JP3962143B2 - Mowing blade substrate - Google Patents
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- JP3962143B2 JP3962143B2 JP03074798A JP3074798A JP3962143B2 JP 3962143 B2 JP3962143 B2 JP 3962143B2 JP 03074798 A JP03074798 A JP 03074798A JP 3074798 A JP3074798 A JP 3074798A JP 3962143 B2 JP3962143 B2 JP 3962143B2
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Description
【０００１】
【産業上の利用分野】
本発明は、延性，靭性，強度及び耐摩耗性に優れた鋼板で作られた草刈刃基板に関する。
【０００２】
【従来の技術】
草刈機に用いられる草刈刃には、基板及び刃先が同一の鋼板で作られているソリッドソーや、刃先に超硬等を接合したチップソー等がある。何れの草刈刃でも、ＪＩＳ ＳＫ５等の炭素工具鋼，ＪＩＳ ＳＫＳ５等の合金工具鋼を基板材として使用している。
草刈刃は、使用時に毎分数千回転で高速回転する。このような高速回転で砂利，石等に接触する環境で使用されることから、切れ味に加えて優れた耐摩耗性が要求される。そこで、草刈刃の基板に使用される従来の鋼板では、焼入れ・焼戻しで４７ＨＲＣ程度の高い硬さ水準に調質することにより、切れ味及び耐摩耗性を確保している。
他方、高速回転中の草刈刃に砂利，石，幹等が当ると、草刈刃の基板自体が折損する虞れがある。折損で生じた破片の飛散は、作業者や周辺にいる人にとって非常に危険なことである。破片の飛散による事故を防止し、安全性を確保するためには、基板の延性，靭性を改善することが有効である。しかし、延性，靭性を向上させると基板の硬さが低下し、切れ味や耐摩耗性が不足しがちとなる。
【０００３】
【発明が解決しようとする課題】
すなわち、草刈刃用基板としては、草刈本来の機能からすると優れた切れ味及び耐摩耗性を得るために高硬度ほど望ましいが、高速回転という使用形態を考慮すると延性，靭性を高めて安全性を確保することが好ましい。特に草刈刃の回転数が高くなって来ている昨今では、高い硬さ水準で従来以上に延性，靭性をバランスさせた草刈刃用基板に対する要求が強くなってきている。
本発明は、このような要求に応えるべく案出されたものであり、各種合金成分を特定された関係で調整した合金設計により、草刈刃に必要な強度及び耐摩耗性を維持し、且つ従来の基板を超える延性，靭性を示す草刈刃用基板を提供することを目的とする。
【０００４】
【課題を解決するための手段】
本発明の草刈刃用基板は、その目的を達成するため、Ｃ：０．３０〜０．７０重量％，Ｓｉ：０．５０重量％以下，Ｍｎ：０．１０〜１．５０重量％，Ｃｒ：０．１８〜１．３１重量％，Ｎ：０．０００５〜０．０２重量％，Ｏ：０．０００５〜０．０１重量％，Ｐ：０．０２重量％以下，Ｓ：０．０１重量％以下，酸可溶Ａｌ：０．０１０〜０．１０重量％を含み、残部がＦｅ及び不可避的不純物からなり、式（１）で定義されるＸ値が１．０以下の成分組成を有する鋼板で作られていることを特徴とする。
Ｘ＝Ｃ％＋１８×Ｎ％＋５２×Ｏ％＋１０×Ｐ％＋１７×Ｓ％・・・・（１）
【０００５】
【作用】
草刈刃用基板に従来から使用されているＳＫ５，ＳＫＳ５等の鋼材は、強度，耐摩耗性を確保するために０．７５重量％以上のＣを含有させている。この鋼種の成分及び熱処理が靭性，延性に及ぼす影響を調査した結果、熱処理後の硬さが同じであってもＣ含有量が低いほど、靭性，延性が向上することが判った。しかし、鋼中で炭化物を形成し耐摩耗性を向上させるＣの作用を活用してることから、Ｃ含有量を極端に低下することはできない。
また、靭性，延性に及ぼす不純物元素の影響を調査したところ、４０〜５０ＨＲＣに調質した鋼材においては特にＮ，Ｏ，Ｐ，Ｓを低減することにより靭性，延性が向上することが判った。更に、草刈刃としての用途では焼入れ・焼戻しの熱処理が通常施されていることから、焼入れ性の確保が要求される。焼入れ性はＭｎ，Ｃｒ，Ｍｏ，Ｖ等の添加によって向上するが、これら添加成分は靭性，延性に悪影響を及ぼす。
そこで、本発明においては、Ｍｎ，Ｃｒ，Ｍｏ，Ｖ等を過剰添加することなく、Ｃｕ，Ｎｉ，Ｂの添加によってＭｎ，Ｃｒ，Ｍｏ，Ｖ等の作用を補っている。Ｃｕ，Ｎｉ，Ｂは、焼入れ性の改善にも有効である。更に、Ａｌ，Ｔｉ，Ｎｂ等の結晶粒微細化作用をもつ元素を添加することによっても、靭性及び延性の改善を図っている。
【０００６】
以下、本発明の草刈刃用基板として使用される鋼板に含まれる合金成分，含有量等について説明する。
Ｃ：０．３０〜０．７０重量％
草刈刃用鋼板に必要とされる強度及び耐摩耗性を確保し、草刈刃の切れ味を高めるために必要な合金成分であり、少なくとも０．３０％以上の添加が必要である。しかし、０．７０重量％を超えるＣ含有量では、熱処理後の炭化物量が増加し、粗大に成長した炭化物が破壊の起点として働くため、延性及び靭性が劣化する。
Ｓｉ：０．５０％重量以下
溶鋼の脱酸剤として有効な成分である。しかし、０．５０重量％を超える過剰量のＳｉを添加すると、脱酸生成物であるＳｉＯ2 が鋼中に残存し、鋼の清浄度を害し、靭性を低下させる。
【０００７】
Ｍｎ：０．１０〜１．５０重量％
溶鋼の脱酸に有効であると共に、強度の向上に必要な鋼の焼入れ性を改善する合金成分である。これらの効果は、０．１０重量％以上のＭｎ含有で顕著になる。しかし、１．５０重量％を超える多量のＭｎを含有させると、靭性が著しく低下する。
Ｃｒ：１．５０重量％以下
Ｍｎと同様に、鋼の焼入れ性の向上に有効な合金成分である。しかし、１．５０重量％を超えるＣｒ含有量では、亀裂の起点となる未溶解炭化物が多量に生成し易くなる。未溶解炭化物は、亀裂の伝播を助長し、曲げ特性や靭性に悪影響を及ぼす。
【０００８】
Ｍｏ：０．５０重量％以下
Ｍｏも、鋼の焼入れ性向上に有効な合金成分である。また、Ｍｏ添加により、Ｍｎ，Ｃｒの過剰添加に起因した靭性の劣化が抑えられる。しかし、高価な元素であり多量に添加すると経済的に不利になることから、Ｍｏ含有量の上限を０．５０重量％に設定した。
Ｖ：０．５０重量％以下
Ｃｒ，Ｍｏと同様に鋼材の強度向上に有効な合金成分である。しかし、０．５０重量％を超える多量のＶを添加すると、却って靭性が劣化する。
Ｃｕ：０．５０重量％以下
良好な焼入れ性を確保すると共に靭性の向上に有効な合金成分である。しかし、０．５０重量％を超える多量のＣｕを添加すると、熱間加工性が損なわれる。
【０００９】
Ｎ：０．０００５〜０．０２重量％
鋼中で窒化物となり、組織を微細化させ鋼を強化する作用を呈する合金成分である。Ｎの添加効果は、０．０００５重量％以上で顕著になる。しかし、０．０２重量％を超える過剰なＮを含ませると、粗大な窒化物が形成され、靭性が劣化する。
Ｏ：０．０００５〜０．０１重量％
Ｓと同様に鋼中で非金属介在物を形成し、鋼の靭性を低下させる有害元素である。Ｏ含有量は低いほど好ましいが、極低酸素レベルまで脱酸することは生産性を低下させ製造コストを上昇させる原因となる。そこで、本発明においては、非金属介在物による悪影響がなく、しかも工業レベルで達成可能な０．０００５〜０．０１重量％の範囲にＯ含有量を設定した。
【００１０】
Ｐ：０．０２重量％以下
焼入時のオーステナイト粒界に偏析し、延性，靭性を劣化させる原因となる成分である。したがって、Ｐ含有量は極力低下させることが必要である。本発明では実質的な悪影響を及ぼさない範囲として、Ｐ含有量の上限を０．０２重量％に規定した。
Ｓ：０．０１重量％以下
鋼中でＭｎＳを形成して亀裂の起点となりやすく、強度，靭性を低下させる有害成分である。そのため、可能な限りＳ含有量を下げることが望ましく、本発明では実質的な悪影響を及ぼさない範囲としてＳ含有量の上限を０．０１重量％に設定した。
酸可溶Ａｌ：０．０１０％〜０．１０重量％
強力な脱酸元素であり、鋼中のＯ含有量を低減する上で必要な合金成分である。Ｏ含有量を０．０１重量％以下にするためには、酸可溶Ａｌとして０．０１重量％以上のＡｌ含有量が必要である。しかし、０．１０重量％を超える多量のＡｌが含まれると、鋼中に存在する非金属介在物が増加し、衝撃特性等に悪影響を及ぼす。
【００１１】
Ｎｉ：０．１０〜２．００重量％
必要に応じて添加される合金成分、焼入れ性及び靭性の向上に有効である。
Ｎｉの添加効果は、０．１０重量％以上で顕著になり、２．００重量％で飽和する。また、２．００重量％を超えるＮｉ含有量は、高価なＮｉを多量に消費することから鋼材コストを上昇させる原因になる。
Ｔｉ：０．０１〜０．１０重量％
必要に応じて添加される合金成分であり、Ｎと結合して窒化物を形成し、高温加熱時のオーステナイト粒の粗大化を抑制し、また焼入れ性向上に有効な固溶Ｂを確保する作用を呈する。このような効果は、０．０１重量％以上のＴｉ含有量で顕著になる。しかし、０．２０重量％を超える過剰なＴｉを含ませると、靭性が劣化する。
【００１２】
Ｎｂ：０．０１〜０．２０重量％
必要に応じて添加される合金成分であり、炭窒化物を形成し、オーステナイト粒の粗大化を抑えて靭性を向上させる作用を呈し、０．０１重量％以上でＮｂの効果が顕著になる。しかし、０．２０重量％を超える過剰なＮｂを添加すると、靭性劣化の原因となる粗大な析出物が形成される。
Ｂ：０．０００５〜０．０１重量％
必要に応じて添加される合金成分であり、焼入れ性を高めると共に、粒界破壊を抑制する作用を呈する。Ｂの添加効果は、０．０００５重量％以上のＢ含有量で顕著になる。しかし、Ｂ含有量が０．０１重量％を超えると、却って靭性が劣化する。
【００１３】
Ｘ値（＝Ｃ％＋１８×Ｎ％＋５２×Ｏ％＋１０×Ｐ％＋１７×Ｓ％）≦１．０
基板の延性，靭性に対して影響を及ぼすＣ，Ｎ，Ｏ，Ｐ，Ｓについて、各成分の影響を総合的に調査・研究した結果として見出された指標である。鋼中に存在するセメンタイトや、Ｃｒ，Ｍｏ等の合金系炭化物や窒化物，Ａｌ2 Ｏ3 系の酸化物，ＭｎＳ系の硫化物等からなる非金属介在物は、基板の延性や靭性に悪影響を及ぼす。また、Ｐは、結晶粒界に偏析して鋼の靭性を低下させる。
本発明者等は、これら非金属介在物を形成する元素やＰが延性，靭性に及ぼす影響の程度を調査し、上式で定義されるＸ値が１．０以下のとき良好な延性，靭性が得られることを多数の実験結果から見出した。Ｘ値が１．０以下になるように基板の成分を調整すると、実施例でも示したように延性，靭性が一層優れ、且つ必要な強度，硬さをもつ草刈刃基板が得られる。
以上のようにＣ，Ｎ，Ｏ，Ｐ，Ｓ等の含有量を規制すると共にＭｎ，Ｃｒ，Ｍｏ，Ｖ，Ｃｕの含有量を相関的に定めた成分設計により、従来と同等以上の強度が維持され、延性，靭性摩耗が向上した草刈刃用基板となる。
【００１４】
【実施例】
表１に示した組成をもつ鋼を溶製し、鋼スラブを製造した。各鋼スラブを常法に従って熱間圧延し板厚３．０ｍｍの鋼板とした後、冷間圧延，焼鈍を経て板厚１．４ｍｍ及び２．５ｍｍの焼きなまし材とした。得られた鋼板を８３０〜９００℃の範囲で１５分加熱保持した後、６０℃で油焼入れした。次いで、２００〜５５０℃の範囲で３０分加熱保持した後、空冷の焼戻しを行い、目標硬さ４２〜４８ＨＲＣに調質した。
【００１５】
調質後の鋼板から、圧延方向に長手方向が直交する試験片を切り出し、曲げ試験及び衝撃試験に供した。
曲げ試験では、板厚１．４ｍｍ，幅３０ｍｍ，長さ２００ｍｍの短冊状の試験片を使用し、Ｖブロックにより９０度突き曲げ試験を行った。そして、ポンチの先端半径によって試験片の曲げ半径を変え、ｎ数５枚で割れなければ、その値を限界曲げ半径として評価した。この試験では、限界曲げ半径が小さいほど延性が優れているものと評価される。
衝撃試験では、板厚２．５ｍｍのＪＩＳ４号サブサイズ試験片を使用し、シャルピー衝撃試験を行い、吸収エネルギーの大きさで靭性を評価した。
【００１７】
表２の調査結果にみられるように、Ｃ含有量が不足する比較鋼Ａは、４８ＨＲＣに調質するとき焼戻し温度が低いため不十分な焼戻し組織となり、低い延性及び靭性を示した。比較鋼Ｂは、Ｍｎを添加していないため焼入れ不良となり、延性及び靭性は確保しているものの十分な硬さが得られなかった。比較鋼Ｃは、Ｐ，Ｓ，Ｏ等の不純物元素を多量に含むためＸ値が１．０を超えており、延性及び靭性が不足していた。また、従来から草刈刃用基板に使用されているＳＫ５相当の比較鋼Ｄ及びＳＫＳ５相当の比較鋼Ｅは、共にＸ値が１．０を超えており、低い延性及び靭性を示した。
これに対し、本発明で規定した条件を満足する鋼Ｆ〜Ｉは、何れも限界曲げ半径が小さく、衝撃値も２７Ｊ／ｃｍ2 以上の高い値を示し、４２〜４８ＨＲＣの硬さレベルにおいても延性及び靭性に優れていることが判る。
【００１８】
【発明の効果】
以上に説明したように、本発明の草刈刃用基板は、Ｃ，Ｎ，Ｏ，Ｐ，Ｓの含有量を低減した状態で所定量のＭｎ，Ｃｒ，Ｍｏ，Ｖ，Ｃｕを添加することにより焼入れ性を改善し、草刈刃用基板に必要な硬さを確保すると共に、延性及び靭性を改善している。そのため、高速回転中に石，砂利等と接触しても折損や摩耗が少なく、長期間にわたって良好な切れ味を示す草刈刃として使用される。[0001]
[Industrial application fields]
The present invention relates to a grass cutting blade substrate made of a steel plate having excellent ductility, toughness, strength, and wear resistance.
[0002]
[Prior art]
As a mowing blade used for a mowing machine, there are a solid saw in which a substrate and a cutting edge are made of the same steel plate, a tip saw in which carbide or the like is bonded to the cutting edge, and the like. Any grass cutting blade uses carbon tool steel such as JIS SK5 or alloy tool steel such as JIS SKS5 as a substrate material.
The mowing blade rotates at a high speed of several thousand revolutions per minute when in use. Since it is used in an environment where it comes into contact with gravel, stones, etc. at such a high speed rotation, excellent wear resistance is required in addition to sharpness. Therefore, the conventional steel sheet used for the grass cutting blade substrate is tempered to a high hardness level of about 47 HRC by quenching and tempering to ensure sharpness and wear resistance.
On the other hand, when gravel, stones, trunks, or the like hit the cutting blade during high-speed rotation, the substrate of the cutting blade itself may be broken. The scattering of debris caused by breakage is very dangerous for workers and people around. It is effective to improve the ductility and toughness of the substrate in order to prevent accidents caused by scattered fragments and to ensure safety. However, when the ductility and toughness are improved, the hardness of the substrate decreases, and the sharpness and wear resistance tend to be insufficient.
[0003]
[Problems to be solved by the invention]
In other words, as a mowing blade substrate, the higher the hardness, the better it is to obtain excellent sharpness and wear resistance from the original functions of mowing, but considering the usage mode of high-speed rotation, the ductility and toughness are increased to ensure safety. It is preferable to do. In particular, with the recent increase in the number of rotations of the cutting blade, there is an increasing demand for a substrate for a cutting blade that balances ductility and toughness at a high hardness level and higher than before.
The present invention has been devised to meet such demands, and maintains the strength and wear resistance required for a mowing blade by an alloy design in which various alloy components are adjusted in a specified relationship. It is an object of the present invention to provide a mowing blade substrate that exhibits ductility and toughness exceeding those of other substrates.
[0004]
[Means for Solving the Problems]
In order to achieve the object, the substrate for mowing blade of the present invention has C: 0.30 to 0.70 wt%, Si: 0.50 wt% or less, Mn: 0.10 to 1.50 wt%, Cr : 0.18 to 1.31 wt%, N: 0.0005 to 0.02 wt%, O: 0.0005 to 0.01 wt%, P: 0.02 wt% or less, S: 0.01 wt% % or less, acid-soluble Al: includes 0.01 0 to 0.10 wt%, the balance being Fe and unavoidable impurities, X values defined by formula (1) is 1.0 the following component composition It is made from the steel plate which has.
X = C% + 18 × N% + 52 × O% + 10 × P% + 17 × S% (1 )
[0005]
[Action]
Steel materials such as SK5 and SKS5 that have been conventionally used for grass cutting blade substrates contain 0.75% by weight or more of C in order to ensure strength and wear resistance. As a result of investigating the influence of the components of this steel type and the heat treatment on toughness and ductility, it was found that the toughness and ductility are improved as the C content is lower even if the hardness after heat treatment is the same. However, since the action of C which forms carbides in steel and improves wear resistance is utilized, the C content cannot be extremely reduced.
Moreover, when the influence of the impurity element on toughness and ductility was investigated, it was found that the toughness and ductility were improved by reducing N, O, P, and S particularly in the steel material tempered to 40 to 50 HRC. Furthermore, since the heat treatment of quenching and tempering is usually performed in the use as a mowing blade, it is required to ensure hardenability. The hardenability is improved by the addition of Mn, Cr, Mo, V, etc., but these added components adversely affect toughness and ductility.
Therefore, in the present invention, the action of Mn, Cr, Mo, V, etc. is supplemented by the addition of Cu, Ni, B without excessive addition of Mn, Cr, Mo, V, etc. Cu, Ni, and B are also effective in improving hardenability. Furthermore, the toughness and ductility are also improved by adding an element such as Al, Ti, Nb or the like having an effect of refining crystal grains.
[0006]
Hereinafter, alloy components, contents, and the like included in the steel plate used as the grass cutting blade substrate of the present invention will be described.
C: 0.30 to 0.70% by weight
It is an alloy component necessary for securing the strength and wear resistance required for the steel blade for mowing blades and enhancing the sharpness of the mowing blades, and it is necessary to add at least 0.30% or more. However, if the C content exceeds 0.70% by weight, the amount of carbide after the heat treatment increases, and the coarsely grown carbide acts as a starting point for fracture, so the ductility and toughness deteriorate.
Si: 0.50% by weight or less Si is an effective component as a deoxidizer for molten steel. However, when an excessive amount of Si exceeding 0.50% by weight is added, SiO 2 which is a deoxidation product remains in the steel, which impairs the cleanliness of the steel and lowers the toughness.
[0007]
Mn: 0.10 to 1.50% by weight
It is an alloy component that is effective in deoxidizing molten steel and improves the hardenability of steel necessary for improving strength. These effects become remarkable when Mn content is 0.10% by weight or more. However, when a large amount of Mn exceeding 1.50% by weight is contained, the toughness is remarkably lowered.
Cr: 1.50% by weight or less Like Mn, it is an effective alloy component for improving the hardenability of steel. However, when the Cr content exceeds 1.50% by weight, a large amount of undissolved carbide that becomes the starting point of cracking is easily generated. Undissolved carbides promote crack propagation and adversely affect bending properties and toughness.
[0008]
Mo: 0.50 wt% or less Mo is also an alloy component effective for improving the hardenability of steel. Further, the addition of Mo suppresses the deterioration of toughness due to the excessive addition of Mn and Cr. However, since it is an expensive element and it is economically disadvantageous if it is added in a large amount, the upper limit of the Mo content is set to 0.50% by weight.
V: 0.50 wt% or less Like Cr and Mo, it is an effective alloy component for improving the strength of steel. However, when a large amount of V exceeding 0.50% by weight is added, the toughness is deteriorated.
Cu: 0.50% by weight or less Cu is an alloy component effective for ensuring good hardenability and improving toughness. However, when a large amount of Cu exceeding 0.50% by weight is added, hot workability is impaired.
[0009]
N: 0.0005 to 0.02% by weight
It is an alloy component that becomes a nitride in steel and has the effect of refining the structure and strengthening the steel. The effect of adding N becomes significant at 0.0005% by weight or more. However, when excessive N exceeding 0.02% by weight is included, coarse nitrides are formed and the toughness deteriorates.
O: 0.0005 to 0.01% by weight
Like S, it is a harmful element that forms non-metallic inclusions in steel and lowers the toughness of steel. The lower the O content, the better. However, deoxidation to an extremely low oxygen level causes a decrease in productivity and an increase in manufacturing cost. Therefore, in the present invention, the O content is set in a range of 0.0005 to 0.01% by weight that is not adversely affected by non-metallic inclusions and can be achieved at an industrial level.
[0010]
P: 0.02% by weight or less P is a component that segregates at the austenite grain boundary during quenching and causes deterioration in ductility and toughness. Therefore, it is necessary to reduce the P content as much as possible. In the present invention, the upper limit of the P content is defined as 0.02% by weight as a range that does not have a substantial adverse effect.
S: 0.01% by weight or less MnS is easily formed in the steel and is a starting point of cracks, and is a harmful component that lowers strength and toughness. Therefore, it is desirable to reduce the S content as much as possible. In the present invention, the upper limit of the S content is set to 0.01% by weight as a range that does not have a substantial adverse effect.
Acid-soluble Al: 0.010% to 0.10% by weight
It is a powerful deoxidizing element and an alloy component necessary for reducing the O content in steel. In order to make the O content 0.01% by weight or less, the acid-soluble Al needs to have an Al content of 0.01% by weight or more. However, when a large amount of Al exceeding 0.10% by weight is contained, non-metallic inclusions present in the steel increase, which adversely affects impact properties and the like.
[0011]
Ni: 0.10 to 2.00% by weight
It is effective for improving alloy components, hardenability and toughness added as necessary.
The effect of adding Ni becomes significant at 0.10% by weight or more, and saturates at 2.00% by weight. Further, Ni content exceeding 2.00% by weight consumes a large amount of expensive Ni, which causes an increase in steel material cost.
Ti: 0.01 to 0.10% by weight
It is an alloy component that is added as necessary, and forms a nitride by combining with N, and suppresses the coarsening of austenite grains during high-temperature heating, and also ensures solid solution B effective for improving hardenability. Presents. Such an effect becomes remarkable when the Ti content is 0.01% by weight or more. However, when excessive Ti exceeding 0.20% by weight is included, toughness deteriorates.
[0012]
Nb: 0.01-0.20% by weight
It is an alloy component added as necessary, and forms carbonitride, suppresses coarsening of austenite grains and improves toughness, and the effect of Nb becomes remarkable at 0.01% by weight or more. However, when excessive Nb exceeding 0.20% by weight is added, coarse precipitates that cause deterioration of toughness are formed.
B: 0.0005 to 0.01% by weight
It is an alloy component added as necessary, and enhances hardenability and exhibits an effect of suppressing grain boundary fracture. The effect of addition of B becomes significant when the B content is 0.0005% by weight or more. However, if the B content exceeds 0.01% by weight, the toughness deteriorates.
[0013]
X value (= C% + 18 × N% + 52 × O% + 10 × P% + 17 × S%) ≦ 1.0
For C, N, O, P, and S that affect the ductility and toughness of the substrate, this is an index that has been found as a result of comprehensive investigation and research of the effects of each component. Non-metallic inclusions such as cementite existing in steel, alloy carbides and nitrides such as Cr and Mo, oxides of Al 2 O 3 and sulfides of MnS have an adverse effect on the ductility and toughness of the substrate. Effect. Further, P segregates at the grain boundaries and lowers the toughness of the steel.
The present inventors investigated the degree of influence of elements and P forming these non-metallic inclusions on ductility and toughness, and good ductility and toughness when the X value defined by the above formula is 1.0 or less. It was found from many experimental results that When the components of the substrate are adjusted so that the X value is 1.0 or less, a grass cutting blade substrate having more excellent ductility and toughness and having necessary strength and hardness can be obtained as shown in the examples.
As described above, by controlling the content of C, N, O, P, S, etc., and by designing the component that correlates the contents of Mn, Cr, Mo, V, Cu, the strength equal to or higher than the conventional one is obtained. This is a mowing blade substrate that is maintained and has improved ductility and tough wear.
[0014]
【Example】
Steel having the composition shown in Table 1 was melted to produce a steel slab. Each steel slab was hot rolled according to a conventional method to obtain a steel plate having a thickness of 3.0 mm, and then subjected to cold rolling and annealing to obtain annealed materials having a thickness of 1.4 mm and 2.5 mm. The obtained steel sheet was heated and held in the range of 830 to 900 ° C. for 15 minutes and then oil-quenched at 60 ° C. Then, after heating and holding in the range of 200 to 550 ° C. for 30 minutes, air-cooled tempering was performed to adjust the target hardness to 42 to 48 HRC.
[0015]
A test piece having a longitudinal direction perpendicular to the rolling direction was cut out from the tempered steel sheet and subjected to a bending test and an impact test.
In the bending test, a strip-shaped test piece having a thickness of 1.4 mm, a width of 30 mm, and a length of 200 mm was used, and a 90-degree bending test was performed using a V block. Then, the bending radius of the test piece was changed depending on the tip radius of the punch, and if the n-number was not broken at five, the value was evaluated as the limit bending radius. In this test, the smaller the critical bending radius, the better the ductility.
In the impact test, a JIS No. 4 sub-size test piece having a thickness of 2.5 mm was used, a Charpy impact test was performed, and the toughness was evaluated by the magnitude of absorbed energy.
[0017]
As can be seen from the results of the investigation in Table 2, the comparative steel A with insufficient C content became an insufficiently tempered structure because of its low tempering temperature when tempering to 48 HRC, and exhibited low ductility and toughness. Comparative steel B was not hardened because Mn was not added, and although sufficient ductility and toughness were ensured, sufficient hardness could not be obtained. Since the comparative steel C contains a large amount of impurity elements such as P, S, and O, the X value exceeds 1.0, and the ductility and toughness are insufficient. Further, the comparative steel D equivalent to SK5 and the comparative steel E equivalent to SKS5 that have been conventionally used for the grass cutting blade substrate both had an X value exceeding 1.0, and exhibited low ductility and toughness.
On the other hand, all of the steels F to I satisfying the conditions defined in the present invention have a small critical bending radius, an impact value as high as 27 J / cm 2 or more, and even at a hardness level of 42 to 48 HRC. It turns out that it is excellent in ductility and toughness.
[0018]
【The invention's effect】
As described above, the mowing blade substrate of the present invention is obtained by adding a predetermined amount of Mn, Cr, Mo, V, Cu in a state where the content of C, N, O, P, S is reduced. It improves hardenability, secures the necessary hardness for the mowing blade substrate, and improves ductility and toughness. Therefore, even if it contacts with stone, gravel, etc. during high-speed rotation, there is little breakage and wear, and it is used as a mowing blade that shows a good sharpness over a long period of time.
Claims (1)
Ｘ＝Ｃ％＋１８×Ｎ％＋５２×Ｏ％＋１０×Ｐ％＋１７×Ｓ％・・・・（１）C: 0.30 to 0.70 wt%, Si: 0.50 wt% or less, Mn: 0.10 to 1.50 wt%, Cr: 0.18 to 1.31 wt%, N: 0.0005 0.02 wt%, O: 0.0005 to 0.01 wt%, P: 0.02 wt% or less, S: 0.01 wt% or less, acid-soluble Al: 0.01 0 to 0.10 A mowing blade substrate that is made of a steel plate that includes wt%, the balance being Fe and inevitable impurities, and having a component composition with an X value defined by formula (1) of 1.0 or less.
X = C% + 18 × N% + 52 × O% + 10 × P% + 17 × S% (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03074798A JP3962143B2 (en) | 1998-02-13 | 1998-02-13 | Mowing blade substrate |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03074798A JP3962143B2 (en) | 1998-02-13 | 1998-02-13 | Mowing blade substrate |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2007065334A Division JP4448525B2 (en) | 2007-03-14 | 2007-03-14 | Mowing blade substrate |
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| Publication Number | Publication Date |
|---|---|
| JPH11229081A JPH11229081A (en) | 1999-08-24 |
| JP3962143B2 true JP3962143B2 (en) | 2007-08-22 |
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| JP03074798A Expired - Fee Related JP3962143B2 (en) | 1998-02-13 | 1998-02-13 | Mowing blade substrate |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4973220B2 (en) * | 2007-02-14 | 2012-07-11 | 日立工機株式会社 | Trimming machine |
| JP5328331B2 (en) * | 2008-12-11 | 2013-10-30 | 日新製鋼株式会社 | Steel materials for wear-resistant quenched and tempered parts and manufacturing method |
| SE543919C2 (en) * | 2019-05-17 | 2021-09-21 | Husqvarna Ab | Steel for a sawing device |
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