JP2004018944A - Cast steel - Google Patents
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- JP2004018944A JP2004018944A JP2002175808A JP2002175808A JP2004018944A JP 2004018944 A JP2004018944 A JP 2004018944A JP 2002175808 A JP2002175808 A JP 2002175808A JP 2002175808 A JP2002175808 A JP 2002175808A JP 2004018944 A JP2004018944 A JP 2004018944A
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、鋳鋼に関する技術分野に属し、特には、靱性および溶接性に優れ、かつ、耐火特性を有する鋳鋼に関する技術分野に属する。
【０００２】
【従来の技術】
溶接構造に用いるもので、特に溶接性に優れた鋳鋼としては、ＪＩＳ Ｇ ５１０２に規定される鋳鋼（溶接構造用鋳鋼）がある。この溶接構造用鋳鋼は、６００ ℃での耐力は常温での耐力の約１／２であり、充分な耐火特性は有しておらず、耐火鋳鋼としては使用できない。
【０００３】
従来、このような溶接構造用鋳鋼に耐火特性をもたせる方法として、Ｍｏ量を増量した組成にすることが開示されている（特開平０７−１８８８３５ 号公報等）。
【０００４】
【発明が解決しようとする課題】
ところが、Ｍｏ量を増量すると、Ｃｅｑ（炭素等量）が上昇し、溶接性が阻害されるという問題点が生じてくる。そこで、必要な溶接性を確保しようとすれば、Ｃ量を低下させることとなる。しかし、Ｃは固液共存温度を広げる元素であるので、Ｃ量を低下させると、鋳鋼材の内部品質、特に引け巣の発生を助長することとなり、内部品質の確保が難しくなる。他の元素を低減すれば、多量に低下させる必要があり、常温での必要特性を満足させることが困難となってくる。（Ｃｅｑ＝Ｃ＋Ｓｉ／６＋Ｍｎ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４から考えれば、Ｃを低下させることが最も効果がある。）
【０００５】
本発明は、このような事情に着目してなされたものであって、その目的は、Ｍｏ量を増量することなく（換言すれば、ＪＩＳ Ｇ ５１０２の成分範囲内において）、靱性および溶接性に優れ、かつ、耐火特性を有する鋳鋼を提供しようとするものである。
【０００６】
【課題を解決するための手段】
上記目的を達成するために、本発明に係る鋳鋼は、請求項１〜２記載の鋳鋼としており、それは次のような構成としたものである。
【０００７】
即ち、請求項１記載の鋳鋼は、質量％で、Ｃ：０．１２〜０．２２％、Ｓｉ：０．２０〜０．６０％、Ｍｎ：０．８０〜１．３０％、Ｎｉ：０．３０〜２．２０％、Ｃｒ：０〜０．３５％（無添加の場合を含む）、Ｍｏ：０〜０．３０％（無添加の場合を含む）、Ｖ：０．００５ 〜０．１５％、Ｗ：０．３０〜０．７５％を含有し、残部がＦｅおよび不可避的不純物からなる鋳鋼である（第１発明）。請求項２記載の鋳鋼は、溶接構造用鋳鋼として用いられる請求項１記載の鋳鋼である（第２発明）。
【０００８】
【発明の実施の形態】
本発明は、例えば次のような形態で実施する。
電気炉による溶解や高周波溶解炉による溶解により、Ｃ：０．１２〜０．２２％、Ｓｉ：０．２０〜０．６０％、Ｍｎ：０．８０〜１．３０％、Ｎｉ：０．３０〜２．２０％、Ｃｒ：０〜０．３５％、Ｍｏ：０〜０．３０％、Ｖ：０．００５ 〜０．１５％、Ｗ：０．３０〜０．７５％を含有し、残部がＦｅおよび不可避的不純物からなる鋼の溶湯を得、必要に応じて精錬（真空処理等含む）を実施した後に、これを所定の鋳型に注入し、鋳造する。そうすると、本発明に係る鋳鋼が得られる。
【０００９】
上記鋳鋼は、所定の焼鈍および熱処理が施され、あるいは更に機械加工された後、所定の用途にて使用される。
【００１０】
このような形態で本発明が実施される。以下、本発明について主にその作用効果を説明する。
【００１１】
本発明に係る鋳鋼は、前述の如く、質量％で、Ｃ：０．１２〜０．２２％、Ｓｉ：０．２０〜０．６０％、Ｍｎ：０．８０〜１．３０％、Ｎｉ：０．３０〜２．２０％、Ｃｒ：０〜０．３５％（無添加の場合を含む）、Ｍｏ：０〜０．３０％（無添加の場合を含む）、Ｖ：０．００５ 〜０．１５％、Ｗ：０．３０〜０．７５％を含有し、残部がＦｅおよび不可避的不純物からなる鋳鋼であり、この鋳鋼の組成、特に、Ｗ：０．３０〜０．７５％、Ｎｉ：０．３０〜２．２０％を含有することにより、Ｍｏ量を増量させずに、優れた靱性および溶接性を有すると共に優れた耐火特性を有することができる。
【００１２】
即ち、本発明に係る鋳鋼は、ＪＩＳ Ｇ ５１０２に規定される溶接構造用鋳鋼に対し、特には、Ｍｏ量を増量させず、新たにＷを０．３０〜０．７５％添加すると共にＮｉ量を０．３０〜２．２０％に調整した組成のものであり、このＷの添加により耐火特性が向上して優れたものとなると共に、このＮｉ量の調整により優れた靱性を確保することができ、また、溶接性の低下がなくて優れた溶接性を確保することができる。
【００１３】
ここで、Ｗ量を０．３０〜０．７５％としているのは、０．３０％未満にすると、耐火特性の向上の程度が小さく、耐火特性が不充分となり、０．７５％超にすると、溶接性に悪影響があり、溶接性が低下して不充分となるからである。また、Ｗは高価な元素であり、大量の添加はコスト上昇を招くという点からも、Ｗ量の上限値を０．７５％とした。
【００１４】
Ｎｉ量を０．３０〜２．２０％としているのは、０．３０未満にすると、靱性が低下し、優れた靱性を確保することができず、靱性が不充分となり、２．２０％超にすると、ＪＩＳ Ｇ ５１０２に記載のＣｅｑ（炭素等量）を満足させることが困難になり、ひいては、優れた溶接性を確保することが難しくなるからである。また、Ｎｉは高価な元素であり、大量の添加はコスト上昇を招くという点からも、Ｎｉ量の上限値を２．２０％とした。
【００１５】
本発明に係る鋳鋼において、不可避的不純物の種類は限定されず、場合によって異なるが、通常は不可避的不純物としてＡｌ、Ｃｕ、Ｐ、Ｓ、Ｎ、Ｏ等が含まれている。これらの量は、場合によって異なるが、通常はＡｌ：０．１ ％以下、Ｃｕ：０．１ ％以下、Ｐ：０．０４％以下、Ｓ：０．０４％以下、Ｎ：１００ｐｐｍ以下、Ｏ：１００ｐｐｍ以下である。
【００１６】
本発明に係る鋳鋼において、これを引張強さ≧４８０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ４８０ に相当する鋳鋼）として用いる場合、その組成については、Ｃ：０．１６〜０．２２％、Ｓｉ：０．３０〜０．６０％、Ｍｎ：０．９０〜１．３０％、Ｎｉ：０．３０〜０．５０％、Ｃｒ：０〜０．５０％（無添加の場合を含む）、Ｍｏ：０〜０．２０％（無添加の場合を含む）、Ｖ：０．００５ 〜０．０７％、Ｗ：０．３０〜０．７５％、残部：Ｆｅおよび不可避的不純物の組成とする。換言すれば、このような組成のものを選択すると、それは引張強さ≧４８０ＭＰａ級の鋳鋼となる。
【００１７】
引張強さ≧５５０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ５５０ に相当する鋳鋼）として用いる場合、Ｃ：０．１４〜０．２０％、Ｓｉ：０．４０〜０．６０％、Ｍｎ：１．００〜１．３０％、Ｎｉ：１．０ 〜２．０ ％、Ｃｒ：０〜０．５０％（無添加の場合を含む）、Ｍｏ：０〜０．３０％（無添加の場合を含む）、Ｖ：０．００５ 〜０．１ ％、Ｗ：０．３０〜０．７５％、残部：Ｆｅおよび不可避的不純物の組成とする。即ち、このような組成のものを選択すると、引張強さ≧５５０ＭＰａ級の鋳鋼となる。
【００１８】
引張強さ≧６２０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ６２０ に相当する鋳鋼）として用いる場合、Ｃ：０．１２〜０．１６％、Ｓｉ：０．２０〜０．６０％、Ｍｎ：０．９０〜１．２０％、Ｎｉ：１．８０〜２．２０％、Ｃｒ：０．１５〜０．３５％、Ｍｏ：０．０５〜０．３０％、Ｖ：０．０５〜０．１５％、Ｗ：０．３０〜０．７５％、残部：Ｆｅおよび不可避的不純物の組成とする。即ち、このような組成のものを選択すると、引張強さ≧６２０ＭＰａ級の鋳鋼となる。
【００１９】
鋳鋼の耐火特性の指標として、一般的に、６００ ℃での耐力が用いられる。この６００ ℃での耐力が高いほど耐火特性が優れているとされる。耐火特性としては、この６００ ℃での耐力が常温での耐力あるいは降伏点の規格値の下限値（規格下限値）の２／３以上であることが望まれる。例えば、引張強さ≧４８０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ４８０ に相当する鋳鋼）の場合、６００ ℃での耐力が２７５ＭＰａ（耐力の規格下限値）×２／３（＝約１８３．３ＭＰａ）以上であることが望まれる。
【００２０】
本発明に係る鋳鋼において、これを引張強さ≧４８０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ４８０ に相当する鋳鋼）として用いる場合、前述のような組成とするが、これと共に下記▲１▼式で求められるＷｅｑが３．４ 以上になるようにすると、６００ ℃での耐力が常温での耐力（ＪＩＳ Ｇ ５１０２でのＳＣＷ ４８０ の耐力の規格下限値：２７５ＭＰａ）の２／３以上となる。従って、このようにすることが、望ましい。
【００２１】
【００２２】
本発明に係る鋳鋼において、これを引張強さ≧５５０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ５５０ に相当する鋳鋼）として用いる場合、前述のような組成とするが、これと共に上記▲１▼式で求められるＷｅｑが３．８ 以上になるようにすると、６００ ℃での耐力が常温での耐力（ＪＩＳ Ｇ ５１０２でのＳＣＷ ５５０ の耐力の規格下限値：３５５ＭＰａ）の２／３以上となる。従って、このようにすることが、望ましい。
【００２３】
本発明に係る鋳鋼において、これを引張強さ≧６２０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ６２０ に相当する鋳鋼）として用いる場合、前述のような組成とするが、これと共に上記▲１▼式で求められるＷｅｑが４．２ 以上になるようにすると、６００ ℃での耐力が常温での耐力（ＪＩＳ Ｇ ５１０２でのＳＣＷ ６２０ の耐力の規格下限値：４３０ＭＰａ）の２／３以上となる。従って、このようにすることが、望ましい。
【００２４】
本発明に係る鋳鋼は、溶接構造用鋳鋼として好適に用いることができる（第２発明）。また、溶接性および耐火特性が要求される用途に好適に用いることができる。さらに、優れた靱性および溶接性を有すると共に優れた耐火特性を有する鋳鋼として好適に用いることができる。
【００２５】
【実施例】
本発明の実施例及び比較例を以下説明する。なお、本発明は本実施例に限定されるものではない。
【００２６】
高周波溶解炉にて原料を溶解し、次いで鋼の溶湯を鋳型［形状寸法：約１００ｔ×５００ｗ×３９０ｈと ６０ｔ×３００ｗ×２３０ｈ（押湯を除いた形状）、材質：クロマイト砂で作製（バインダー：フラン）］に注入して鋳造する。これにより、種々の組成の鋳鋼を得た。これらの鋳鋼の組成を表１に示す。なお、表１においては、組成（成分）元素の含有量として、本発明に係る鋳鋼での必須成分元素であるＣ、Ｓｉ、Ｍｎ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ、Ｗの含有量の他にＣｕの含有量も示している。これらの成分元素の他（残部）は、Ｆｅおよび不可避的不純物からなるものである。
【００２７】
上記鋳鋼について熱処理［焼鈍として９２０ ℃×３Ｈｒ保持後→放冷、９２０ ℃×１Ｈｒ保持後→５０℃／ｍｉｎ の冷却速度でＲ．Ｔ．まで、６００ ℃×６Ｈｒ保持後→放冷（昇温速度：いずれも８０℃／Ｈｒ）］を施した後、引張試験片、シャルピー衝撃試験片、溶接性評価試験片を採取し製作した。そして、これらの試験片を用いて、常温（室温）での引張試験、シャルピー衝撃試験、６００ ℃での引張試験、溶接性評価試験を行った。
【００２８】
なお、引張試験片の形状及び寸法は、ＪＩＳ Ｚ ２２０１の１４Ａ号試験片、シャルピー衝撃試験片の形状及び寸法は、ＪＩＳ Ｚ ２２０２のＶノッチシャルピー衝撃試験片のものとした。室温での引張試験は、ＪＩＳ Ｚ ２２４１に記載の方法により行った。６００ ℃での引張試験は、ＪＩＳ Ｇ ０５６７記載の方法（試験片形状：ＩＩ−６形試験片）により行った。シャルピー衝撃試験は、ＪＩＳ Ｚ ２２４２に記載の方法により行った。
【００２９】
溶接性評価試験片としては、ＪＩＳ Ｚ ３１５８に記載の試験片とし、ｔ＝５０ｍｍ、ｇ＝２．０ｍｍ を採用した。溶接性評価試験の条件は、次の通りである。ｙスリット部の溶接方法：ＳＭＡＷ、溶接材料：（株）神戸製鋼所製ＬＢ−４９０ＦＲφ４．０ｍｍ（耐火鋼用被覆アーク溶接棒）、棒乾燥条件：３５０ ℃×１Ｈｒ、試験雰囲気：５０℃予熱では温度２７℃，湿度５３％、１００ ℃予熱では温度２４℃，湿度４０％、溶接電流：１７０ Ａ、運棒比：０．８（溶接長さ／溶接棒消耗長さ）、放置時間：４８Ｈｒである。
【００３０】
上記試験の結果を表２に示す。表２からわかるように、本発明の実施例に係る鋳鋼と比較例に係る鋳鋼とを同一強度（引張強さ）級のもの同士で比較すると、本発明の実施例に係る鋳鋼は、比較例に係る鋳鋼に比較して、６００ ℃での耐力が高くて耐火特性に優れ、また、シャルピー衝撃値が高くて靱性に優れている。また、ｙスリット割れ率は同等に低く、比較例に係る鋳鋼と同等に溶接性に優れている。
【００３１】
即ち、比較例５の鋳鋼および実施例４の鋳鋼はいずれも引張強さ≧４８０ＭＰａ級の鋳鋼であり、両者を比較するに、実施例４の鋳鋼は比較例５の鋳鋼に比較して、６００ ℃での耐力が非常に高くて耐火特性に極めて優れ、また、シャルピー衝撃値が著しく高くて靱性に極めて優れている。また、５０℃でのｙスリット割れ率は同等であり、比較例５の鋳鋼と同様に溶接性に優れている。
【００３２】
比較例６の鋳鋼および実施例５の鋳鋼はいずれも引張強さ≧５５０ＭＰａ級の鋳鋼であり、両者を比較するに、実施例５の鋳鋼は比較例６の鋳鋼に比較して、６００ ℃での耐力が非常に高くて耐火特性に極めて優れ、また、シャルピー衝撃値が高くて靱性に優れている。また、５０℃でのｙスリット割れ率は同等もしくはそれよりも低く、比較例６の鋳鋼と同等に溶接性に優れている。
【００３３】
比較例１，２，３，７，８の鋳鋼および実施例１，２，３の鋳鋼はいずれも引張強さ≧６２０ＭＰａ級の鋳鋼である。この中、比較例２の鋳鋼および実施例２の鋳鋼は、Ｃｒ、Ｍｏ、Ｖの含有量において両者は同程度であり、両者を比較するに、実施例２の鋳鋼は比較例２の鋳鋼に比較して、６００ ℃での耐力が著しく高くて耐火特性に極めて優れている。シャルピー衝撃値は同等である。また、５０℃でのｙスリット割れ率は同等であり、比較例２の鋳鋼と同等に溶接性に優れている。
【００３４】
なお、比較例３はＷ上限を超えたために、ｙスリットの割れ率が非常に高い。比較例１は耐火特性を満足しているが、ｙスリットの割れ率が非常に高い。
【００３５】
上記試験結果に基づき、引張強さ≧６２０ＭＰａ級の鋳鋼についてＷの含有量と１００ ℃におけるｙスリット割れ率との関係、及び、Ｗの含有量と６００ ℃における耐力との関係に関する図を作成した。この図を図１の（Ａ）及び（Ｂ）に示す。この図１の（Ａ）からわかるように、Ｗの含有量が増えると６００ ℃での耐力が高くなり、Ｗ量：０．３０％以上において６００ ℃での耐力が充分な水準となり、さらにＷ量の増大に伴って６００ ℃での耐力が高くなる。一方、図１の（Ｂ）からわかるように、Ｗの含有量が約０．５０％以上に増えると１００ ℃でのｙスリット割れ率が高くなり、Ｗ量：０．７５％超ではｙスリット割れ率：２０％超となるが、Ｗ量：０．７５％以下に抑えればｙスリット割れ率が充分に低く、充分な水準の溶接性が得られる。
【００３６】
また、上記試験結果に基づき、引張強さ≧４８０ＭＰａ級の鋳鋼についてＮｉの含有量とシャルピー衝撃値との関係に関する図を作成した。この図を図２に示す。図２からわかるように、Ｎｉの含有量：約０．２０％の場合、Ｗ添加せず（図中●印：比較例５）の場合に比べてＷ添加（図中■印：比較例４）の場合はシャルピー衝撃値は若干低下するが、Ｎｉの含有量を増やすことにより、シャルピー衝撃値を高くすることができ、Ｎｉ量：０．３０％以上にするとシャルピー衝撃値が充分に高くなり、充分な水準の靱性を得ることができる。なお、図２において、Ｎｉ量：０．４０％での■印は、実施例４の鋳鋼に係るデータのプロットに相当するものである。
【００３７】
更に、上記試験結果に基づき、Ｗｅｑ（％）、即ち、（Ｍｎ／６＋Ｓｉ／９＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４）×１０＋（Ｍｏ＋Ｗ＋Ｃｕ／２）と６００ ℃における耐力との関係に関する図を作成した。この図を図３に示す。図３に示すように、Ｗｅｑが大きくなるに伴って６００ ℃での耐力は高くなる。
【００３８】
ＪＩＳ Ｇ ５１０２でのＳＣＷ ４８０ 、ＳＣＷ ５５０ 、ＳＣＷ ６２０ の耐力の規格下限値は、それぞれ２７５ＭＰａ、３５５ＭＰａ、４３０ＭＰａである。図３からわかるように、Ｗｅｑ：３．４ 以上の場合、６００ ℃での耐力はＳＣＷ ４８０ の耐力の規格下限値の２／３以上となる。Ｗｅｑ：３．８ 以上の場合、６００ ℃での耐力はＳＣＷ ５５０ の耐力の規格下限値の２／３以上となる。Ｗｅｑ：４．２ 以上の場合、６００ ℃での耐力はＳＣＷ ６２０ の耐力の規格下限値の２／３以上となる。
【００３９】
これは、本発明に係る鋳鋼を引張強さ≧４８０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ４８０ に相当する鋳鋼）として用いる場合、Ｗｅｑ：３．４ 以上にすると、６００ ℃での耐力が常温での耐力（ＪＩＳ Ｇ ５１０２でのＳＣＷ ４８０ の耐力の規格下限値：２７５ＭＰａ）の２／３以上となり、耐火特性の点で特に望ましいことを示している。また、引張強さ≧５５０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ５５０ に相当する鋳鋼）として用いる場合、同様の意味で、Ｗｅｑ：３．８ 以上にすることが望ましく、更に、引張強さ≧６２０ＭＰａ級の鋳鋼（引張強さの面でＪＩＳ Ｇ ５１０２に記載のＳＣＷ ６２０ に相当する鋳鋼）として用いる場合、同様の意味で、Ｗｅｑ：４．２ 以上にすることが望ましいことを示している。
【００４０】
【表１】
【表２】
【発明の効果】
本発明に係る鋳鋼は、Ｍｏ量を増量させずに、優れた靱性および溶接性を有すると共に優れた耐火特性を有することができる。従って、Ｍｏ量の増量による場合のような問題点を生じることなく、優れた靱性および溶接性を有すると共に優れた耐火特性を有する鋳鋼として好適に用いることができる。
【図面の簡単な説明】
【図１】実施例および比較例に係る鋳鋼のＷ量と１００ ℃におけるｙスリット割れ率および６００ ℃における０．２％耐力との関係を示す図であって、図１の（Ａ） はＷ量と１００ ℃におけるｙスリット割れ率との関係、図１の（Ｂ） はＷ量と６００ ℃における０．２％耐力との関係を示す図である。
【図２】実施例および比較例に係る鋳鋼のＮｉ添加量と常温のシャルピ衝撃値との関係を示す図である。
【図３】実施例および比較例に係る鋳鋼の（Ｍｎ／６＋Ｓｉ／９＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４）×１０＋（Ｍｏ＋Ｗ＋Ｃｕ／２）と６００ ℃における０．２ ％耐力との関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention belongs to the technical field related to cast steel, and particularly to the technical field related to cast steel having excellent toughness and weldability and having fire resistance.
[0002]
[Prior art]
Cast steel which is used for a welded structure and has particularly excellent weldability includes cast steel (cast steel for welded structures) specified in JIS G 5102. This welded structural steel has a proof stress at 600 ° C. that is about の of the proof stress at room temperature, does not have sufficient refractory properties, and cannot be used as a refractory cast steel.
[0003]
Conventionally, as a method of imparting fire resistance to such a cast steel for a welded structure, it has been disclosed to use a composition with an increased Mo amount (Japanese Patent Application Laid-Open No. 07-188835).
[0004]
[Problems to be solved by the invention]
However, when the amount of Mo is increased, C eq (equivalent carbon) increases, which causes a problem that weldability is impaired. Therefore, if the required weldability is to be ensured, the C content will be reduced. However, since C is an element that increases the solid-liquid coexistence temperature, lowering the amount of C promotes the internal quality of the cast steel material, particularly the occurrence of shrinkage cavities, and makes it difficult to secure the internal quality. If other elements are reduced, it is necessary to reduce the amount in a large amount, and it becomes difficult to satisfy required characteristics at normal temperature. (Considering C eq = C + Si / 6 + Mn / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14, decreasing C is most effective.)
[0005]
The present invention has been made in view of such circumstances, and its object is to improve the toughness and weldability without increasing the Mo amount (in other words, within the component range of JIS G 5102). An object of the present invention is to provide a cast steel having excellent fire resistance.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a cast steel according to the present invention is a cast steel according to
[0007]
That is, the cast steel according to
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is implemented, for example, in the following form.
C: 0.12 to 0.22%, Si: 0.20 to 0.60%, Mn: 0.80 to 1.30%, Ni: 0.30 by melting using an electric furnace or high-frequency melting furnace. 0.20%, Cr: 0 to 0.35%, Mo: 0 to 0.30%, V: 0.005 to 0.15%, W: 0.30 to 0.75%, with the balance being the balance Obtains a molten steel made of Fe and unavoidable impurities, performs refining (including vacuum treatment, etc.) as necessary, and then injects the molten metal into a predetermined mold to perform casting. Then, the cast steel according to the present invention is obtained.
[0009]
The above-mentioned cast steel is subjected to a predetermined annealing and heat treatment or further machined, and then used for a predetermined application.
[0010]
The present invention is implemented in such a form. Hereinafter, the operation and effect of the present invention will be mainly described.
[0011]
As described above, the cast steel according to the present invention has, by mass%, C: 0.12 to 0.22%, Si: 0.20 to 0.60%, Mn: 0.80 to 1.30%, and Ni: 0.30 to 2.20%, Cr: 0 to 0.35% (including the case without addition), Mo: 0 to 0.30% (including the case without addition), V: 0.005 to 0 .15%, W: 0.30 to 0.75%, the balance being Fe and unavoidable impurities, and the composition of the cast steel, especially W: 0.30 to 0.75%, Ni : 0.30 to 2.20%, it is possible to have excellent toughness and weldability and excellent fire resistance without increasing the amount of Mo.
[0012]
That is, the cast steel according to the present invention, in particular, does not increase the amount of Mo, but newly adds 0.30 to 0.75% of W and the amount of Ni with respect to the cast steel for a welding structure specified in JIS G 5102. Is adjusted to 0.30 to 2.20%. The addition of this W improves the fire-resistant properties and makes the alloy excellent, and the adjustment of the Ni content ensures excellent toughness. Also, excellent weldability can be ensured without a decrease in weldability.
[0013]
Here, the reason why the W amount is set to 0.30 to 0.75% is that if the W amount is less than 0.30%, the degree of improvement of the fire resistance is small, the fire resistance becomes insufficient, and if it exceeds 0.75%, This is because the weldability is adversely affected, and the weldability is reduced and becomes insufficient. Further, W is an expensive element, and the upper limit of the amount of W is set to 0.75% from the viewpoint that a large amount of addition causes an increase in cost.
[0014]
The reason for setting the Ni content to 0.30 to 2.20% is that if the Ni content is less than 0.30, the toughness decreases, excellent toughness cannot be secured, the toughness becomes insufficient, and the toughness exceeds 2.20%. This makes it difficult to satisfy C eq (carbon equivalent weight) described in JIS G 5102, and it becomes difficult to ensure excellent weldability. Further, Ni is an expensive element, and the upper limit of the amount of Ni is set to 2.20% from the viewpoint that a large amount of addition increases the cost.
[0015]
In the cast steel according to the present invention, the types of unavoidable impurities are not limited, and vary depending on the case. However, usually, unavoidable impurities include Al, Cu, P, S, N, O, and the like. These amounts vary depending on the case, but usually, Al: 0.1% or less, Cu: 0.1% or less, P: 0.04% or less, S: 0.04% or less, N: 100ppm or less, O: : 100 ppm or less.
[0016]
In the cast steel according to the present invention, when it is used as a cast steel having a tensile strength of ≧ 480 MPa class (a cast steel corresponding to SCW 480 described in JIS G 5102 in terms of tensile strength), its composition is C: 0. 16 to 0.22%, Si: 0.30 to 0.60%, Mn: 0.90 to 1.30%, Ni: 0.30 to 0.50%, Cr: 0 to 0.50% (none Mo: 0 to 0.20% (including no addition), V: 0.005 to 0.07%, W: 0.30 to 0.75%, balance: Fe and The composition of unavoidable impurities. In other words, if such a composition is selected, it becomes a cast steel having a tensile strength of ≧ 480 MPa.
[0017]
When used as a cast steel with a tensile strength of ≧ 550 MPa (a cast steel corresponding to SCW 550 described in JIS G 5102 in terms of tensile strength), C: 0.14 to 0.20%, Si: 0.40 to 0 0.60%, Mn: 1.00 to 1.30%, Ni: 1.0 to 2.0%, Cr: 0 to 0.50% (including the case of no addition), Mo: 0 to 0.30 % (Including the case of no addition), V: 0.005 to 0.1%, W: 0.30 to 0.75%, and the balance: Fe and unavoidable impurities. That is, if such a composition is selected, a cast steel having a tensile strength of ≧ 550 MPa is obtained.
[0018]
When used as a cast steel having a tensile strength of ≧ 620 MPa (a cast steel corresponding to SCW 620 described in JIS G 5102 in terms of tensile strength), C: 0.12 to 0.16%, Si: 0.20 to 0 0.60%, Mn: 0.90 to 1.20%, Ni: 1.80 to 2.20%, Cr: 0.15 to 0.35%, Mo: 0.05 to 0.30%, V: 0.05 to 0.15%, W: 0.30 to 0.75%, balance: Fe and unavoidable impurities. That is, if such a composition is selected, a cast steel having a tensile strength of ≧ 620 MPa is obtained.
[0019]
As an index of the refractory properties of cast steel, the proof stress at 600 ° C. is generally used. It is said that the higher the proof stress at 600 ° C., the better the fire resistance. As for the fire resistance, it is desired that the proof stress at 600 ° C. is not less than 2/3 of the proof stress at room temperature or the lower limit of the specified value of the yield point (specified lower limit value). For example, in the case of cast steel having a tensile strength of ≧ 480 MPa (a cast steel corresponding to SCW 480 described in JIS G 5102 in terms of tensile strength), the proof stress at 600 ° C. is 275 MPa (lower limit value of proof stress) × 2 / 3 (= about 183.3 MPa) or more is desired.
[0020]
When the cast steel according to the present invention is used as a cast steel having a tensile strength of ≧ 480 MPa (a cast steel corresponding to SCW 480 described in JIS G 5102 in terms of tensile strength), the composition is as described above. At the same time, when the W eq obtained by the following equation (1) is made to be 3.4 or more, the proof stress at 600 ° C. is the proof stress at normal temperature (the lower limit of the proof stress of SCW 480 in JIS G 5102: 275 MPa). Is 2/3 or more. Therefore, this is desirable.
[0021]
[0022]
In the cast steel according to the present invention, when it is used as a cast steel of a tensile strength ≧ 550 MPa class (a cast steel corresponding to SCW 550 described in JIS G 5102 in terms of tensile strength), the composition is as described above. At the same time, when the W eq obtained by the above equation (1) is set to 3.8 or more, the proof stress at 600 ° C. becomes the proof stress at normal temperature (the lower limit of the proof stress of SCW 550 in JIS G 5102: 355 MPa). Is 2/3 or more. Therefore, this is desirable.
[0023]
In the cast steel according to the present invention, when it is used as a cast steel having a tensile strength of ≧ 620 MPa (a cast steel corresponding to SCW 620 described in JIS G 5102 in terms of tensile strength), the composition is as described above. At the same time, when the Weq obtained by the above equation (1) is set to 4.2 or more, the proof stress at 600 ° C. is the proof stress at normal temperature (the lower limit of the proof stress of SCW 620 in JIS G 5102: 430 MPa). Is 2/3 or more. Therefore, this is desirable.
[0024]
The cast steel according to the present invention can be suitably used as a cast steel for welded structures (second invention). Further, it can be suitably used for applications requiring weldability and fire resistance. Further, it can be suitably used as a cast steel having excellent toughness and weldability and excellent fire resistance.
[0025]
【Example】
Examples of the present invention and comparative examples will be described below. Note that the present invention is not limited to the present embodiment.
[0026]
The raw material is melted in a high-frequency melting furnace, and then a molten steel of steel is prepared with a mold [shape dimensions: about 100 t × 500 w × 390 h and 60 t × 300 w × 230 h (shape excluding the riser), material: chromite sand (binder: Franc)] and cast. Thereby, cast steels of various compositions were obtained. Table 1 shows the compositions of these cast steels. In Table 1, in addition to the contents of C, Si, Mn, Ni, Cr, Mo, V, and W, which are essential component elements in the cast steel according to the present invention, The content of Cu is also shown. Other than these component elements (the rest) are Fe and unavoidable impurities.
[0027]
Heat treatment of the above cast steel [after annealing at 920 ° C. × 3 hrs → cooling, after holding at 920 ° C. × 1 hr → R.C. At a cooling rate of 50 ° C./min. T. After holding at 600 ° C. for 6 hours, the sample was allowed to cool (temperature rising rate: 80 ° C./Hr in each case)], and tensile test pieces, Charpy impact test pieces, and weldability evaluation test pieces were collected and manufactured. Using these test pieces, a tensile test at normal temperature (room temperature), a Charpy impact test, a tensile test at 600 ° C., and a weldability evaluation test were performed.
[0028]
The shape and dimensions of the tensile test pieces were JIS Z 2201 No. 14A test pieces, and the shape and dimensions of the Charpy impact test pieces were those of JIS Z 2202 V-notch Charpy impact test pieces. The tensile test at room temperature was performed according to the method described in JIS Z 2241. The tensile test at 600 ° C. was performed by the method described in JIS G 0567 (test piece shape: II-6 type test piece). The Charpy impact test was performed according to the method described in JIS Z 2242.
[0029]
As the weldability evaluation test piece, a test piece described in JIS Z 3158 was used, with t = 50 mm and g = 2.0 mm. The conditions for the weldability evaluation test are as follows. Welding method of y-slit part: SMAW, welding material: LB-490FR φ4.0mm (Coated arc welding rod for fire-resistant steel) manufactured by Kobe Steel Co., Ltd., rod drying condition: 350 ° C × 1Hr, test atmosphere: 50 ° C preheating At a temperature of 27 ° C, a humidity of 53%, and a preheating of 100 ° C, the temperature is 24 ° C, the humidity is 40%, the welding current is 170 A, the rod ratio is 0.8 (welding length / welding rod consumption length), and the leaving time is 48 hours. is there.
[0030]
Table 2 shows the results of the above test. As can be seen from Table 2, when the cast steel according to the example of the present invention and the cast steel according to the comparative example are compared with each other in the same strength (tensile strength) class, the cast steel according to the example of the present invention is comparative example. As compared with the cast steel according to the above, the steel has a high proof stress at 600 ° C. and is excellent in fire resistance, and has a high Charpy impact value and is excellent in toughness. Also, the y-slit cracking rate is equally low, and the weldability is as good as the cast steel according to the comparative example.
[0031]
That is, the cast steel of Comparative Example 5 and the cast steel of Example 4 were both cast steels having a tensile strength of ≧ 480 MPa, and the cast steel of Example 4 was compared with the cast steel of Comparative Example 5 by 600. The proof stress at ℃ is very high and the fire resistance is extremely excellent, and the Charpy impact value is extremely high and the toughness is extremely excellent. Further, the y-slit cracking ratio at 50 ° C. is equivalent, and is excellent in weldability like the cast steel of Comparative Example 5.
[0032]
The cast steel of Comparative Example 6 and the cast steel of Example 5 were both cast steels having a tensile strength of ≧ 550 MPa, and the cast steel of Example 5 was compared with the cast steel of Comparative Example 6 at 600 ° C. Has very high proof stress and extremely excellent fire resistance, and has a high Charpy impact value and excellent toughness. Further, the y-slit cracking ratio at 50 ° C. is equal to or lower than that, and is excellent in weldability as in the cast steel of Comparative Example 6.
[0033]
The cast steels of Comparative Examples 1, 2, 3, 7, 8 and the cast steels of Examples 1, 2, 3 are cast steels having a tensile strength of ≧ 620 MPa. Among them, the cast steel of Comparative Example 2 and the cast steel of Example 2 were almost the same in the content of Cr, Mo, and V, and the cast steel of Example 2 was compared with the cast steel of Comparative Example 2. In comparison, the proof stress at 600 ° C. is extremely high, and the fire resistance is extremely excellent. Charpy impact values are equivalent. Further, the y-slit cracking ratio at 50 ° C. is equivalent, and is excellent in weldability as in the cast steel of Comparative Example 2.
[0034]
In Comparative Example 3, since the upper limit of W was exceeded, the crack rate of the y-slit was very high. Comparative Example 1 satisfies the fire resistance characteristics, but has a very high crack rate of the y-slit.
[0035]
Based on the above test results, a diagram was prepared concerning the relationship between the W content and the y-slit cracking rate at 100 ° C. and the relationship between the W content and the proof stress at 600 ° C. for cast steels with a tensile strength of ≧ 620 MPa. . This figure is shown in FIG. 1 (A) and (B). As can be seen from FIG. 1A, the proof stress at 600 ° C. increases as the W content increases, and the proof stress at 600 ° C. at a W content of 0.30% or more becomes a sufficient level. As the amount increases, the proof stress at 600 ° C. increases. On the other hand, as can be seen from FIG. 1B, when the W content increases to about 0.50% or more, the y-slit cracking rate at 100 ° C. increases, and when the W content exceeds 0.75%, the y-slit Although the cracking rate is more than 20%, if the W content is suppressed to 0.75% or less, the y-slit cracking rate is sufficiently low, and a sufficient level of weldability can be obtained.
[0036]
In addition, based on the above test results, a drawing was made on the relationship between the Ni content and the Charpy impact value for cast steel having a tensile strength of ≧ 480 MPa. This figure is shown in FIG. As can be seen from FIG. 2, when the Ni content is about 0.20%, W is added (in the figure: mark: Comparative Example 4) compared to the case in which W is not added (marked in the figure: Comparative Example 5). In the case of ()), the Charpy impact value is slightly reduced, but the Charpy impact value can be increased by increasing the Ni content. When the Ni content is 0.30% or more, the Charpy impact value becomes sufficiently high. , A sufficient level of toughness can be obtained. In FIG. 2, the symbol “■” at the Ni content of 0.40% corresponds to a plot of data relating to the cast steel of Example 4.
[0037]
Further, based on the above test results, a diagram regarding the relationship between Weq (%), that is, (Mn / 6 + Si / 9 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) × 10 + (Mo + W + Cu / 2) and the proof stress at 600 ° C. was created. did. This figure is shown in FIG. As shown in FIG. 3, the proof stress at 600 ° C. increases as W eq increases.
[0038]
The lower limits of proof stress of SCW 480, SCW 550, and SCW 620 according to JIS G 5102 are 275 MPa, 355 MPa, and 430 MPa, respectively. As can be seen from FIG. 3, in the case of W eq : 3.4 or more, the proof stress at 600 ° C. is ／ or more of the lower limit of the proof stress of SCW 480. In the case of W eq : 3.8 or more, the proof stress at 600 ° C. is ／ or more of the lower limit of the proof stress of SCW 550. In the case of W eq : 4.2 or more, the proof stress at 600 ° C. is ２ or more of the lower limit of the proof stress of SCW 620.
[0039]
This, when used as a cast steel tensile cast steel strength ≧ 480 MPa class according to the present invention (cast steel equivalent to SCW 480 according to JIS G 5102 in terms of tensile strength), W eq: 3.4 When the above , At 600 ° C., is ２ or more of the proof stress at room temperature (lower limit of proof stress of SCW 480 according to JIS G 5102: 275 MPa), indicating that it is particularly desirable in terms of fire resistance. When used as a cast steel with a tensile strength of ≧ 550 MPa (a cast steel corresponding to SCW 550 described in JIS G 5102 in terms of tensile strength), W eq : 3.8 or more in the same sense. Desirably, when used as a cast steel with a tensile strength of ≧ 620 MPa (a cast steel corresponding to SCW 620 described in JIS G 5102 in terms of tensile strength), W eq : 4.2 or more in the same sense. Indicates that it is desirable.
[0040]
[Table 1]
[Table 2]
【The invention's effect】
The cast steel according to the present invention can have excellent toughness and weldability and excellent fire resistance without increasing the amount of Mo. Therefore, it can be suitably used as a cast steel having excellent toughness and weldability and excellent fire resistance without causing problems as in the case of increasing the amount of Mo.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the W content of cast steels according to Examples and Comparative Examples, the y-slit cracking rate at 100 ° C., and the 0.2% proof stress at 600 ° C., wherein FIG. FIG. 1B shows the relationship between the amount of W and the y-slit cracking rate at 100 ° C., and FIG. 1B shows the relationship between the amount of W and 0.2% proof stress at 600 ° C.
FIG. 2 is a diagram showing the relationship between the amount of Ni added and the Charpy impact value at normal temperature in cast steels according to Examples and Comparative Examples.
FIG. 3 is a diagram showing the relationship between (Mn / 6 + Si / 9 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) × 10 + (Mo + W + Cu / 2) and 0.2% proof stress at 600 ° C. of cast steels according to Examples and Comparative Examples. It is.
Claims (2)
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| JP2002175808A JP3848598B2 (en) | 2002-06-17 | 2002-06-17 | Cast steel |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100420766C (en) * | 2007-01-24 | 2008-09-24 | 中国重型汽车集团有限公司 | Cast steel and method for preparing same |
| WO2011037210A1 (en) * | 2009-09-25 | 2011-03-31 | 株式会社日本製鋼所 | High-strength high-toughness cast steel material and manufacturing method therefor |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100420766C (en) * | 2007-01-24 | 2008-09-24 | 中国重型汽车集团有限公司 | Cast steel and method for preparing same |
| WO2011037210A1 (en) * | 2009-09-25 | 2011-03-31 | 株式会社日本製鋼所 | High-strength high-toughness cast steel material and manufacturing method therefor |
| EP2481826A4 (en) * | 2009-09-25 | 2016-11-23 | Japan Steel Works Ltd | High-strength high-toughness cast steel material and manufacturing method therefor |
| US9797034B2 (en) | 2009-09-25 | 2017-10-24 | The Japan Steel Works, Ltd. | High strength and high toughness cast steel material and method for producing the same |
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