KR102492644B1 - Wire rod and parts with improved delayed fracture resisitance and method for manufacturing the same - Google Patents
Wire rod and parts with improved delayed fracture resisitance and method for manufacturing the same Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/525—Heat 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous 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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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Abstract
지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법이 개시된다. 본 발명에 따른 지연파괴 저항성이 향상된 선재는 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함하고,
하기 관계식1을 만족한다.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
(관계식1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)Disclosed are wire rods and parts with improved delayed fracture resistance and a method for manufacturing the same. The wire rod with improved delayed fracture resistance according to the present invention contains, by weight, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the balance including Fe and unavoidable impurities,
The following relational expression 1 is satisfied.
[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
(In relational expression 1, each of [Si] and [Mn] means the content (% by weight) of the corresponding element)
Description
본 발명은 지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법에 관한 것으로, 더욱 상세하게는 다양한 응력 및 부식 환경에 노출되는 자동차, 구조물의 체결용 볼트 등에 사용할 수 있는 선재, 부품 및 그 제조방법에 관한 것이다.The present invention relates to wire rods, parts with improved delayed fracture resistance, and a method for manufacturing the same, and more particularly, to wire rods, parts, and manufacturing methods that can be used for fastening bolts of automobiles and structures exposed to various stress and corrosive environments. it's about
자동차, 구조물의 체결용 볼트 등의 소재로 사용되는 선재는 자동차의 경량화 및 구조물의 소형화에 따라 고강도화가 요구되고 있다. 일반적으로, 강재의 강도 증가를 위해서는 금속의 강화기구인 냉간가공, 결정립 미세화, 마르텐사이트 강화 및 석출강화 등을 활용하게 된다. Wire rods used as materials for fastening bolts of automobiles and structures are required to have high strength according to the weight reduction of automobiles and the miniaturization of structures. In general, in order to increase the strength of steel materials, cold working, crystal grain refinement, martensite strengthening, precipitation hardening, etc., which are metal strengthening mechanisms, are utilized.
그러나, 이러한 강화기구로 활용된 전위, 결정립계, 마르텐사이트 래쓰(lath) 경계 및 미세 석출물 경계 등은 강재 내 수소의 트랩부로 작용하여 지연파괴를 열위시키는 원인으로도 작용한다. 이러한 이유로, 인장강도 1GPa 이상의 고강도 볼트에서는 지연파괴가 열위해지는 문제가 있다.However, dislocations, grain boundaries, martensite lath boundaries and fine precipitate boundaries, etc., utilized as such a strengthening mechanism, act as hydrogen traps in steel materials and also act as a cause of inferior delayed fracture. For this reason, there is a problem that delayed fracture is inferior to high-strength bolts having a tensile strength of 1 GPa or more.
이러한 문제를 해결하기 위해 종래에는 템퍼드 마르텐사이트(Tempered Martensite) 조직을 갖는 1GPa 이상의 볼트용 강재는 Mo를 첨가한 Cr-Mo 합금강을 사용하고 있었으나, 볼트 제조공정 기술의 발전에 따른 원가절감 니즈에 대응하기 위해 Cr-Mo강을 Cr-B강으로 대체하려는 시도가 있어 왔다. 그 결과 안전에 큰 영향이 없는 구조물에 사용되는 볼트부터 Cr-B 강을 활용하여 원가절감을 구현하였고, 그 안전성을 확인한 후 자동차의 일부 체결용 볼트에도 Cr-B 강을 적용 중에 있다.In order to solve this problem, in the past, Cr-Mo alloy steel with Mo added was used for bolt steel with a tempered martensite structure of 1 GPa or more. To counter this, attempts have been made to replace Cr-Mo steel with Cr-B steel. As a result, cost reduction was realized by using Cr-B steel from bolts used in structures that do not have a significant impact on safety, and after confirming its safety, Cr-B steel is being applied to some fastening bolts of automobiles.
더 나아가, 자동차 업계에서는 극한의 원가절감을 위해 Cr-B 강 보다 더욱 원가절감이 가능한 볼트용 소재를 개발하기 위한 니즈가 있다. 이러한 니즈에 대응하기 위하여 최근에는 Cr 대비 저렴한 Mn을 활용하는 Mn-B 강을 1GPa 이상의 고강도 볼트용 소재로 적용하기 위한 기술 개발이 이루어지고 있다. Furthermore, in the automobile industry, there is a need to develop a material for bolts that is more cost-effective than Cr-B steel for extreme cost reduction. In order to respond to these needs, recently, technology development has been made to apply Mn-B steel, which uses Mn, which is inexpensive compared to Cr, as a material for high-strength bolts of 1 GPa or more.
그러나, Mn은 Cr에 비해 페라이트 기지 내 높은 고용강화를 유발하므로 Mn-B의 강은 볼트제조시 볼트의 나사부에 크랙이 발생할 수 있다. 따라서 1GPa 이상의 고강도 볼트로 제조하기 위해 첨가되는 Mn의 함량이 높은 강은 볼트 나사부의 크랙에 의해 지연파괴가 발생할 수 있는 단점이 있어 고강도 볼트로 적용하기에 어려움이 있다.However, since Mn causes higher solid solution hardening in the ferrite matrix than Cr, Mn-B steel may cause cracks in the threaded part of the bolt when manufacturing the bolt. Therefore, steel with a high Mn content added to manufacture high-strength bolts of 1 GPa or more has a disadvantage in that delayed fracture may occur due to cracks in bolt threads, making it difficult to apply them as high-strength bolts.
본 발명의 일 측면은 합금 원소의 제어를 통해, Mn-B강의 고용강화 효과를 최적화하고, 성형성을 향상시킴으로써 지연파괴 저항성이 향상된 고강도 볼트용 선재, 볼트 및 그 제조방법을 제공하고자 한다. One aspect of the present invention is to provide a high-strength bolt wire rod with improved delayed fracture resistance by optimizing the solid solution strengthening effect of Mn-B steel and improving formability through control of alloy elements, a bolt, and a manufacturing method thereof.
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재는 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 관계식1을 만족한다. The wire rod with improved delayed fracture resistance according to an embodiment of the present invention contains, by weight, C: 0.15 to 0.3%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030% Hereinafter, Ti: 0.015 to 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the remainder including Fe and unavoidable impurities, and satisfying the following relational expression 1.
[관계식1] 2.0 
(관계식1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 1, each of [Si] and [Mn] means the content (% by weight) of the corresponding element)
또한, 본 발명의 일 실시 예에 따르면, 하기 관계식2를 만족할 수 있다.In addition, according to an embodiment of the present invention, the following relational expression 2 may be satisfied.
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(관계식2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 2, each of [Ti] and [N] means the content (wt%) of the corresponding element)
또한, 본 발명의 일 실시 예에 따르면, TiN 개재물의 크기는, 15㎛ 이하일 수 있다.In addition, according to an embodiment of the present invention, the size of the TiN inclusions may be 15 μm or less.
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재의 제조방법은 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 관계식1을 만족하는 강재를 880 내지 980℃에서 마무리 압연하는 단계; 및In the method for manufacturing a wire rod having improved delayed fracture resistance according to an embodiment of the present invention, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the rest includes Fe and unavoidable impurities, and finishes steel materials satisfying the following relational expression 1 at 880 to 980 ° C. rolling; and
830 내지 930℃에서 권취하는 단계;를 포함한다.It includes; winding at 830 to 930 ° C.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
(관계식1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 1, each of [Si] and [Mn] means the content (% by weight) of the corresponding element)
또한, 본 발명의 일 실시 예에 따르면, 강재는 하기 관계식2를 만족할 수 있다.In addition, according to an embodiment of the present invention, the steel material may satisfy the following relational expression 2.
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(관계식2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 2, each of [Ti] and [N] means the content (wt%) of the corresponding element)
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 부품의 제조방법은 본 발명에 따라 제조된 선재를 신선하는 단계; 신선재를 745 내지 770℃에서 구상화 열처리하는 단계; 구상화 열처리된 신선재를 870 내지 940℃의 온도 범위에서 가열하는 단계; 구상화 열처리된 신선재를 50 내지 80℃의 온도 범위에서 담금질하는 단계; 및 담금질된 부품을 400 내지 600℃의 온도범위에서 템퍼링하는 단계;를 포함한다. A manufacturing method of a part having improved delayed fracture resistance according to an embodiment of the present invention includes the steps of drawing a wire rod manufactured according to the present invention; Spheroidizing heat treatment of the wire rod at 745 to 770 ° C; Heating the spheroidizing heat-treated wire rod in a temperature range of 870 to 940 ° C; Quenching the spheroidizing heat-treated wire rod in a temperature range of 50 to 80 ° C; and tempering the quenched part in a temperature range of 400 to 600°C.
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 부품은 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 관계식1을 만족한다. Parts with improved delayed fracture resistance according to an embodiment of the present invention, in weight%, C: 0.15 to 0.3%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030% Hereinafter, Ti: 0.015 to 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the remainder including Fe and unavoidable impurities, and satisfying the following relational expression 1.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
(관계식1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 1, each of [Si] and [Mn] means the content (% by weight) of the corresponding element)
또한, 본 발명의 일 실시 예에 따르면, 부품은 하기 관계식2를 만족한다.In addition, according to an embodiment of the present invention, the component satisfies the following relational expression 2.
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0 [Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(관계식2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)(In relational expression 2, each of [Ti] and [N] means the content (wt%) of the corresponding element)
또한, 본 발명의 일 실시 예에 따르면, 부품은 부피 분율로, 잔류 오스테나이트를 0.3 내지 2% 및 잔여 템퍼드 마르텐사이트 조직을 포함한다.In addition, according to one embodiment of the present invention, the part includes retained austenite in a volume fraction of 0.3 to 2% and a residual tempered martensitic structure.
본 발명의 실시 예에 따른 지연파괴 저항성이 향상된 고강도 볼트용 부품은 Mn-B 강의 볼트 나사부 가공시의 성형성을 향상시킴으로써, 볼트 나사부의 크랙을 발생시키지 않아 1Gpa급 고강도 볼트에서 지연파괴를 억제할 수 있다.The high-strength bolt component with improved delayed fracture resistance according to an embodiment of the present invention improves formability during processing of the bolt thread of Mn-B steel, thereby suppressing delayed fracture in a 1Gpa class high-strength bolt without cracking the bolt thread. can
도1은 지연파괴 저항성 평가 전 비교예3의 나사부를 관찰한 사진이다.1 is a photograph of the screw portion of Comparative Example 3 before evaluation of delayed fracture resistance.
본 명세서가 실시 예들의 모든 요소들을 설명하는 것은 아니며, 본 발명이 속하는 기술분야에서 일반적인 내용 또는 실시 예들 간에 중복되는 내용은 생략한다. This specification does not describe all elements of the embodiments, and general content or overlapping content between the embodiments in the technical field to which the present invention pertains will be omitted.
또한 어떤 부분이 어떤 구성요소를 "포함"한다고 할 때, 이는 특별히 반대되는 기재가 없는 한 다른 구성요소를 제외하는 것이 아니라 다른 구성요소를 더 포함할 수 있는 것을 의미한다.In addition, when a certain component is said to "include", this means that it may further include other components without excluding other components unless otherwise stated.
단수의 표현은 문맥상 명백하게 예외가 있지 않는 한, 복수의 표현을 포함한다.Expressions in the singular number include plural expressions unless the context clearly dictates otherwise.
이하, 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail.
이하의 실시 예는 본 발명이 속하는 기술분야에서 통상의 지식을 가진 자에게 본 발명의 사상을 충분히 전달하기 위해 제시하는 것이다. 본 발명은 여기서 제시한 실시예만으로 한정되지 않고 다른 형태로 구체화될 수도 있다. The following examples are presented to sufficiently convey the spirit of the present invention to those skilled in the art. The present invention may be embodied in other forms without being limited only to the embodiments presented here.
본 발명의 발명자들은 Si 및 Mn의 함량을 제어하면 고용강화 효과를 최적화하여 강도를 확보하면서도 성형성을 향상시킬 수 있고, 나사부의 성형열위에 의한 크랙 발생이 억제되어 지연파괴저항성을 향상시킬 수 있다는 것을 알아내었다.The inventors of the present invention believe that controlling the contents of Si and Mn can optimize the solid solution strengthening effect to improve formability while securing strength, and suppress crack generation due to molding heat of the threaded portion to improve delayed fracture resistance. found out what
또한, Ti 및 N의 함량을 제어하고, TiN 개재물의 크기를 제어함으로써 결정립을 미세화할 수 있고, 이에 따라 성형성이 향상되고, 지연파괴저항성을 확보할 수 있다는 것을 알아내고, 본 발명을 완성하기에 이르렀다.In addition, by controlling the contents of Ti and N and controlling the size of TiN inclusions, it is possible to refine the crystal grains, thereby improving formability and securing delayed fracture resistance, and to complete the present invention. has reached
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재는 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함한다.The wire rod with improved delayed fracture resistance according to an embodiment of the present invention contains, by weight, C: 0.15 to 0.3%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030% Hereinafter, Ti: 0.015 to 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the balance including Fe and unavoidable impurities.
이하, 본 발명의 실시 예에서의 합금성분 원소 함량의 수치한정 이유에 대하여 설명한다. 이하에서는 특별한 언급이 없는 한 단위는 중량%이다.Hereinafter, the reason for limiting the numerical value of the alloy component element content in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, units are % by weight.
C의 함량은 0.15 내지 0.3%이다.The content of C is 0.15 to 0.3%.
C는 제품의 강도를 확보하기 위해 첨가되는 원소이다. 탄소 함량이 0.15% 미만일 경우, 본 발명에서 목표하는 강도를 확보하는 것이 어렵고, 0.30%를 초과하는 경우, 담금질(Quenching)시 래쓰 마르텐사이트(lath Martensite) 경계에서 정수압에 의해 형성되는 기계적 안정성(mechanical stabilization)이 우수한 잔류 오스테나이트 형성을 방해하여, 지연파괴 저항성이 열위해질 수 있다. 따라서, 본 발명에서는 C의 함량을 0.15 내지 0.30%로 제한한다.C is an element added to ensure product strength. If the carbon content is less than 0.15%, it is difficult to secure the target strength in the present invention, and if it exceeds 0.30%, the mechanical stability formed by hydrostatic pressure at the lath martensite boundary during quenching (quenching) stabilization) may hinder the formation of excellent retained austenite, resulting in poor delayed fracture resistance. Therefore, in the present invention, the content of C is limited to 0.15 to 0.30%.
Si의 함량은 0.15 내지 0.25%이다. The content of Si is 0.15 to 0.25%.
Si은 강의 탈산을 위해서 유용할 뿐만 아니라, 고용 강화를 통한 강도 확보에도 효과적인 원소이다. Si의 함량이 0.15% 미만일 경우, 강의 탈산 및 고용 강화를 통한 강도 확보가 충분치 않고, 0.25%를 초과하는 경우에는 고용강화에 의한 성형성 및 충격특성이 열위해질 수 있다. 따라서, 본 발명에서는 Si의 함량을 0.15 내지 0.25%로 제한한다. Si is not only useful for deoxidation of steel, but also an effective element for securing strength through solid solution strengthening. When the content of Si is less than 0.15%, strength is not sufficiently secured through deoxidation and solid solution strengthening of the steel, and when it exceeds 0.25%, formability and impact properties due to solid solution strengthening may be inferior. Therefore, in the present invention, the content of Si is limited to 0.15 to 0.25%.
Mn의 함량은 0.95 내지 1.35%이다.The content of Mn is 0.95 to 1.35%.
Mn은 경화능을 향상시키는 원소이고, 기지조직 내에 치환형 고용체를 형성하여 고용강화 효과를 내는 매우 유용한 원소이다. Mn의 함량이 0.95% 미만인 경우, 전술한 고용강화 효과와 경화능이 충분하지 못하여 본 발명에서 목표로하는 강도 확보가 어렵고, 1.35%를 초과하는 경우에는 고용강화 효과에 의해 성형성이 열위해질 수 있다. 따라서, 본 발명에서는 Mn의 함량을 0.95 내지 1.35%로 제한한다.Mn is an element that improves hardenability and is a very useful element that produces a solid solution strengthening effect by forming a substitutional solid solution in a matrix structure. When the content of Mn is less than 0.95%, the above-mentioned solid solution strengthening effect and hardenability are not sufficient, making it difficult to secure the target strength in the present invention. . Therefore, in the present invention, the content of Mn is limited to 0.95 to 1.35%.
P의 함량은 0.030% 이하이다. (0%는 제외)The content of P is 0.030% or less. (Excluding 0%)
P은 결정립계에 편석되어 인성을 저하시키고, 지연파괴 저항성을 감소시키는 원소이다. 따라서, 본 발명에서는 P의 상한을 0.030%로 제한한다.P is an element that is segregated at grain boundaries to decrease toughness and reduce delayed fracture resistance. Therefore, in the present invention, the upper limit of P is limited to 0.030%.
S의 함량은 0.030% 이하이다. (0%는 제외)The content of S is 0.030% or less. (Excluding 0%)
S은 P과 마찬가지로 결정립계에 편석되어 인성을 저하시킬 뿐만 아니라, 저융점 유화물을 형성시켜 열간 압연을 저해하는 원소이다. 따라서, 본 발명에서는 S의 상한을 0.030%로 제한한다.S, like P, is an element that segregates at grain boundaries to reduce toughness and also inhibits hot rolling by forming a low-melting emulsifier. Therefore, in the present invention, the upper limit of S is limited to 0.030%.
Ti의 함량은 0.015 내지 0.03% 이다.The content of Ti is 0.015 to 0.03%.
Ti은 강중 내 유입되는 N와 결합하여 티타늄 탄질화물(TiN)을 형성하는 원소이다. 본 발명에서 TiN은 결정립을 미세화함으로써, 부품 성형시 성형 열위에 의한 크랙 발생을 억제하고, 지연파괴저항성을 향상시킬 수 있다. 또한, Ti는 TiN을 형성하므로, free-N(자유 N)이 B과 결합하는 것을 방지하여, 성형성을 열위하게하는 BN 형성을 억제시킬 수도 있다. Ti의 함량이 0.015% 미만인 경우, 전술한 바와 같이 충분한 TiN이 형성되지 못하고, 자유 N이 BN을 형성하므로, B의 경화능 효과를 활용하기 어렵고, 0.03%를 초과하는 경우에는 조대한 탄질화물이 형성되어 지연파괴 저항성이 열위해질 수 있다. 따라서, 본 발명에서는 Ti의 함량을 0.015 내지 0.03%로 제한한다.Ti is an element that combines with N introduced into steel to form titanium carbonitride (TiN). In the present invention, by miniaturizing the crystal grains of TiN, it is possible to suppress the generation of cracks due to molding defects during part molding and to improve delayed fracture resistance. In addition, since Ti forms TiN, it is also possible to prevent free-N (free N) from binding to B, thereby suppressing the formation of BN, which deteriorates formability. When the content of Ti is less than 0.015%, sufficient TiN is not formed as described above, and since free N forms BN, it is difficult to utilize the hardenability effect of B, and when the content exceeds 0.03%, coarse carbonitrides are formed. Formation may lead to poor delayed fracture resistance. Therefore, in the present invention, the content of Ti is limited to 0.015 to 0.03%.
B의 함량은 0.001 내지 0.004% 이다.The content of B is 0.001 to 0.004%.
B은 경화능을 향상시키는 원소이다. B의 함량이 0.001% 미만인 경우, 전술한 경화능 향상 효과를 기대하기 어렵고, 0.004%를 초과하는 경우에는 결정립계에 Fe23(CB)6 탄화물을 형성시켜 오스테나이트 결정립계의 취성을 유발하고, BN을 형성하여 성형성을 열위하게함으로써 지연파괴 저항성을 열위하게한다. 따라서, 본 발명에서는 B함량을 0.001 내지 0.004%로 제한한다.B is an element that improves hardenability. If the B content is less than 0.001%, it is difficult to expect the above-mentioned hardenability improvement effect, and if it exceeds 0.004%, Fe 23 (CB) 6 carbides are formed at the grain boundaries to cause brittleness of austenite grain boundaries, and BN By forming it, the moldability is inferior, and the delayed fracture resistance is inferior. Therefore, in the present invention, the B content is limited to 0.001 to 0.004%.
N의 함량은 0.001 내지 0.008% 이다.The content of N is 0.001 to 0.008%.
N은 탄질화물을 형성하는 원소이다. N의 함량이 0.001% 미만일 경우, 결정립을 미세화하는 TiN 석출물을 충분히 형성할 수 없고, 0.008%를 초과할 경우, 고용 질소량이 증가하여 강의 인성 및 연성이 열위해질 수 있고, free-N(자유 N)이 B과 결합하여, 성형성을 열위하게하는 BN을 형성할 수 있다. 따라서, 본 발명에서는 N의 함량을 0.001 내지 0.008%로 제한한다.N is an element that forms carbonitrides. If the content of N is less than 0.001%, it is not possible to sufficiently form TiN precipitates that refine crystal grains, and if it exceeds 0.008%, the amount of solid solution nitrogen may increase and the toughness and ductility of the steel may be inferior, and free-N (free N ) may combine with B to form BN, which deteriorates formability. Therefore, in the present invention, the N content is limited to 0.001 to 0.008%.
합금조성 외 잔부는 Fe이다. 본 발명의 지연파괴 저항성이 향상된 선재는 통상 강의 공업적 생산 과정에서 포함될 수 있는 기타의 불순물을 포함할 수 있다. 이러한 불순물들은 본 발명이 속하는 기술분야에서 통상의 지식을 가지는 자라면 누구라도 알 수 있는 내용이므로 본 발명에서 특별히 그 종류와 함량을 제한하지는 않는다.The balance other than the alloy composition is Fe. The wire rod having improved delayed fracture resistance of the present invention may contain other impurities that may be included in a typical industrial production process of steel. Since these impurities can be known by anyone having ordinary knowledge in the art to which the present invention belongs, the type and content are not particularly limited in the present invention.
본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재는 하기 관계식 1을 만족한다. The wire rod having improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression 1.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
관계식1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다. In relational expression 1, each of [Si] and [Mn] means the content (wt%) of the corresponding element.
본 발명에서는 Si 및 Mn의 함량을 제어하여 고용강화 효과를 통해 강도를 확보하면서도, 지나친 고용강화 효과를 억제하여 선재의 성형성을 향상시키고, 지연파괴저항성을 향상시키고자 하였다. 이에 따라 도출된 관계식 1은 고용강화 효과를 최적화하기 위한 수식이다. 관계식 1의 5.5Х[Si]+[Mn] 값이 2.0 미만일 경우, 본 발명에서 목표로하는 강도를 확보할 수 없고, 5.5Х[Si]+[Mn] 값이 2.4를 초과할 경우, 지나친 고용강화 효과로 고강도 부품의 성형시, 성형 열위에 의한 크랙이 발생하여, 지연파괴를 유발할 수 있다. 따라서, 본 발명에서는 지연파괴저항성을 향상시키기 위해 5.5Х[Si]+[Mn]의 값을 2.0 내지 2.4로 제한한다. In the present invention, while securing the strength through the solid solution strengthening effect by controlling the contents of Si and Mn, it is intended to improve the formability of the wire rod and improve the delayed fracture resistance by suppressing the excessive solid solution strengthening effect. Relational Equation 1 derived accordingly is a formula for optimizing the employment enhancement effect. When the value of 5.5Х[Si]+[Mn] in relational expression 1 is less than 2.0, the target strength in the present invention cannot be secured, and when the value of 5.5Х[Si]+[Mn] exceeds 2.4, excessive employment During molding of high-strength parts due to the strengthening effect, cracks may occur due to molding defects, which may cause delayed fracture. Therefore, in the present invention, the value of 5.5Х[Si]+[Mn] is limited to 2.0 to 2.4 in order to improve the delayed fracture resistance.
또한, 본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재는 하기 관계식2를 만족한다.In addition, the wire rod having improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression 2.
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
관계식2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다. In relational expression 2, each of [Ti] and [N] means the content (wt%) of the corresponding element.
본 발명에서는 결정립을 미세화하고, 성형성을 향상시킴으로써 선재의 지연파괴저항성을 향상시키고자 하였다. 본 발명의 발명자들은 연구 끝에 TiN 개재물을 형성하고, 그 크기를 제어하여 결정립을 미세화하고, BN을 억제함으로써 성형성 및 지연파괴저항성을 확보할 수 있었다. 이에 따라 도출된 관계식2는 TiN 개재물 크기를 제어하고, BN의 형성을 억제하기 위한 수식이다. 관계식2의 [Ti]/3.42[N] 값이 1.0 이하일 경우, Ti와 결합하지 않은 free-N에 의해 형성되는 BN 등에 의해 성형성이 열위해질 수 있고, [Ti]/3.42[N] 값이 2.0 이상일 경우 초과 Ti(excess Ti)에 의해 TiN이 조대화되고, 결정립 미세화 효과를 발휘할 수 없다. 따라서, 본 발명에서는 [Ti]/3.42[N] 값을 1.0 내지 2.0으로 제한한다. In the present invention, it is intended to improve the delayed fracture resistance of the wire rod by miniaturizing the crystal grains and improving the formability. After research, the inventors of the present invention were able to secure formability and delayed fracture resistance by forming TiN inclusions, controlling their size to refine crystal grains, and suppressing BN. Relational Expression 2 derived accordingly is a formula for controlling the size of TiN inclusions and suppressing the formation of BN. When the value of [Ti]/3.42[N] in relational expression 2 is 1.0 or less, formability may be deteriorated due to BN formed by free-N not bonded to Ti, and the value of [Ti]/3.42[N] is When it is 2.0 or more, TiN is coarsened by excess Ti (excess Ti), and the crystal grain refinement effect cannot be exhibited. Therefore, in the present invention, the value of [Ti]/3.42[N] is limited to 1.0 to 2.0.
본 발명에서 결정립을 미세화하기 위한 TiN 개재물의 크기는 15㎛ 이하일 수 있다. 전술할 것처럼 TiN 개재물의 최대 크기가 15㎛를 초과할 경우, 결정립 미세화로 인한 지연파괴 저항성을 확보하기 어렵다.In the present invention, the size of TiN inclusions for miniaturizing 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 secure delayed fracture resistance due to crystal grain refinement.
또한, 본 발명에 따른 선재에 의해 제조된 지연파괴 저항성이 향상된 부품은 부피 분율로, 잔류 오스테나이트를 0.3 내지 2% 및 잔여 템퍼드 마르텐사이트 조직을 포함한다. 잔류 오스테나이트 조직 분율이 0.3% 미만일 경우, 지연파괴 저항성을 열위하게 하는 수소확산을 지연시키는 장애물 역할을 기대하기 어렵고, 2%를 초과할 경우, 잔류 오스테나이트가 래쓰 경계뿐 아니라, 오스테나이트 결정립계 등에 두껍게 형성되어 수소 확산을 지연시키기 어렵고, 이에 따라 지연파괴 저항성 개선효과가 저감될 수 있다.In addition, the part with improved delayed fracture resistance manufactured by the wire rod according to the present invention includes retained austenite in a volume fraction of 0.3 to 2% and a residual tempered martensitic structure. If the retained austenite structure fraction is less than 0.3%, it is difficult to expect an obstacle to delay hydrogen diffusion that deteriorates the delayed fracture resistance. Since it is formed thick, it is difficult to delay hydrogen diffusion, and accordingly, the effect of improving delayed fracture resistance may be reduced.
다음으로, 본 발명의 일 실시 예에 따른 지연파괴 저항성이 향상된 선재 및 부품의 제조방법에 대하여 설명한다.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.
본 발명에 따른 지연파괴 저항성이 향상된 선재 및 부품은 다양한 방법으로 제조될 수 있으며, 그 제조방법은 특별히 제한되지 않는다. 다만, 일 실시 예로써 다음과 같은 방법에 의해 제조될 수 있다. The wire rod and parts 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 an example, it may be manufactured by the following method.
본 발명에 따른 지연파괴 저항성이 향상된 선재는 중량%로, C: 0.15 내지 0.3%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.03%, B: 0.001 내지 0.004%, N: 0.001 내지 0.008%, 나머지는 Fe 및 불가피한 불순물을 포함하는 강재를 880 내지 980℃에서 마무리 압연하는 단계; 및 830 내지 930℃에서 권취하는 단계;를 포함한다.The wire rod with improved delayed fracture resistance according to the present invention contains, by weight, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004%, N: 0.001 to 0.008%, the rest comprising Fe and unavoidable impurities, finishing rolling at 880 to 980 ° C; and winding at 830 to 930°C.
먼저, 전술한 합금 조성을 만족하는 강재를 마련하고, 880 내지 980℃에서 마무리 선재 압연한다. 이후, 압연된 선재를 830 내지 930℃에서 코일 형상으로 권취한다. First, a steel material satisfying the alloy composition described above is prepared, and finish wire rolling is performed at 880 to 980 ° C. Thereafter, the rolled wire is wound into a coil shape at 830 to 930 ° C.
이때, 선재압연 온도가 880℃ 미만이거나 또는 권취 온도가 830℃ 미만일 경우, 표면층이 준 2상역이기때문에 상변태에 의한 표면 페라이트 탈탄층이 형성될 수 있고, 볼트의 열처리시에도 표면에 페라이트 탈탄층이 형성되어 지연파괴 저항성을 열위해질 수 있다. 또한, 볼트 제품의 구오스테나이트 결정립 크기가 미세해지고, 잔류 오스테나이트 분율이 높아져 지연파괴 저항성을 열위해질 수 있다. 한편, 선재 마무리압연 온도가 980℃를 초과하거나 권취온도가 930℃를 초과할 경우, 확산에 의해 탈탄이 가속화되어 표면에 페라이트 탈탄층이 형성될 수 있고, 구오스테나이트 결정립 크기가 조대해져, 지연파괴 저항성을 열위해질 수 있다. At this time, when the wire rolling temperature is less than 880 ° C or the coiling temperature is less than 830 ° C, a surface ferrite decarburized layer can be formed by phase transformation because the surface layer is a quasi-two-phase, and a ferrite decarburized layer is formed on the surface even during the heat treatment of the bolt. It can form and deteriorate the delayed fracture resistance. In addition, the size of the old austenite crystal grains of the bolt product becomes fine, and the retained austenite fraction increases, resulting in inferior delayed fracture resistance. On the other hand, when the wire rod finish rolling temperature exceeds 980 ° C or the coiling temperature exceeds 930 ° C, decarburization is accelerated by diffusion, a ferrite decarburized layer may be formed on the surface, and the prior austenite grain size becomes coarse, resulting in a delay. The fracture resistance may be inferior.
이어서, 권취된 선재는 목적에 맞게 신선-구상화열처리-피막처리-볼트 성형-오스테나이트화(austenitenizing)-담금질-템퍼링하여 최종 볼트용 부품으로 제조될 수 있다. 다만, 일 실시 예로써 다음과 같은 방법에 의해 제조될 수 있다. Subsequently, the coiled wire rod may be manufactured into final parts for bolts by wire drawing, spheroidizing heat treatment, coating treatment, bolt forming, austenizing, quenching, and tempering according to the purpose. However, as an example, it may be manufactured by the following method.
본 발명의 일 실시 예에 따른 볼트용 부품의 제조방법은, 본 발명에 따라 제조된 선재를 신선하는 단계; 신선재를 745 내지 770℃에서 구상화 열처리하는 단계; 구상화 열처리된 신선재를 870 내지 940℃에서 가열하는 단계; 구상화 열처리된 신선재를 50 내지 80℃에서 담금질하는 단계; 및 400 내지 600℃에서 템퍼링하는 단계;를 포함한다. A manufacturing method of a component for a bolt according to an embodiment of the present invention includes the steps of drawing a wire rod manufactured according to the present invention; Spheroidizing heat treatment of the wire rod at 745 to 770 ° C; Heating the spheroidizing heat-treated wire rod at 870 to 940 ° C; Quenching the spheroidizing heat-treated wire rod at 50 to 80 ° C.; and tempering at 400 to 600°C.
이때, 구상화 열처리는 745 내지 770℃에서 수행될 수 있다. 열처리 온도가 745℃ 미만이거나 770℃를 초과할 경우, 구상화율이 낮아짐에따라, 구상화 열처리재의 경도가 높아지고 볼트 성형 후 나사부 가공 시 성형성이 열위해지며, 이로 인해 나사부 크랙을 유발할 수 있다.At this time, the spheroidization heat treatment may be performed at 745 to 770 ° C. When the heat treatment temperature is less than 745 ° C or exceeds 770 ° C, as the spheroidization rate decreases, the hardness of the spheroidized heat treatment material increases and the moldability deteriorates during thread processing after bolt molding, which may cause thread cracks.
오스테나이트화 열처리는 870 내지 940℃에서 수행될 수 있다. 열처리 온도가 870℃ 미만일 경우, 오스테나이트 역변태가 충분히 일어나지 않아 담금질 후 마르텐사이트 조직이 불균일하게 형성되어 인성이 열위해질 수 있다. 한편, 열처리 온도가 940℃를 초과할 경우, 구오스테나이트 결정립도가 조대해져 지연파괴 저항성이 열위해질 수 있다. The austenitizing heat treatment may be performed at 870 to 940 °C. When the heat treatment temperature is less than 870° C., reverse austenite transformation does not sufficiently occur, and a martensitic structure is non-uniformly formed after quenching, resulting in inferior toughness. On the other hand, when the heat treatment temperature exceeds 940 ° C., the grain size of prior austenite becomes coarse, and delayed fracture resistance may be inferior.
또한, 담금질은 50 내지 80℃의 온도 범위에서 수행될 수 있다. 담금질 냉매의 온도가 50℃ 미만일 경우, 볼트의 나사산에서 열변형에 의한 미세한 담금질 균열(Quenching Crack)이 발생할 수 있어 지연파괴를 유발할 수 있고, 80℃를 초과할 경우, 충분한 소입이 되지 않아 래쓰에 기계적 안정 잔류 오스테나이트 외에 구오스테나이트 결정립계에 잔류 오스테나이트가 형성되고, 오히려 수소의 집적부로 작용하여 지연파괴를 유발할 수 있다.In addition, quenching may be performed in a temperature range of 50 to 80 °C. If the temperature of the quenching refrigerant is less than 50℃, fine quenching cracks due to thermal deformation may occur in the thread of the bolt, causing delayed fracture. In addition to mechanically stable retained austenite, retained austenite is formed at the old austenite grain boundary, and rather acts as a hydrogen accumulator to cause delayed fracture.
또한, 템퍼링은 400 내지 600℃의 온도 범위에서 수행될 수 있고, 최종 제품의 용도 및 목적에 맞게 강도 및 인성을 부여할 수 있다. 템퍼링 온도가 400℃ 미만일 경우, 템퍼링에 의한 취성이 유발될 수 있고, 600℃를 초과할 경우 본 발명에서 의도하는 강도를 구현하기 어렵다. In addition, tempering may be performed in a temperature range of 400 to 600 ° C., and strength and toughness may be imparted to suit the use and purpose of the final product. When the tempering temperature is less than 400 ° C, brittleness due to tempering may be induced, and when it exceeds 600 ° C, it is difficult to implement the strength intended in the present invention.
본 발명에 따라 제조된 지연파괴 저항성이 향상된 부품은 부피 분율로, 잔류 오스테나이트를 0.3 내지 2% 및 잔여 템퍼드 마르텐사이트 조직을 포함한다. The part with improved delayed fracture resistance manufactured according to the present invention contains retained austenite in a volume fraction of 0.3 to 2% and a residual tempered martensitic structure.
이하, 본 발명을 실시예를 통하여 보다 상세하게 설명한다. 그러나, 이러한 실시예의 기재는 본 발명의 실시를 예시하기 위한 것일 뿐 이러한 실시예의 기재에 의하여 본 발명이 제한되는 것은 아니다. 본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의하여 결정되는 것이기 때문이다.Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is only for exemplifying the practice of the present invention, and the present invention is not limited by the description of these examples. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.
실시 예embodiment
하기 표 1의 합금 조성을 만족하는 발명예 1 내지 9, 비교예 1 내지 7의 선재를 본 발명에 따른 제조 조건으로 제조하여 최종 시험용 볼트를 얻었다. 구체적으로, 하기 표 1의 합금 조성을 만족하는 강편을 880 내지 980℃에서 마무리 선재압연하고, 830 내지 930℃에서 코일 형상으로 권취한 후, 권취된 선재를 최대온도 745 내지 770℃에서 구상화 열처리하였다. 이어서, 구상화 열처리된 선재를 볼트로 성형하고, 870 내지 940℃에서 오스테나이트화한 후 50 내지 80℃의 냉매에 담금질하고, 이후, 1050±16 MPa의 인장강도를 확보하기 위해 400 내지 600℃의 온도에서 템퍼링하여 최종 볼트 제품을 얻었다. Wire rods of Inventive Examples 1 to 9 and Comparative Examples 1 to 7 satisfying the alloy compositions shown in Table 1 below were manufactured under manufacturing conditions according to the present invention to obtain final test bolts. Specifically, a steel piece satisfying the alloy composition of Table 1 below was finished wire rod rolled at 880 to 980 ° C, wound into a coil shape at 830 to 930 ° C, and then the coiled wire rod was spheroidized at a maximum temperature of 745 to 770 ° C. It was heat treated. Subsequently, the wire rod subjected to spheroidizing heat treatment is formed into bolts, austenitized at 870 to 940 ° C, quenched in a refrigerant at 50 to 80 ° C, and then heated at 400 to 600 ° C to secure a tensile strength of 1050 ± 16 MPa. Tempering at this temperature gave the final bolted product.
이어서, 발명예 1 내지 9, 비교예 1 내지 7의 볼트 제품에 대하여 TiN 석출물 최대 크기, 지연파괴 크랙 유무를 평가하고, 관계식1 및 관계식2 값과 함께 표2에 나타내었다.TiN 석출물의 최대 크기는 볼트 제품을 L단면(Longitudinal direction)으로 절개하고, 160mm2 면적을 30 field 관찰하여 극치통계 분석(extreme value analysis)을 통하여 측정되는 개재물의 크기를 최대 개재물 크기로 정의하고, 그 값을 하기 표2에 나타내었다. Subsequently, the maximum size of TiN precipitates and the presence or absence of delayed fracture cracks were evaluated for the bolt products of Inventive Examples 1 to 9 and Comparative Examples 1 to 7, and are shown in Table 2 together with the values of Relational Expression 1 and Relational Expression 2. Maximum size of TiN precipitates cuts the bolt product in the L section (Longitudinal direction), observes a 160 mm 2 area in 30 fields, defines the size of the inclusion measured through extreme value analysis as the maximum inclusion size, and the value is shown in the table below 2.
지연파괴저항성은 볼트 제품을 항복강도의 체결력으로 구조물에 체결한 후, 5% 염산 + 95% 증류수 용액에 10분간 침지하고, 응력집중부인 나사산에 크랙 유무를 관찰하는 지연파괴 모사법으로 진행하였다. 크랙이 발생되지 않는 경우는 X, 크랙이 발생된 경우는 ○로 나타내었다.The delayed fracture resistance was performed by a delayed fracture simulation method in which the bolt product was fastened to the structure with the clamping force of the yield strength, immersed in 5% hydrochloric acid + 95% distilled water solution for 10 minutes, and the presence or absence of cracks was observed in the screw thread, which was the stress concentration part. The case where cracks did not occur was indicated by X, and the case where cracks occurred was indicated by ○.
5.5Si+Mnrelational expression 1
5.5Si+Mn
Ti/3.42Nrelational expression 2
Ti/3.42N
(㎛)TiN max size
(μm)
크랙 유무delayed destruction
presence or absence of cracks
표2에서 확인할 수 있듯이, 본 발명에서 제안하는 합금 조성, 관계식 및 TiN 크기를 만족하는 발명예1 내지 발명예6은 지연파괴 저항성 평가 전/후에서 볼트 제품의 나사부에서 지연파괴 크랙이 발생하지 않았다.반면, 비교예1은 Ti/3.42N 값이 2.506으로 본 발명에서 제안하는 하한값인 2.0을 초과하여, 조대한 TiN이 형성되었고, 이로 인해 지연파괴 크랙이 발생하였다.As can be seen in Table 2, in Inventive Examples 1 to 6 satisfying the alloy composition, relational expression, and TiN size proposed in the present invention, delayed fracture cracks did not occur at the screw portion of the bolt product before and after the delayed fracture resistance evaluation. On the other hand, Comparative Example 1 had a Ti/3.42N value of 2.506, exceeding the lower limit of 2.0 proposed in the present invention, and coarse TiN was formed, resulting in delayed fracture cracks.
비교예2는 Ti/3.42N 값이 3.070으로 본 발명에서 제안하는 하한값인 2.0을 초과하여, 조대한 TiN이 형성되었고, 이로 인해 지연파괴 크랙이 발생하였다. Comparative Example 2 had a Ti/3.42N value of 3.070, exceeding the lower limit of 2.0 proposed in the present invention, and coarse TiN was formed, resulting in delayed fracture cracks.
비교예3은 Si의 함량이 0.26%로 본 발명에서 제안하는 상한값인 0.25%를 초과하고, 5.5Si+Mn값이 2.58로 본 발명에서 제안하는 상한값인 2.5를 초과하여 과도한 고용강화 효과에 의해 구상화 열처리후 볼트 나사부 성형성이 열위해져 지연파괴 크랙이 발생하였다. 도1은 지연파괴 저항성 평가 전 비교예3의 나사부를 관찰한 사진이다. 도1을 참조하면, 비교예3은 본 발명에서 제안하는 조건을 만족하지 못하여 지연파괴 크랙이 발생하였고, 지연파괴저항성을 확보하지 못하였음을 확인할 수 있다.In Comparative Example 3, the Si content was 0.26%, exceeding the upper limit of 0.25% proposed in the present invention, and the 5.5Si+Mn value was 2.58, exceeding the upper limit of 2.5 proposed in the present invention, resulting in spheroidization due to excessive solid solution strengthening effect. After heat treatment, the formability of the bolt threads was deteriorated, resulting in delayed fracture cracks. 1 is a photograph of the screw portion of Comparative Example 3 before evaluation of delayed fracture resistance. Referring to FIG. 1, it can be seen that Comparative Example 3 did not satisfy the conditions proposed in the present invention, causing delayed fracture cracks and failing to secure delayed fracture resistance.
비교예4는 Mn의 함량이 1.45%로 본 발명에서 제안하는 상한값인 1.35%를 초과하고, 5.5Si+Mn 값이 2.61로 본 발명에서 제안하는 상한값인 2.5를 초과하여, 과도한 고용강화 효과에 의해 구상화 열처리후 볼트 나사부 성형성이 열위해져 지연파괴 크랙이 발생하였다. In Comparative Example 4, the Mn content was 1.45%, exceeding the upper limit of 1.35% proposed in the present invention, and the 5.5Si+Mn value was 2.61, exceeding the upper limit of 2.5 proposed in the present invention, resulting in an excessive solid solution strengthening effect. After the spheroidization heat treatment, the formability of the bolt threads was deteriorated, resulting in delayed fracture cracks.
비교예5는 C의 함량이 0.33%로 본 발명에서 제안하는 상한값인 0.3%를 초과하여 기계적 안정성이 우수한 잔류 오스테나이트 조직의 형성이 억제되어 지연파괴 크랙이 발생하였다. In Comparative Example 5, the C content was 0.33%, exceeding the upper limit of 0.3% proposed in the present invention, so that the formation of a retained austenite structure having excellent mechanical stability was inhibited, resulting in delayed fracture cracks.
이어서, 본 발명에 따른 상기 표 1의 발명예 3의 합금조성을 만족하는 발명예 3, 비교예 3-1 내지 3-6를 하기 표 3과 같은 제조 조건으로 제조하여 최종 볼트 제품을 얻었다. Subsequently, Inventive Example 3 and Comparative Examples 3-1 to 3-6 satisfying the alloy composition of Inventive 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.
크랙유무delayed destruction
presence or absence of cracks
온도finishing rolling
Temperature
온도winding
Temperature
온도Nodular heat treatment
Temperature
온도austenitization
Temperature
본 발명에 따른 마무리 압연 온도, 권취 온도, 구상화열처리 온도 및 오스테나이트화 온도를 만족하는 발명예3은 지연파괴 크랙이 발생하지 않았다. 반면, 비교예 3-1은 압연 온도가 990℃로 본 발명에서 제안하는 상한인 980℃를 초과하고, 권취 온도도 940℃로 본 발명에서 제안하는 상한인 930℃를 초과하여, 선재에서 구오스테나이트 결정립 크기가 조대해지고, 볼트 제품의 구오스테나이트 결정립 크기도 조대해짐에 따라 지연파괴 크랙이 발생하였다.Inventive example 3 satisfying the finish rolling temperature, coiling temperature, nodularization heat treatment temperature and austenitization temperature according to the present invention did not generate delayed fracture cracks. On the other hand, Comparative Example 3-1 had a rolling temperature of 990 ° C, exceeding the upper limit of 980 ° C proposed in the present invention, and a coiling temperature of 940 ° C, exceeding the upper limit of 930 ° C proposed in the present invention. As the size of the crystal grains of the nitrite became coarse and the size of the old austenite crystal grains of the bolt product also became coarse, delayed fracture cracks occurred.
비교예 3-2는 압연 온도가 870℃로 본 발명에서 제안하는 하한인 880℃에 미치지 못하고, 권취 온도도 820℃로 본 발명에서 제안하는 하한인 830℃에 미달하여 선재에서 구오스테나이트 결정립 크기가 미세해지고, 볼트 제품의 구오스테나이트 결정립 크기도 미세해짐에 따라, 잔류 오스테나이트 분율이 높아지고, 지연파괴 크랙이 발생하였다. Comparative Example 3-2 had a rolling temperature of 870 ° C, which did not reach the lower limit of 880 ° C proposed in the present invention, and a coiling temperature of 820 ° C, which did not reach the lower limit of 830 ° C proposed in the present invention, so that the grain size of the old austenite in the wire rod , and as the size of old austenite crystal grains in bolt products also became fine, the retained austenite fraction increased and delayed fracture cracks occurred.
비교예 3-3은 오스테나이트화 열처리 온도가 950℃로 본 발명에서 제안하는 상한인 940℃를 초과하여 볼트 제품의 구오스테나이트 결정립 크기가 조대해짐에 따라 지연파괴 크랙이 발생하였다.In Comparative Example 3-3, the austenitization heat treatment temperature was 950 ° C, exceeding the upper limit of 940 ° C proposed in the present invention, and delayed fracture cracks occurred as the size of the prior austenite crystal grains of the bolt product became coarse.
비교예 3-4는 오스테나이트화 열처리 온도가 860℃로 본 발명에서 제안하는 하한인 870℃에 미치지 못하여, 볼트 제품이 충분히 오스테나이트화 되지 않은 상태에서 QT열처리가 되어 미고용 펄라이트가 형성되었고, 이에 따라 지연파괴 크랙이 발생하였다.In Comparative Examples 3-4, the austenitizing heat treatment temperature was 860 ° C., which was less than the lower limit of 870 ° C. proposed in the present invention, so that the QT heat treatment was performed in a state where the bolt product was not sufficiently austenitized, resulting in the formation of unsolved pearlite, Accordingly, delayed fracture cracks occurred.
비교예 3-5는 구상화 온도가 740℃로 본 발명에서 제안하는 하한인 745℃에 미치지 못하고, 비교예 3-6은 구상화 온도가 760℃로 본 발명에서 제안하는 상한인 770℃을 초과하여, 구상화율이 낮고 열처리가 충분히 되지 않아 성형성이 열위하여 지연파괴 크랙이 발생하였다.Comparative Example 3-5 had a nodularization temperature of 740 ° C, which did not reach the lower limit of 745 ° C proposed in the present invention, and Comparative Example 3-6 had a nodularization temperature of 760 ° C, exceeding the upper limit of 770 ° C, Due to low spheroidization rate and insufficient heat treatment, formability was poor and delayed fracture cracks occurred.
상술한 바에 있어서, 본 발명의 예시적인 실시예들을 설명하였지만, 본 발명은 이에 한정되지 않으며 해당 기술 분야에서 통상의 지식을 가진 자라면 다음에 기재하는 청구범위의 개념과 범위를 벗어나지 않는 범위 내에서 다양한 변경 및 변형이 가능함을 이해할 수 있을 것이다.In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those skilled in the art within the scope that does not deviate from the concept and scope of the claims described below. It will be appreciated that many changes and modifications are possible.
Claims (9)
하기 관계식1 및 관계식2를 만족하는 지연파괴 저항성이 향상된 선재.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0
(관계식1 및 관계식 2에서, [Si], [Mn], [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)In weight percent, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004% , N: 0.001 to 0.008%, the balance including Fe and unavoidable impurities,
A wire rod with improved delayed fracture resistance that satisfies the following relational expression 1 and relational expression 2.
[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(In relational expression 1 and relational expression 2, each of [Si], [Mn], [Ti] and [N] means the content (wt%) of the corresponding element)
TiN 개재물의 크기는 15㎛ 이하인 지연파괴 저항성이 향상된 선재.According to claim 1,
A wire rod with improved delayed fracture resistance in which the size of TiN inclusions is 15㎛ or less.
830 내지 930℃에서 권취하는 단계;를 포함하는 지연파괴 저항성이 향상된 선재의 제조방법.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0
(관계식1 및 관계식 2에서, [Si], [Mn], [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)In weight percent, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004% , N: 0.001 to 0.008%, the remainder including Fe and unavoidable impurities, and finish rolling a steel material satisfying the following relational expressions 1 and 2 at 880 to 980 ° C.; and
A method for manufacturing a wire rod having improved delayed fracture resistance, comprising: winding at 830 to 930 ° C.
[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(In relational expression 1 and relational expression 2, each of [Si], [Mn], [Ti] and [N] means the content (wt%) of the corresponding element)
신선재를 745 내지 770℃에서 구상화 열처리하는 단계;
상기 구상화 열처리된 신선재를 870 내지 940℃의 온도 범위에서 가열하는 단계;
상기 구상화 열처리된 신선재를 50 내지 80℃의 온도 범위에서 담금질하는 단계; 및
상기 담금질된 부품을 400 내지 600℃의 온도범위에서 템퍼링하는 단계;를 포함하는 지연파괴 저항성이 향상된 부품의 제조방법.Drawing the wire rod manufactured according to claim 4;
Spheroidizing heat treatment of the wire rod at 745 to 770 ° C;
Heating the spheroidizing heat-treated wire rod in a temperature range of 870 to 940 ° C;
Quenching the spheroidizing heat-treated wire rod in a temperature range of 50 to 80 ° C; and
Method of manufacturing a part with improved delayed fracture resistance comprising; tempering the quenched part in a temperature range of 400 to 600 ° C.
[관계식1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[관계식2] 1.0 < [Ti]/3.42[N] < 2.0
(관계식1 및 관계식 2에서, [Si], [Mn], [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)In weight percent, C: 0.15 to 0.3%, 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 0.03%, B: 0.001 to 0.004% , N: 0.001 to 0.008%, the remainder including Fe and unavoidable impurities, and a part with improved delayed fracture resistance that satisfies the following relational expressions 1 and 2.
[Relationship 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4
[Relationship 2] 1.0 < [Ti]/3.42 [N] < 2.0
(In relational expression 1 and relational expression 2, each of [Si], [Mn], [Ti] and [N] means the content (wt%) of the corresponding element)
부피 분율로, 잔류 오스테나이트를 0.3 내지 2% 및 잔여 템퍼드 마르텐사이트 조직을 포함하는 지연파괴 저항성이 향상된 부품.
According to claim 7,
A part with improved delayed fracture resistance comprising, by volume fraction, 0.3 to 2% retained austenite and a residual tempered martensitic structure.
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| PCT/KR2021/018977 WO2022131752A1 (en) | 2020-12-18 | 2021-12-14 | Wire rod and parts with improved delayed fracture resistance, and methods for manufacturing same |
| JP2023537438A JP2024500152A (en) | 2020-12-18 | 2021-12-14 | Wire rods and parts with improved delayed fracture resistance and their manufacturing method |
| US18/268,061 US20240060162A1 (en) | 2020-12-18 | 2021-12-14 | Wire rod and part with improved delayed fracture resistance, and methods for manufacturing same |
| EP21907056.2A EP4265766A1 (en) | 2020-12-18 | 2021-12-14 | Wire rod and parts with improved delayed fracture resistance, and methods for manufacturing same |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000336457A (en) | 1999-05-26 | 2000-12-05 | Nippon Steel Corp | Wire rod for cold forging and its manufacture |
| 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 |
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| WO2006088019A1 (en) * | 2005-02-16 | 2006-08-24 | Nippon Steel Corporation | Hot rolled wire material excellent in cold forging property after spheroidizing treatment, spheroidizing-annealed steel wire having excellent cold forging property, and method for production thereof |
| KR101091446B1 (en) * | 2008-12-26 | 2011-12-07 | 주식회사 포스코 | High Strength Steel Plate with Excellent Resistance of Cyclic Pressure for Low-Temperature Pressure Vessel, Manufacturing Method Thereof and Manufacturing Method of Deep Drawing Article |
| KR101297539B1 (en) * | 2010-03-02 | 2013-08-14 | 신닛테츠스미킨 카부시키카이샤 | 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 |
| 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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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000336457A (en) | 1999-05-26 | 2000-12-05 | Nippon Steel Corp | Wire rod for cold forging and its manufacture |
| 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 |
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| CN116783316A (en) | 2023-09-19 |
| US20240060162A1 (en) | 2024-02-22 |
| EP4265766A1 (en) | 2023-10-25 |
| WO2022131752A1 (en) | 2022-06-23 |
| KR20220087847A (en) | 2022-06-27 |
| JP2024500152A (en) | 2024-01-04 |
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