JP2024500152A - Wire rods and parts with improved delayed fracture resistance and their manufacturing method - Google Patents

Wire rods and parts with improved delayed fracture resistance and their manufacturing method Download PDF

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JP2024500152A
JP2024500152A JP2023537438A JP2023537438A JP2024500152A JP 2024500152 A JP2024500152 A JP 2024500152A JP 2023537438 A JP2023537438 A JP 2023537438A JP 2023537438 A JP2023537438 A JP 2023537438A JP 2024500152 A JP2024500152 A JP 2024500152A
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ジョン,ヨンス
イ,サン-ユン
チェ,ソク-ファン
チェ,ミョンス
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ポスコ カンパニー リミテッド
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
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    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
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    • 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
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    • C21D1/18Hardening; Quenching with or without subsequent tempering
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    • 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
    • C21D1/26Methods of annealing
    • C21D1/32Soft annealing, e.g. spheroidising
    • 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
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    • 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
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    • 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
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    • 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
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    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/002Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
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    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/14Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/001Austenite
    • 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/008Martensite

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Abstract

【課題】本発明の目的は、遅れ破壊抵抗性が向上した線材、部品およびその製造方法を提供することである。【解決手段】本発明による遅れ破壊抵抗性が向上した線材は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たすことを特徴とする。[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)【選択図】図1An object of the present invention is to provide a wire rod, a component, and a method for manufacturing the same, which have improved delayed fracture resistance. [Solution] The wire rod with improved delayed fracture resistance according to the present invention has C: 0.15 to 0.30%, Si: 0.15 to 0.25%, and Mn: 0.95 to 1 in weight percent. .35%, P: 0.030% or less, S: 0.030% or less, Ti: 0.015-0.030%, B: 0.0010-0.0040%, N: 0.0010-0. 0080%, the remainder being Fe and unavoidable impurities, and satisfying the following relational expression 1. [Relational Expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4 (In Relational Expression 1, [Si] and [Mn] each represent the content (wt%) of the element concerned. Meaning) [Selection diagram] Figure 1

Description

本発明は、遅れ破壊抵抗性が向上した線材、部品およびその製造方法に係り、より詳細には、多様な応力および腐食環境に露出する自動車、構造物の締結用ボルトなどに使用できる線材、部品およびその製造方法に関する。 The present invention relates to wire rods and parts with improved delayed fracture resistance, and a method for manufacturing the same, and more particularly, the present invention relates to wire rods and parts that can be used for fastening bolts of automobiles and structures exposed to various stress and corrosive environments. and its manufacturing method.

自動車、構造物の締結用ボルトなどの素材に使用される線材は、自動車の軽量化および構造物の小型化に伴い、高強度化が要求されている。一般的に、鋼材の強度増加のためには、金属の強化機構である冷間加工、結晶粒微細化、マルテンサイト強化および析出強化などを活用する。 Wire rods used as materials for fastening bolts for automobiles and structures are required to have higher strength as automobiles become lighter and structures become smaller. Generally, to increase the strength of steel materials, metal strengthening mechanisms such as cold working, grain refinement, martensitic strengthening, and precipitation strengthening are utilized.

しかしながら、このような強化機構として活用された冷間加工、結晶粒界、マルテンサイトラス(lath)境界および微細析出物境界などは、鋼材内水素のトラップ部として作用し、また、遅れ破壊を劣化させる原因として作用する。このような理由で、引張強度1GPa以上の高強度ボルトでは、遅れ破壊が劣化する問題がある。 However, cold working, grain boundaries, martensite lath boundaries, fine precipitate boundaries, etc. that are utilized as such strengthening mechanisms act as traps for hydrogen within the steel material, and also deteriorate delayed fracture. Act as a cause. For this reason, high-strength bolts with a tensile strength of 1 GPa or more have a problem of delayed fracture.

このような問題を解決するために、従来、焼き戻しマルテンサイト(Tempered Martensite)組織を有する1GPa以上のボルト用鋼材は、Moを添加したCr-Mo合金鋼を使用していたが、ボルト製造工程技術の発展によるコスト低減ニーズに対応するためにCr-Mo鋼をCr-B鋼に置き換えようとする試みがあった。その結果、安全に大きな影響がない構造物に使用されるボルトからCr-B鋼を活用してコスト低減を具現し、その安全性を確認した後、自動車の一部締結用ボルトにもCr-B鋼が適用されている。 In order to solve these problems, conventionally, Cr-Mo alloy steel with Mo added was used for bolt steel materials with a tempered martensite structure of 1 GPa or higher, but the bolt manufacturing process There have been attempts to replace Cr--Mo steel with Cr--B steel in order to meet the need for cost reduction due to technological development. As a result, we realized cost reduction by using Cr-B steel for bolts used in structures that do not have a major impact on safety, and after confirming its safety, we also used Cr-B steel for some fastening bolts in automobiles. B steel is used.

ひいては、自動車業界では、極限までのコスト低減のためにCr-B鋼よりさらにコスト低減が可能なボルト用素材を開発するためのニーズがある。このようなニーズに対応するために、最近では、Crに比べて安価なMnを活用するMn-B鋼を1GPa以上の高強度ボルト用素材に適用するための技術開発が行われている。 Furthermore, in the automobile industry, there is a need to develop a material for bolts that can be even more cost-reduced than Cr-B steel in order to reduce costs to the utmost. In order to meet such needs, technology has recently been developed to apply Mn-B steel, which utilizes Mn, which is cheaper than Cr, as a material for high-strength bolts of 1 GPa or more.

しかしながら、Mnは、Crに比べてフェライト基地内に高い固溶強化を誘発するので、Mn-Bの鋼は、ボルトの製造時にボルトのねじ部にクラックが発生することがある。したがって、1GPa以上の高強度ボルトを製造するために添加されるMnの含有量が高い鋼は、ボルトねじ部のクラックによって遅れ破壊が発生しうる短所があり、高強度ボルトに適用するのには問題がある。 However, since Mn induces higher solid solution strengthening in the ferrite base than Cr, cracks may occur in the threaded portion of the bolt when Mn-B steel is manufactured. Therefore, steel with a high content of Mn, which is added to produce high-strength bolts of 1 GPa or more, has the disadvantage of causing delayed fracture due to cracks in the bolt threads, and is therefore not suitable for use in high-strength bolts. There's a problem.

本発明の目的とするところは、合金元素の制御を通じて、Mn-B鋼の固溶強化効果を最適化し、成形性を向上させることによって、遅れ破壊抵抗性が向上した高強度ボルト用線材、ボルトおよびその製造方法を提供しようとするものである。 The purpose of the present invention is to optimize the solid solution strengthening effect of Mn-B steel through control of alloying elements and improve formability, thereby providing wire rods for high-strength bolts with improved delayed fracture resistance. and its manufacturing method.

本発明の遅れ破壊抵抗性が向上した線材は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たすことを特徴とする。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
The wire rod with improved delayed fracture resistance of the present invention has, in weight percent, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, Contains P: 0.030% or less, S: 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%. , the remainder consists of Fe and unavoidable impurities, and the following relational expression 1 is satisfied.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational expression 1, [Si] and [Mn] each mean the content (wt%) of the element)

また、下記関係式2を満たすことができる。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
Moreover, the following relational expression 2 can be satisfied.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)

また、本発明の一TiN介在物のサイズは、15μm以下であってもよい。 Moreover, the size of one TiN inclusion of the present invention may be 15 μm or less.

本発明の遅れ破壊抵抗性が向上した線材の製造方法は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たす鋼材を880~980℃で仕上げ圧延する段階と、
830~930℃で巻き取る段階とを含むことを特徴とする。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
The method for manufacturing a wire rod with improved delayed fracture resistance according to the present invention is as follows: C: 0.15-0.30%, Si: 0.15-0.25%, Mn: 0.95-1. 35%, P: 0.030% or less, S: 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080 %, the remainder consists of Fe and unavoidable impurities, and the step of finish rolling a steel material that satisfies the following relational expression 1 at 880 to 980 ° C.
The method is characterized in that it includes a step of winding at 830 to 930°C.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational expression 1, [Si] and [Mn] each mean the content (wt%) of the element)

また、本発明の、鋼材は、下記関係式2を満たすことができる。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
Moreover, the steel material of the present invention can satisfy the following relational expression 2.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)

本発明の遅れ破壊抵抗性が向上した部品の製造方法は、本発明によって製造した線材を伸線する段階と、伸線した線材を745~770℃で球状化熱処理する段階と、球状化熱処理した線材を870~940℃の温度範囲で加熱する段階と、球状化熱処理した線材を50~80℃の温度範囲で焼入する段階と、焼入した部品を400~600℃の温度範囲で焼き戻しする段階とを含むことを特徴とする。 The method of manufacturing a component with improved delayed fracture resistance of the present invention includes the steps of drawing the wire produced according to the present invention, subjecting the drawn wire to spheroidizing heat treatment at 745 to 770°C, and spheroidizing the wire rod. A step of heating the wire rod in a temperature range of 870 to 940 degrees Celsius, a step of quenching the spheroidized wire rod in a temperature range of 50 to 80 degrees Celsius, and a step of tempering the quenched parts in a temperature range of 400 to 600 degrees Celsius. The method is characterized by including the step of:

本発明の遅れ破壊抵抗性が向上した部品は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たすことを特徴とする。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
The parts with improved delayed fracture resistance of the present invention include, in weight percent, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, Contains P: 0.030% or less, S: 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%. , the remainder consists of Fe and unavoidable impurities, and the following relational expression 1 is satisfied.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational expression 1, [Si] and [Mn] each mean the content (wt%) of the element)

また、本発明の部品は、下記関係式2を満たす。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
Further, the component of the present invention satisfies the following relational expression 2.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)

また、本発明の部品は、体積分率で、残留オーステナイトを0.3~2%および残余の焼き戻しマルテンサイト組織を含む。 The parts of the invention also contain, by volume fraction, 0.3 to 2% retained austenite and a residual tempered martensitic structure.

本発明によれば、遅れ破壊抵抗性が向上した高強度ボルト用部品は、Mn-B鋼のボルトねじ部の加工時の成形性を向上させることによって、ボルトねじ部のクラックを発生させないので、1Gpa級高強度ボルトで遅れ破壊を抑制することができる。 According to the present invention, the high-strength bolt parts with improved delayed fracture resistance do not cause cracks in the bolt thread part by improving the formability during machining of the Mn-B steel bolt thread part. Delayed fracture can be suppressed with 1 Gpa class high strength bolts.

遅れ破壊抵抗性の評価前の比較例3のねじ部を観察した写真である。It is a photograph of the threaded portion of Comparative Example 3 before evaluation of delayed fracture resistance.

本明細書が実施例のすべての要素を説明するものではなく、本発明の属する技術分野において一般的な内容または実施例の間に重複する内容は省略する。 This specification does not describe all elements of the embodiments, and content that is common in the technical field to which the present invention pertains or content that overlaps between the embodiments is omitted.

また、任意の部分が或る構成要素を「含む」というとき、これは、特に反対になる記載がない限り、他の構成要素を除くものではなく、他の構成要素をさらに含むことができることを意味する。 Furthermore, when we say that any part "contains" a certain component, this does not mean that it excludes other components, unless there is a statement to the contrary, but it does not mean that it excludes other components, and that it can further include other components. means.

単数の表現は、文脈上、明白に例外がない限り、複数の表現を含む。 References to the singular include the plural unless the context clearly dictates otherwise.

以下、本発明を詳細に説明する。
以下の実施形態は、本発明の属する技術分野における通常の知識を有する者に本発明の思想を十分に伝達するために提示するものである。本発明は、ここで提示した実施例のみに限定されず、他の形態で具体化することもできる。
The present invention will be explained in detail below.
The following embodiments are provided so that the spirit of the invention will be fully conveyed to those skilled in the art to which the invention pertains. The invention is not limited only to the embodiments presented here, but can also be embodied in other forms.

本発明の発明者らは、SiおよびMnの含有量を制御する場合、固溶強化効果を最適化して強度を確保しながらも、成形性を向上させることができ、ねじ部の成形劣化によるクラック発生を抑制し、遅れ破壊抵抗性を向上させることができることを知見した。 The inventors of the present invention have found that when controlling the content of Si and Mn, it is possible to optimize the solid solution strengthening effect and ensure strength while improving formability and preventing cracks due to deterioration in forming of threaded parts. We found that it is possible to suppress the occurrence of cracking and improve delayed fracture resistance.

また、TiおよびNの含有量を制御し、TiN介在物のサイズを制御することによって、結晶粒を微細化することができ、これによって、成形性が向上し、遅れ破壊抵抗性を確保することができることを知見し、本発明を完成するに至った。 In addition, by controlling the content of Ti and N and the size of TiN inclusions, it is possible to refine the crystal grains, thereby improving formability and ensuring delayed fracture resistance. The present invention was completed based on the discovery that this can be done.

本発明の一実施形態による遅れ破壊抵抗性が向上した線材は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなる。 The wire rod with improved delayed fracture resistance according to an embodiment of the present invention has C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1 in weight percent. .35%, P: 0.030% or less, S: 0.030% or less, Ti: 0.015-0.030%, B: 0.0010-0.0040%, N: 0.0010-0. The remainder consists of Fe and unavoidable impurities.

以下、本発明の実施形態における合金成分元素含有量の数値限定理由について説明する。以下では、特段の言及がない限り、単位は、重量%である。 Hereinafter, the reason for numerically limiting the content of alloy component elements in the embodiment of the present invention will be explained. In the following, units are % by weight, unless otherwise stated.

炭素(C)の含有量は、0.15~0.30%である。
Cは、製品の強度を確保するために添加される元素である。炭素含有量が0.15%未満の場合、本発明において目標とする強度を確保することが難しく、0.30%を超過する場合、焼入(Quenching)の際に、ラスマルテンサイト(lath Martensite)境界で静水圧により形成される機械的安定性(mechanical stabilization)に優れた残留オーステナイト形成を妨害し、遅れ破壊抵抗性が劣化することができる。したがって、本発明では、Cの含有量を0.15~0.30%に制限する。
The carbon (C) content is 0.15 to 0.30%.
C is an element added to ensure the strength of the product. When the carbon content is less than 0.15%, it is difficult to secure the target strength in the present invention, and when it exceeds 0.30%, lath martensite (lath martensite) is formed during quenching. ) The formation of retained austenite with excellent mechanical stability formed by hydrostatic pressure at the boundary can be hindered, and the delayed fracture resistance can be deteriorated. Therefore, in the present invention, the C content is limited to 0.15 to 0.30%.

シリコン(Si)の含有量は、0.15~0.25%である。
Siは、鋼の脱酸のために有用であるだけでなく、固溶強化を通した強度確保にも効果的な元素である。Siの含有量が0.15%未満の場合、鋼の脱酸および固溶強化を通した強度確保が不十分であり、0.25%を超過する場合には、固溶強化による成形性および衝撃特性が劣化することができる。したがって、本発明では、Siの含有量を0.15~0.25%に制限する。
The content of silicon (Si) is 0.15 to 0.25%.
Si is an element that is not only useful for deoxidizing steel, but also effective for ensuring strength through solid solution strengthening. If the Si content is less than 0.15%, the strength obtained through deoxidation and solid solution strengthening of the steel will be insufficient, and if it exceeds 0.25%, the formability and formability due to solid solution strengthening will be insufficient. Impact properties may deteriorate. Therefore, in the present invention, the Si content is limited to 0.15 to 0.25%.

マンガン(Mn)の含有量は、0.95~1.35%である。
Mnは、硬化能を向上させる元素であり、基地組織内に置換型固溶体を形成し、固溶強化効果を奏する非常に有用な元素である。Mnの含有量が0.95%未満の場合、前述した固溶強化効果と硬化能が不十分で、本発明において目標とする強度確保が難しく、1.35%を超過する場合には、固溶強化効果によって成形性が劣化することができる。したがって、本発明では、Mnの含有量を0.95~1.35%に制限する。
The content of manganese (Mn) is 0.95 to 1.35%.
Mn is an element that improves hardenability, and is a very useful element that forms a substitutional solid solution within the matrix structure and has a solid solution strengthening effect. If the Mn content is less than 0.95%, the above-mentioned solid solution strengthening effect and hardening ability will be insufficient, making it difficult to secure the target strength in the present invention, and if it exceeds 1.35%, Formability can deteriorate due to the melt strengthening effect. Therefore, in the present invention, the Mn content is limited to 0.95 to 1.35%.

リン(P)の含有量は、0.030%以下である(0%は除外)。
Pは、結晶粒界に偏析して靭性を低下させ、遅れ破壊抵抗性を減少させる元素である。したがって、本発明では、Pの上限を0.030%に制限する。
The content of phosphorus (P) is 0.030% or less (0% is excluded).
P is an element that segregates at grain boundaries and reduces toughness and delayed fracture resistance. Therefore, in the present invention, the upper limit of P is limited to 0.030%.

硫黄(S)の含有量は、0.030%以下である(0%は除外)。
Sは、Pと同様に、結晶粒界に偏析して靭性を低下させるだけでなく、低融点硫化物を形成させて熱間圧延を阻害する元素である。したがって、本発明では、Sの上限を0.030%に制限する。
The content of sulfur (S) is 0.030% or less (0% is excluded).
Like P, S is an element that not only segregates at grain boundaries and reduces toughness, but also forms low melting point sulfides and inhibits hot rolling. Therefore, in the present invention, the upper limit of S is limited to 0.030%.

チタン(Ti)の含有量は、0.015~0.030%である。
Tiは、鋼中内に流入するNと結合し、チタン炭窒化物(TiN)を形成する元素である。本発明においてTiNは、結晶粒を微細化することによって、部品成形時に成形劣化によるクラック発生を抑制し、遅れ破壊抵抗性を向上させることができる。また、Tiは、TiNを形成するので、free-N(自由N)がBと結合するのを防止し、成形性を劣化させるBN形成を抑制させることもできる。Tiの含有量が0.015%未満の場合、前述したように、十分なTiNが形成されず、自由NがBNを形成するので、Bの硬化能効果を活用しにくく、0.03%を超過する場合には、粗大な炭窒化物が形成され、遅れ破壊抵抗性が劣化することができる。したがって、本発明では、Tiの含有量を0.015~0.03%に制限する。
The content of titanium (Ti) is 0.015 to 0.030%.
Ti is an element that combines with N flowing into the steel to form titanium carbonitride (TiN). In the present invention, TiN can suppress the occurrence of cracks due to molding deterioration during component molding by making the crystal grains finer, and can improve delayed fracture resistance. Furthermore, since Ti forms TiN, it is possible to prevent free-N from bonding with B, thereby suppressing the formation of BN which deteriorates formability. If the Ti content is less than 0.015%, as described above, sufficient TiN will not be formed and free N will form BN, making it difficult to utilize the hardenability effect of B. If it exceeds, coarse carbonitrides may be formed and delayed fracture resistance may deteriorate. Therefore, in the present invention, the Ti content is limited to 0.015 to 0.03%.

ボロン(B)の含有量は、0.0010~0.0040%である。
Bは、硬化能を向上させる元素である。Bの含有量が0.0010%未満の場合、前述した硬化能向上効果を期待しにくく、0.0040%を超過する場合には、結晶粒界にFe23(CB)炭化物を形成させてオーステナイト結晶粒界の脆性を誘発し、BNを形成して成形性を劣化させることによって、遅れ破壊抵抗性を劣化させる。したがって、本発明では、B含有量を0.0010~0.0040%に制限する。
The content of boron (B) is 0.0010 to 0.0040%.
B is an element that improves hardenability. If the B content is less than 0.0010%, it is difficult to expect the above-mentioned hardenability improvement effect, and if it exceeds 0.0040%, Fe 23 (CB) 6 carbide is formed at the grain boundaries. Delayed fracture resistance is deteriorated by inducing brittleness of austenite grain boundaries, forming BN and deteriorating formability. Therefore, in the present invention, the B content is limited to 0.0010 to 0.0040%.

窒素(N)の含有量は、0.0010~0.0080%である。
Nは、炭窒化物を形成する元素である。Nの含有量が0.0010%未満の場合、結晶粒を微細化するTiN析出物を十分に形成できず、0.0080%を超過する場合、固溶窒素量が増加し、鋼の靭性および軟性が劣化することができ、free-N(自由N)がBと結合し、成形性を劣化させるBNを形成することができる。したがって、本発明では、Nの含有量を0.0010~0.0080%に制限する。
The nitrogen (N) content is 0.0010 to 0.0080%.
N is an element that forms carbonitrides. If the N content is less than 0.0010%, TiN precipitates that refine grains cannot be sufficiently formed, and if it exceeds 0.0080%, the amount of solid solute nitrogen increases, which deteriorates the toughness of the steel. Softness can deteriorate, and free-N can combine with B to form BN, which deteriorates formability. Therefore, in the present invention, the N content is limited to 0.0010 to 0.0080%.

合金組成以外の残部は、鉄(Fe)である。本発明の遅れ破壊抵抗性が向上した線材は、通常、鋼の工業的生産過程で含まれ得るその他の不純物を含んでもよい。このような不純物は、本発明の属する技術分野における通常の知識を有する者なら誰でも知ることができる内容であるから、本発明において特にその種類と含有量を制限しない。 The remainder other than the alloy composition is iron (Fe). The wire rod with improved delayed fracture resistance of the present invention may contain other impurities that may normally be included in the industrial production process of steel. Since such impurities are known to anyone with ordinary knowledge in the technical field to which the present invention pertains, the present invention does not particularly limit the type and content thereof.

本発明の一実施形態による遅れ破壊抵抗性が向上した線材は、下記関係式1を満たす。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
A wire rod with improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression 1.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4

関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する。 In relational formula 1, [Si] and [Mn] each mean the content (weight %) of the element.

本発明では、SiおよびMnの含有量を制御して固溶強化効果を通じて強度を確保しながらも、過度な固溶強化効果を抑制して線材の成形性を向上させ、遅れ破壊抵抗性を向上させようとした。これによって、導き出された関係式1は、固溶強化効果を最適化するための数式である。関係式1の5.5×[Si]+[Mn]の値が2.0未満の場合、本発明において目標とする強度を確保できず、5.5×[Si]+[Mn]の値が2.4を超過する場合、過度な固溶強化効果によって、高強度部品の成形の際に成形劣化によるクラックが発生し、遅れ破壊を誘発することができる。したがって、本発明では、遅れ破壊抵抗性を向上させるために、5.5×[Si]+[Mn]の値を2.0~2.4に制限する。 In the present invention, the content of Si and Mn is controlled to ensure strength through the solid solution strengthening effect, while suppressing excessive solid solution strengthening effect to improve the formability of the wire rod and improve delayed fracture resistance. I tried to make it happen. Accordingly, the derived relational expression 1 is a mathematical expression for optimizing the solid solution strengthening effect. If the value of 5.5×[Si]+[Mn] in relational expression 1 is less than 2.0, the target strength cannot be secured in the present invention, and the value of 5.5×[Si]+[Mn] If the ratio exceeds 2.4, cracks may occur due to molding deterioration during molding of high-strength parts due to excessive solid solution strengthening effect, and delayed fracture may be induced. Therefore, in the present invention, in order to improve delayed fracture resistance, the value of 5.5×[Si]+[Mn] is limited to 2.0 to 2.4.

また、本発明の一実施形態による遅れ破壊抵抗性が向上した線材は、下記関係式2を満たす。 Further, the wire rod with improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression 2.

[関係式2]1.0<[Ti]/3.42[N]<2.0 [Relational expression 2] 1.0<[Ti]/3.42[N]<2.0

関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する。 In relational formula 2, [Ti] and [N] each mean the content (weight %) of the element.

本発明では、結晶粒を微細化し、成形性を向上させることによって、線材の遅れ破壊抵抗性を向上させようとした。本発明の発明者らは、研究を重ねたところ、TiN介在物を形成し、そのサイズを制御して結晶粒を微細化し、BNを抑制することによって、成形性および遅れ破壊抵抗性を確保することができた。これによって、導き出された関係式2は、TiN介在物のサイズを制御し、BNの形成を抑制するための数式である。関係式2の[Ti]/3.42[N]値が1.0以下の場合、Tiと結合しないfree-Nにより形成されるBNなどによって成形性が劣化することができ、[Ti]/3.42[N]値が2.0以上の場合、超過Ti(excess Ti)によってTiNが粗大化し、結晶粒微細化効果を発揮することができない。したがって、本発明では、[Ti]/3.42[N]値を1.0超過~2.0未満に制限する。 In the present invention, an attempt was made to improve the delayed fracture resistance of the wire by making the crystal grains finer and improving the formability. After repeated research, the inventors of the present invention have found that formability and delayed fracture resistance are ensured by forming TiN inclusions, controlling their size to refine crystal grains, and suppressing BN. I was able to do that. Accordingly, the derived relational expression 2 is a mathematical expression for controlling the size of TiN inclusions and suppressing the formation of BN. When the [Ti]/3.42 [N] value in relational expression 2 is 1.0 or less, the formability may be deteriorated by BN formed by free-N that does not combine with Ti, and the [Ti]/ 3.42 When the [N] value is 2.0 or more, TiN becomes coarse due to excess Ti, and the crystal grain refining effect cannot be exhibited. Therefore, in the present invention, the [Ti]/3.42[N] value is limited to more than 1.0 and less than 2.0.

本発明において結晶粒を微細化するためのTiN介在物のサイズは、15μm以下であってもよい。前述したように、TiN介在物の最大サイズが15μmを超過する場合、結晶粒微細化による遅れ破壊抵抗性を確保しにくい。 In the present invention, the size of TiN inclusions for refining crystal grains may be 15 μm or less. As described above, when the maximum size of TiN inclusions exceeds 15 μm, it is difficult to ensure delayed fracture resistance due to grain refinement.

また、本発明による線材により製造した遅れ破壊抵抗性が向上した部品は、体積分率で、残留オーステナイトを0.3~2%および残余の焼き戻しマルテンサイト組織を含む。残留オーステナイト組織分率が0.3%未満の場合、遅れ破壊抵抗性を劣化させる水素拡散を遅延させる障害物の役割を期待しにくく、2%を超過する場合、残留オーステナイトがラス境界だけでなく、オーステナイト結晶粒界などに厚く形成され、水素拡散を遅延させにくく、これによって、遅れ破壊抵抗性の改善効果を低減することができる。 In addition, the parts with improved delayed fracture resistance produced by the wire according to the present invention contain a volume fraction of 0.3 to 2% retained austenite and a residual tempered martensitic structure. If the retained austenite structure fraction is less than 0.3%, it is difficult to expect that it will play a role as an obstacle that retards hydrogen diffusion, which deteriorates delayed fracture resistance, and if it exceeds 2%, retained austenite will not only form at lath boundaries , is formed thickly at austenite grain boundaries, etc., and is difficult to delay hydrogen diffusion, thereby reducing the effect of improving delayed fracture resistance.

次に、本発明の一実施形態による遅れ破壊抵抗性が向上した線材および部品の製造方法について説明する。 Next, a method for manufacturing wire rods and components with improved delayed fracture resistance according to an embodiment of the present invention will be described.

本発明による遅れ破壊抵抗性が向上した線材および部品は、多様な方法で製造することができ、その製造方法は特に制限されない。ただし、一実施形態として次のような方法によって製造することができる。 The wire rod and component with improved delayed fracture resistance according to the present invention can be manufactured by various methods, and the manufacturing method is not particularly limited. However, as one embodiment, it can be manufactured by the following method.

本発明による遅れ破壊抵抗性が向上した線材は、重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなる鋼材を880~980℃で仕上げ圧延する段階と、830~930℃で巻き取る段階とを含む。 The wire rod with improved delayed fracture resistance according to the present invention has, in weight percent, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, Contains P: 0.030% or less, S: 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%. , a step of finish rolling a steel material with the balance consisting of Fe and unavoidable impurities at 880 to 980°C, and a step of winding it at 830 to 930°C.

まず、前述した合金組成を満たす鋼材を用意し、880~980℃で仕上げ線材圧延する。その後、圧延した線材を830~930℃でコイル形状に巻き取る。 First, a steel material satisfying the alloy composition described above is prepared and finished wire rod rolled at 880 to 980°C. Thereafter, the rolled wire is wound into a coil shape at 830 to 930°C.

この際、線材圧延温度が880℃未満または巻取温度が830℃未満の場合、表面層が準二相域であるから、相変態による表面フェライト脱炭層を形成することができ、ボルトの熱処理時にも表面にフェライト脱炭層が形成され、遅れ破壊抵抗性を劣化させることができる。また、ボルト製品の旧オーステナイト結晶粒径が微細になり、残留オーステナイト分率が高まって、遅れ破壊抵抗性を劣化さることができる。なお、線材仕上げ圧延温度が980℃を超過したり、巻取温度が930℃を超過したりする場合、拡散によって脱炭が加速化し、表面にフェライト脱炭層を形成することができ、旧オーステナイト結晶粒径が粗大になり、遅れ破壊抵抗性を劣化することができる。 At this time, if the wire rolling temperature is less than 880°C or the coiling temperature is less than 830°C, the surface layer is in a quasi-two-phase region, so a surface ferrite decarburized layer can be formed due to phase transformation, and even during heat treatment of the bolt. A ferrite decarburized layer is formed on the surface, which can deteriorate delayed fracture resistance. In addition, the prior austenite crystal grain size of the bolt product becomes fine, the retained austenite fraction increases, and the delayed fracture resistance can be deteriorated. In addition, when the wire finish rolling temperature exceeds 980°C or the coiling temperature exceeds 930°C, decarburization is accelerated due to diffusion, and a ferrite decarburized layer can be formed on the surface, and prior austenite crystals The grain size becomes coarse and delayed fracture resistance can deteriorate.

次に、巻き取られた線材は、目的に合うように、伸線-球状化熱処理-皮膜処理-ボルト成形-オーステナイト化(austenitizing)-焼入-焼き戻しを行うことによって、最終ボルト用部品に製造することができる。ただし、一実施形態として次のような方法によって製造することができる。 The wound wire rod is then subjected to wire drawing, spheroidization heat treatment, film treatment, bolt forming, austenitizing, quenching, and tempering to form the final bolt part. can be manufactured. However, as one embodiment, it can be manufactured by the following method.

本発明の一実施形態によるボルト用部品の製造方法は、本発明によって製造した線材を伸線する段階と、伸線した線材を745~770℃で球状化熱処理する段階と、球状化熱処理した線材を870~940℃で加熱する段階と、球状化熱処理した線材を50~80℃で焼入する段階と、400~600℃で焼き戻しする段階とを含む。 A method for manufacturing bolt parts according to an embodiment of the present invention includes the steps of drawing a wire rod manufactured according to the present invention, a step of subjecting the drawn wire rod to a spheroidizing heat treatment at 745 to 770°C, and a step of spheroidizing the wire rod subjected to the spheroidizing heat treatment. The steps include heating the wire at 870 to 940°C, quenching the spheroidized wire at 50 to 80°C, and tempering it at 400 to 600°C.

この際、球状化熱処理は、745~770℃で行われ得る。熱処理温度が745℃未満であるか、770℃を超過する場合、球状化率が低くなるにつれて、球状化熱処理材の硬度が高まり、ボルト成形後、ねじ部の加工時に成形性が劣化し、そのため、ねじ部クラックを誘発することができる。 At this time, the spheroidization heat treatment may be performed at 745 to 770°C. When the heat treatment temperature is less than 745℃ or exceeds 770℃, the hardness of the spheroidization heat-treated material increases as the spheroidization rate decreases, and the formability deteriorates when processing the threaded part after bolt formation. , can induce thread cracks.

オーステナイト化熱処理は、870~940℃で行われ得る。熱処理温度が870℃未満の場合、オーステナイト逆変態が十分に起こらないので、焼入後、マルテンサイト組織が不均一に形成され、靭性が劣化することができる。なお、熱処理温度が940℃を超過する場合には、旧オーステナイト結晶粒度が粗大になり、遅れ破壊抵抗性が劣化することができる。 The austenitizing heat treatment may be performed at 870-940°C. When the heat treatment temperature is less than 870° C., austenite reverse transformation does not occur sufficiently, so that after quenching, a martensitic structure is formed non-uniformly, and the toughness may deteriorate. Note that if the heat treatment temperature exceeds 940° C., the prior austenite crystal grain size becomes coarse and delayed fracture resistance may deteriorate.

また、焼入は、50~80℃の温度範囲で行われ得る。焼入冷媒の温度が50℃未満の場合、ボルトのねじ山で熱変形による微細な焼入割れ(Quenching Crack)が発生することがあり、遅れ破壊を誘発することができ、80℃を超過する場合、十分な焼入が行われず、ラスに機械的安定残留オーステナイトの他に、旧オーステナイト結晶粒界に残留オーステナイトが形成され、かえって水素の捕捉部として作用し、遅れ破壊を誘発することができる。 Also, quenching can be performed at a temperature range of 50-80°C. If the temperature of the quenching refrigerant is less than 50℃, fine quenching cracks may occur due to thermal deformation on the bolt threads, which can induce delayed fracture, and if the temperature exceeds 80℃. In this case, sufficient quenching is not performed, and in addition to the mechanically stable retained austenite in the lath, retained austenite is formed at the grain boundaries of prior austenite, which acts as a hydrogen trap and can induce delayed fracture. .

また、焼き戻しは、400~600℃の温度範囲で行われ得、最終製品の用途および目的に合うように、強度および靭性を付与することができる。焼き戻し温度が400℃未満の場合、焼き戻しによる脆性を誘発することができ、600℃を超過する場合、本発明において意図する強度を具現し難い。 Tempering can also be carried out at temperatures ranging from 400 to 600° C. to impart strength and toughness to suit the application and purpose of the final product. If the tempering temperature is less than 400°C, brittleness may occur due to tempering, and if it exceeds 600°C, it is difficult to achieve the strength intended in the present invention.

本発明によって製造した遅れ破壊抵抗性が向上した部品は、体積分率で、残留オーステナイトを0.3~2%および残余の焼き戻しマルテンサイト組織を含む。 Parts with improved delayed fracture resistance produced according to the present invention contain, by volume fraction, 0.3 to 2% retained austenite and a residual tempered martensitic structure.

以下、実施例に基づいて本発明をより具体的に説明する。ただし、下記の実施例は、本発明を例示してより詳細に説明するためのものであり、本発明の権利範囲を限定するためのものではないという点に留意すべきである。本発明の権利範囲は、特許請求範囲に記載された事項とこれから合理的に類推される事項によって決定されるものであるからである。 Hereinafter, the present invention will be explained more specifically based on Examples. However, it should be noted that the following examples are intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of rights in the present invention is determined by the matters stated in the claims and matters reasonably inferred from these matters.

実施例
下記表1の合金組成を満たす発明例1~6、比較例1~5の線材を本発明による製造条件で製造し、最終試験用ボルトを得た。具体的には、下記表1の合金組成を満たす鋼片を880~980℃で仕上げ線材圧延し、830~930℃でコイル形状に巻き取った後、巻き取られた線材を最大温度745~770℃で球状化熱処理した。次に、球状化熱処理した線材をボルトに成形し、870~940℃でオーステナイト化した後、50~80℃の冷媒に焼入し、その後、1050±16MPaの引張強度を確保するために、400~600℃の温度で焼き戻しを行い、最終ボルト製品を得た。
Examples Wire rods of Invention Examples 1 to 6 and Comparative Examples 1 to 5 satisfying the alloy compositions shown in Table 1 below were manufactured under the manufacturing conditions of the present invention to obtain bolts for final testing. Specifically, a steel billet satisfying the alloy composition shown in Table 1 below is finished wire-rolled at 880 to 980°C, wound into a coil shape at 830 to 930°C, and then the wound wire is heated to a maximum temperature of 745 to 770°C. Spheroidization heat treatment was carried out at ℃. Next, the spheroidized wire rod is formed into a bolt, austenitized at 870-940℃, quenched in a refrigerant at 50-80℃, and then heated to 400℃ to ensure a tensile strength of 1050±16MPa. Tempering was carried out at a temperature of ~600°C to obtain the final bolt product.

Figure 2024500152000002
Figure 2024500152000002

次に、発明例1~6、比較例1~5のボルト製品について、TiN析出物の最大サイズ、遅れ破壊クラックの有無を評価し、関係式1および関係式2の値と共に表2に示した。TiN析出物の最大サイズは、ボルト製品をL断面(Longitudinal direction)に切開し、160mm面積を30field観察し、極値解析(extreme value analysis)を通じて測定される介在物のサイズを最大介在物のサイズと定義し、その値を下記表2に示した。 Next, the bolt products of Invention Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated for the maximum size of TiN precipitates and the presence or absence of delayed fracture cracks, and the results are shown in Table 2 along with the values of Relational Expressions 1 and 2. . The maximum size of TiN precipitates can be determined by cutting the bolt product into an L cross section (Longitudinal direction), observing 30 fields of 2 areas of 160 mm, and determining the size of the inclusions measured through extreme value analysis. The value is shown in Table 2 below.

遅れ破壊抵抗性は、ボルト製品を降伏強度の締結力で構造物に締結した後、5%塩酸+95%蒸留水溶液に10分間浸漬し、応力集中部であるねじ山にクラック有無を観察する遅れ破壊シミュレーションで進めた。クラックが発生しない場合は、X、クラックが発生した場合は、○で示した。 Delayed fracture resistance is measured by fastening a bolt product to a structure with a fastening force of yield strength, then immersing it in a solution of 5% hydrochloric acid + 95% distilled water for 10 minutes, and observing the presence or absence of cracks in the threads, which are stress concentration areas. Proceeded through simulation. If no cracks occurred, it was marked with an X, and if cracks did occur, it was marked with an O.

Figure 2024500152000003
Figure 2024500152000003

表2から確認できるように、本発明において提案する合金組成、関係式およびTiNサイズを満たす発明例1~6は、遅れ破壊抵抗性の評価前後にボルト製品のねじ部で遅れ破壊クラックが発生しなかった。一方、比較例1は、[Ti]/3.42[N]値が2.506であり、本発明において提案する上限値である2.0を超過し、粗大なTiNが形成され、そのため、遅れ破壊クラックが発生した。 As can be confirmed from Table 2, in Invention Examples 1 to 6 that satisfy the alloy composition, relational expression, and TiN size proposed in the present invention, delayed fracture cracks occurred in the threaded part of the bolt product before and after evaluating delayed fracture resistance. There wasn't. On the other hand, in Comparative Example 1, the [Ti]/3.42[N] value was 2.506, which exceeded the upper limit of 2.0 proposed in the present invention, and coarse TiN was formed. Delayed fracture cracks occurred.

比較例2は、[Ti]/3.42[N]値が3.070であり、本発明において提案する上限値である2.0を超過し、粗大なTiNが形成され、そのため、遅れ破壊クラックが発生した。 In Comparative Example 2, the [Ti]/3.42[N] value was 3.070, which exceeded the upper limit of 2.0 proposed in the present invention, and coarse TiN was formed, resulting in delayed fracture. A crack occurred.

比較例3は、Siの含有量が0.26%であり、本発明において提案する上限値である0.25%を超過し、5.5×[Si]+[Mn]値が2.58であり、本発明において提案する上限値である2.4を超過し、過度な固溶強化効果によって球状化熱処理後にボルトねじ部の成形性が劣化し、遅れ破壊クラックが発生した。図1は、遅れ破壊抵抗性の評価前の比較例3のねじ部を観察した写真である。図1を参照すると、比較例3は、本発明において提案する条件を満たしていないので、遅れ破壊クラックが発生し、遅れ破壊抵抗性を確保しなかったことを確認することができる。 In Comparative Example 3, the Si content was 0.26%, which exceeded the upper limit of 0.25% proposed in the present invention, and the 5.5×[Si]+[Mn] value was 2.58. This exceeded the upper limit of 2.4 proposed in the present invention, and due to the excessive solid solution strengthening effect, the formability of the bolt thread portion deteriorated after the spheroidization heat treatment, and delayed fracture cracks occurred. FIG. 1 is a photograph of the threaded portion of Comparative Example 3 before evaluation of delayed fracture resistance. Referring to FIG. 1, it can be confirmed that Comparative Example 3 did not meet the conditions proposed in the present invention, so delayed fracture cracks occurred and delayed fracture resistance was not ensured.

比較例4は、Mnの含有量が1.45%であり、本発明において提案する上限値である1.35%を超過し、5.5×[Si]+[Mn]値が2.61であり、本発明において提案する上限値である2.4を超過し、過度な固溶強化効果によって球状化熱処理後にボルトねじ部の成形性が劣化し、遅れ破壊クラックが発生した。 In Comparative Example 4, the Mn content was 1.45%, which exceeded the upper limit of 1.35% proposed in the present invention, and the 5.5×[Si]+[Mn] value was 2.61. This exceeded the upper limit of 2.4 proposed in the present invention, and due to the excessive solid solution strengthening effect, the formability of the bolt thread portion deteriorated after the spheroidization heat treatment, and delayed fracture cracks occurred.

比較例5は、Cの含有量が0.33%であり、本発明において提案する上限値である0.30%を超過し、機械的安定性に優れた残留オーステナイト組織の形成が抑制され、遅れ破壊クラックが発生した。 Comparative Example 5 has a C content of 0.33%, which exceeds the upper limit of 0.30% proposed in the present invention, and the formation of a retained austenite structure with excellent mechanical stability is suppressed. Delayed fracture cracks occurred.

次に、本発明による前記表1の発明例3の合金組成を満たす発明例3、比較例6-1~6-6を下記表3のような製造条件で製造し、最終ボルト製品を得た。 Next, Invention Example 3 and Comparative Examples 6-1 to 6-6 satisfying the alloy composition of Invention Example 3 in Table 1 according to the present invention were manufactured under the manufacturing conditions shown in Table 3 below to obtain final bolt products. .

Figure 2024500152000004
Figure 2024500152000004

本発明による仕上げ圧延温度、巻取温度、球状化熱処理温度およびオーステナイト化温度を満たす発明例3は、遅れ破壊クラックが発生しなかった。一方、比較例6-1は、圧延温度が990℃であり、本発明において提案する上限である980℃を超過し、巻取温度も940℃であり、本発明において提案する上限である930℃を超過し、線材において旧オーステナイト結晶粒径が粗大になり、ボルト製品の旧オーステナイト結晶粒径も粗大になるにつれて、遅れ破壊クラックが発生した。 In Invention Example 3, which satisfied the finish rolling temperature, coiling temperature, spheroidizing heat treatment temperature, and austenitizing temperature according to the present invention, delayed fracture cracks did not occur. On the other hand, in Comparative Example 6-1, the rolling temperature is 990°C, which exceeds the upper limit of 980°C proposed in the present invention, and the coiling temperature is 940°C, which is 930°C, which is the upper limit proposed in the present invention. was exceeded, the prior austenite crystal grain size in the wire became coarse, and as the prior austenite crystal grain size of the bolt product also became coarse, delayed fracture cracks occurred.

比較例6-2は、圧延温度が870℃であり、本発明において提案する下限である880℃に達せず、巻取温度も820℃であり、本発明において提案する下限である830℃に達せず、線材において旧オーステナイト結晶粒径が微細になり、ボルト製品の旧オーステナイト結晶粒径も微細になるにつれて、残留オーステナイト分率が高まり、遅れ破壊クラックが発生した。 In Comparative Example 6-2, the rolling temperature was 870°C, which did not reach the lower limit of 880°C proposed in the present invention, and the coiling temperature was 820°C, which did not reach the lower limit of 830°C proposed in the present invention. First, as the prior austenite crystal grain size in the wire became finer and the prior austenite crystal grain size in the bolt product also became finer, the retained austenite fraction increased and delayed fracture cracks occurred.

比較例6-3は、オーステナイト化熱処理温度が950℃であり、本発明において提案する上限である940℃を超過し、ボルト製品の旧オーステナイト結晶粒径が粗大になるにつれて、遅れ破壊クラックが発生した。 In Comparative Example 6-3, the austenitizing heat treatment temperature was 950°C, which exceeded the upper limit of 940°C proposed in the present invention, and delayed fracture cracks occurred as the prior austenite crystal grain size of the bolt product became coarser. did.

比較例6-4は、オーステナイト化熱処理温度が860℃であり、本発明において提案する下限である870℃に達せず、ボルト製品が十分にオーステナイト化しない状態でQT熱処理が行われ、未固溶のパーライトが形成され、これによって、遅れ破壊クラックが発生した。 In Comparative Example 6-4, the austenitizing heat treatment temperature was 860°C, which did not reach the lower limit of 870°C proposed in the present invention, and the QT heat treatment was performed in a state where the bolt product was not sufficiently austenitized. pearlite was formed, which caused delayed fracture cracks.

比較例6-5は、球状化温度が740℃であり、本発明において提案する下限である745℃に達せず、比較例6-6は、球状化温度が775℃であり、本発明において提案する上限である770℃を超過し、球状化率が低く、熱処理が十分に行われず、成形性が劣化し、遅れ破壊クラックが発生した。 Comparative Example 6-5 has a spheroidization temperature of 740°C, which does not reach the lower limit of 745°C proposed in the present invention, and Comparative Example 6-6 has a spheroidization temperature of 775°C, which does not reach the lower limit of 745°C proposed in the present invention. The upper limit of 770° C. was exceeded, the spheroidization rate was low, heat treatment was not performed sufficiently, formability deteriorated, and delayed fracture cracks occurred.

以上、本発明の例示的な実施例を説明したが、本発明は、これに限定されず、当該技術分野における通常の知識を有する者なら、本明細書に記載する請求範囲の概念と範囲を逸脱しない範囲内で多様な変更および変形が可能であることを理解することができる。

Although the exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and a person having ordinary knowledge in the technical field will understand the concept and scope of the claims described in this specification. It can be understood that various changes and modifications can be made without departing from the scope.

Claims (9)

重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、
下記関係式1を満たすことを特徴とする、遅れ破壊抵抗性が向上した線材。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
In weight%, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030 % or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%, the remainder consisting of Fe and inevitable impurities,
A wire rod with improved delayed fracture resistance, characterized by satisfying the following relational expression 1.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational formula 1, [Si] and [Mn] each mean the content (wt%) of the element)
下記関係式2を満たすことを特徴とする請求項1に記載の遅れ破壊抵抗性が向上した線材。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
The wire rod with improved delayed fracture resistance according to claim 1, which satisfies the following relational expression 2.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)
TiN介在物のサイズが15μm以下であることを特徴とする請求項1に記載の線材。 The wire according to claim 1, wherein the size of the TiN inclusions is 15 μm or less. 重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たす鋼材を880~980℃で仕上げ圧延する段階と、
830~930℃で巻き取る段階と、を含むことを特徴とする遅れ破壊抵抗性が向上した、線材の製造方法。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
In weight%, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030 % or less, including Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%, the remainder consisting of Fe and unavoidable impurities, and the following relationship Finish rolling a steel material satisfying formula 1 at 880 to 980°C;
A method for producing a wire with improved delayed fracture resistance, the method comprising the step of winding at 830 to 930°C.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational formula 1, [Si] and [Mn] each mean the content (wt%) of the element)
前記鋼材は、下記関係式2を満たすことを特徴とする請求項4に記載の線材の製造方法。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
5. The method for manufacturing a wire rod according to claim 4, wherein the steel material satisfies the following relational expression 2.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)
請求項4又は請求項5によって製造した線材を伸線する段階と、
前記伸線した線材を745~770℃で球状化熱処理する段階と、
前記球状化熱処理した線材を870~940℃の温度範囲で加熱する段階と、
前記球状化熱処理した線材を50~80℃の温度範囲で焼入する段階と、
前記焼入した部品を400~600℃の温度範囲で焼き戻しする段階と、を含むことを特徴とする遅れ破壊抵抗性が向上した部品の製造方法。
drawing the wire produced according to claim 4 or claim 5;
heat-treating the drawn wire rod at 745 to 770°C to spheroidize it;
heating the wire rod subjected to the spheroidization heat treatment in a temperature range of 870 to 940°C;
Quenching the spheroidized wire at a temperature range of 50 to 80°C;
A method for manufacturing a component with improved delayed fracture resistance, comprising the step of tempering the quenched component at a temperature range of 400 to 600°C.
重量%で、C:0.15~0.30%、Si:0.15~0.25%、Mn:0.95~1.35%、P:0.030%以下、S:0.030%以下、Ti:0.015~0.030%、B:0.0010~0.0040%、N:0.0010~0.0080%を含み、残部がFeおよび不可避な不純物からなり、下記関係式1を満たすことを特徴とする遅れ破壊抵抗性が向上した部品。
[関係式1]2.0≦5.5×[Si]+[Mn]≦2.4
(関係式1中、[Si]および[Mn]それぞれは、当該元素の含有量(重量%)を意味する)
In weight%, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030 % or less, including Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%, the remainder consisting of Fe and unavoidable impurities, and the following relationship A component with improved delayed fracture resistance, characterized by satisfying Formula 1.
[Relational expression 1] 2.0≦5.5×[Si]+[Mn]≦2.4
(In relational formula 1, [Si] and [Mn] each mean the content (wt%) of the element)
下記関係式2を満たすことを特徴とする請求項7に記載の部品。
[関係式2]1.0<[Ti]/3.42[N]<2.0
(関係式2中、[Ti]および[N]それぞれは、当該元素の含有量(重量%)を意味する)
The component according to claim 7, characterized in that the following relational expression 2 is satisfied.
[Relational expression 2] 1.0<[Ti]/3.42[N]<2.0
(In relational expression 2, [Ti] and [N] each mean the content (wt%) of the element)
体積分率で、残留オーステナイトを0.3~2%および残余の焼き戻しマルテンサイト組織を含むことを特徴とする請求項7に記載の部品。

8. Part according to claim 7, characterized in that it comprises, by volume fraction, 0.3 to 2% retained austenite and a residual tempered martensitic structure.

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JP3966493B2 (en) * 1999-05-26 2007-08-29 新日本製鐵株式会社 Cold forging wire and method for producing the same
TWI318645B (en) * 2005-02-16 2009-12-21 Nippon Steel Corp Hot rolled steel wire material having superior processability for cold forgine after spheroidization, spheroidized steel wire having superior processability for cold forgine and methods for manufacturing the same
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WO2011108459A1 (en) * 2010-03-02 2011-09-09 新日本製鐵株式会社 Steel wire with excellent cold forging characteristics and manufacturing process thereof
JP6034632B2 (en) * 2012-03-26 2016-11-30 株式会社神戸製鋼所 Boron-added steel for high strength bolts and high strength bolts with excellent delayed fracture resistance
JP5776623B2 (en) * 2012-05-08 2015-09-09 新日鐵住金株式会社 Steel wire rods / bars with excellent cold workability and manufacturing method thereof
KR101665886B1 (en) * 2015-09-04 2016-10-13 주식회사 포스코 Non-quenched and tempered steel having excellent cold workability and impact toughness and method for manufacturing same
CN107815594A (en) * 2017-11-12 2018-03-20 湖南华菱湘潭钢铁有限公司 A kind of production method of cold extrusion gear wire rod

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