JP2007513259A - Steel wire for cold heading having excellent low temperature impact characteristics and method for producing the same - Google Patents

Steel wire for cold heading having excellent low temperature impact characteristics and method for producing the same Download PDF

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JP2007513259A
JP2007513259A JP2006543738A JP2006543738A JP2007513259A JP 2007513259 A JP2007513259 A JP 2007513259A JP 2006543738 A JP2006543738 A JP 2006543738A JP 2006543738 A JP2006543738 A JP 2006543738A JP 2007513259 A JP2007513259 A JP 2007513259A
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steel
steel wire
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アン,スン−テ
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サンワ・スチール・カンパニー・リミテッド
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Priority to PCT/KR2004/003107 priority patent/WO2005059192A1/en
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18Hardening; Quenching with or without subsequent tempering
    • C21D1/25Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0093Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Abstract

本発明は、低温衝撃特性の優れる冷間圧造用鋼線とその製造方法を提供するためのものである。本発明の鋼線は、C 0.10〜0.40wt%、Si 1.0wt%以下、Mn
0.30〜2.0wt%、P 0.03wt%以下、S 0.03wt%以下が含まれ、残部がFeと不純物からなる。本発明の鋼線は、オーステナイト結晶粒の大きさが5〜20μmであり、−40℃での衝撃吸収エネルギーが60J/cm2以上であり、引張強度が70〜130kgf/mm2である。本発明の冷間成型用鋼材は、従来の球状化焼鈍材や非調質鋼材に比べて−40℃の低温で格段に高い衝撃靭性特性を示す。
The present invention is to provide a steel wire for cold heading having excellent low-temperature impact characteristics and a method for producing the same. The steel wire of the present invention has C 0.10 to 0.40 wt%, Si 1.0 wt% or less, Mn
It contains 0.30 to 2.0 wt%, P 0.03 wt% or less, and S 0.03 wt% or less, with the balance being Fe and impurities. The steel wire of the present invention has an austenite grain size of 5 to 20 μm, an impact absorption energy at −40 ° C. of 60 J / cm 2 or more, and a tensile strength of 70 to 130 kgf / mm 2 . The steel material for cold forming according to the present invention exhibits significantly higher impact toughness characteristics at a low temperature of −40 ° C. than conventional spheroidized annealing materials and non-tempered steel materials.

Description

本発明は、比較的高い強度を有する各種機械構造用部品に適用される各種ボルト類、シャフト及び建築用PC鋼棒などの材料として使われる鋼線や鋼棒(以下、‘鋼線’と称する)に関し、より詳しくは、冷間鍛造及び冷間転造プロセスに適用可能で、かつ、使用の際の低温靭性を向上させた低温衝撃特性の優れる冷間圧造用鋼線及びその製造方法に関する。   The present invention is a steel wire or steel rod (hereinafter referred to as “steel wire”) used as a material for various bolts, shafts and PC steel bars for construction, which are applied to various mechanical structural parts having relatively high strength. More particularly, the present invention relates to a steel wire for cold heading that can be applied to cold forging and cold rolling processes and that has improved low temperature toughness during use and has excellent low temperature impact characteristics and a method for producing the same.
従来の冷間塑性用鋼材としては球状化焼鈍材と非調質鋼材などが知られている。
球状化焼鈍材は、ボルトなどの最終製品を製作するために使用される場合、冷間鍛造工程後に要求される望ましい特性としての引張強度を得るために別途の焼入れ/焼戻しを行なわなければならないという点が問題であり、これは製造を複雑化させ、結果製造コストが増加する。
As conventional cold plastic steel materials, spheroidized annealing materials and non-heat treated steel materials are known.
When spheroidized annealed materials are used to produce finished products such as bolts, they must be separately quenched / tempered to obtain the desired tensile strength required after the cold forging process. This is a problem, which complicates manufacturing and results in increased manufacturing costs.
一方、非調質鋼材は70年代中半に開発されて以来、日本及びヨーロッパを中心に自動車及び産業機械部品などにその使用量が増加されている鋼材である。合金設計を適切にし、製鉄所などでの熱間圧延の間、冷却条件及び圧延条件を調節して材料の組織制御がなされるようにすることで、後続の熱処理(焼入れ/焼戻し)がなくても高強度を示しつつ、冷間鍛造工程の実施が可能である。したがって、非調質鋼材は製造工程の単純化と製造費用の低減を図ることができる長所がある。   On the other hand, the non-heat treated steel material has been used in automobiles and industrial machine parts mainly in Japan and Europe since its development in the middle of the 1970s. Appropriate alloy design and adjustment of cooling and rolling conditions during hot rolling at steelworks, etc., so that the structure of the material can be controlled, so that there is no subsequent heat treatment (quenching / tempering). However, it is possible to perform a cold forging process while exhibiting high strength. Therefore, non-tempered steel has the advantages that the manufacturing process can be simplified and the manufacturing cost can be reduced.
非調質鋼材の代表的な一例として、日本公開特許公報昭59−136420号ではマンガンの含有量が高く、通常の機械構造用炭素鋼に、析出硬化元素としてのバナジウムを少量添加して、熱間鍛造後の冷却工程中にフェライト基地組織内に炭窒化物を少量析出させることが開示されている。これにより強度が増加し、したがって、後続する焼入れ/焼戻し工程の省略が可能である。しかしながら、前記非調質鋼材は、冷間成型性と切削加工性に乏しく、冷間加工用材料には適していないという短所がある。   As a typical example of non-tempered steel material, Japanese Patent Publication No. Sho 59-136420 has a high manganese content, and a small amount of vanadium as a precipitation hardening element is added to ordinary carbon steel for machine structural use. It is disclosed that a small amount of carbonitride is precipitated in the ferrite matrix structure during the cooling step after the forging. This increases the strength and therefore allows the subsequent quenching / tempering step to be omitted. However, the non-tempered steel material has a disadvantage that it is poor in cold formability and cutting workability and is not suitable as a material for cold work.
非調質鋼材の他の例として、日本公開特許公報平7−54940号にはボルトを製造する技術が開示されている。この技術においては、熱間ワイヤロッドの圧延後、冷間圧造工程を通じて特定の形状の部品を製造する過程において、冷間加工性の向上のために、炭素含有量を低めて、組織微細化を通じた強度と靭性の改善のためにニオビウムを少量添加し、熱間圧延後の冷却過程で加熱処理を行なう。ところが、前記非調質鋼材で製作されたボルトは軸方向への引張及び圧縮応力が反復的に加えられる環境での使用寿命に問題があるため、自動車などの部品には適していない。   As another example of the non-heat treated steel material, Japanese Laid-Open Patent Publication No. 7-54940 discloses a technique for manufacturing a bolt. In this technology, after rolling a hot wire rod, in the process of manufacturing a part with a specific shape through a cold forging process, the carbon content is reduced and the structure is refined to improve cold workability. In order to improve the strength and toughness, a small amount of niobium is added and heat treatment is performed in the cooling process after hot rolling. However, the bolt made of the non-heat treated steel material has a problem in the service life in an environment where tensile and compressive stress in the axial direction is repeatedly applied, and is not suitable for parts such as automobiles.
更に他の従来の非調質鋼材の一例として、米国特許第5,554,233号には強度増加のための強化元素を含むビレットを順次的な熱間鍛造及び制御冷却を通じてワイヤロッドに加工することにおいて、最後の熱間鍛造過程でオーステナイトの粒子微細化がなされるようにして、後続する冷却工程中に微細なベイナイト構造が生成されるようにしている。前記特許の非調質鋼材は、微細ベイナイト構造により強度と靭性が増加し、ボルトを製造するための冷間圧造工程中に付加的な熱処理を必要とせず、残留圧縮応力を有するという特徴がある。   As another example of conventional non-heat treated steel, US Pat. No. 5,554,233 processes a billet containing a strengthening element for increasing strength into a wire rod through sequential hot forging and controlled cooling. In this regard, the fine austenite particles are refined in the final hot forging process so that a fine bainite structure is generated during the subsequent cooling step. The non-tempered steel material of the above patent has the characteristics that the strength and toughness are increased by the fine bainite structure, and no additional heat treatment is required during the cold forging process for manufacturing the bolt, and it has a residual compressive stress. .
前記特許は、低温靭性面において、衝撃吸収エネルギーは−40℃で10J/cm2程度であることを開示している。 The patent discloses that in terms of low temperature toughness, the impact absorption energy is about 10 J / cm 2 at −40 ° C.
一方、酷寒地や極地における装置や車両などに使われる部品には、低温衝撃靭性に優れる材料が要求されるが、前記特許の鋼材を含む従来の非調質鋼材は十分な低温衝撃靭性を有しておらず、低温衝撃特性の優れる新たな鋼材を開発する必要性がある。
日本公開特許公報昭59−136420号 日本公開特許公報平7−54940号 米国特許第5,554,233号
On the other hand, materials used in equipment and vehicles in extremely cold and polar regions are required to have materials with excellent low-temperature impact toughness, but conventional non-tempered steel materials including the above-mentioned steel materials have sufficient low-temperature impact toughness. There is a need to develop a new steel material with excellent low-temperature impact characteristics.
Japanese Patent Publication No. 59-136420 Japanese Published Patent Publication No. 7-54940 US Pat. No. 5,554,233
本発明は、前記従来の冷間圧造用鋼材の短所と問題点を勘案してなされたものであって、使用の際の低温靭性が大きく向上され、低温衝撃吸収エネルギー値の優れる冷間圧造用鋼線及びその製造方法を提供することを目的とする。   The present invention was made in consideration of the disadvantages and problems of the conventional cold forging steel materials, and the cold toughness for use in cold forging is greatly improved in low temperature toughness during use and excellent in low temperature shock absorption energy value. It aims at providing a steel wire and its manufacturing method.
本発明の発明者は、前記の目的が達成できる新たな鋼材の開発のために多様な試みと繰り返された実験を遂行した結果、次のような発見に至った。鋼線に対して、低温(−40℃)での衝撃試験を行った場合、当該鋼線は、従来の方法(球状化焼鈍後、焼入れ/焼戻し工程)に比べて優れた低温衝撃吸収エネルギーを示すということが見られ得る。当該鋼線を製造する方法は、焼入れ可能な通常の機械構造用炭素鋼を、Ac3変態点以上の温度に急速加熱して、オーステナイトの結晶粒のサイズを5〜20μmに制限する工程と、水または油に加熱した鋼材を焼入れする工程と、下記の式(1)によって定義される焼戻しパラメータ(P)が21,800〜30,000の範囲で、引張強度が70〜130kgf/mm2となるような焼戻し条件の下で焼入れされた鋼材を焼戻す工程とを含む。 The inventor of the present invention has made various discoveries and repeated experiments for the development of a new steel material that can achieve the above object, and as a result, has found the following findings. When an impact test is performed on a steel wire at a low temperature (−40 ° C.), the steel wire has excellent low-temperature impact absorption energy compared to the conventional method (after spheroidizing annealing and quenching / tempering step). It can be seen that it shows. The method of manufacturing the steel wire includes a step of rapidly heating a normal hardenable carbon steel for mechanical structure to a temperature equal to or higher than the Ac3 transformation point to limit the size of austenite crystal grains to 5 to 20 μm, and water. Alternatively, the step of quenching the steel heated to oil and the tempering parameter (P) defined by the following formula (1) is in the range of 21,800 to 30,000, and the tensile strength is 70 to 130 kgf / mm 2. Tempering a steel material quenched under such tempering conditions.
P=1.8×(T+273)×(14.44+logt) …式(1)
ここで、Tは焼戻し温度(℃)、tは焼戻し時間(秒)
言い換えると、本発明は、オーステナイトの結晶粒の大きさが5〜20μmの範囲で、極めて微細になるように材料を焼入れしつつ、焼戻しパラメータが21,800〜30,000の範囲で引張強度が70〜130kgf/mm2になるような焼戻し条件下で当該材料を焼戻す場合、得られる材料は、高強度であるにも拘わらず、−40℃の低温でシャルピー衝撃吸収エネルギーが60J/cm2以上であって従来の鋼材に比べて優れる衝撃特性を示すことに特徴がある。
P = 1.8 * (T + 273) * (14.44 + logt) ... Formula (1)
Where T is the tempering temperature (° C.) and t is the tempering time (seconds).
In other words, the present invention has a tensile strength in the range of 21,800 to 30,000 while quenching the material so that the austenite grain size is in the range of 5 to 20 μm and extremely fine. When the material is tempered under a tempering condition of 70 to 130 kgf / mm 2 , the Charpy impact absorption energy is 60 J / cm 2 at a low temperature of −40 ° C. even though the obtained material has high strength. It is the above and is characterized by exhibiting superior impact characteristics compared to conventional steel materials.
本発明に従い、前記のような特徴を有する鋼材を製造するためには、機械構造用鋼材の中でも、特定の成分を含む鋼材が適切に焼入れされ、焼戻しされなければならない。これに関し、本発明の鋼材を製造するために必要な鋼材の化学成分と熱処理方法は次の通りである。   In order to produce a steel material having the above-described characteristics according to the present invention, a steel material containing a specific component must be appropriately quenched and tempered among steel materials for mechanical structure. In this regard, the chemical components of the steel material and the heat treatment method necessary for producing the steel material of the present invention are as follows.
まず、本発明に係る鋼材は、ほとんどC−Si−Mnの成分を含み、当該C−Si−Mn成分は、0.10〜0.40wt%のC、1.0wt%以下のSi、0.30〜2.0wt%のMnを含み、鋼材の残りの成分はFeと不純物である。必要に応じて当該鋼材はさらに、0.05〜2.0wt% Cr、0.05〜1.5wt% Mo及び0.0003〜0.0050wt% Bからなる群から選択される少なくとも1つの成分を含む。これらの成分範囲を限定した理由は次の通りである。   First, the steel material according to the present invention mostly includes a C—Si—Mn component, and the C—Si—Mn component includes 0.10 to 0.40 wt% C, 1.0 wt% or less of Si, 0. It contains 30 to 2.0 wt% Mn, and the remaining components of the steel are Fe and impurities. If necessary, the steel material further contains at least one component selected from the group consisting of 0.05 to 2.0 wt% Cr, 0.05 to 1.5 wt% Mo, and 0.0003 to 0.0050 wt% B. Including. The reason for limiting these component ranges is as follows.
C:0.10〜0.40wt%
Cは焼入れ工程の間の強度の増加のために不可欠な最も重要な元素であって、カーバイドを生成させて強度を増大させるが、衝撃遷移温度を上昇させ、破壊エネルギーを減少させる等、ノッチ靭性に悪影響を及ぼす有力な合金元素の1つである。その含量が0.10
wt%未満では焼入れによる硬化効果が低いものであり、0.40wt%を超過することになれば、多量のカーバイドが析出して衝撃靭性の低下をもたらすことになる。
C: 0.10 to 0.40 wt%
C is the most important element indispensable for increasing the strength during the quenching process. It generates carbide to increase the strength, but increases the impact transition temperature, reduces the fracture energy, etc. It is one of the powerful alloying elements that adversely affect Its content is 0.10
If it is less than wt%, the hardening effect by quenching is low, and if it exceeds 0.40 wt%, a large amount of carbide precipitates, resulting in a reduction in impact toughness.
Si:1.0wt%以下
Siは鋼の脱酸素のために使用される元素であって、固溶強化により強度を向上させる。Siの含量が1.0wt%を超過すればSiがカーバイド析出物中で多量固溶されるため、焼戻し工程の際、炭素の動きを妨害することによって、カーバイドが球形化されることを妨害するため、衝撃靭性を低下させる。したがって1.0wt%以下に制限する必要がある。
Si: 1.0 wt% or less Si is an element used for deoxidizing steel, and improves the strength by solid solution strengthening. If the Si content exceeds 1.0 wt%, Si is dissolved in a large amount in the carbide precipitate, and therefore, during the tempering process, the movement of carbon is prevented, thereby preventing the carbide from being spheroidized. Therefore, impact toughness is reduced. Therefore, it is necessary to limit to 1.0 wt% or less.
Mn:0.30〜2.0wt%
Mnは固溶強化のための元素であって、C及びSiの過剰使用によってもたらされる衝撃靭性の低下を避けるために、および低いC、Si含有量を有する鋼の強度低下を補うための元素である。これらを達成するためには、少なくとも0.30wt%の量でMnを使用する必要があるが、Mnが過剰添加されれば靭性と変形抵抗を増大させるので、Mnの含有量は2.0wt%を超過しないようにする。
Mn: 0.30 to 2.0 wt%
Mn is an element for solid solution strengthening, in order to avoid a decrease in impact toughness caused by excessive use of C and Si, and to compensate for a decrease in strength of a steel having a low C and Si content. is there. In order to achieve these, it is necessary to use Mn in an amount of at least 0.30 wt%, but if Mn is added excessively, toughness and deformation resistance are increased, so the Mn content is 2.0 wt%. Do not exceed.
Cr:0.05〜2.0wt%
Crは強度と焼入れ硬度及び靭性の向上のために使用される元素である。Crの含有量が0.05wt%未満では前記物性の向上効果が微弱である。Crは比較的高価であるので、2.0wt%を超過することになれば経済効率が低下する。したがって、Cr含有量の下限値を0.05wt%にし、上限値を2.0wt%に設定する。
Cr: 0.05-2.0 wt%
Cr is an element used for improving strength, quenching hardness and toughness. When the Cr content is less than 0.05 wt%, the effect of improving the physical properties is weak. Since Cr is relatively expensive, if it exceeds 2.0 wt%, the economic efficiency is lowered. Therefore, the lower limit value of the Cr content is set to 0.05 wt%, and the upper limit value is set to 2.0 wt%.
Mo:0.05〜1.5wt%
Moの使用による効果はCrの効果とほとんど同一である。Moの含有量が0.05wt%未満では効果が微弱であり、1.5wt%を超過することになれば冷間加工に関して変形抵抗が増大するので、その含有量は1.5wt%以下に設定する。
Mo: 0.05 to 1.5 wt%
The effect of using Mo is almost the same as that of Cr. If the Mo content is less than 0.05 wt%, the effect is weak, and if it exceeds 1.5 wt%, deformation resistance increases with respect to cold working, so the content is set to 1.5 wt% or less. To do.
B:0.0003〜0.0050wt%
Bは硬化能力を向上させるための元素である。Bの含有量が0.0003wt%未満ではBの効果は弱い。一方、0.0050wt%を超過すれば、硬化能力は低下する。一方、Bは使用中に組織の内部でNと結合してBNを形成し得、これは粒界を脆化させる原因となる。したがって、Nと親和力がBより大きいTiを0.01〜0.05wt%、Bと共に添加してBの使用効果を高めることが一般的である。さらに、Tiと同一の作用をするZr、Nb、またはAlの一種以上を添加することも好ましい。
B: 0.0003 to 0.0050 wt%
B is an element for improving the curing ability. When the B content is less than 0.0003 wt%, the effect of B is weak. On the other hand, if it exceeds 0.0050 wt%, the curing ability is lowered. On the other hand, B can combine with N inside the structure during use to form BN, which causes embrittlement of the grain boundaries. Therefore, it is common to increase the effect of using B by adding 0.01 to 0.05 wt% of Ti with an affinity for N greater than B together with B. Furthermore, it is also preferable to add one or more of Zr, Nb, or Al that have the same action as Ti.
PとSは鋼の不可避な不純物元素であって、焼戻し工程の間、結晶粒界の偏析をもたらし、衝撃靭性を低下させる。さらに冷間加工工程の間、変形率を低下させるので、できる限りその含量が各々0.030wt%以下に制限する必要がある。   P and S are unavoidable impurity elements of steel and cause segregation of grain boundaries during the tempering process, thereby reducing impact toughness. Furthermore, since the deformation rate is lowered during the cold working process, it is necessary to limit the content to 0.030 wt% or less as much as possible.
上記のような組成を有する鋼材を使用して本発明の鋼材を製造する方法について、本発明者はさらなる研究を行った結果、焼入れ/焼戻しが行われた鋼材において、低温衝撃吸収エネルギーに影響を及ぼす因子としてはオーステナイトの結晶粒の大きさと焼戻し条件(析出したカーバイドの分布状態、形状及びフェライトの比率等)が非常に重要であることを発見するに至った。   As a result of further research on the method of manufacturing the steel material of the present invention using the steel material having the above composition, the present inventor has an effect on the low-temperature impact absorption energy in the steel material that has been quenched / tempered. It has been found that the austenite crystal grain size and tempering conditions (distributed carbide distribution, shape, ferrite ratio, etc.) are very important factors.
本発明の方法において、焼入れ工程後のオーステナイト結晶粒の大きさを5〜20μmに限定した理由は、次のとおりである。実験を繰返した結果、大きさが20μmを超過する場合、−40℃の低温で顕著な衝撃靭性の低下を確認することができる。また、5μm未満の大きさを有する結晶粒の製造は一般的な焼入れ/焼戻し工程によっては困難である
ことが確認できる。
In the method of the present invention, the reason why the size of the austenite crystal grains after the quenching step is limited to 5 to 20 μm is as follows. As a result of repeating the experiment, when the size exceeds 20 μm, a significant decrease in impact toughness can be confirmed at a low temperature of −40 ° C. Moreover, it can be confirmed that the production of crystal grains having a size of less than 5 μm is difficult by a general quenching / tempering process.
次に、本発明に従い、低温(−40℃)で優れた衝撃吸収エネルギーを有する焼入れ/焼戻しした鋼線を製造する場合において、焼戻し条件を前記(1)式のパラメータの範囲が21,800〜30,000に限定される理由は下記の通りである。   Next, in the case of producing a quenched / tempered steel wire having excellent impact absorption energy at a low temperature (−40 ° C.) according to the present invention, the parameter range of the formula (1) ranges from 21,800 to The reason for being limited to 30,000 is as follows.
本発明者は、JIS G 4105 SCM420とJIS G 4051 S22Cの直径15mmワイヤロッドを、各ワイヤロッドが直径13.7mmとなるように引出し、オーステナイトの結晶粒の大きさが8〜14μmになるように、引出されたワイヤをAc3点以上に急速加熱し、水または油中で加熱したワイヤを焼入れし、そして引張強度70〜130kgf/mm2の範囲内で加熱温度及び加熱時間を調節して焼戻しパラメータを変化させて焼入れしたワイヤを焼戻し処理をした。さらに、得られた鋼線に対してVノッチ(V−Notch)加工を行って、−40℃でシャルピー衝撃試験を実施した。その結果を図1に表わした。 The present inventor draws out 15 mm diameter wire rods of JIS G 4105 SCM420 and JIS G 4051 S22C so that each wire rod has a diameter of 13.7 mm so that the size of the austenite crystal grains is 8 to 14 μm. Tempering parameters by rapidly heating the drawn wire to Ac3 point or higher, quenching the wire heated in water or oil, and adjusting the heating temperature and heating time within the range of tensile strength 70-130 kgf / mm 2 The tempered wire was subjected to tempering treatment by changing. Furthermore, V-notch processing was performed on the obtained steel wire, and a Charpy impact test was performed at −40 ° C. The results are shown in FIG.
図1に示すように、焼戻しパラメータ値が21,800〜30,000である場合には−40℃での衝撃吸収エネルギーが60J/cm2以上であった。 As shown in FIG. 1, when the tempering parameter value was 21,800 to 30,000, the impact absorption energy at −40 ° C. was 60 J / cm 2 or more.
ここで、前記衝撃吸収エネルギーが60J/cm2以上に限定される理由は、SCM435の球状化焼鈍材を冷間鍛造し、焼入れおよび焼戻し処理して従来の高張力ボルトを製造する場合、−40℃で衝撃吸収エネルギーが約60J/cm2であるからである。 Here, the reason why the impact absorption energy is limited to 60 J / cm 2 or more is that when a conventional high-tensile bolt is manufactured by cold forging, quenching and tempering a spheroidized annealed material of SCM435, −40 This is because the shock absorption energy at 60 ° C. is about 60 J / cm 2 .
21,800〜30,000の焼戻しパラメータは、材料の成分に応じ目的とする引張強度の範囲内で焼入れ及び焼戻し工程の加熱温度、加熱時間、加熱速度などを適切に制御することにより保障し得る。   Tempering parameters of 21,800 to 30,000 can be ensured by appropriately controlling the heating temperature, heating time, heating rate, etc. of the quenching and tempering processes within the range of the target tensile strength depending on the composition of the material. .
したがって、焼入れ/焼戻しした鋼線の低温衝撃靭性に関していえば、微細な結晶粒と適切な組成を有する焼入れされた材料が、(1)式の焼戻しパラメータが21,800〜30,000であるように焼戻しされる場合、−40℃の低温で優れた衝撃吸収エネルギーを有する鋼線が製造できることが明らかである。したがって、このことは低温衝撃特性の優れる焼入れ/焼戻し鋼線の製造の過程において非常に重要な因子であることが理解し得る。   Therefore, with regard to the low temperature impact toughness of the quenched / tempered steel wire, the quenched material having fine crystal grains and appropriate composition seems to have a tempering parameter of formula (1) of 21,800-30,000. It is clear that a steel wire having excellent shock absorption energy can be produced at a low temperature of -40 ° C. when tempered. Therefore, it can be understood that this is a very important factor in the process of manufacturing a quenched / tempered steel wire having excellent low-temperature impact properties.
本発明に従う鋼線とその製造方法のよりよい理解は、以下の例示された実施例を通して得ることができるが、当該実施例は本発明の限定として解釈されるべきではない。   A better understanding of the steel wire according to the present invention and the method of making the same can be gained through the following illustrated examples, which should not be construed as a limitation of the present invention.
次の表1の化学組成(wt%)を有し、熱間圧延された直径16mmのワイヤーロッドを直径14.7mmになるように伸線した後、連続プロセスからなる高周波誘導加熱装置を利用して焼入れ/焼戻しを行った。この際、オーステナイトの結晶粒の大きさが5〜20μm、引張強度が70〜140kgf/mm2になるように加熱温度、加熱時間及び加熱速度を調節して焼戻しパラメータを変更させながら各々の試料を製作した。 A wire rod having a chemical composition (wt%) shown in Table 1 and hot-rolled and having a diameter of 16 mm is drawn to a diameter of 14.7 mm, and then a high-frequency induction heating apparatus composed of a continuous process is used. Quenching / tempering was performed. At this time, each sample was adjusted while changing the tempering parameters by adjusting the heating temperature, heating time and heating rate so that the austenite crystal grain size was 5 to 20 μm and the tensile strength was 70 to 140 kgf / mm 2. Produced.
上記のような条件で製作された各試料を加工してJIS Z 2202の4号試験片(Vノッチ、10mm×10mm)を形成して、当該試験片についてJIS Z 2242に従い−40℃の低温でシャルピー衝撃試験を実施して衝撃吸収エネルギー値を求めた。その結果を次の表2に表わした。   Each sample manufactured under the above conditions is processed to form a JIS Z 2202 No. 4 test piece (V notch, 10 mm × 10 mm), and the test piece is subjected to a low temperature of −40 ° C. according to JIS Z 2242. A Charpy impact test was performed to determine the impact absorption energy value. The results are shown in Table 2 below.
表2から、本発明の試料はオーステナイト結晶粒の大きさが5〜20μm、焼戻しパラメータが21,800〜30,000であるように熱処理される場合、−40℃の低温で60J/cm2以上の優れた衝撃吸収エネルギーを有し、したがって優れた低温衝撃靭性を保障することがわかる。さらに、引張強度が同一であってもオーステナイトの結晶粒の大きさまたは焼戻しパラメータ値が異なれば、衝撃吸収エネルギー値は顕著に異なり得ることもわかる。 From Table 2, when the sample of the present invention is heat-treated so that the austenite grain size is 5 to 20 μm and the tempering parameter is 21,800 to 30,000, it is 60 J / cm 2 or more at a low temperature of −40 ° C. It can be seen that it has excellent shock absorption energy and thus ensures excellent low temperature impact toughness. It can also be seen that even if the tensile strength is the same, if the size of the austenite crystal grains or the tempering parameter value is different, the impact absorption energy value can be significantly different.
さらに、本発明の優秀性を立証するために、本発明の材料と従来の球状化焼鈍材及び非調質鋼材を使用してJIS規格に従い、9T級のボルトを製作し、当該ボルトから試験片を採取した。当該試験片を−40℃で加工してVノッチを形成し、10×10mmのサイズの標準試験片を作製した。当該標準試験片についてシャルピー衝撃試験を実施して比較した。その結果は図2の通りである。   Further, in order to prove the superiority of the present invention, a 9T-class bolt is manufactured according to the JIS standard using the material of the present invention, a conventional spheroidized annealing material and a non-heat treated steel material, and a test piece is prepared from the bolt. Were collected. The test piece was processed at −40 ° C. to form a V-notch, and a standard test piece having a size of 10 × 10 mm was produced. The standard test pieces were subjected to a Charpy impact test and compared. The result is as shown in FIG.
この際、本発明の材料としてSCM 420(JIS G 4105)を使用して本発明の製造方法に従い、製造された9T級のワイヤロッドを、ボルトを製造するために冷間鍛造及び転造工程に供した。従来の方法に従い、SCM 435(JIS G 4105)を760℃で6時間加熱することによって、球状化焼鈍された上記従来の球状化焼鈍材に関していえば、9T級のボルトを製造するために、冷間鍛造工程と転造工程を行い、焼入れ/焼戻しした。上記従来の非調質鋼材については、SMn 433(JIS G 4106)を含むビレットを熱間圧延してワイヤロッドにする際、9T級の引張強度を有する非調質鋼材を製造するために、圧延工程と冷却工程を制御して、組織を微細にした。得られた非調質鋼材に冷間鍛造及び転造工程を施し、ボルトを製造した。   At this time, SCM 420 (JIS G 4105) is used as the material of the present invention, and the manufactured 9T-class wire rod is subjected to a cold forging and rolling process in order to manufacture a bolt. Provided. According to the conventional method, SCM 435 (JIS G 4105) is heated at 760 ° C. for 6 hours to produce a 9T-class bolt for the above-mentioned conventional spheroidized annealed material. The forging process and the rolling process were performed and quenched / tempered. For the conventional non-tempered steel material, when a billet containing SMn 433 (JIS G 4106) is hot-rolled into a wire rod, rolling is performed in order to produce a non-tempered steel material having a tensile strength of 9T class. The process and cooling process were controlled to refine the structure. The obtained non-tempered steel was subjected to cold forging and rolling processes to produce bolts.
前記図2の結果から、本発明の材料を使用して製造されたボルトは、従来の球状化焼鈍材や非調質鋼材を使用したボルトに比べて優れた衝撃靭性を有していることがわかる。   From the results of FIG. 2, the bolt manufactured using the material of the present invention has superior impact toughness compared to a bolt using a conventional spheroidized annealing material or non-tempered steel material. Recognize.
以上、考察したように、本発明の鋼材は、−40℃の低温で従来材に比べて約3.7倍、従来の非調質鋼材に比べて約20倍程度の優れた低温衝撃吸収エネルギーを有する。   As discussed above, the steel material of the present invention has an excellent low-temperature impact absorption energy of about 3.7 times that of the conventional material at a low temperature of −40 ° C. and about 20 times that of the conventional non-tempered steel material. Have
本発明に従う焼戻しパラメータと−40℃での低温衝撃吸収エネルギーとの間の相関関係を示すグラフである。4 is a graph showing the correlation between the tempering parameters according to the present invention and the low temperature shock absorption energy at −40 ° C. FIG. 本発明の材料、球状化焼鈍材及び非調質鋼材を使用して製造した9T級ボルトについての−40℃での低温衝撃吸収エネルギーを示す比較グラフである。It is a comparative graph which shows the low temperature impact absorption energy in -40 degreeC about the 9T class bolt manufactured using the material of this invention, a spheroidization annealing material, and a non-tempered steel material.

Claims (4)

  1. C 0.10〜0.40wt%、Si 1.0wt%以下、Mn 0.30〜2.0wt%、P 0.03wt%以下、S 0.03wt%以下、および残部としてFeと不純物を含む冷間圧造用鋼線であって、オーステナイト結晶粒の大きさが5〜20μmであり、−40℃での衝撃吸収エネルギーが60J/cm2以上であり、かつ引張強度が70〜130kgf/mm2である、優れた低温衝撃特性を有する冷間圧造用鋼線。 C 0.10 to 0.40 wt%, Si 1.0 wt% or less, Mn 0.30 to 2.0 wt%, P 0.03 wt% or less, S 0.03 wt% or less, and the balance including Fe and impurities It is a steel wire for intermediate forging, the size of austenite crystal grains is 5 to 20 μm, the impact absorption energy at −40 ° C. is 60 J / cm 2 or more, and the tensile strength is 70 to 130 kgf / mm 2 . A steel wire for cold heading that has excellent low temperature impact properties.
  2. 前記鋼線はCr 0.05〜2.0wt%、Mo 0.05〜1.5wt%、B 0.0003〜0.0050wt%からなる群から選択される少なくとも1つの成分をさらに含む、請求項1に記載の鋼線。   The steel wire further includes at least one component selected from the group consisting of Cr 0.05 to 2.0 wt%, Mo 0.05 to 1.5 wt%, B 0.0003 to 0.0050 wt%. The steel wire according to 1.
  3. C 0.10〜0.40wt%、Si 1.0wt%以下、Mn 0.30〜2.0wt%、P 0.03wt%以下、S 0.03wt%以下、および残部としてFeと不純物を含む鋼材を、オーステナイト結晶粒の大きさが5〜20μmとなるように、Ac3変態点以上に急速に加熱する工程と、
    加熱された鋼材を冷却する工程と、
    冷却された鋼材を下記の式(1)で表わされる、焼戻しパラメータ(P)が21,800〜30,000の範囲で、引張強度が70〜130kgf/mm2となるように熱処理して、−40℃における衝撃吸収エネルギーが60J/cm2以上となるようにする工程と、を含む、優れた低温衝撃特性を有する冷間圧造用鋼線の製造方法。
    P=1.8×(T+273)×(14.44+logt) …式(1)
    ここで、Tは焼戻し温度(℃)、tは焼戻し時間(秒)
    Steel material containing C 0.10 to 0.40 wt%, Si 1.0 wt% or less, Mn 0.30 to 2.0 wt%, P 0.03 wt% or less, S 0.03 wt% or less, and the balance Fe and impurities A step of rapidly heating above the Ac3 transformation point so that the size of the austenite crystal grains is 5 to 20 μm;
    Cooling the heated steel material;
    The cooled steel material is heat treated so that the tempering parameter (P) is in the range of 21,800 to 30,000 and the tensile strength is 70 to 130 kgf / mm 2 represented by the following formula (1): A method for producing a steel wire for cold heading having excellent low-temperature impact characteristics, comprising a step of causing impact absorption energy at 40 ° C. to be 60 J / cm 2 or more.
    P = 1.8 * (T + 273) * (14.44 + logt) ... Formula (1)
    Where T is the tempering temperature (° C.) and t is the tempering time (seconds).
  4. 前記鋼材はCr 0.05〜2.0wt%、Mo 0.05〜1.5wt%、B 0.0003〜0.0050wt%からなる群から選択される少なくとも1つの成分をさらに含む、請求項3に記載の方法。   The steel material further includes at least one component selected from the group consisting of Cr 0.05 to 2.0 wt%, Mo 0.05 to 1.5 wt%, B 0.0003 to 0.0050 wt%. The method described in 1.
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KR100469671B1 (en) * 2002-07-11 2005-02-02 삼화강봉주식회사 Quenched and tempered steel wire with superior characteristics of cold forging

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013531737A (en) * 2011-06-02 2013-08-08 サンワスチール株式会社 High strength cold forging steel wire with improved die life and method for producing the same

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CN1894432A (en) 2007-01-10
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EP1697552A4 (en) 2011-01-12
US20070006947A1 (en) 2007-01-11
KR100536660B1 (en) 2005-12-14
US20070256767A1 (en) 2007-11-08
EP1697552A1 (en) 2006-09-06

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