JP2001234238A - Producing method for highly wear resistant and high toughness rail - Google Patents
Producing method for highly wear resistant and high toughness railInfo
- Publication number
- JP2001234238A JP2001234238A JP2000040636A JP2000040636A JP2001234238A JP 2001234238 A JP2001234238 A JP 2001234238A JP 2000040636 A JP2000040636 A JP 2000040636A JP 2000040636 A JP2000040636 A JP 2000040636A JP 2001234238 A JP2001234238 A JP 2001234238A
- Authority
- JP
- Japan
- Prior art keywords
- rolling
- rail
- steel
- toughness
- pearlite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Abstract
Description
【０００１】本発明は、鉄道その他産業機械用として使
用される強度と耐摩耗性に優れた高炭素のパーライト組
織を呈した鋼に靱性を付与した高靱性レールの製造方法
に関するものである。[0001] The present invention relates to a method for manufacturing a high toughness rail obtained by imparting toughness to a steel exhibiting a high carbon pearlite structure having excellent strength and wear resistance and used for railways and other industrial machines.
【０００２】[0002]
【従来の技術】高炭素でパーライトの金属組織を呈した
鋼は強度が高く、耐摩耗性が良好なことから、構造材料
として使用され、中でも鉄道車両の質量増加に伴う高軸
荷重化や高速輸送化に対応してレールに特に多く使用さ
れている。2. Description of the Related Art High carbon steel having a pearlitic metal structure is used as a structural material because of its high strength and good abrasion resistance. Especially used for rails in response to transportation.
【０００３】このような鋼材の製造法としては、例えば
特開昭５５−２７６号公報には「パーライト組織を呈し
やすい特定成分の鋼をＡｃ3 点以上の加熱温度から冷却
して４５０〜６００℃の温度で恒温変態させて、微細パ
ーライト組織を生成させる硬質レールの製造法」、また
特開昭５８−２２１２２９号公報には「Ｃ：０．６５〜
０．８５％、Ｍｎ：０．５〜２．５％を含有して高温度
の熱を保有した高Ｍｎレールを急冷し、レールまたはレ
ールヘッドの組織を微細なパーライトとして耐摩耗性を
改善したレールの熱処理法」、さらに特開昭５９−１３
３３２２号公報には「安定してパーライト組織が得られ
る特定成分の圧延レールを、Ａｒ3 点以上の温度から特
定温度の溶融塩浴中に浸漬して、レール頭頂部表面下約
１０ｍｍまでにＨｖ＞３５０の硬さをもつ微細なパーラ
イト組織を呈するレールの熱処理方法」が開示されてい
るごとく、多くの技術が知られている。[0003] As a method for producing such a steel material, for example, Japanese Patent Application Laid-Open No. 55-276 discloses that "steel of a specific component which easily exhibits a pearlite structure is cooled from a heating temperature of the Ac3 point or higher to 450-600 ° C. A method for producing a hard rail in which a fine pearlite structure is formed by isothermal transformation at a temperature ”, and JP-A-58-221229 discloses“ C: 0.65 to
A high Mn rail containing 0.85% and Mn: 0.5-2.5% and having high-temperature heat was quenched to improve the wear resistance by making the structure of the rail or rail head fine pearlite. Rail heat treatment method ", and JP-A-59-13
No. 3322 discloses that a rolling rail of a specific component capable of stably obtaining a pearlite structure is immersed in a molten salt bath at a temperature of not less than the Ar3 point and a specific temperature so that Hv> Many techniques are known, as disclosed in "Method of heat treatment of rail exhibiting fine pearlite structure having hardness of 350".
【０００４】しかしながら、パーライト鋼の強度や耐摩
耗性は合金元素の添加によって所要の規格品が容易に得
られるとは言え、靭性はフェライト組織を主体とした鋼
に比較して著しく低く、例えばパーライトレール鋼では
ＪＩＳ３号Ｕノッチシャルピー試験での常温試験値で１
０〜２０Ｊ程度である。このように靭性の低い鋼を繰り
返し荷重や振動の掛かる分野で構造部材として使用した
場合、微小な初期欠陥や疲労き裂から低応力脆性破壊を
引き起こす問題があった。However, although the strength and wear resistance of pearlite steel can be easily obtained as required standard products by the addition of alloying elements, the toughness is remarkably lower than that of steel mainly composed of ferrite. For rail steel, JIS No. 3 U notch Charpy test at room temperature test value is 1
It is about 0 to 20J. When such a low toughness steel is used as a structural member in a field where a repeated load or vibration is applied, there is a problem that low stress brittle fracture is caused from minute initial defects and fatigue cracks.
【０００５】一般に、鋼の靭性を向上させる手段には金
属組織の微細化、すなわちオーステナイト組織の細粒化
や粒内変態によって達成されるものと言われている。オ
ーステナイト組織の細粒化は、例えば圧延時の低温加熱
あるいは特開昭６３−２７７７２１号公報に開示されて
いるように制御圧延と加熱処理の組み合わせ、また圧延
後の低温加熱処理などが利用されている。しかし、レー
ルの製造法においては、成形性確保の観点から圧延時の
低温加熱や制御圧延における低温圧延、大圧下圧延の適
用が困難な理由から、今日においても従来から低温加熱
熱処理による靭性の向上が図られている。ところがこの
方法も近来の各鋼製品における省力化・生産性向上技術
の開発が進められる中で、製造コストが高く、生産性も
低いなどの問題があり、これらの早期開発が望まれてい
る。In general, it is said that the means for improving the toughness of steel is achieved by refining the metal structure, that is, by refining the austenite structure and transgranular transformation. The austenite structure is refined by, for example, low-temperature heating during rolling or a combination of controlled rolling and heat treatment as disclosed in JP-A-63-277721, or low-temperature heat treatment after rolling. I have. However, in the rail manufacturing method, low-temperature heating during rolling, low-temperature rolling in controlled rolling, and application of large reduction rolling are difficult in terms of ensuring formability. Is planned. However, this method also has problems such as high production cost and low productivity while the development of labor saving and productivity improvement techniques for each steel product has been advanced recently, and early development of these methods is desired.
【０００６】[0006]
【発明が解決しようとする課題】本発明は上記した問題
点を解消しようとするものであり、レール成形上、低温
あるいは大圧下に依っていた制御圧延の問題を克服し、
共析鋼特有の制御圧延をおこない、レール鋼等のような
共析炭素鋼の靱性を向上させる方法を提供することを目
的とする。SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and overcomes the problem of controlled rolling that has been dependent on low temperatures or large pressures in forming rails.
An object of the present invention is to provide a method of performing controlled rolling specific to eutectoid steel and improving the toughness of eutectoid carbon steel such as rail steel.
【０００７】[0007]
【課題を解決するための手段】本発明者らは、細粒のパ
ーライト組織を得て靱性を向上させた鋼を製造するため
に、鋼成分とその製造法から多くの実験を試みた結果、
共析炭素鋼に近い高炭素の鋼はそのオーステナイト状態
での加工において、比較的低温で、かつ小さい圧下量で
も圧延直後に再結晶することを見いだし、小圧下の連続
圧延によって整粒の微細オーステナイト粒を得、その結
果、細粒のパーライト組織が得られることを知見した。Means for Solving the Problems The inventors of the present invention have conducted a number of experiments on steel components and their production methods in order to obtain a fine-grained pearlite structure and produce steel with improved toughness.
High-carbon steel, which is close to eutectoid carbon steel, was found to recrystallize immediately after rolling at a relatively low temperature and with a small rolling reduction during processing in the austenitic state. It was found that granules were obtained, and as a result, a fine-grained pearlite structure was obtained.
【０００８】本発明はこのような知見に基づいて構成し
たものであって、その要旨とするところは、質量％で Ｃ ：０．６０〜１．２０％を含有し、さらに必要に応じて、 Ｓｉ：０．１０〜１．２０％、 Ｍｎ：０．４０〜１．５０％、 Ｃｒ：０．０５〜２．００％、 Ｍｏ：０．０１〜０．３０％、 Ｖ ：０．０１〜０．３０％、 Ｎｂ：０．００２〜０．０５０％、 Ｃｕ：０．０５〜２．００％、 Ｎｉ：０．０５〜２．００％、 Ｃｏ：０．１０〜２．００％、 Ｔｉ：０．００５〜０．１００％、 Ｃａ：０．０００５〜０．０１００％、Ｍｇ：０．０００５〜０．０１００％ の一種または２種以上を含有し、その金属組織がパーラ
イトを呈する鋼をレール圧延するに際して、粗形圧延を
経たのち、最終仕上げ圧延工程において該レールの表面
温度が８５０〜１０００℃の間を１パス当たり断面減少
圧下率が５〜３０％の圧延を２パス以上でかつ圧延パス
間を１０秒以下とする連続仕上げ圧延を施し、続いてレ
ール表面での冷却速度が０．５℃／秒（ｓ）以上で８０
０〜９５０℃まで冷却し、その後放冷、または加速冷却
を行うことを特徴とするパーライト金属組織を呈した高
耐摩耗・高靭性レールの製造方法である。上記加速冷却
は７００℃以上の温度から５００℃までの間を２〜１５
℃／ｓで冷却することが好ましい。The present invention has been made on the basis of such findings, and the gist of the present invention is to contain C: 0.60 to 1.20% by mass%, and further, Si: 0.10 to 1.20%, Mn: 0.40 to 1.50%, Cr: 0.05 to 2.00%, Mo: 0.01 to 0.30%, V: 0.01 to 0.30%, Nb: 0.002 to 0.050%, Cu: 0.05 to 2.00%, Ni: 0.05 to 2.00%, Co: 0.10 to 2.00%, Ti : 0.005 to 0.100%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, and steel having a pearlite metal structure. When performing rail rolling, after rough rolling, the surface of the rail is subjected to final finishing rolling. Continuous finishing rolling is performed at a temperature of 850 to 1000 ° C. and rolling at a cross-sectional reduction reduction of 5 to 30% per pass is performed in two or more passes and the rolling pass is performed for 10 seconds or less. 80 at cooling rate of 0.5 ° C / sec (s) or more
This is a method for producing a high wear-resistant and high-toughness rail exhibiting a pearlite metal structure, characterized in that the rail is cooled to 0 to 950 ° C., and then cooled or accelerated. The accelerated cooling is performed at a temperature of 700 ° C. or more to 500 ° C. for 2 to 15 hours.
Cooling at a rate of ° C./s is preferred.
【０００９】[0009]
【発明の実施の形態】以下、本発明について詳細に説明
する。先ず、本発明において鋼成分を上記のように限定
した理由について説明する。BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the reason why the steel components are limited as described above in the present invention will be described.
【００１０】Ｃはパーライト組織を生成させて耐摩耗性
を確保する有効な成分として０．６０％以上の含有が必
要である。しかし、１．２０％を超える高い含有量では
セメンタイト組織を多く析出して硬さは増加するが、延
性は低下し、本発明の目的である靱性を著しく低下させ
る。C is required to contain 0.60% or more as an effective component for forming a pearlite structure and ensuring abrasion resistance. However, when the content is higher than 1.20%, a large amount of cementite structure precipitates to increase the hardness, but the ductility is reduced, and the toughness, which is the object of the present invention, is significantly reduced.
【００１１】本発明は、少なくとも上記のような共析炭
素近傍の炭素含有量の鋼特有のオーステナイトの再結晶
挙動の知見に基づいているため、さらに各種合金を添加
しても金属組織がパーライトを呈する範囲では何ら差し
障りはない。このため、強度や延性、靭性を向上させる
ことを目的として、以下の合金元素を適宜添加すること
ができる。[0011] The present invention is based on the knowledge of the recrystallization behavior of austenite peculiar to steel having a carbon content near at least eutectoid carbon as described above. There is no hindrance in the range presented. For this reason, the following alloy elements can be appropriately added for the purpose of improving strength, ductility, and toughness.
【００１２】Ｓｉは、パーライト組織中のフェライト相
への固溶体硬化によりレール頭部の硬度（強度）を上昇
させる元素であるが、０．１０％未満ではその効果が十
分に期待できず、また１．２０％を超えると、熱間圧延
時に表面疵が多く生成することや、酸化物の生成により
溶接性が低下するため、Ｓｉ量を０．１０〜１．２０％
に限定した。Si is an element which raises the hardness (strength) of the rail head by solid solution hardening into the ferrite phase in the pearlite structure, but if its content is less than 0.10%, its effect cannot be expected sufficiently. If it exceeds 20%, a large amount of surface flaws are generated during hot rolling and the weldability is reduced due to the formation of oxides.
Limited to.
【００１３】Ｍｎは、パーライト変態温度を低下させ、
焼入れ性を高めることによって高強度化に寄与し、さら
に初析セメンタイト組織の生成を抑制する元素である
が、０．４０％未満の含有量ではその効果が小さく、レ
ール頭部に必要とされる硬さの確保が困難となる。ま
た、１．５０％を超えると、焼入れ性が著しく増加し、
マルテンサイト組織が生成し易くなることや、偏析が助
長され、偏析部にレールの靭性に有害な初析セメンタイ
ト組織が生成し易くなるため、Ｍｎ量を０．４０〜１．
５０％に限定した。Mn lowers the pearlite transformation temperature,
It is an element that contributes to high strength by enhancing hardenability and further suppresses the formation of a pro-eutectoid cementite structure. However, if its content is less than 0.40%, its effect is small, and it is required for the rail head. It is difficult to secure hardness. Further, when the content exceeds 1.50%, the hardenability increases remarkably,
Since a martensitic structure is easily generated, segregation is promoted, and a pro-eutectoid cementite structure harmful to the toughness of the rail is easily generated in the segregated portion.
Limited to 50%.
【００１４】Ｃｒは、パーライトの平衡変態点を上昇さ
せ、結果としてパーライト組織を微細にして高強度化に
寄与すると同時に、パーライト組織中のセメンタイト相
を強化することにより耐摩耗性を向上させる元素である
が、０．０５％未満ではその効果が小さく、２．００％
を超える過剰な添加を行うと、マルテンサイト組織が多
量に生成し、レールの靱性を低下させるため、Ｃｒ量を
０．０５〜２．００％に限定した。Cr is an element that raises the equilibrium transformation point of pearlite and consequently makes the pearlite structure finer and contributes to high strength, and at the same time improves the wear resistance by strengthening the cementite phase in the pearlite structure. However, if less than 0.05%, the effect is small, and 2.00%
When an excessive addition exceeding that is performed, a large amount of martensite structure is generated and the toughness of the rail is reduced, so the Cr content is limited to 0.05 to 2.00%.
【００１５】Ｍｏは、Ｃｒ同様パーライトの平衡変態点
を上昇させ、結果としてパーライト組織を微細にするこ
とにより高強度化に寄与し、耐摩耗性を向上させる元素
であるが、０．０１％未満ではその効果が小さく、０．
３０％を超える過剰な添加を行うと偏析が助長され、さ
らにパーライト変態速度が低下し、偏析部にマルテンサ
イト組織が生成し、レールの靱性が低下するため、Ｍｏ
量を０．０１〜０．３０％に限定した。Mo is an element that, like Cr, raises the equilibrium transformation point of pearlite and consequently refines the pearlite structure, thereby contributing to higher strength and improving wear resistance, but less than 0.01%. The effect is small.
If an excessive addition exceeds 30%, segregation is promoted, the pearlite transformation speed is further reduced, a martensite structure is generated in the segregated portion, and the toughness of the rail is reduced.
The amount was limited to 0.01-0.30%.
【００１６】Ｖはレール頭部の熱処理において、レール
頭表部と比較して冷却速度の遅いレール頭部内部で炭化
物や窒化物を形成し、パーライト組織中のフェライト地
に析出することにより、頭部内部の硬度を向上させる元
素であるが、０．０１％未満では、炭化物や窒化物の形
成が困難となり、レール頭部内部のパーライト組織の析
出硬化が困難となる。また、０．３０％を超えて添加し
てもそれ以上の効果が期待できないため、Ｖ量を０．０
１〜０．３０％に限定した。In the heat treatment of the rail head, V forms carbides and nitrides inside the rail head, which has a lower cooling rate than the rail head surface part, and precipitates on the ferrite ground in the pearlite structure. Although it is an element that improves the hardness inside the part, if it is less than 0.01%, it becomes difficult to form carbides and nitrides, and it becomes difficult to precipitate and harden the pearlite structure inside the rail head. Further, if more than 0.30% is added, no further effect can be expected.
Limited to 1 to 0.30%.
【００１７】Ｎｂは、Ｖと同様にＮｂ炭化物、Ｎｂ窒化
物による析出硬化で強度を高め、さらに、高温度に加熱
する熱処理が行われる際に結晶粒の成長を抑制する作用
によりオーステナイト粒を微細化させ、そのオーステナ
イト粒成長抑制効果はＶよりも高温度域（１２００℃近
傍）まで作用し、パーライト組織の延性と靭性を改善す
る。その効果は、０．００２％未満では期待できず、ま
た０．０５０％を超える過剰な添加を行ってもそれ以上
の効果が期待できない。従って、Ｎｂ量を０．００２〜
０．０５０％に限定した。Nb increases the strength by precipitation hardening with Nb carbides and Nb nitrides like V, and further suppresses the growth of crystal grains during heat treatment at a high temperature to reduce austenite grains. The effect of suppressing austenite grain growth acts up to a temperature range higher than V (around 1200 ° C.), and improves the ductility and toughness of the pearlite structure. The effect cannot be expected if it is less than 0.002%, and no further effect can be expected even if an excessive addition exceeding 0.050% is performed. Therefore, the amount of Nb is 0.002 to
Limited to 0.050%.
【００１８】Ｃｕは、パーライト鋼の靭性を損なわず強
度を向上させる元素であり、その効果は０．０５〜２．
００％の範囲で最も大きく、また２．００％を超えると
赤熱脆化を生じやすくなることから、Ｃｕ量を０．０５
〜２．００％に限定した。Cu is an element which improves the strength without impairing the toughness of the pearlite steel, and its effect is 0.05 to 2.0.
The largest amount is in the range of 00%, and if it exceeds 2.00%, red heat embrittlement is likely to occur.
To 2.00%.
【００１９】Ｎｉは、パーライト鋼の延性と靭性を向上
させ、同時に、固溶強化によりパーライト鋼の高強度化
を図る元素であるが、０．０５％未満ではその効果が著
しく小さく、また２．００％を超える過剰な添加を行っ
てもそれ以上の効果が期待できない。したがって、Ｎｉ
量を０．０５〜２．００％に限定した。Ni is an element that improves the ductility and toughness of the pearlite steel and, at the same time, increases the strength of the pearlite steel by solid solution strengthening. Even if an excessive addition exceeding 00% is performed, no further effect can be expected. Therefore, Ni
The amount was limited to 0.05-2.00%.
【００２０】Ｃｏは、パーライトの変態エネルギーを増
加させて、パーライト組織を微細にすることにより強度
を向上させる元素であるが、０．１０％未満ではその効
果が期待できず、また２．００％を超える過剰な添加を
行ってもその効果が飽和域に達してしまうため、Ｃｏ量
を０．１０〜２．００％に限定した。Co is an element that increases the transformation energy of pearlite to improve the strength by making the pearlite structure finer, but its effect cannot be expected if it is less than 0.10%, and 2.00%. However, the effect reaches the saturation range even if an excessive amount of addition is performed, so the Co content is limited to 0.10 to 2.00%.
【００２１】Ｔｉは、レール圧延時の再加熱において、
析出したＴｉ炭化物、Ｔｉ窒化物が溶解しないことを利
用して、圧延加熱時のオーステナイト結晶粒の微細化を
図り、パーライト組織の延性や靭性を向上させるのに有
効な成分である。しかし、０．００５％未満ではその効
果が少なく、０．１００％を超えて添加すると、粗大な
Ｔｉ炭化物、Ｔｉ窒化物が生成して、レール使用中の疲
労損傷の起点となり、き裂を発生させるため、Ｔｉ量を
０．００５〜０．１００％に限定した。In the reheating at the time of rail rolling, Ti
Utilizing the fact that precipitated Ti carbides and Ti nitrides do not dissolve, it is an effective component for refining austenite crystal grains during rolling and heating and improving ductility and toughness of pearlite structure. However, if the content is less than 0.005%, the effect is small, and if it is added more than 0.100%, coarse Ti carbides and Ti nitrides are formed, which becomes a starting point of fatigue damage during use of the rail and cracks are generated. For this purpose, the amount of Ti is limited to 0.005 to 0.100%.
【００２２】Ｃａは、不可避的不純物であるＳとの結合
力が強く、ＣａＳとして硫化物を形成し、さらにＣａＳ
がＭｎＳを微細に分散させ、ＭｎＳの周囲にＭｎの希薄
帯を形成し、パーライト変態の生成に寄与し、その結果
パーライトブロックサイズを微細化することにより、パ
ーライト組織の延性や靭性を向上させるのに有効な元素
である。しかし、０．０００５％未満ではその効果は弱
く、０．０１００％を超えて添加するとＣａの粗大酸化
物が生成してレール延性や靭性を劣化させるため、Ｃａ
量を０．０００５〜０．０１００％に限定した。Ca has a strong binding force with S, which is an unavoidable impurity, and forms sulfide as CaS.
Disperses MnS finely, forms a rare band of Mn around MnS, contributes to the generation of pearlite transformation, and thereby improves the ductility and toughness of the pearlite structure by reducing the size of the pearlite block. It is an effective element. However, if the content is less than 0.0005%, the effect is weak. If the content is more than 0.0100%, a coarse oxide of Ca is generated to deteriorate rail ductility and toughness.
The amount was limited to 0.0005-0.0100%.
【００２３】Ｍｇは、Ｏ、またはＳやＡｌ等と結合して
微細な酸化物を形成し、レール圧延時の再加熱において
結晶粒の粒成長を抑制し、オーステナイト粒の微細化を
図り、パーライト組織の延性や靭性を向上させるのに有
効な元素である。さらに、ＭｇＯ、ＭｇＳがＭｎＳを微
細に分散させ、ＭｎＳの周囲にＭｎの希薄帯を形成し、
パーライト変態の生成に寄与し、その結果、パーライト
ブロックサイズを微細化することにより、パーライト組
織の延性や靭性を向上させるのに有効な元素である。し
かし、０．０００５％未満ではその効果は弱く、また
０．０１００％を超えて添加するとＭｇの粗大酸化物が
生成してレール延性や靭性を劣化させるため、Ｍｇ量を
０．０００５〜０．０１００％に限定した。Mg combines with O, S or Al to form a fine oxide, suppresses the growth of crystal grains during reheating during rail rolling, refines austenite grains, and improves pearlite. It is an element effective for improving the ductility and toughness of the structure. Further, MgO and MgS finely disperse MnS, and form a thin band of Mn around MnS,
It is an element that contributes to the generation of pearlite transformation and, as a result, is effective in improving the ductility and toughness of the pearlite structure by reducing the pearlite block size. However, if the content is less than 0.0005%, the effect is weak. If the content exceeds 0.0100%, a coarse oxide of Mg is generated to deteriorate the ductility and toughness of the rail. Limited to 0100%.
【００２４】上記のような成分組成で構成されるレール
鋼は、転炉、電気炉などの通常使用される溶解炉で溶製
を行い、この溶鋼を造塊・分塊法あるいは連続鋳造法、
さらに熱間圧延を経てレールとして製造される。次に、
この熱間圧延した高温度の熱を保有するレール、あるい
は熱処理する目的で高温に再加熱されたレール頭部に熱
処理を施すことにより、レール頭部に硬さの高いパーラ
イト組織を安定的に生成させることが可能となる。The rail steel having the above-mentioned composition is melted in a commonly used melting furnace such as a converter or an electric furnace, and the molten steel is subjected to an ingot-bulking method or a continuous casting method.
Further, it is manufactured as a rail through hot rolling. next,
By applying heat treatment to this hot-rolled rail that holds high-temperature heat or to the rail head that has been reheated to a high temperature for the purpose of heat treatment, a pearlite structure with high hardness is generated stably on the rail head. It is possible to do.
【００２５】レール鋼の圧延では鋳片の粗形圧延を行っ
た後の仕上げ圧延段階においては、レールの成形性確保
の観点からその１パス当たりの圧下量は断面減少率にし
て通常５〜３０％の比較的小さい範囲であり、仕上げ温
度は１０００℃程度である。これに対して、最近はより
低温で圧延し、延性や靱性の改善を目的とした制御圧延
も行われている。In the rolling of rail steel, in the finish rolling stage after the rough rolling of the slab, the rolling reduction per pass is usually 5 to 30 in terms of the cross-sectional reduction rate from the viewpoint of ensuring the formability of the rail. % And the finishing temperature is on the order of 1000 ° C. On the other hand, recently, controlled rolling for the purpose of improving ductility and toughness has been performed at a lower temperature.
【００２６】一般にフェライトを主体にした鋼の制御圧
延の場合はオーステナイトの未再結晶領域まで圧延温度
を低下させ、加工オーステナイト中へのひずみの導入に
よりフェライト核の増大を図り、細粒フェライトを得る
制御圧延法が採られている。しかしながらパーライト鋼
の場合は、共析変態のためパーライトの成長速度が大き
く、オーステナイト粒内変態核が有効に作用せず、実質
的に細粒パーライトが得られ難いことがわかった。した
がって、整粒の細粒オーステナイト鋼を得ることがパー
ライト細粒化に必要なことがわかった。In general, in the case of controlled rolling of steel mainly composed of ferrite, the rolling temperature is lowered to a non-recrystallized region of austenite, and ferrite nuclei are increased by introducing strain into worked austenite to obtain fine-grain ferrite. The controlled rolling method is adopted. However, in the case of pearlite steel, it was found that the growth rate of pearlite was high due to eutectoid transformation, the austenite intragranular transformation nuclei did not work effectively, and it was difficult to obtain substantially fine pearlite. Therefore, it was found that obtaining a fine-grained austenitic steel was necessary for reducing pearlite.
【００２７】かかる観点から、高炭素鋼のオーステナイ
トの再結晶挙動を詳細に検討した結果、１）低炭素鋼に
比較して低い温度まで、かつ低加工度で再結晶するこ
と、２）加工後、完全再結晶に要する時間が非常に小さ
い、すなわち圧延直後に再結晶を完了すること、３）小
さな圧下でも連続的に加工を加えると、その都度再結晶
を繰り返し、次の加工までの粒成長が抑制されるため、
整細粒の再結晶オーステナイト粒が得られることを知見
した。これらの知見をもとにその最適な加工条件範囲を
見出した。以下に条件の限定理由を述べる。From this point of view, the recrystallization behavior of austenite of a high carbon steel was examined in detail. As a result, 1) recrystallization at a lower temperature and a lower workability than that of a low carbon steel, 2) after processing The time required for complete recrystallization is very short, that is, recrystallization is completed immediately after rolling. 3) When processing is continuously performed even under a small pressure, recrystallization is repeated each time, and grain growth until the next processing is performed. Is suppressed,
It has been found that fine-grained recrystallized austenite grains can be obtained. Based on these findings, the optimum processing condition range was found. The reasons for limiting the conditions are described below.
【００２８】仕上げ圧延温度については８５０〜１００
０℃の範囲が最適で８５０℃未満ではオーステナイトが
未再結晶状態となり、先に述べたようにパーライトの微
細化に有効でない。一方、１０００℃超の場合は圧延後
のオーステナイト粒の成長が大きく、パーライト変態時
に混粒の粗粒オーステナイトとなり、パーライトの微細
化に有効でない。The final rolling temperature is 850-100.
If the range of 0 ° C. is optimal, and if it is lower than 850 ° C., austenite is in an unrecrystallized state, which is not effective for miniaturization of pearlite as described above. On the other hand, when the temperature is higher than 1000 ° C., the growth of austenite grains after rolling is large and becomes coarse austenite of mixed grains at the time of pearlite transformation, which is not effective for miniaturization of pearlite.
【００２９】圧下率については５〜３０％の範囲で５％
未満の場合は再結晶を発現させうるに有効なひずみの導
入ができず、また３０％超の場合は再結晶には有効であ
るが、レール圧延工程での全断面減少量から圧延パス回
数が十分に採れなくなることおよびレール成形が困難に
なることから有効でない。The rolling reduction is 5% in the range of 5 to 30%.
If it is less than 30%, it is not possible to introduce a strain effective for causing recrystallization, and if it is more than 30%, it is effective for recrystallization. It is not effective because it cannot be taken sufficiently and rail forming becomes difficult.
【００３０】パス間時間については１０秒以下が必要で
ある。高温におけるオーステナイト粒は隣接粒同士の合
体による結晶粒の粗大化、混粒化、いわゆる粒成長が起
こる。通常のリバース圧延や圧延機間の距離が大きい場
合、パス間時間は２０〜２５秒程度となり、この間に圧
延されたオーステナイト粒のひずみの回復、再結晶、さ
らには粒成長が起こる。本発明では圧延直後に再結晶を
完了するため、先に示したようなパス間時間の間に粒成
長が生じ、再結晶により細粒となった効果が減じられ
る。パス間時間が１０秒を超えるとこのパス間での粒成
長の影響が看過できなくなる程に大きくなり、圧延再結
晶によるオーステナイト粒の細粒化効果が減じ、目的を
達成できない。The inter-pass time needs to be 10 seconds or less. Austenite grains at a high temperature cause coarsening and mixing of crystal grains due to coalescence of adjacent grains, so-called grain growth. When the distance between the normal reverse rolling and rolling mills is large, the inter-pass time is about 20 to 25 seconds, during which recovery of strain, recrystallization, and further grain growth of the rolled austenite grains occur. In the present invention, since recrystallization is completed immediately after rolling, grain growth occurs during the inter-pass time as described above, and the effect of recrystallization to reduce fine grains is reduced. If the time between passes exceeds 10 seconds, the effect of grain growth between passes becomes so large that it cannot be overlooked, and the effect of austenite grain refinement by rolling recrystallization is reduced, so that the object cannot be achieved.
【００３１】また、先に述べたように再結晶の繰り返し
による細粒化の観点から、少なくとも２パス以上の連続
圧延が必要である。As described above, continuous rolling of at least two passes is required from the viewpoint of grain refinement by repeating recrystallization.
【００３２】以上の圧延を完了後、続いてレール表面で
の冷却速度が０．５℃／ｓ以上で８００〜９５０℃まで
冷却を行う理由について述べる。先に圧延パス間のオー
ステナイトの粒成長は圧延後１０秒を超えるとその影響
を看過できなくなることを述べたが、圧延終了後のオー
ステナイトの粒成長も同様な挙動をとる。この時、オー
ステナイトの温度を低下させることで粒成長の抑制が可
能となる。したがって、レール表面での冷却速度が０．
５℃／ｓ以上で８００〜９５０℃まで冷却することで粒
成長への温度の影響を回避する必要がある。なお冷却速
度の上限は特に規定しないが、例えばガスを吹き付けて
冷却する方法ではおよそ５０℃／ｓ位までの速度で冷却
することができる。After the above-mentioned rolling is completed, the reason for cooling to 800 to 950 ° C. at a cooling rate of 0.5 ° C./s or more on the rail surface will be described. It has been described above that the effect of austenite grain growth between rolling passes cannot be overlooked if it exceeds 10 seconds after rolling. However, austenite grain growth after rolling has the same behavior. At this time, grain growth can be suppressed by lowering the temperature of austenite. Therefore, the cooling rate on the rail surface is 0.
It is necessary to avoid the influence of temperature on grain growth by cooling to 800 to 950 ° C. at 5 ° C./s or more. Although the upper limit of the cooling rate is not particularly defined, for example, in a method of cooling by blowing a gas, the cooling can be performed at a speed of about 50 ° C./s.
【００３３】レールはその後さらに常温まで冷却され
る。この冷却は放冷でもよいが、強度をさらに向上させ
る場合は加速冷却を行う。加速冷却は７００以上の温度
から５００℃までの間で２〜１５℃／ｓで行うことが好
ましく、以下にその限定理由について述べる。冷却開始
温度は鋼のオーステナイト域、少なくとも７００℃以上
が必要でこれを下回る場合は有効な変態強化ができな
い。また、冷却速度は鋼の変態にかかわる温度範囲、す
なわち７００以上の温度から５００℃までの間で２〜１
５℃／ｓが必要で、２℃／ｓ未満では放冷と比較して差
が顕著でない変態強化しか得られない。また１５℃／ｓ
超ではベイナイトあるいはマルテンサイトなどの異常組
織の混入を招き、耐摩耗性や靱性を著しく阻害する。The rail is then further cooled to room temperature. This cooling may be allowed to cool, but if the strength is to be further improved, accelerated cooling is performed. The accelerated cooling is preferably performed at a temperature of 700 ° C. or more to 500 ° C. at a rate of 2 to 15 ° C./s. The reason for the limitation is described below. The cooling start temperature is required to be at least 700 ° C. in the austenite region of steel, and if it is lower than this, effective transformation strengthening cannot be performed. Further, the cooling rate is 2 to 1 in the temperature range related to the transformation of steel, that is, from a temperature of 700 or more to 500 ° C.
5 ° C./s is required, and if it is less than 2 ° C./s, only transformation strengthening whose difference is not remarkable as compared with cooling is obtained. 15 ° C / s
If it is excessively high, an abnormal structure such as bainite or martensite is mixed, and wear resistance and toughness are significantly impaired.
【００３４】上記のような本発明法によれば、細粒のパ
ーライト組織を得、耐摩耗性に加え、靱性を向上させた
レールを製造することができる。According to the method of the present invention as described above, a fine-grained pearlite structure can be obtained, and a rail having improved abrasion resistance and toughness can be manufactured.
【００３５】[0035]
【実施例】表１に金属組織がパーライトを呈する供試鋼
の化学成分を示す。表２は加熱条件と仕上げ圧延条件に
ついて本発明法および比較法を示す。表３は圧延直後の
冷却条件を示す。表４は高強度化のための熱処理冷却条
件を示す。表５に、表１から表４に示した鋼成分、圧延
条件、圧延直後の冷却条件および高強度化のための熱処
理冷却条件を組み合わせてレールを製造した場合の、本
発明法および比較法のレール鋼の機械的性質を示す。本
発明法では、鋼成分および冷却条件によりレールの強度
は変化するが、延性値、靱性値は比較法のそれに比較し
て著しく高い値を示すことがわかる。EXAMPLES Table 1 shows the chemical composition of a test steel having a pearlite metal structure. Table 2 shows the method of the present invention and the comparative method for the heating conditions and the finish rolling conditions. Table 3 shows the cooling conditions immediately after rolling. Table 4 shows heat treatment cooling conditions for increasing the strength. Table 5 shows the results of the method of the present invention and the comparative method when rails were manufactured by combining the steel components, rolling conditions, cooling conditions immediately after rolling, and heat treatment cooling conditions for increasing the strength shown in Tables 1 to 4. 1 shows the mechanical properties of rail steel. According to the method of the present invention, the strength of the rail changes depending on the steel composition and the cooling conditions, but the ductility value and the toughness value are significantly higher than those of the comparative method.
【００３６】[0036]
【表１】 [Table 1]
【００３７】[0037]
【表２】 [Table 2]
【００３８】[0038]
【表３】 [Table 3]
【００３９】[0039]
【表４】 [Table 4]
【００４０】[0040]
【表５】 [Table 5]
【００４１】[0041]
【発明の効果】以上述べたように、本発明の方法により
圧延中および圧延後の再結晶細粒オーステナイト（γ）
の粒成長を抑制することで、強度と耐摩耗性に優れた高
炭素のパーライト組織を呈した鋼にさらに靭性を付与し
た高靭性レールを得ることができる。As described above, the recrystallized fine austenite (γ) during and after rolling by the method of the present invention.
By suppressing the grain growth of the steel, it is possible to obtain a high toughness rail obtained by further imparting toughness to a steel exhibiting a high carbon pearlite structure having excellent strength and wear resistance.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 狩峰 健一 北九州市戸畑区飛幡町１−１ 新日本製鐵 株式会社八幡製鐵所内 Ｆターム(参考） 4K032 AA06 AA07 AA08 AA09 AA10 AA11 AA12 AA14 AA15 AA16 AA19 AA22 AA23 AA24 AA31 AA32 AA35 AA36 CB01 CC04 CD01 CD02 CD03 CD05 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenichi Kamine 1-1 Futaba-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works F-term (reference) 4K032 AA06 AA07 AA08 AA09 AA10 AA11 AA12 AA16 AA15 AA16 AA19 AA22 AA23 AA24 AA31 AA32 AA35 AA36 CB01 CC04 CD01 CD02 CD03 CD05
Claims (3)
む鋼片を、レール形状に粗圧延した後、該レールの表面
温度が８５０〜１０００℃の間を１パス当たり断面減少
圧下率が５〜３０％の圧延を２パス以上でかつ圧延パス
間を１０秒以下とする連続仕上げ圧延を施し、続いてレ
ール表面での冷却速度を０．５℃／秒以上で８００〜９
５０℃まで冷却し、その後、放冷もしくは加速冷却を行
うことを特徴とするパーライト金属組織を呈した高耐摩
耗・高靭性レールの製造方法。1. A steel slab containing C: 0.60 to 1.20% by mass is roughly rolled into a rail shape, and then the surface temperature of the rail decreases from 850 to 1000 ° C. in cross section per pass. Continuous finishing rolling is performed in which the rolling at a rolling reduction of 5 to 30% is 2 passes or more and the interval between the rolling passes is 10 seconds or less, and subsequently, the cooling rate on the rail surface is 0.5 to 9 ° C./sec.
A method for producing a highly wear-resistant and high-toughness rail exhibiting a pearlite metal structure, wherein the rail is cooled to 50 ° C., and then cooled or accelerated.
避的不純物からなる鋼片をレール形状に粗圧延した後、
該レールの表面温度が８５０〜１０００℃の間を１パス
当たり断面減少圧下率が５〜３０％の圧延を２パス以上
でかつ圧延パス間を１０秒以下とする連続仕上げ圧延を
施し、続いてレール表面での冷却速度が０．５℃／秒以
上で８００〜９５０℃まで冷却し、その後、放冷もしく
は加速冷却を行うことを特徴とするパーライト金属組織
を呈した高耐摩耗・高靭性レールの製造方法。2. The composition according to claim 1, further comprising: C: 0.60 to 1.20% by mass%; Si: 0.10 to 1.20%; Mn: 0.40 to 1.50%; 05 to 2.00%, Mo: 0.01 to 0.30%, V: 0.01 to 0.30%, Nb: 0.002 to 0.050%, Cu: 0.05 to 2.00% Ni: 0.05 to 2.00%, Co: 0.10 to 2.00%, Ti: 0.005 to 0.100%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 After roughly rolling a steel slab containing up to 0.0100% of one or more kinds and the remainder consisting of Fe and unavoidable impurities into a rail shape,
When the surface temperature of the rail is between 850 and 1000 ° C., rolling is performed at a rolling reduction of 5 to 30% in cross-section per pass for 2 or more passes and continuous finishing rolling is performed for 10 seconds or less between rolling passes. A high wear-resistant and high toughness rail exhibiting a pearlite metal structure characterized by cooling to a temperature of 800 to 950 ° C. at a cooling rate of 0.5 ° C./sec or more on the rail surface, and then performing cooling or accelerated cooling. Manufacturing method.
避的不純物からなる鋼片をレール形状に粗圧延した後、
該レールの表面温度が８５０〜１０００℃の間を１パス
当たり断面減少圧下率が５〜３０％の圧延を２パス以上
でかつ圧延パス間を１０秒以下とする連続仕上げ圧延を
施し、続いてレール表面での冷却速度が０．５℃／秒以
上で８００〜９５０℃まで冷却し、その後、７００℃以
上の温度から５００℃までの間を２〜１５℃／秒で冷却
することを特徴とするパーライト金属組織を呈した高耐
摩耗・高靭性レールの製造方法。3. A mass% containing C: 0.6-1.20%, Si: 0.10-1.20%, Mn: 0.40-1.50%, Cr: 0. 05 to 2.00%, Mo: 0.01 to 0.30%, V: 0.01 to 0.30%, Nb: 0.002 to 0.050%, Cu: 0.05 to 2.00% Ni: 0.05 to 2.00%, Co: 0.10 to 2.00%, Ti: 0.005 to 0.100%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 After roughly rolling a steel slab containing up to 0.0100% of one or more kinds and the remainder consisting of Fe and unavoidable impurities into a rail shape,
When the surface temperature of the rail is between 850 and 1000 ° C., rolling is performed at a rolling reduction of 5 to 30% in cross-section per pass for 2 or more passes and continuous finishing rolling is performed for 10 seconds or less between rolling passes. The cooling rate on the rail surface is 0.5 ° C./sec or more, and it is cooled to 800 to 950 ° C., and then, from 700 ° C. or more to 500 ° C. at 2 to 15 ° C./sec. For producing high wear-resistant and high-toughness rails exhibiting a pearlite metal structure.
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| JP2000040636A JP2001234238A (en) | 2000-02-18 | 2000-02-18 | Producing method for highly wear resistant and high toughness rail |
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| JP2000040636A JP2001234238A (en) | 2000-02-18 | 2000-02-18 | Producing method for highly wear resistant and high toughness rail |
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| WO2003085149A1 (en) * | 2002-04-05 | 2003-10-16 | Nippon Steel Corporation | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
| WO2008013300A1 (en) | 2006-07-24 | 2008-01-31 | Nippon Steel Corporation | Process for producing pearlitic rail excellent in wearing resistance and ductility |
| EP2071044A1 (en) | 2004-03-09 | 2009-06-17 | Nippon Steel Corporation | A method for producing high-carbon steel rails excellent in wear resistance and ductility |
| JP2010001500A (en) * | 2008-06-18 | 2010-01-07 | Nippon Steel Corp | Pearlite-base high-carbon steel rail excellent in ductility |
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