.5%. Further, the content of the silicon (Si) can be 0.253 to 0.34%.

マンガン（Ｍｎ）：２．５％以下（０％を除く）、及びクロム（Ｃｒ）：１．５％以下（０％を除く）
マンガン（Ｍｎ）とクロム（Ｃｒ）は、いずれもマルテンサイト変態点を大きく低下させる元素であり、通常、鋼に添加される元素の中で炭素に続いて変態点低下の効果が大きく、低価の元素であるため、経済的に活用できる元素である。 Manganese (Mn): 2.5% or less (excluding 0%), and chromium (Cr): 1.5% or less (excluding 0%)
Both manganese (Mn) and chromium (Cr) are elements that significantly lower the transformation point of martensitic transformation, and are usually the elements added to steel that have the greatest effect of lowering the transformation point following carbon and are low in price. Because it is an element of, it is an element that can be economically utilized.

上記マンガン含量の上限は、２．５％に制限することが好ましく、上記クロム含量の上限は、１．５％に制限することが好ましい。 The upper limit of the manganese content is preferably limited to 2.5%, and the upper limit of the chromium content is preferably limited to 1.5%.

上記マンガンとクロムの含量が過度に高いと、オーステナイトが常温で残留するようになり、目標とする９５ｖｏｌ．％以上のマルテンサイト組織が得られなくなる恐れがある。 If the contents of manganese and chromium are excessively high, austenite will remain at room temperature, and the target 95 vol. There is a risk that more than% martensite tissue will not be obtained.

上記マンガンの含量は１．４〜２．５％であることができる。さらに、上記マンガンの含量は２．１〜２．５％であることができる。 The manganese content can be 1.4-2.5%. Further, the manganese content can be 2.1-2.5%.

モリブデン（Ｍｏ）：１．０％以下（０％を除く）、及びニッケル（Ｎｉ）：１．０％以下（０％を除く）
モリブデン（Ｍｏ）とニッケル（Ｎｉ）は、マルテンサイト変態開始温度を低下させる元素である。 Molybdenum (Mo): 1.0% or less (excluding 0%), and nickel (Ni): 1.0% or less (excluding 0%)
Molybdenum (Mo) and nickel (Ni) are elements that lower the martensitic transformation start temperature.

しかしながら、マルテンサイト変態開始温度を低下させる程度は、ＭｎとＣｒよりは低く、高価な元素であるため、これらの元素の添加量の上限は、それぞれ１．０％に制限することが好ましい。 However, the degree to which the martensitic transformation start temperature is lowered is lower than that of Mn and Cr, and they are expensive elements. Therefore, the upper limit of the amount of these elements added is preferably limited to 1.0%, respectively.

ニオブ（Ｎｂ）：０．１％以下（０％を除く）、及びチタン（Ｔｉ）：０．１％以下（０％を除く）
ニオブ（Ｎｂ）とチタン（Ｔｉ）は、それぞれ０．１％以下（０％を除く）のレベルで添加することができ、オーステナイト結晶粒微細化によって鋼板の衝撃特性を改善するという効果がある。しかしながら、Ｎｂ及びＴｉを過度に多く添加すると、結晶粒境界を固定するＮｂ炭窒化物の粗大化を引き起こし、結晶粒微細化効果を減少させるため、その上限は、それぞれ０．１％に限定することが好ましい。 Niobium (Nb): 0.1% or less (excluding 0%), and Titanium (Ti): 0.1% or less (excluding 0%)
Niobium (Nb) and titanium (Ti) can be added at a level of 0.1% or less (excluding 0%), respectively, and have the effect of improving the impact characteristics of the steel sheet by refining the austenite grains. However, if Nb and Ti are added in an excessively large amount, the Nb carbonitride that fixes the grain boundary is coarsened and the crystal grain refinement effect is reduced. Therefore, the upper limit thereof is limited to 0.1%, respectively. Is preferable.

一方、Ｔｉは、Ｂの添加時に、ＢをＮから保護するために必須に添加する場合が多く、チタン（Ｔｉ）が鋼中の炭素又は窒素と先に反応してＴｉＣ又はＴｉＮを形成することで、ホウ素（Ｂ）の添加効果を上げる。この場合、チタン（Ｔｉ）の含量は、鋼中の窒素量との化学量論に基づき、下記の関係式２を満たせばよい。 On the other hand, Ti is often added indispensably to protect B from N when B is added, and titanium (Ti) reacts first with carbon or nitrogen in steel to form TiC or TiN. Then, the effect of adding boron (B) is increased. In this case, the content of titanium (Ti) may satisfy the following relational expression 2 based on the stoichiometry with the amount of nitrogen in the steel.

［関係式２］
Ｔｉ（ｗｔ％）＞Ｎ（ｗｔ％）×３．４２ [Relational expression 2]
Ti (wt%)> N (wt%) x 3.42

バナジウム（Ｖ）：０．１％以下（０％を除く）
バナジウム（Ｖ）は、０．１％以下（０％を除く）のレベルで添加することができ、微細なＶ炭化物を形成することで、析出硬化及び溶接部の物性低下を防止する役割を果たす。 Vanadium (V): 0.1% or less (excluding 0%)
Vanadium (V) can be added at a level of 0.1% or less (excluding 0%), and by forming fine V carbides, it plays a role in preventing precipitation hardening and deterioration of physical properties of welded parts. ..

その添加量が過度に多いと、炭化物の粗大化によってその効果が減少するため、その含量の上限は、０．１％に制限することが好ましい。 If the amount added is excessively large, the effect is reduced due to the coarsening of carbides, so the upper limit of the content is preferably limited to 0.1%.

ホウ素（Ｂ）：０．０１％以下（０％を除く）
ホウ素（Ｂ）は、０．０１％以下（０％を除く）のレベルで添加することができるが、フェライト及びパーライトの核生成を阻害して、鋼材の硬化能を大幅に向上させる元素であり、鋼材の厚さが厚いほど、その活用度が非常に大きくなる。 Boron (B): 0.01% or less (excluding 0%)
Boron (B), which can be added at a level of 0.01% or less (excluding 0%), is an element that inhibits the nucleation of ferrite and pearlite and greatly improves the hardening ability of steel materials. , The thicker the steel material, the greater its utilization.

本発明では、最終微細組織を９５ｖｏｌ．％以上のマルテンサイトとして得るにあたり、その製造過程に対する制約は特になく、必要に応じて、硬化能確保のためにＢを添加することができる。但し、Ｂの含量が過度に多く添加されると、却って、フェライト相やパーライト相の核生成サイトとして作用し、硬化能を損なうようになるため、その含量の上限は、０．０１％に制限することが好ましい。 In the present invention, the final microstructure is 95 vol. When obtained as% or more martensite, there are no particular restrictions on the manufacturing process, and B can be added to ensure the curing ability, if necessary. However, if the content of B is added in an excessively large amount, it acts as a nucleation site for the ferrite phase and the pearlite phase and impairs the curability, so the upper limit of the content is limited to 0.01%. It is preferable to do so.

アルミニウム（Ａｌ）：０．１％以下（０％を除く）
アルミニウム（Ａｌ）は、脱酸と結晶粒微細化のために添加し、その含量は、０．１％以下（０％を除く）に制限することが好ましい。 Aluminum (Al): 0.1% or less (excluding 0%)
Aluminum (Al) is preferably added for deoxidation and grain refinement, and its content is preferably limited to 0.1% or less (excluding 0%).

前述した元素以外の残りは、鉄（Ｆｅ）、及びその他不可避な不純物を含む。 The rest of the elements other than those mentioned above contain iron (Fe) and other unavoidable impurities.

本発明では、上記炭素（Ｃ）の最小含量が下記関係式（１）を満たす。 In the present invention, the minimum content of carbon (C) satisfies the following relational expression (1).

［関係式１］
Ｃ（炭素（Ｃ）の最小含量）≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］ [Relationship formula 1]
C (minimum content of carbon (C)) ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, Mn, Si, Cr, Ni, and Mo are values in which the content of each element is expressed in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]

上記関係式（１）は、上記ケイ素（Ｓｉ）、マンガン（Ｍｎ）、クロム（Ｃｒ）、モリブデン（Ｍｏ）、ニッケル（Ｎｉ）、及びクロム（Ｃｒ）の組成から５００ＨＢ以上のブリネル硬度を得るための最小炭素（Ｃ）含量を示す。 The above relational expression (1) is for obtaining a Brinell hardness of 500 HB or more from the composition of the above silicon (Si), manganese (Mn), chromium (Cr), molybdenum (Mo), nickel (Ni), and chromium (Cr). Shows the minimum carbon (C) content of.

上記炭素（Ｃ）含量が０．０５〜０．３重量％を満たしていたとしても、上記関係式（１）を満たしていなければ、５００ＨＢ以上のブリネル硬度を得ることができない。 Even if the carbon (C) content satisfies 0.05 to 0.3% by weight, a Brinell hardness of 500 HB or more cannot be obtained unless the relational expression (1) is satisfied.

上記関係式（１）は、例えば、下記関係式（３）を用いて設計されてもよい。 The relational expression (1) may be designed using, for example, the following relational expression (3).

［関係式３］
ＨＢ（ブリネル硬度）＝１００．４＋８３０．５＊Ｃ＋８６．５＊Ｍｎ＋２８．８＊Ｓｉ＋７３．４＊Ｃｒ＋４４．５＊Ｎｉ＋２８．８＊Ｍｏ＋０．２５２＊Ｃ．Ｒ．
［ここで、Ｃ、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］ [Relational expression 3]
HB (Brinell hardness) = 100.4 + 830.5 * C + 86.5 * Mn + 28.8 * Si + 73.4 * Cr + 44.5 * Ni + 28.8 * Mo + 0.252 * C. R.
[Here, C, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]

上記関係式（３）から、ＨＢ≧５００になるための最小炭素含量に対する関係式（１）を導出することができる。 From the above relational expression (3), the relational expression (1) for the minimum carbon content for HB ≧ 500 can be derived.

また、本発明の鋼板の成分範囲内において関係式（３）を用いることによって、３５０ＨＢ以上のいかなる必要硬度レベルを得るための適正な合金成分設計の条件を導出することもできる。 Further, by using the relational expression (3) within the component range of the steel sheet of the present invention, it is possible to derive the conditions for designing an appropriate alloy component in order to obtain any required hardness level of 350 HB or more.

本発明の鋼板の微細組織は、９５ｖｏｌ．％以上のマルテンサイト相を含む。 The fine structure of the steel sheet of the present invention is 95 vol. Includes% or more martensite phase.

上記マルテンサイト相の分率が９５ｖｏｌ．％未満であると、目的とする強度及び硬度を確保できなくなることもある。 The fraction of the martensite phase is 95 vol. If it is less than%, the desired strength and hardness may not be secured.

本発明の鋼板の微細組織は、マルテンサイト以外の第２相組織であって、５．０ｖｏｌ．％未満のフェライト及びベイナイトのうち１種又は２種を含むことができる。 The microstructure of the steel sheet of the present invention is a phase 2 structure other than martensite, and is 5.0 vol. It can contain one or two of less than% ferrite and bainite.

本発明の鋼板は、５００ＨＢ以上のブリネル硬度を有する。 The steel sheet of the present invention has a Brinell hardness of 500 HB or more.

以下、本発明の好ましい他の一側面による鋼板の製造方法について説明する。 Hereinafter, a method for manufacturing a steel sheet according to another preferable aspect of the present invention will be described.

本発明の好ましい他の一側面による鋼板の製造方法では、重量％で、炭素（Ｃ）：０．０５〜０．３％、ケイ素（Ｓｉ）：０．５％以下（０％を除く）、マンガン（Ｍｎ）：２．５％以下（０％を除く）、クロム（Ｃｒ）：１．５％以下（０％を除く）、モリブデン（Ｍｏ）：１．０％以下（０％を除く）、ニッケル（Ｎｉ）：１．０％以下（０％を除く）、ニオブ（Ｎｂ）：０．１％以下（０％を除く）、チタン（Ｔｉ）：０．１％以下（０％を除く）、バナジウム（Ｖ）：０．１％以下（０％を除く）、ホウ素（Ｂ）：０．０１％以下（０％を除く）、アルミニウム（Ａｌ）：０．１％以下（０％を除く）、残部鉄（Ｆｅ）、及びその他不可避な不純物からなる鋼スラブを熱延鋼板として熱間圧延した後、冷却して、９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織、及び５００ＨＢ以上のブリネル硬度を有する鋼板を製造する。 In the method for producing a steel sheet according to another preferable aspect of the present invention, in% by weight, carbon (C): 0.05 to 0.3%, silicon (Si): 0.5% or less (excluding 0%), Manganese (Mn): 2.5% or less (excluding 0%), Chromium (Cr): 1.5% or less (excluding 0%), Molybdenum (Mo): 1.0% or less (excluding 0%) , Nickel (Ni): 1.0% or less (excluding 0%), Niobium (Nb): 0.1% or less (excluding 0%), Titanium (Ti): 0.1% or less (excluding 0%) ), Vanadium (V): 0.1% or less (excluding 0%), Boron (B): 0.01% or less (excluding 0%), Aluminum (Al): 0.1% or less (0%) A steel slab composed of (excluding), residual iron (Fe), and other unavoidable impurities is hot-rolled as a hot-rolled steel sheet and then cooled to obtain 95 vol. A steel sheet having a microstructure containing% or more of the martensite phase and a Brinell hardness of 500 HB or more is produced.

上記鋼スラブの炭素（Ｃ）の最小含量は、下記関係式（１）を満たす。 The minimum carbon (C) content of the steel slab satisfies the following relational expression (1).

［関係式１］
Ｃ（炭素（Ｃ）の最小含量）≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］ [Relationship formula 1]
C (minimum content of carbon (C)) ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]

上記鋼スラブを、熱延鋼板として熱間圧延する前に再加熱することができる。 The steel slab can be reheated as a hot-rolled steel sheet before it is hot-rolled.

スラブ再加熱条件は、特に限定されず、均質化が進行すればよい。 The slab reheating conditions are not particularly limited, and homogenization may proceed.

スラブ再加熱温度は、１１００〜１３００℃が好ましい。 The slab reheating temperature is preferably 1100 to 1300 ° C.

上記熱間圧延条件は、特に限定されるものではないが、熱間仕上げ圧延温度は、オーステナイト化が十分進行する温度であればよい。 The hot rolling conditions are not particularly limited, but the hot finish rolling temperature may be any temperature at which austenitization proceeds sufficiently.

上記熱間仕上げ圧延温度は、例えば、８７０〜９３０℃であることができ、全熱間圧延は、加熱炉から抽出した後、１１５０℃〜熱間仕上げ圧延温度の温度範囲で行うことができる。 The hot finish rolling temperature can be, for example, 870 to 930 ° C., and the total hot rolling can be performed in the temperature range of 1150 ° C. to the hot finish rolling temperature after extraction from the heating furnace.

上記熱延鋼板の冷却時における冷却速度は、９５ｖｏｌ．％以上のマルテンサイト相が得られる冷却速度であれば、特に限定されるものではなく、例えば、２０℃／ｓ以上、好ましくは２０〜１５０℃／ｓである。 The cooling rate at the time of cooling the hot-rolled steel sheet is 95 vol. The cooling rate is not particularly limited as long as the martensite phase of% or more can be obtained, and is, for example, 20 ° C./s or more, preferably 20 to 150 ° C./s.

上記熱延鋼板の冷却時における冷却終了温度は、Ｍｓ点（マルテンサイト変態開始温度）以下であり、９５ｖｏｌ．％以上のマルテンサイト相が得られる温度であれば、特に限定されるものではない。 The cooling end temperature at the time of cooling the hot-rolled steel sheet is not less than the Ms point (martensite transformation start temperature), and is 95 vol. The temperature is not particularly limited as long as the martensite phase of% or more can be obtained.

以下、実施例を通じて本発明をより具体的に説明する。但し、このような実施例は本発明を例示するためのものであり、本発明はこれに限定されるものではない。 Hereinafter, the present invention will be described in more detail through examples. However, such examples are for exemplifying the present invention, and the present invention is not limited thereto.

下記表１の組成（単位：重量％）を有するＡ〜Ｑの１７種類の鋼を使用して実験した。 Experiments were carried out using 17 types of steels A to Q having the compositions (unit:% by weight) shown in Table 1 below.

下記表１の鋼の組成は、いずれも本発明の組成範囲を満たす。 All of the steel compositions in Table 1 below satisfy the composition range of the present invention.

下記表１の鋼組成を有し、厚さ３０ｍｍ及び幅２００ｍｍの鋼板を製造した後、１２００℃で１８０分間再加熱した。次いで、再加熱された鋼板を９００℃の熱間仕上げ温度範囲で熱間圧延することで、厚さ３．０ｍｍの熱延鋼板を製造し、２００℃まで下記表２の冷却速度で冷却した。 A steel sheet having the steel composition shown in Table 1 below, having a thickness of 30 mm and a width of 200 mm was produced, and then reheated at 1200 ° C. for 180 minutes. Next, the reheated steel sheet was hot-rolled in a hot finishing temperature range of 900 ° C. to produce a hot-rolled steel sheet having a thickness of 3.0 mm, which was cooled to 200 ° C. at the cooling rate shown in Table 2 below.

上記のように製造された熱延鋼板のブリネル硬度（ＨＢ）及び微細組織を測定し、その結果を下記表２に示した。 The Brinell hardness (HB) and microstructure of the hot-rolled steel sheet manufactured as described above were measured, and the results are shown in Table 2 below.

下記表２の第２相組織では、マルテンサイト以外の第２相組織を示しており、第２相以外の組織はマルテンサイトであり、１００％マルテンサイトは１００％Ｍとして示した。 In the phase 2 organization shown in Table 2 below, the phase 2 organization other than martensite is shown, the organization other than phase 2 is martensite, and 100% martensite is shown as 100% M.

下記の第２相組織において、Ｆはフェライトを示し、Ｂはベイナイトを示し、Ｍはマルテンサイトを示す。 In the phase 2 structure below, F represents ferrite, B represents bainite, and M represents martensite.

また、下記表２には、関係式（１）により求められた必要炭素含量、実際炭素含量、及び実際炭素含量と必要炭素含量との差を併せて示した。 In addition, Table 2 below also shows the required carbon content, the actual carbon content, and the difference between the actual carbon content and the required carbon content obtained by the relational expression (1).

Figure 0006843119
Figure 0006843119

Figure 0006843119
Figure 0006843119

上記表２において、本発明のように実際炭素含量が必要炭素含量よりも高い発明例１〜９では、ブリネル硬度（ＨＢ）値が５００ＨＢ以上であることがわかる。 In Table 2 above, it can be seen that the Brinell hardness (HB) value is 500 HB or more in Invention Examples 1 to 9 in which the actual carbon content is higher than the required carbon content as in the present invention.

一方、実際炭素含量が必要炭素含量よりも低い比較例１〜９では、ブリネル硬度値が５００ＨＢ未満であることがわかる。 On the other hand, in Comparative Examples 1 to 9 in which the actual carbon content is lower than the required carbon content, it can be seen that the Brinell hardness value is less than 500 HB.

以上、実施例を参照して説明したが、当該技術分野の熟練した当業者は、添付の特許請求の範囲に記載された本発明の思想及び領域から外れない範囲内で、本発明を多様に修正及び変更できることが理解できるであろう。 Although the above description has been made with reference to the examples, those skilled in the art will be able to use the present invention in various ways within the scope of the idea and domain of the present invention described in the appended claims. You will understand that it can be modified and changed.

Claims (4)

熱間圧延された熱延鋼板を２０〜１５０℃／ｓの冷却速度で冷却する工程を含んで製造される鋼板であって、
重量％で、炭素（Ｃ）：０．１９〜０．３％、ケイ素（Ｓｉ）：０．２１〜０．５％、マンガン（Ｍｎ）：１．４〜２．５％、クロム（Ｃｒ）：１．５％以下（０％を除く）、モリブデン（Ｍｏ）：１．０％以下（０％を除く）、ニッケル（Ｎｉ）：１．０％以下（０％を除く）、ニオブ（Ｎｂ）：０．１％以下（０％を除く）、チタン（Ｔｉ）：０．１％以下（０％を除く）、バナジウム（Ｖ）：０．１％以下（０％を除く）、ホウ素（Ｂ）：０．０１％以下（０％を除く）、アルミニウム（Ａｌ）：０．１％以下（０％を除く）、残部鉄（Ｆｅ）、及びその他不可避な不純物からなり；
前記炭素（Ｃ）が下記関係式（１）を満たし、
［関係式１］
Ｃ≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｃ、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］
前記関係式（１）は、下記関係式（３）から導出され、
［関係式３］
ＨＢ（ブリネル硬度）＝１００．４＋８３０．５Ｃ＋８６．５Ｍｎ＋２８．８Ｓｉ＋７３．４Ｃｒ＋４４．５Ｎｉ＋２８．８Ｍｏ＋０．２５２Ｃ．Ｒ．≧５００
［ここで、Ｃ、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］
９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織を有し、並びに
５００ＨＢ以上のブリネル硬度を有する、
高硬度鋼板。 A steel sheet manufactured by including a step of cooling a hot-rolled hot-rolled steel sheet at a cooling rate of 20 to 150 ° C./s.
By weight%, carbon (C): 0.19 to 0.3%, silicon (Si): 0.21 to 0.5%, manganese (Mn): 1.4 to 2.5%, chromium (Cr) : 1.5% or less (excluding 0%), molybdenum (Mo): 1.0% or less (excluding 0%), nickel (Ni): 1.0% or less (excluding 0%), niobium (Nb) ): 0.1% or less (excluding 0%), titanium (Ti): 0.1% or less (excluding 0%), vanadium (V): 0.1% or less (excluding 0%), boron (excluding 0%) B): Consists of 0.01% or less (excluding 0%), aluminum (Al): 0.1% or less (excluding 0%), residual iron (Fe), and other unavoidable impurities;
The carbon (C) satisfies the following relational expression (1), and the carbon (C) satisfies the following relational expression (1).
[Relationship formula 1]
C ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, C, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]
The relational expression (1) is derived from the following relational expression (3).
[Relational expression 3]
HB (Brinell hardness) = 100.4 + 830.5C + 86.5Mn + 28.8Si + 73.4Cr + 44.5Ni + 28.8Mo + 0.252C. R. ≧ 500
[Here, C, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]
95 vol. It has a microstructure containing% or more of the martensite phase and has a Brinell hardness of 500 HB or more.
High hardness steel plate. 前記微細組織は、マルテンサイト以外の第２相組織として、５．０ｖｏｌ．％未満のフェライト及びベイナイトのうち１種又は２種を含むことを特徴とする、請求項１に記載の高硬度鋼板。 The microstructure was prepared as a second phase structure other than martensite in 5.0 vol. The high-hardness steel sheet according to claim 1, wherein the high-hardness steel sheet contains one or two of ferrite and bainite, which is less than%. 重量％で、炭素（Ｃ）：０．１９〜０．３％、ケイ素（Ｓｉ）：０．２１〜０．５％、マンガン（Ｍｎ）：１．４〜２．５％、クロム（Ｃｒ）：１．５％以下（０％を除く）、モリブデン（Ｍｏ）：１．０％以下（０％を除く）、ニッケル（Ｎｉ）：１．０％以下（０％を除く）、ニオブ（Ｎｂ）：０．１％以下（０％を除く）、チタン（Ｔｉ）：０．１％以下（０％を除く）、バナジウム（Ｖ）：０．１％以下（０％を除く）、ホウ素（Ｂ）：０．０１％以下（０％を除く）、アルミニウム（Ａｌ）：０．１％以下（０％を除く）、残部鉄（Ｆｅ）、及びその他不可避な不純物からなる鋼スラブを熱延鋼板として熱間圧延した後、２０〜１５０℃／ｓの冷却速度で冷却して、９５ｖｏｌ．％以上のマルテンサイト相を含む微細組織、及び５００ＨＢ以上のブリネル硬度を有する鋼板を製造する方法であって、前記炭素（Ｃ）が下記関係式（１）を満たし、
下記関係式（１）は、下記関係式（３）から導出される、
高硬度鋼板の製造方法。
［関係式１］
Ｃ≧０．４８１−０．１０４Ｍｎ−０．０３５Ｓｉ−０．０８８Ｃｒ−０．０５４Ｎｉ−０．０３５Ｍｏ−０．０００３Ｃ．Ｒ．
［ここで、Ｃ、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］
［関係式３］
ＨＢ（ブリネル硬度）＝１００．４＋８３０．５Ｃ＋８６．５Ｍｎ＋２８．８Ｓｉ＋７３．４Ｃｒ＋４４．５Ｎｉ＋２８．８Ｍｏ＋０．２５２Ｃ．Ｒ．≧５００
［ここで、Ｃ、Ｍｎ、Ｓｉ、Ｃｒ、Ｎｉ、及びＭｏは各元素の含有量を重量％で示した値であり、Ｃ．Ｒ．は熱延鋼板の冷却時における冷却速度を示した値であり、単位は℃／ｓである。］ By weight%, carbon (C): 0.19 to 0.3%, silicon (Si): 0.21 to 0.5%, manganese (Mn): 1.4 to 2.5%, chromium (Cr) : 1.5% or less (excluding 0%), molybdenum (Mo): 1.0% or less (excluding 0%), nickel (Ni): 1.0% or less (excluding 0%), niobium (Nb) ): 0.1% or less (excluding 0%), titanium (Ti): 0.1% or less (excluding 0%), vanadium (V): 0.1% or less (excluding 0%), boron (excluding 0%) B): Hot-rolled steel slab consisting of 0.01% or less (excluding 0%), aluminum (Al): 0.1% or less (excluding 0%), residual iron (Fe), and other unavoidable impurities. After hot rolling as a steel plate, it was cooled at a cooling rate of 20 to 150 ° C./s to 95 vol. A method for producing a steel sheet having a fine structure containing a martensite phase of% or more and a Brinell hardness of 500 HB or more, wherein the carbon (C) satisfies the following relational expression (1).
The following relational expression (1) is derived from the following relational expression (3).
Manufacturing method of high hardness steel sheet.
[Relationship formula 1]
C ≧ 0.481-0.104Mn-0.035Si-0.088Cr-0.054Ni-0.035Mo-0.0003C. R.
[Here, C, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ]
[Relational expression 3]
HB (Brinell hardness) = 100.4 + 830.5C + 86.5Mn + 28.8Si + 73.4Cr + 44.5Ni + 28.8Mo + 0.252C. R. ≧ 500
[Here, C, Mn, Si, Cr, Ni, and Mo are values indicating the content of each element in% by weight, and C.I. R. Is a value indicating the cooling rate at the time of cooling the hot-rolled steel sheet, and the unit is ° C./s. ] 前記熱延鋼板の冷却時における冷却終了温度は、Ｍｓ点（マルテンサイト変態開始温度）以下であることを特徴とする、請求項３に記載の高硬度鋼板の製造方法。 The method for producing a high-hardness steel sheet according to claim 3, wherein the cooling end temperature at the time of cooling the hot-rolled steel sheet is equal to or lower than the Ms point (martensite transformation start temperature).
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