JP2004223531A - Method for manufacturing high carbon steel rail - Google Patents
Method for manufacturing high carbon steel rail Download PDFInfo
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- JP2004223531A JP2004223531A JP2003011701A JP2003011701A JP2004223531A JP 2004223531 A JP2004223531 A JP 2004223531A JP 2003011701 A JP2003011701 A JP 2003011701A JP 2003011701 A JP2003011701 A JP 2003011701A JP 2004223531 A JP2004223531 A JP 2004223531A
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【0001】
【発明の属する技術分野】
本発明は、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の加熱条件の適正化を図り、圧延時の鋼片の割れや破断を防止し、さらに、鋼片外表面部の脱炭を抑制し、高効率に高品質なレールを製造することを目的とした高炭素鋼レールの製造方法に関するものである。
【0002】
【従来の技術】
近年、海外の石炭や鉄鉱石を輸送する重荷重鉄道や国内の貨物鉄道では、より一層の鉄道輸送の高効率化のために、貨物の高積載化を強力に進めており、特に急曲線のレールでは、G.C.部や頭側部の耐摩耗性が十分確保できず、摩耗によるレール寿命の低下が問題となってきた。このような背景から、現状の共析炭素含有の高強度レール以上の耐摩耗性を有するレールの開発が求められるようになってきた。
【0003】
この問題を解決するため、本発明者らは下記に示すようなレールを開発した。
▲1▼過共析鋼(C:0.85%超〜1.20%)を用いて、パーライト組織中のラメラ中のセメンタイト密度を増加させた耐摩耗性に優れたレール(特許文献1)。
▲2▼過共析鋼(C:0.85超〜1.20%)を用いて、パーライト組織中のラメラ中のセメンタイト密度を増加させ、同時に、頭部を熱処理することにより硬さを制御した、耐摩耗性に優れたレールおよびその製造法(特許文献2)。
これらのレールの特徴は、鋼の炭素量を増加し、パーライトラメラ中のセメタイト相の体積比率を増加させ、硬さや組織を制御することにより、パーライト組織の耐摩耗性を向上させるものであった。
【0004】
【特許文献1】
特開平8−144016号公報)
【特許文献2】
特開平8−246100号公報
【0005】
【発明が解決しようとする課題】
上記の▲1▼に示されたパーライト組織を呈する発明レール鋼では、高炭素化により耐摩耗性の向上が図れる。しかし、上記の発明レール鋼は、現行の共析炭素含有(C:0.80%)の高強度レール鋼よりも炭素量が高いため、圧延用鋼片を用いて熱間圧延を行う再加熱工程において、加熱温度の選択が不適切であると、鋼片の一部が溶融状態となり、1)圧延中に鋼片に割れが発生し、鋼片が破断することや、さらに、2)最終圧延後のレールに割れが残留することにより、製品の歩留まりが著しく低下すると言った問題があった。
【0006】
また、圧延用鋼片を用いて熱間圧延を行う再加熱工程において、加熱時の保持時間の選択が不適切であると、鋼片の外表面部の脱炭が促進され、最終圧延後のレール外表面部のパーライト組織の炭素量や硬さが低下し、レール頭部の耐摩耗性が損なわれ、さらには、レールの疲労強度が低下しやすいといった問題があった。
【0007】
このような背景から、高炭素含有のレール鋼において、圧延時の鋼片の割れを防止し、さらに、レール外表面部の脱炭を抑制することにより、耐摩耗性や疲労強度の低下を抑制し、高効率に高品質なレールを製造する高炭素鋼レールの製造方法の開発が求められていた。
【0008】
すなわち、本発明は、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の最大加熱温度やある一定温度以上に加熱される時間の適正化を図り、圧延時の鋼片の割れや破断を防止し、さらに、レール外表面部の脱炭を抑制することにより、耐摩耗性や疲労強度の低下を抑制し、高効率に高品質なレールを製造することを目的としたものである。
【0009】
【課題を解決するための手段】
本発明は上記目的を達成するものであって、その要旨とするところは次の通りである。
質量%で、C:0.80〜1.40%を含有するレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の最大加熱温度(Tmax;℃)が鋼レールの炭素含有量からなる下式で示される値(CT)に対して、Tmax≦CTとなり、かつ、鋼片が1100℃以上に加熱される保持時間(Mmax;min)が鋼レールの炭素含有量からなる下式で示される値(CM)に対して、Mmax≦CMとなる鋼片の加熱を行うことを特徴とした高炭素鋼レールの製造方法。
CT=1500−140(〔mass%C〕)−80(〔mass%C〕)2
CM=600−120(〔mass%C〕)−60(〔mass%C〕)2
【0010】
【発明の実施の形態】
以下に本発明について詳細に説明する。
まず、本発明者らは、高炭素含有のレール圧延用鋼片を再加熱し、熱間圧延を行う工程において、鋼片に割れが発生する原因について調査を行った。その結果、鋼片の割れは、鋼片の加熱温度が最も高い外表面近傍の凝固組織の偏析部において、鋼片の一部が溶融し、これが圧延により開口することで発生していること。さらに、この割れの発生は、鋼片の最高加熱温度が高いほど、また、鋼片の炭素量が高いほど発生しやすことが明らかとなった。
【0011】
そこで、本発明者らは、割れの原因である部分的な溶融が発生する鋼片の最高加熱温度と鋼片の炭素量の関係を実験により検討した。その結果、鋼片の部分的な溶融が発生する最高加熱温度は、下記(1式)に示す鋼片の炭素量(mass%)を用いた2次式で表すことができ、鋼片の最高加熱温度(Tmax;℃)をこの2次式から求められるCT値以下に制御することにより、再加熱状態での鋼片の部分的な溶融やこれにともなう熱間圧延時の割れや破断が防止できることを見出した。
CT=1500−140(〔mass%C〕)−80(〔mass%C〕)2 ・・・・・1
【0012】
次に、本発明者らは、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の外表面部の脱炭が促進される要因を解析した。その結果、鋼片の外表面部の脱炭は、鋼片を再加熱する際の温度やその保持時間、さらには、鋼片の炭素量に大きく影響されていることがわかった。
そこで、本発明者らは、鋼片を再加熱する際の温度やその保持時間、さらには、鋼片の炭素量と鋼片外表面部の脱炭量の関係を明らかにした。その結果、鋼片の外表面部の脱炭量は、ある一定温度以上に保持される時間が長いほど、さらに、鋼片の炭素量が高いほど促進されることがわかった。
【0013】
さらに本発明者らは、鋼片の炭素量と最終圧延後のレールの諸特性が低下しない鋼片の再加熱時における保持時間の関係を実験により検討した。その結果、鋼片の保持時間は、再加熱温度1100℃以上を基準とした場合、下記(2式)に示す鋼片の炭素量(mass%)を用いた2次式で表すことができ、鋼片の再加熱時間(Mmax;min)をこの2次式から求められるCM値以下に制御することにより、鋼片外表面部のパーライト組織の炭素量や硬さの低下が抑制され、最終圧延後のレールの耐摩耗性や疲労強度の低下が抑制できることを見出した。
CM=600−120(〔mass%C〕)−60(〔mass%C〕)2
・・・・・・2
【0014】
したがって、本発明では、高炭素含有のレール鋼において、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の最大加熱温度や、ある一定温度以上に加熱される保持時間の適正化を図り、鋼片の部分的な溶融を防止しすることにより、熱間圧延時の割れや破断を防止し、さらに、レール外表面部の脱炭を抑制することにより、耐摩耗性や疲労強度の低下を抑制し、高効率に高品質なレールが製造できること知見した。
すなわち、本発明は、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の部分的な溶融を防止し、さらに、鋼片外表面部の脱炭を抑制し、高効率に高品質なレールを製造することを目的とした高炭素鋼レールの製造方法に関するものである。
【0015】
次に、本発明の限定理由について詳細に説明する。
(1)鋼レールの化学成分の限定理由
請求項1において、レール鋼の炭素量を上記請求範囲に限定した理由について詳細に説明する。
Cは、パーライト変態を促進させて、かつ、耐摩耗性を確保する有効な元素である。C量が0.80%未満では、パーライト組織中のセメンタイト相の体積比率が確保できず、耐摩耗性が維持できない。また、C量が0.80%未満では、鋼片を熱間圧延を行う再加熱工程において、上記限定の温度制御を行わなくても、鋼片の部分的な溶融やこれにともなう熱間圧延時の割れや破断が発生し難く、鋼片の外表面部において脱炭が発生した場合においても、最終圧延後のレールの耐摩耗性や疲労強度が低下し難い。したがって、本発明の製造方法を適用しても十分な効果が得られない。また、C量が1.40%を超えると、本発明の製造方法を適用しても、鋼片の部分的な溶融や圧延時の微小な割れの発生を抑制することが困難である。さらに、鋼片の外表面部の脱炭が促進され、最終圧延後のレールの耐摩耗性や疲労強度が著しく低下する。このため、C量を0.80〜1.40%に限定した。
【0016】
なお、熱間圧延を施したレールは、▲1▼高硬度化による耐摩耗性の向上、▲2▼疲労き裂や脆性き裂の発生に有害な初析セメンタイト組織の生成を防止し、耐摩耗性の高いパーライト組織を安定的に生成させるため、高温度の熱を保有するレール頭部に加速冷却を施すこと場合もある。
また、本発明製造方法において、鋼片の成分系については、上記の炭素量以外については、特に限定するものではないが、圧延したレールのパーライト組織の硬度(強化)の向上、パーライト組織の延性や靭性の向上、溶接部の熱影響部の軟化の防止、レール頭部内部の断面硬度分布の制御、初析セメンタイト組織の生成抑制を図る目的で、必要に応じて、Si,Mn,Cr,Mo,V,Nb,B,Co,Cu,Ni,Ti,Mg,Ca,Al,Zr,N等の元素を1種または2種以上を含有する成分系が望ましい。
【0017】
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・分塊あるいは連続鋳造により鋼片を製造する。さらに、この鋼片を再加熱し、熱間圧延を施すことによりレールとして製造される。
【0018】
(2)熱間圧延を行う再加熱工程における鋼片の最大加熱温度(Tmax;℃)の限定理由について
請求項1において、レール圧延用鋼片に熱間圧延を行う際の再加熱工程において、鋼片の最大加熱温度(Tmax;℃)を、鋼レールの炭素含有量から求められるCT値以下に限定した理由について詳細に説明する。
高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片に部分的な溶融が発生し、熱間圧延を行う際に、鋼片に割れが発生する要因を実験により調査した。その結果、鋼片の最高加熱温度が高いほど、また、鋼片の炭素量が高いほど、再加熱時に鋼片に部分的な溶融が発生し、圧延時に割れが発生し易いことを確認した。
そこで、鋼片の炭素量と鋼片も部分的な溶融が発生する最高加熱温度との関係を重相関により求めた。以下にその相関式(1式)を示す。
CT=1500−140(〔mass%C〕)−80(〔mass%C〕)2 ・・・・・・1
【0019】
したがって、1式は実験回帰式であり、鋼片の最高加熱温度(Tmax;℃)を鋼片の炭素量を用いた2次式から求められるCT値以下に制御することにより、再加熱時の鋼片の部分的な溶融やこれにともなう圧延時の鋼片の割れや破断を防止することができる。
【0020】
(3)熱間圧延を行う再加熱工程における鋼片の加熱保持時間(Mmax;min)の限定理由について
請求項1において、レール圧延用鋼片に熱間圧延を行う際の再加熱工程において、鋼片が1100℃以上に加熱される保持時間(Mmax;min)を、鋼レールの炭素含有量から求められるCM値以下に限定した理由について詳細に説明する。
高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の外表面部の脱炭量が増加する要因を実験により調査した。その結果、ある一定温度以上に保持される時間が長いほど、さらに、鋼片の炭素量が高いほど、再加熱時に脱炭が促進されることがわかった。
そこで、鋼片の脱炭が著しい再加熱温度1100℃以上の温度域において、鋼片の炭素量と最終圧延後のレールの諸特性が低下しない鋼片の加熱保持時間の関係を重相関により求めた。以下にその相関式(2式)を示す。
CM=600−120(〔mass%C〕)−60(〔mass%C〕)2
・・・・・・2
【0021】
したがって、2式は実験回帰式であり、鋼片の再加熱温度1100℃以上の温度域において、加熱保持時間(Mmax;min)をこの2次式から求められるCM値以下に制御することにより、鋼片外表面部のパーライト組織の炭素量や硬さの低下が抑制され、最終圧延後のレールの耐摩耗性や疲労強度の低下が抑制できる。
なお、加熱保持時間(Mmax;min)の下限値については、特に限定しないが、鋼片を均一に熟熱させ、レール圧延時の成形性を確保する観点から、250min以上とすることが望ましい。
【0022】
上記限定のレール圧延用鋼片の再加熱工程における加熱温度やその時間の制御については、直接、鋼片の外表面部を測温し、その温度や時間を制御することが望ましい。しかし、工業的にその測定が困難な場合は、加熱炉の平均的な雰囲気温度や所定の雰囲気温度における在炉時間を制御しても同様の効果が得られ、高効率に高品質なレールを製造することが可能となる。
【0023】
また、上記限定の再加熱を行い、熱間圧延を行った鋼レールの頭部金属組織は、耐摩耗性の高いパーライト組織であることが望ましい。さらに、このパーライト組織を安定的に生成させ、高硬度化を図るため、圧延後のレール頭部に加速冷却を行うことが望ましい。また、圧延後のレール頭部の硬さは、耐摩耗性を確保する目的から、Hv300〜500の範囲にあることが望ましい。
【0024】
【実施例】
次に、本発明の実施例について説明する。
表1に供試レール鋼の化学成分を示す。なお残部はFeおよび不可避的不純物である。
表2は、表1に示す供試レール鋼を用いて、本発明の製造方法でレールを製造する際の鋼片の再加熱条件(CT値、CM値、鋼片の最高加熱温度:Tmax、1100℃以上に加熱される保持時間:Mmax)、レール熱間圧延および圧延後の諸特性(熱間圧延時および圧延後の表面性状、頭表面の組織、頭表面の硬さ)を示す。さらに、本発明の製造方法で製造したレールの摩耗試験結果を示す。
【0025】
表3は、表1に示す供試レール鋼を用いて、比較製造方法でレールを製造する際の鋼片の再加熱条件(CT値、CM値、鋼片の最高加熱温度:Tmax、1100℃以上に加熱される保持時間:Mmax)、レール熱間圧延および圧延後の諸特性(熱間圧延時および圧延後の表面性状、頭表面の組織、頭表面の硬さ)を示す。さらに、本発明の製造方法で製造したレールの摩耗試験結果を示す。
【0026】
ここで、本明細書中の図について説明する。図1はレールと車輪の転動摩耗試験機の概要を示したものである。
図1において、1はレール移動用スライダーであり、この上にレール2が設置される。5はモーター4で回転する車輪3の左右の動きおよび荷重を制御する荷重負荷装置である。試験は左右に移動するレール2上を車輪3が転動する。
【0027】
レールの構成は以下のとおりである。
・本発明熱処理レール(9本) 符号A〜I
上記成分範囲内のレール鋼を、上記限定範囲内の製造方法で製造した鋼片およびレール。
・比較熱処理レール (8本) 符号J〜Q
上記成分範囲内のレール鋼を、上記限定範囲外の製造方法で製造した鋼片およびレール。
【0028】
試験条件は下記のとおり。
・転動疲労試験
試験機:転動疲労試験機(図1参照)
試験片形状
レール:136ポンドレール×2m
車 輪:AARタイプ(直径920mm)
荷重条件(重荷重鉄道再現)
ラジアル荷重:147000N(15トン)
スラスト荷重: 9800N( 1トン)
繰返し回数:10000回
潤滑条件:ドライ(乾燥状態)
【0029】
表2、表3に示すように、表1に示した高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の最大加熱温度やある一定温度以上に加熱される時間の適正化を図ることにより、上記限定範囲内の再加熱条件で製造したレール(符号:A〜I)は、比較再加熱条件で製造したレール(符号:J〜Q)と比べて、圧延時の鋼片の割れや破断を防止し、さらに、レール外表面部の脱炭を抑制し、初析フェライト組織の生成を防止することにより、耐摩耗性の低下を抑制し、高効率に高品質なレールを製造することができた。
【0030】
【表1】
【0031】
【表2】
【0032】
【表3】
【0033】
【発明の効果】
以上のように本発明によれば、高炭素含有のレール圧延用鋼片を用いて熱間圧延を行う再加熱工程において、鋼片の加熱条件の適正化を図り、圧延時の鋼片の割れや破断を防止し、さらに、鋼片外表面部の脱炭を抑制し、高効率に高品質なレールを製造することができる。
【図面の簡単な説明】
【図1】レールと車輪の転動摩耗試験機の概要を示した図。
【符号の説明】
1:レール移動用スライダー
2:レール
3:車輪
4:モーター
5:荷重負荷装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention, in the reheating step of hot rolling using a high carbon content rail rolling steel slab, in order to optimize the heating conditions of the steel slab, to prevent cracking and breakage of the steel slab during rolling, Further, the present invention relates to a method for manufacturing a high-carbon steel rail for the purpose of suppressing decarburization of an outer surface portion of a billet and manufacturing a high-quality rail with high efficiency.
[0002]
[Prior art]
In recent years, heavy-duty railways that transport coal and iron ore abroad and freight railways in Japan have been strongly promoting the loading of cargo in order to further increase the efficiency of rail transportation. In the rail, C. The abrasion resistance of the part and the head side cannot be sufficiently secured, and the reduction in rail life due to wear has become a problem. From such a background, development of a rail having wear resistance higher than that of the current high-strength rail containing eutectoid carbon has been required.
[0003]
In order to solve this problem, the present inventors have developed a rail as shown below.
{Circle around (1)} Hypereutectoid steel (C: more than 0.85% to 1.20%) is used to increase the cementite density in the lamella in the pearlite structure and to provide a rail with excellent wear resistance (Patent Document 1). .
{Circle around (2)} Using hypereutectoid steel (C: more than 0.85 to 1.20%), increase the cementite density in the lamella in the pearlite structure, and at the same time, heat-treat the head to control the hardness A rail having excellent wear resistance and a method of manufacturing the same (Patent Document 2).
The characteristics of these rails were to increase the carbon content of the steel, increase the volume ratio of the cemetite phase in the pearlite lamella, and control the hardness and structure, thereby improving the wear resistance of the pearlite structure. .
[0004]
[Patent Document 1]
(JP-A-8-144016)
[Patent Document 2]
JP-A-8-246100
[Problems to be solved by the invention]
In the invention rail steel exhibiting the pearlite structure shown in (1) above, the wear resistance can be improved by increasing the carbon content. However, the above-mentioned invention rail steel has a higher carbon content than the current high-strength rail steel containing eutectoid carbon (C: 0.80%), and thus is reheated by hot rolling using a rolling billet. In the process, if the heating temperature is not properly selected, a part of the steel slab is in a molten state. 1) The steel slab cracks during rolling, and the steel slab breaks. There is a problem in that cracks remain on the rail after rolling, which significantly lowers the product yield.
[0006]
Further, in the reheating step of performing hot rolling using the rolling slab, if the selection of the holding time during heating is inappropriate, decarburization of the outer surface portion of the slab is promoted, and after the final rolling. There has been a problem that the carbon content and hardness of the pearlite structure on the outer surface of the rail are reduced, the wear resistance of the rail head is impaired, and the fatigue strength of the rail is apt to be reduced.
[0007]
Against this background, rail steel with high carbon content prevents the slab from cracking during rolling and suppresses the decarburization of the outer surface of the rail, thereby suppressing a decrease in wear resistance and fatigue strength. However, there has been a demand for the development of a method for manufacturing a high-carbon steel rail for efficiently manufacturing a high-quality rail.
[0008]
That is, the present invention, in the reheating step of performing hot rolling using a high carbon content rail rolling steel slab, in order to optimize the maximum heating temperature of the slab or the time to be heated to a certain temperature or more, Prevent cracking and breakage of billets during rolling, and also suppress decarburization on the outer surface of the rail, thereby suppressing reductions in wear resistance and fatigue strength, and produce high-quality rails with high efficiency. It is intended for that purpose.
[0009]
[Means for Solving the Problems]
The present invention achieves the above object, and the gist thereof is as follows.
In the reheating step of performing hot rolling using a rail slab containing 0.80 to 1.40% by mass of C: 0.80 to 1.40%, the maximum heating temperature (Tmax; ° C) of the slab is determined by the steel rail. With respect to the value (CT) represented by the following formula consisting of the carbon content, Tmax ≦ CT, and the holding time (Mmax; min) in which the steel slab is heated to 1100 ° C. or higher is calculated from the carbon content of the steel rail. A method for manufacturing a high-carbon steel rail, comprising heating a steel slab satisfying Mmax ≦ CM with respect to a value (CM) represented by the following expression:
CT = 1500-140 ([mass% C])-80 ([mass% C]) 2
CM = 600-120 ([mass% C])-60 ([mass% C]) 2
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the present inventors investigated the cause of cracks occurring in the steel slab in the step of reheating the hot-rolled steel slab for rolling and performing hot rolling. As a result, the slab cracks are caused by a part of the slab melting at the segregated portion of the solidified structure near the outer surface where the heating temperature of the slab is the highest, which is opened by rolling. Further, it has been clarified that the cracks are more likely to occur as the maximum heating temperature of the slab is higher and as the carbon content of the slab is higher.
[0011]
Then, the present inventors examined by experiment the relationship between the maximum heating temperature of the steel slab where the partial melting causing the crack occurs and the carbon content of the steel slab. As a result, the maximum heating temperature at which partial melting of the steel slab occurs can be expressed by a quadratic equation using the carbon content (mass%) of the steel slab shown in the following (formula 1). By controlling the heating temperature (Tmax; ° C) to a value equal to or lower than the CT value obtained from the quadratic equation, partial melting of the steel slab in the reheated state and accompanying cracking or fracture during hot rolling are prevented. I found what I can do.
CT = 1500-140 ([mass% C])-80 ([mass% C]) 2 ... 1
[0012]
Next, the present inventors analyzed the factor which promotes decarburization of the outer surface portion of the steel slab in the reheating step of performing hot rolling using the rail slab containing high carbon. As a result, it was found that the decarburization of the outer surface portion of the slab was greatly affected by the temperature when the slab was reheated, the holding time, and the carbon content of the slab.
Then, the present inventors clarified the temperature and the holding time at the time of reheating the slab, and further, the relationship between the carbon content of the slab and the decarburization amount of the outer surface of the slab. As a result, it was found that the decarburization amount of the outer surface portion of the slab was accelerated as the time during which the slab was kept at a certain temperature or higher and the carbon content of the slab was increased.
[0013]
Furthermore, the present inventors have examined by experiment the relationship between the carbon content of the slab and the holding time at the time of reheating of the slab where the various characteristics of the rail after the final rolling are not reduced. As a result, the holding time of the slab can be expressed by a quadratic equation using the carbon content (mass%) of the slab shown in the following (Equation 2), based on the reheating temperature of 1100 ° C. or higher, By controlling the reheating time (Mmax; min) of the slab to be equal to or less than the CM value obtained from the quadratic equation, a reduction in the carbon content and hardness of the pearlite structure on the outer surface of the slab is suppressed, and the final rolling is performed. It has been found that a decrease in wear resistance and fatigue strength of the subsequent rail can be suppressed.
CM = 600-120 ([mass% C])-60 ([mass% C]) 2
・ ・ ・ ・ ・ ・ 2
[0014]
Therefore, in the present invention, in the high carbon content rail steel, in the reheating step of hot rolling using a high carbon content rail rolling steel slab, the maximum heating temperature of the steel slab, heating to a certain temperature or more By maintaining the appropriate holding time, preventing partial melting of the billet, preventing cracking and breaking during hot rolling, and suppressing decarburization of the rail outer surface. It has been found that high-quality rails can be manufactured with high efficiency by suppressing a decrease in wear resistance and fatigue strength.
That is, the present invention, in the reheating step of performing hot rolling using a high carbon content rail rolling steel slab, prevents partial melting of the steel slab, and further decarburizes the steel slab outer surface portion. The present invention relates to a method for manufacturing a high-carbon steel rail for the purpose of suppressing the occurrence of a high-quality rail with high efficiency.
[0015]
Next, the reasons for limitation of the present invention will be described in detail.
(1) Reasons for Limiting Chemical Composition of Steel Rail In
C is an effective element that promotes pearlite transformation and secures abrasion resistance. If the C content is less than 0.80%, the volume ratio of the cementite phase in the pearlite structure cannot be secured, and the wear resistance cannot be maintained. If the C content is less than 0.80%, in the reheating step of hot rolling the steel slab, even if the above-mentioned limited temperature control is not performed, partial melting of the steel slab or hot rolling associated therewith is required. It is difficult for cracks and breaks to occur at the time, and even when decarburization occurs on the outer surface of the steel slab, the abrasion resistance and fatigue strength of the rail after final rolling are not easily reduced. Therefore, even if the manufacturing method of the present invention is applied, a sufficient effect cannot be obtained. Further, if the C content exceeds 1.40%, it is difficult to suppress the partial melting of the steel slab and the generation of minute cracks during rolling even when the production method of the present invention is applied. Furthermore, decarburization of the outer surface of the billet is promoted, and the wear resistance and fatigue strength of the rail after final rolling are significantly reduced. For this reason, the C amount was limited to 0.80 to 1.40%.
[0016]
The hot-rolled rails have the following features: (1) improved wear resistance due to higher hardness; and (2) prevention of the formation of a proeutectoid cementite structure harmful to the generation of fatigue cracks and brittle cracks. In order to stably generate a pearlite structure having high abrasion, accelerated cooling may be performed on a rail head holding high-temperature heat in some cases.
In the production method of the present invention, the composition of the billet is not particularly limited except for the above-mentioned carbon content, but the hardness (strength) of the pearlite structure of the rolled rail is improved, and the ductility of the pearlite structure is improved. Si, Mn, Cr, as necessary, for the purpose of improving the hardness and toughness, preventing the heat-affected zone of the weld zone from softening, controlling the cross-sectional hardness distribution inside the rail head, and suppressing the formation of proeutectoid cementite structure. A component system containing one or more elements such as Mo, V, Nb, B, Co, Cu, Ni, Ti, Mg, Ca, Al, Zr, and N is desirable.
[0017]
Rail steel composed of the above component composition is melted in a commonly used melting furnace such as a converter, an electric furnace, etc., and the molten steel is made into a slab by ingot-bulking or continuous casting. . Further, the steel slab is reheated and hot-rolled to produce a rail.
[0018]
(2) Regarding the reason for limiting the maximum heating temperature (Tmax; ° C.) of the steel slab in the reheating step of performing hot rolling according to
In the reheating process of hot rolling using high carbon content rail rolling billets, factors that cause partial melting of the billets and cause cracks in the billets when performing hot rolling. Investigated by experiment. As a result, it was confirmed that the higher the maximum heating temperature of the steel slab and the higher the carbon content of the steel slab, the more the steel slab was partially melted during reheating, and the easier it was for cracks to occur during rolling.
Therefore, the relationship between the carbon content of the slab and the maximum heating temperature at which the slab is partially melted was determined by multiple correlation. The correlation equation (Equation 1) is shown below.
CT = 1500-140 ([mass% C])-80 ([mass% C]) 2 ... 1
[0019]
Therefore,
[0020]
(3) Regarding the reason for limiting the heating holding time (Mmax; min) of the steel slab in the reheating step of performing hot rolling, in
In a reheating step of performing hot rolling using a steel strip for rail rolling having a high carbon content, the cause of an increase in the amount of decarburization on the outer surface of the steel slab was investigated by experiments. As a result, it was found that the decarburization at the time of reheating is promoted as the time of maintaining the temperature at or above a certain temperature is longer and the carbon content of the slab is higher.
Therefore, in the temperature range of reheating temperature of 1100 ° C. or more where the decarburization of the slab is remarkable, the relationship between the carbon content of the slab and the heating and holding time of the slab that does not reduce the various characteristics of the rail after final rolling is determined by a multiple correlation. Was. The correlation equation (2 equations) is shown below.
CM = 600-120 ([mass% C])-60 ([mass% C]) 2
・ ・ ・ ・ ・ ・ 2
[0021]
Therefore,
The lower limit of the heating holding time (Mmax; min) is not particularly limited, but is preferably 250 min or more from the viewpoint of uniformly heating the steel slab and ensuring formability during rail rolling.
[0022]
Regarding the control of the heating temperature and the time in the step of reheating the steel slab for rail rolling described above, it is desirable to directly measure the temperature of the outer surface of the steel slab and control the temperature and the time. However, if the measurement is industrially difficult, the same effect can be obtained by controlling the average atmosphere temperature of the heating furnace or the furnace time at a predetermined atmosphere temperature, and a highly efficient and high quality rail can be obtained. It can be manufactured.
[0023]
Further, it is desirable that the head metal structure of the steel rail subjected to the above-described limited reheating and hot rolling is a pearlite structure having high wear resistance. Further, in order to stably generate the pearlite structure and increase the hardness, it is desirable to perform accelerated cooling on the rail head after rolling. Further, the hardness of the rail head after rolling is desirably in the range of Hv 300 to 500 for the purpose of securing wear resistance.
[0024]
【Example】
Next, examples of the present invention will be described.
Table 1 shows the chemical composition of the test rail steel. The balance is Fe and inevitable impurities.
Table 2 shows the reheating conditions (CT value, CM value, maximum heating temperature of steel slab: Tmax, Tb) of the steel slab when the rail is manufactured by the manufacturing method of the present invention using the test rail steels shown in Table 1. (Holding time to be heated to 1100 ° C. or more: Mmax), rail hot rolling and various properties after rolling (surface properties during hot rolling and after rolling, head surface texture, head surface hardness). Further, the results of the wear test of the rail manufactured by the manufacturing method of the present invention are shown.
[0025]
Table 3 shows the reheating conditions (CT value, CM value, maximum heating temperature of the steel slab: Tmax, 1100 ° C.) of the steel slab when manufacturing the rail by the comparative manufacturing method using the test rail steels shown in Table 1. The above shows the holding time during heating: Mmax), the properties of the rail after hot rolling and after rolling (surface properties during hot rolling and after rolling, texture of the head surface, hardness of the head surface). Further, the results of the wear test of the rail manufactured by the manufacturing method of the present invention are shown.
[0026]
Here, the drawings in this specification will be described. FIG. 1 shows an outline of a rolling wear tester for rails and wheels.
In FIG. 1,
[0027]
The configuration of the rail is as follows.
・ Heat treatment rail of the present invention (9) Symbols A to I
A slab and a rail manufactured from the rail steel within the above-described component range by a manufacturing method within the above-described limited range.
・ Comparative heat treatment rail (8 pieces)
A steel slab and a rail manufactured by using a rail steel within the above-mentioned component range by a manufacturing method outside the above-mentioned limited range.
[0028]
The test conditions are as follows.
-Rolling fatigue test machine: Rolling fatigue test machine (see Fig. 1)
Test piece shape rail: 136 pound rail x 2m
Wheel: AAR type (920mm in diameter)
Load conditions (heavy load railway reproduction)
Radial load: 147000N (15 tons)
Thrust load: 9800N (1 ton)
Number of repetitions: 10000 times Lubrication conditions: dry (dry state)
[0029]
As shown in Tables 2 and 3, in the reheating step of performing hot rolling using the high carbon content rail rolling steel slabs shown in Table 1, the steel slabs were heated to a maximum heating temperature or a certain temperature or higher. By adjusting the time to be performed, the rails (codes: A to I) manufactured under the reheating conditions within the above-described limited range are compared with the rails (codes: J to Q) manufactured under the comparative reheating conditions. Prevents cracking and breakage of the billet during rolling, suppresses decarburization of the outer surface of the rail, and prevents the formation of proeutectoid ferrite structure, thereby suppressing a decrease in wear resistance and achieving high efficiency A high quality rail could be manufactured.
[0030]
[Table 1]
[0031]
[Table 2]
[0032]
[Table 3]
[0033]
【The invention's effect】
As described above, according to the present invention, in the reheating step of performing hot rolling using a steel strip for rail rolling having a high carbon content, in order to optimize the heating conditions of the steel slab, cracking of the steel slab during rolling In addition, it is possible to manufacture a high-quality rail with high efficiency by preventing cracks and breaks and suppressing decarburization of the outer surface of the billet.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a rolling wear tester for rails and wheels.
[Explanation of symbols]
1: Slider for rail movement 2: Rail 3: Wheel 4: Motor 5: Load device
Claims (1)
CT=1500−140(〔mass%C〕)−80(〔mass%C〕)2
CM=600−120(〔mass%C〕)−60(〔mass%C〕)2 In the reheating step when hot rolling is performed on the rail slab containing 0.80 to 1.40% by mass C: 0.80 to 1.40%, the maximum heating temperature (Tmax; ° C.) of the slab is changed to the steel rail. With respect to the value (CT) represented by the following formula consisting of the carbon content of Tmax, Tmax ≦ CT, and the holding time (Mmax; min) during which the slab is heated to 1100 ° C. or more is determined by the carbon content of the steel rail. A method for manufacturing a high carbon steel rail, comprising heating a steel slab so that Mmax ≦ CM with respect to a value (CM) represented by the following expression consisting of an amount.
CT = 1500-140 ([mass% C])-80 ([mass% C]) 2
CM = 600-120 ([mass% C])-60 ([mass% C]) 2
Priority Applications (12)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2003011701A JP4272437B2 (en) | 2003-01-20 | 2003-01-20 | High carbon steel rail manufacturing method |
CNB03800576XA CN1304618C (en) | 2002-04-05 | 2003-04-04 | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
CA2451147A CA2451147C (en) | 2002-04-05 | 2003-04-04 | Pearlitic steel rail excellent in wear resistance and ductility and method for producing the same |
AU2003236273A AU2003236273B2 (en) | 2002-04-05 | 2003-04-04 | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
CA2749503A CA2749503C (en) | 2002-04-05 | 2003-04-04 | Pearlitic steel rail excellent in wear resistance and ductility and method for producing the same |
EP03745927A EP1493831A4 (en) | 2002-04-05 | 2003-04-04 | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
EP11175030A EP2388352A1 (en) | 2002-04-05 | 2003-04-04 | Pearlitic steel rail excellent in wear resistance and ductility and method for producing the same |
US10/482,753 US20040187981A1 (en) | 2002-04-05 | 2003-04-04 | Pealite base rail excellent in wear resistance and ductility and method for production thereof |
PCT/JP2003/004364 WO2003085149A1 (en) | 2002-04-05 | 2003-04-04 | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
BRPI0304718A BRPI0304718B1 (en) | 2002-04-05 | 2003-04-04 | method for producing an excellent perlite steel rail for wear resistance and ductility |
HK05101368A HK1068926A1 (en) | 2002-04-05 | 2005-02-18 | Pealite based rail excellent in wear resistance and ductility and method for production thereof |
US11/780,166 US7972451B2 (en) | 2002-04-05 | 2007-07-19 | Pearlitic steel rail excellent in wear resistance and ductility and method for producing same |
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JP2003011701A JP4272437B2 (en) | 2003-01-20 | 2003-01-20 | High carbon steel rail manufacturing method |
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JP4272437B2 JP4272437B2 (en) | 2009-06-03 |
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Cited By (6)
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DE102010016282A1 (en) * | 2010-03-31 | 2011-10-06 | Max-Planck-Institut Für Eisenforschung GmbH | Ultrahigh-strength and wear-resistant quasi-eutectoid rail steels |
CN111809027A (en) * | 2020-07-20 | 2020-10-23 | 武汉钢铁有限公司 | Heating method of copper-containing high-carbon corrosion-resistant steel rail |
CN113789433A (en) * | 2021-09-18 | 2021-12-14 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing thickness of decarburization layer of steel rail |
CN113817911A (en) * | 2021-09-18 | 2021-12-21 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for preparing steel rail with low decarburized layer |
US11492689B2 (en) * | 2018-03-30 | 2022-11-08 | Jfe Steel Corporation | Rail and method for manufacturing same |
US11566307B2 (en) | 2018-03-30 | 2023-01-31 | Jfe Steel Corporation | Rail |
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2003
- 2003-01-20 JP JP2003011701A patent/JP4272437B2/en not_active Expired - Fee Related
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE102010016282A1 (en) * | 2010-03-31 | 2011-10-06 | Max-Planck-Institut Für Eisenforschung GmbH | Ultrahigh-strength and wear-resistant quasi-eutectoid rail steels |
US11492689B2 (en) * | 2018-03-30 | 2022-11-08 | Jfe Steel Corporation | Rail and method for manufacturing same |
US11566307B2 (en) | 2018-03-30 | 2023-01-31 | Jfe Steel Corporation | Rail |
CN111809027A (en) * | 2020-07-20 | 2020-10-23 | 武汉钢铁有限公司 | Heating method of copper-containing high-carbon corrosion-resistant steel rail |
CN113789433A (en) * | 2021-09-18 | 2021-12-14 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for reducing thickness of decarburization layer of steel rail |
CN113817911A (en) * | 2021-09-18 | 2021-12-21 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for preparing steel rail with low decarburized layer |
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