KR20020078830A - A method for manufacturing steel wire rod for cold forging with low deviation in mechanical properties - Google Patents
A method for manufacturing steel wire rod for cold forging with low deviation in mechanical properties Download PDFInfo
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- C—CHEMISTRY; METALLURGY
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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- 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
- C21D2211/002—Bainite
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Abstract
Description
본 발명은 자동차 부품 등의 소재로 사용되는 냉간압조용 강 선재의 제조방법에 관한 것으로서, 보다 상세하게는 강 선재의 미세조직을 극저탄소 베이나이트 조직으로 바꾸어 줌으로써 재질편차를 크게 개선시킨 냉간압조용 강 선재의 제조방법에 관한 것이다.The present invention relates to a method for manufacturing a cold-rolled steel wire used as a material for automobile parts, and more particularly, to a cold-rolled steel for greatly improving the material deviation by changing the microstructure of the steel wire into an ultra low carbon bainite structure. It relates to a method for producing a steel wire.
일반적으로 자동차 부품 등의 소재로서 많이 사용되는 중탄소강 선재 및 냉간압조용 비조질강 선재는, 열간압연을 마친 상태에서의 주된 미세조직이 페라이트(Ferrite)와 펄라이트(Pearlite)이지만, 냉각과정에서 코일 위치별로 냉각속도가 다르기 때문에 코일 위치별로 미세조직에도 차이가 발생한다. 예를 들어, 냉각속도가 상대적으로 빠른 부위는 페라이트의 크기가 작으며 펄라이트의 분율이 높아지고 베이나이트(Bainite)와 같은 저온변태조직이 일부 혼입되어 강도가 높아진다. 이와는 달리, 냉각속도가 상대적으로 느린 부위는 페라이트의 크기가 커지고 페라이트의 분율이 높아져서 강도가 낮아진다. 따라서, 페라이트와 펄라이트를 주된 조직으로 하는 중탄소강 선재나 비조질강 선재의 경우, 냉각속도 편차에서 기인하는 미세조직 편차 발생 및 이것에 기인한 재질 불균일을 피할 수가 없다.In general, the medium carbon steel wire rods and cold-rolled non-coarse steel wire rods, which are commonly used as materials for automobile parts, are mainly composed of ferrite and pearlite in the hot-rolled state. The cooling rate is different for each coil, so a difference occurs in the microstructure of each coil position. For example, a relatively fast cooling rate is small in the size of the ferrite, the fraction of pearlite is increased, and the low temperature transformation tissue, such as bainite (Bainite) is partly mixed to increase the strength. On the contrary, in the region where the cooling rate is relatively slow, the size of the ferrite is increased and the fraction of the ferrite is increased, thereby decreasing the strength. Therefore, in the case of the medium carbon steel wire or the non-coarse steel wire mainly composed of ferrite and pearlite, the occurrence of microstructure variation due to the cooling rate variation and the material unevenness due to this cannot be avoided.
통상, 선재 1코일(coil)의 무게는 2톤인데, 인장강도 80kg/㎟급 강 선재를 2톤 중량의 코일로 권취하여 냉각시키는 경우, 코일내 인장강도 편차는 약 10kg/㎟ 정도이다. 이러한 선재상태에서의 재질편차는 최종 제품의 재질편차로 이어져 제품 불량율을 높이는 문제를 야기시킨다.In general, the weight of one coil of wire is 2 tons, and when the 80 kg / mm 2 grade steel wire is wound and cooled by a coil of 2 ton weight, the variation in tensile strength in the coil is about 10 kg / mm 2. This material deviation in the wire condition leads to a material deviation of the final product, causing a problem of increasing the product failure rate.
상기한 바와 같은 문제점을 해결하기 위하여, 선재의 재질편차를 개선할 수 있는 제조방법에 대한 기술들이 제안되어 왔다. 일례로, 일본특개평9-67622호에서는, 중량%로 C: 0.15~0.35%, Si: 0.05%이하, Mn:0.70~1.50%, N: 0.005%이하, Cr: 0.20% 이하를 함유하는 강을 사용하여 열간압연 후 2℃/초 이상의 속도로 냉각하여 얻은 선재를 20~30% 신선하여 인장강도 700~930 N/㎟의 강선을 제조하는 것을 특징으로 하는 코일내 재질편차가 적은 강 선재의 제조방법을 제시하고 있다. 그러나, 이 기술의 경우, 평이한 성분의 중탄소강을 단지 냉각속도만 제어함으로써 재질편차를 줄일 수 있다는 장점이 있지만, 냉각속도가 빠른 코일 끝단부나 코일 외부뿐 아니라 냉각속도가 느린 코일 가운데 부분 및 코일 내부까지도 냉각속도를 2℃/초이상으로 해주어야 하기 때문에, 선재 코일을 강제로 냉각하는 냉각설비가 필요한 문제가 있다. 즉, 선재 코일을 대기중에서 방냉하면, 대기와 접촉이 원활하지 하지 않는 코일 내부에서는 이와 같은 냉각속도를 얻을 수 없기 때문에, 권취된 선재 코일을 급냉시켜줄 수 있는 설비 및 매체가 필요한 것이다.In order to solve the problems as described above, techniques for a manufacturing method that can improve the material deviation of the wire rod has been proposed. For example, in Japanese Patent Laid-Open No. 9-67622, a steel containing by weight% C: 0.15 to 0.35%, Si: 0.05% or less, Mn: 0.70 to 1.50%, N: 0.005% or less, and Cr: 0.20% or less. The steel wire with low material deviation in the coil, characterized in that the steel wire with a tensile strength of 700 ~ 930 N / ㎜ is produced by drawing 20 ~ 30% of the wire obtained by cooling at a rate of 2 ℃ / sec or more after hot rolling using The preparation method is presented. However, this technique has the advantage that the material deviation can be reduced by controlling only the cooling rate of the medium carbon steel of the plain component, but the coil end or the outside of the coil as well as the middle of the coil and the coil having a slow cooling rate Since even the cooling rate should be 2 ℃ / sec or more, there is a problem that a cooling facility for forcibly cooling the wire coil. That is, when the wire rod coil is cooled in the air, such a cooling rate cannot be obtained inside the coil that is not in contact with the atmosphere. Therefore, a facility and a medium capable of quenching the wound wire coil are needed.
이에, 본 발명의 발명자들은 상기와 같은 문제를 해결하기 위하여 연구 및 실험을 거듭하고 그 결과에 근거하여 본 발명을 제안하게 된 것으로, 본 발명은 강 성분 및 압연후 냉각조건을 조절하여 선재의 조직을 극저탄소 베이나이트로 함으로써, 선재 코일내의 재질 편차가 극히 적은 냉간압조용 강 선재의 제조방법을 제공하고자 하는데, 그 목적이 있다.Accordingly, the inventors of the present invention have repeatedly studied and experimented to solve the above problems and proposed the present invention based on the results, and the present invention controls the steel components and cooling conditions after rolling to control the structure of the wire rod. By using the ultra-low carbon bainite, to provide a method for producing a cold-rolled steel wire rod with a very small material variation in the wire coil, an object thereof.
도 1은 냉각속도에 따른 경도변화를 나타내는 그래프1 is a graph showing the change in hardness according to the cooling rate
도 2(a),(b),(c)는 발명강, 비교강(1), 및 비교강(2)의 미세조직을 나타내는 현미경 사진(A), (b), (c) are micrographs showing the microstructure of the inventive steel, comparative steel 1, and comparative steel 2;
상기한 목적을 달성하기 위한 본 발명은,The present invention for achieving the above object,
중량%로, C: 0.10%이하, Si: 0.1~0.7%, Mn: 1.0~3.0%, P: 0.03%이하, S: 0.03%이하, Cr: 0.20~1.0%, Mo: 0.10~0.50%, Ni: 0.2~1.0%, Cu: 0.3~1.5% V: 0.05~0.20%, Ti: 0.01~0.03%, B: 0.0010~0.0050%, 잔부 Fe 및 기타 불가피한 불순물로 조성되는 강편을 재가열한 다음 마무리 압연온도를 800℃ 이상으로 하여 선재형태로 열간압연하고, 상기 마무리 압연온도부터 300~400℃의 온도구간을 0.1~10℃/초의 속도로 냉각하는 것을 포함하여 이루어지는 것을 특징으로 하는 기계적 성질의 편차가 적은 냉간압조용 강 선재의 제조방법에 관한 것이다.By weight%, C: 0.10% or less, Si: 0.1-0.7%, Mn: 1.0-3.0%, P: 0.03% or less, S: 0.03% or less, Cr: 0.20-1.0%, Mo: 0.10-0.50%, Ni: 0.2 ~ 1.0%, Cu: 0.3 ~ 1.5% V: 0.05 ~ 0.20%, Ti: 0.01 ~ 0.03%, B: 0.0010 ~ 0.0050%, Re-heated steel sheet composed of residual Fe and other unavoidable impurities Hot rolling is carried out in the form of a wire rod at a temperature of 800 ° C. or higher, and cooling the temperature section of 300 to 400 ° C. at a rate of 0.1 to 10 ° C./second from the finish rolling temperature is characterized in that the variation in mechanical properties is achieved. The present invention relates to a method for producing a cold rolled steel wire.
이하, 본 발명의 강 성분 및 제조조건에 대하여 설명한다.Hereinafter, the steel component and manufacturing conditions of this invention are demonstrated.
먼저, 본 발명에서는, 기계적 성질이 우수하면서도 냉각속도차이에 기인되는 재질편차를 줄이기 위해, 탄소(C)의 함량을 0.10% 이하로 관리하는 것이 바람직하다. 그 이유는, 탄소(C)는 강의 미세조직 및 기계적 성질에 큰 영향을 미치는데, 그 함량이 0.10% 이상이면 목표로 하는 극저탄소 베이나이트 조직을 얻을 수 없고, 또한 강의 재질편차가 커지며 인성이 열화되어, 비록 냉각제어를 통해 베이나이트 조직을 얻는다 하더라도 강 선재의 재질편차가 커지며, 취성이 매우 나빠지는 문제가 있기 때문이다. 따라서, 기계적 성질이 우수하면서도 냉각속도차이에 기인되는 재질편차를 줄이려면 반드시 탄소함량이 적은 극저탄소 베이나이트 조직을 얻어야만 하기 때문에, 탄소 함량은 0.10% 이하로 설정하는 것이 바람직하다.First, in the present invention, it is preferable to manage the content of carbon (C) to 0.10% or less in order to reduce the material deviation caused by the difference in cooling rate while having excellent mechanical properties. The reason is that carbon (C) has a great influence on the microstructure and mechanical properties of the steel. If the content is 0.10% or more, the target ultra low carbon bainite structure cannot be obtained, and the material deviation of the steel becomes large and the toughness is high. Deterioration, even if the bainite structure is obtained through cooling control, the material deviation of the steel wire is increased, the brittleness is very bad. Therefore, it is preferable to set the carbon content to 0.10% or less because very low carbon bainite structure having a low carbon content must be obtained in order to reduce the material deviation caused by the difference in cooling rate with excellent mechanical properties.
규소(Si)는 통상 제강시 탈산을 위해서 첨가하는 요소로서, 제품에서 필요로 하는 강도를 확보하는 역할도 한다. 그러나, 상기 Si의 함량이 0.1% 미만이면 탈산작용이 원활이 이루어지지 않고 필요한 강도를 확보하기가 곤란하고, 0.7% 이상이 되면 냉간가공시 변형저항을 크게 증가시켜 냉간압조성을 급격히 떨어뜨리므로 바람직하지 않다.Silicon (Si) is usually added for deoxidation during steelmaking, and also plays a role of securing strength required for products. However, when the content of Si is less than 0.1%, deoxidation is not performed smoothly, and it is difficult to secure the required strength. When the content of Si is more than 0.7%, the deformation resistance during cold working is greatly increased, thereby rapidly decreasing the cold pressure composition. Not.
망간(Mn)은 강의 소입성을 증가시키고 조직 미세화 효과를 갖는 원소로서, 충격인성의 저하 없이도 강의 강도를 높인다. 상기 망간을 첨가하여, 강의 소입성을 증가시키고 느린 냉각속도 구간에서도 베이나이트 조직을 안정적으로 얻기 위해서는, 그 함량을 1.0% 이상으로 설정하는 것이 바람직하지만, 그 첨가량이 3.0% 보다 많아지면 망간 편석부에 마르텐사이트(Martensite)조직이 발생하여 인성저하가 심해지므로, 상기 망간의 첨가범위는 1.0~3.0%로 제한하는 것이 바람직하다.Manganese (Mn) is an element that increases the hardenability of steel and has a structure refining effect, and increases the strength of steel without deteriorating impact toughness. In order to increase the hardenability of the steel by adding manganese and to stably obtain bainite structure even in a slow cooling rate section, it is preferable to set the content to 1.0% or more. Since martensite tissue is formed in the toughness deterioration, the addition range of the manganese is preferably limited to 1.0 ~ 3.0%.
인(P)은 입계에 편석되어 강의 인성을 떨어뜨리므로, 그 함량을 0.03%이하로 제한하는 것이 바람직하다.Phosphorus (P) is segregated at the grain boundary, and the toughness of the steel is reduced, it is preferable to limit the content to 0.03% or less.
황(S)은 강의 충격인성을 감소시키므로, 그 함량을 0.03%이하로 제한하는 것이 바람직하다.Since sulfur (S) reduces the impact toughness of the steel, it is preferable to limit the content to 0.03% or less.
한편, 크롬(Cr)은 강의 소입성을 증가시켜 극저탄소 베이나이트 조직을 안정적으로 얻게 하는 작용을 한다. 그 함량이 적으면 이러한 효과를 얻기 힘들고 첨가량이 많으면 취성이 큰 마르텐사이트 조직을 발생시키므로, 상기 크롬의 함량은 0.2~1.0%로 설정하는 것이 바람직하다.On the other hand, chromium (Cr) increases the hardenability of the steel and acts to stably obtain the ultra-low carbon bainite structure. If the content is small, it is difficult to obtain such an effect, and if the amount is large, brittle martensite structure is generated. Therefore, the content of chromium is preferably set to 0.2 to 1.0%.
또한, 붕소(B)는 본 발명의 특징적인 원소로서 강의 소입성을 증가시켜 극저탄소 베이나이트 조직을 안정적으로 얻게 하는 작용을 하는 원소이다. 특히 본 발명에서 얻고자 하는 페라이트가 함유되지 않은 순수한 베이나이트 조직을 안정적으로 확보하기 위해서는, 냉각과정에서 통상 베이나이트 조직보다 고온에서 먼저 출현하는 페라이트 조직으로의 변태를 억제시켜야 하는데, 본 발명에서와 같이 적정 함량의 붕소(B)를 첨가하면, 고온상태에서 붕소(B)가 강내의 오스테나이트(Austenite) 입계에 편석되어 입계에너지를 낮추어 줌으로써 냉각과정에서 페라이트 조직으로의 변태를 효과적으로 억제하는 역할을 하게 된다. 따라서, 페라이트가 혼입되지 않은 순수한 베이나이트 조직을 얻을 수 있게 된다. 여기서, 상기 붕소(B)의 함량이 0.0010% 미만인 경우에는 상기한 작용효과를 얻기 힘들고, 0.0050% 보다 많이 첨가되면 그 효과가 포화 되므로, 0.0010~0.0050%로 첨가하는 것이 바람직하다.In addition, boron (B) is a characteristic element of the present invention is an element that serves to increase the hardenability of steel to stably obtain the ultra-low carbon bainite structure. In particular, in order to stably secure the pure bainite structure containing no ferrite to be obtained in the present invention, it is necessary to suppress the transformation into the ferrite structure that appears at a higher temperature than the bainite structure in general during the cooling process. When boron (B) is added in an appropriate amount, boron (B) is segregated in the austenite grain boundary in the steel at a high temperature, thereby lowering the grain boundary energy, thereby effectively inhibiting transformation into ferrite tissue during cooling. Done. Thus, it is possible to obtain pure bainite structure in which ferrite is not incorporated. Here, when the content of the boron (B) is less than 0.0010%, it is difficult to obtain the above-described functional effect, and when the content is added more than 0.0050%, the effect is saturated, so it is preferable to add it in 0.0010 ~ 0.0050%.
몰리브덴(Mo)은 강의 소입성을 증가시켜 극저탄소 베이나이트 조직을 안정적으로 얻게 하는 작용을 하는 원소로서, 그 함량이 적으면 이러한 효과를 얻기 힘들고 첨가량이 많으면 강의 강도를 지나치게 증가시키므로, 0.1~0.5%로 첨가하는 것이 바람직하다.Molybdenum (Mo) is an element that increases the hardenability of the steel to obtain an ultra low carbon bainite structure stably. If the content is small, it is difficult to obtain this effect. Preference is given to adding in%.
구리(Cu)는 냉각과정에서 강중의 철(Fe)과 결합하여 석출물을 형성함으로써 강도를 증가시키는 역할을 한다. 특히, 본 발명강에서는 냉각속도가 느린 영역, 즉 0.1~1.0℃/초의 범위에서 다량 석출됨으로 인해, 냉각속도 감소에 따른 강도저하를 보상하여 재질편차를 줄여준다. 상기 구리(Cu)의 함량이 0.3% 미만인 경우에는 상기한 효과를 얻기 힘들고, 1.5%보다 많이 첨가되면 강도를 지나치게 증가시켜 오히려 재질편차를 조장하므로, 그 함량은 0.3~1.5%로 설정하는 것이 바람직하다Copper (Cu) serves to increase the strength by combining with iron (Fe) in the steel during the cooling process to form a precipitate. Particularly, in the present invention steel, due to a large amount of precipitation in the region of the slow cooling rate, that is, 0.1 ~ 1.0 ℃ / second, to compensate for the decrease in strength due to the decrease in the cooling rate to reduce the material deviation. When the content of copper (Cu) is less than 0.3%, it is difficult to obtain the above-described effects, and when it is added more than 1.5%, the strength is excessively increased to promote material deviations, so the content is preferably set to 0.3 to 1.5%. Do
니켈(Ni)은 강의 소입성을 증가시켜 극저탄소 베이나이트 조직을 안정적으로 얻게 하며, 인성의 감소 없이 강의 강도를 증가시키는 역할을 한다. 상기 니켈의 함량이 0.2% 미만인 경우에는 상기한 효과를 얻기 힘들고, 1.0%보다 많이 첨가되면 강의 강도를 지나치게 증가시키므로, 그 함량은 0.2~1.0%로 설정하는 것이 바람직하다.Nickel (Ni) increases the hardenability of the steel to obtain a very low carbon bainite structure stably, and serves to increase the strength of the steel without reducing the toughness. When the content of nickel is less than 0.2%, it is difficult to obtain the above-mentioned effects, and when more than 1.0% is added, the strength of the steel is excessively increased. Therefore, the content is preferably set to 0.2 to 1.0%.
바나듐(V)은 강중에서 탄소와 결합하여 탄화물을 형성시켜 강의 강도를 증가시키는 원소로서, 그 함량이 0.05% 미만인 경우에는 상기한 효과를 얻기 힘들고 0.20% 이상 첨가되면 강이 취화되므로, 0.05~0.20%로 첨가하는 것이 바람직하다.Vanadium (V) is an element that combines with carbon in steel to form carbides to increase the strength of steel.If the content is less than 0.05%, it is difficult to achieve the above-mentioned effects, and when 0.20% or more is added, the steel becomes brittle. Preference is given to adding in%.
티탄(Ti)은 탄소 및 질소와 결합하여 탄질화물을 형성시켜 강의 인성 및 강도를 증가시키는 원소로서, 이와 같은 작용 효과를 얻기 위해서는, 그 함량이 0.01%이상인 것이 바람직하지만, 0.03% 이상으로 과잉 첨가되는 경우에는 강이 취화되므로, 상기 티탄함량의 상한은 0.03%로 설정하는 것이 바람직하다.Titanium (Ti) is an element that combines with carbon and nitrogen to form carbonitrides to increase the toughness and strength of steel. In order to obtain such an effect, the content is preferably 0.01% or more, but is excessively added to 0.03% or more. In this case, since the steel is embrittled, the upper limit of the titanium content is preferably set to 0.03%.
한편, 상기와 같이 조성된 강편은 재가열한 다음 열간에서 선재압연하고, 800℃ 이상의 온도에서 마무리 압연한다. 상기 마무리 압연을 800℃ 이상의 온도에서 실시하는 이유는, 마무리 압연온도가 800℃ 미만이면 압연 변형을 받는 중에 페라이트가 형성되어 강도저하 및 재질의 불균일을 초래할 수 있기 때문이다.On the other hand, the steel strips prepared as described above are reheated and then wire rod hot rolled, and finish-rolled at a temperature of 800 ℃ or more. The reason why the finish rolling is carried out at a temperature of 800 ° C. or higher is that if the finish rolling temperature is less than 800 ° C., ferrite may be formed during rolling deformation, resulting in a decrease in strength and unevenness of materials.
이후, 상기한 열간 선재압연이 종료되면, 열간압연이 마무리되는 온도부터 300~400℃ 사이의 온도구간을 0.1~10℃/초의 속도로 냉각하는 것이 바람직한데, 그 이유는, 상기 냉각속도가 0.1℃/초 미만이면 변태중 페라이트 조직이 발생하여 강의 강도를 심하게 감소시키고 10℃/초 보다 빠르면 변태중 취성이 강한 경질의 마르텐사이트 조직이 발생하여 강의 강도를 지나치게 증가시키고 인성을 떨어뜨리기 때문이다. 즉, 열간압연된 선재에 대하여 인위적인 강재공냉이나 보열커버 등을 이용한 인위적인 서냉을 적용하지 않고, 공냉각속도인 0.1~10℃/초의 냉각속도로 대기중에서 자연 방냉시키면, 원하는 조직인 극저탄소 베이나이트 조직을 확보하여, 기계적 성질의 편차를 줄일 수 있는 것이다. 여기서, 상기한 온도구간, 즉 열간압연이 마무리되는 온도부터 300~400℃ 사이의 온도구간은, 조직이 극저탄소 베이나이트 조직으로 변태되는 구간을 의미하며, 300℃~상온 까지의 냉각은 공정 편의대로 계속 자연방냉을 하여도 좋고 인위적으로 냉각속도를 바꾸어도 무방하다.Subsequently, when the hot wire rolling is finished, it is preferable to cool the temperature section between 300 to 400 ° C. at a rate of 0.1 to 10 ° C./second from the temperature at which the hot rolling is finished, because the cooling rate is 0.1 If it is less than ℃ / seconds ferritic structure occurs during metamorphosis, the strength of the steel is severely reduced, if faster than 10 ℃ / seconds hard martensite structure of the brittle strong during transformation, the strength of the steel is excessively increased and toughness is reduced. In other words, without cold artificial steel air cooling or artificial thermal cooling to the hot-rolled wire rod without applying artificial slow cooling in the air at a cooling rate of 0.1 ~ 10 ℃ / second air cooling rate, ultra-low-carbon bainite structure of the desired structure By securing, it is possible to reduce the deviation of the mechanical properties. Here, the temperature section, that is, the temperature section between 300 ~ 400 ℃ hot rolling finish means a section in which the tissue is transformed into ultra-low carbon bainite structure, cooling to 300 ℃ ~ room temperature is a process convenience Natural cooling may be continued as it is, or the cooling rate may be artificially changed.
상기와 같이 하여 제조된 강 선재는, 강 성분 중 소량의 탄소(C) 및 붕소(B)를 함유하여, 그 조직이 코일위치에 상관없이 극저탄소 베이나이트 조직으로 되기 때문에, 냉각속도가 느린 코일 내부를 별도로 냉각시키는 일 없이, 열간선재압연이후 극저탄소 베이나이트로의 변태가 완료되는 온도구간까지의 냉각을 자연냉각속도인 0.1~10℃/초로 하여도, 기계적 편차가 획기적으로 줄어들게 된다. 이와 같은 낮은 재질편차는, 제품에까지 이어지므로, 제품측면에서도 이점이 있다.The steel wire produced as described above contains a small amount of carbon (C) and boron (B) in the steel component, so that the structure becomes an extremely low carbon bainite structure regardless of the coil position, so that the cooling rate is slow. Without cooling the inside separately, even if the cooling from the hot wire rod rolling to the temperature range where transformation to ultra-low carbon bainite is completed is 0.1 to 10 ° C / sec, the mechanical deviation is significantly reduced. This low material deviation extends to the product, which is advantageous in terms of the product.
한편, 상기 선재는, 이후 통상의 방법을 통해 냉간신선가공 후 냉간단조되어 제품으로 가공된다.On the other hand, the wire rod is cold forged after the cold wire processing through a conventional method is processed into a product.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다.Hereinafter, the present invention will be described in more detail with reference to Examples.
(실시예 1)(Example 1)
하기 표1과 같이 조성되는 강을 110 mm x 110 mm x 250 mm의 소형 강편으로 제작하고 1100℃에서 2시간 가열한 다음, 열간압연하여 850℃에서 판 형태로 압연을 완료하였다. 압연 완료후에는 실제 현장에서의 선재 코일 내외부의 냉각속도 차이를 모사하기 위하여 공기 및 물을 강재로 압연판에 뿌려주는 방법으로, 상기 압연이 종료된 온도부터 400℃의 온도구간에 대하여 냉각속도를 0.1~100℃/s로 변화시키면서 냉각한 후, 경도를 측정하고 그 결과를 도 1에 나타내었다.To produce steel as shown in Table 1 as a small steel piece of 110 mm x 110 mm x 250 mm After heating at 1100 ° C. for 2 hours, hot rolling was performed to complete rolling in the form of a plate at 850 ° C. After the rolling is completed, air and water are sprayed on the rolled plate with steel to simulate the difference in cooling rate between the wire coil and the outside in the actual site. After cooling while changing to 0.1-100 ° C./s, the hardness was measured and the results are shown in FIG. 1.
도1에 나타난 바와 같이, 발명강의 경우에는 냉각속도가 0.1~10℃/초로 변화하는 구간에서, 경도 변화가 매우 적은 것을 알 수 있다. 특히, 냉각속도가 0.1~4℃/초로 변화하는 구간에서는, 경도편차가 17Hv이고, 이를 인장강도로 환산하면 5.5kg/㎟로 된다.As shown in Figure 1, in the case of the invention steel it can be seen that the hardness change is very small in the section where the cooling rate is changed to 0.1 ~ 10 ℃ / sec. In particular, in the section where the cooling rate is changed to 0.1 ~ 4 ℃ / sec, the hardness deviation is 17Hv, when converted into the tensile strength is 5.5kg / ㎜.
그러나, 페라이트와 펄라이트 조직을 갖는 비교강(1)의 경우에는, 0.1~10℃/초의 냉각속도 변화 구간에서 경도편차가 매우 큰 것을 알 수 있다. 특히, 냉각속도가 0.1~4℃/초로 변화하는 구간에서는, 경도편차가 52Hv이고 이를 인장강도로 환산한 결과 16.8kg/㎟였다.However, in the case of the comparative steel (1) having a ferrite and pearlite structure, it can be seen that the hardness deviation is very large in the cooling rate change range of 0.1 ~ 10 ℃ / sec. In particular, in the section where the cooling rate is changed to 0.1 ~ 4 ℃ / sec, the hardness deviation is 52Hv and converted to tensile strength was 16.8kg / ㎜.
또한, 탄소(C)의 함량이 0.10% 이상으로 저탄소강인 비교강(2)의 경우, 냉각속도가 0.1~4℃/초로 변화하는 구간에서의 경도편차가 49Hv이고, 이를 인장강도로 환산하면 16.0kg/㎟로 였다. 즉, 탄소의 함량이 증가하여 미세조직이 저탄소 베이나이트 조직으로 됨으로 인해, 냉각속도 차이에서 기인되는 재질편차가 매우 커짐을 알 수 있다.In addition, the comparative steel (2), which is a low carbon steel with a carbon content of 0.10% or more, has a hardness deviation of 49 Hv in a section in which the cooling rate changes from 0.1 to 4 ° C./sec. kg / mm 2. That is, it can be seen that due to the increase in the carbon content, the microstructure becomes a low carbon bainite structure, resulting in a very large material deviation caused by the difference in cooling rate.
따라서, 이 결과들을 발명강과 비교하면, 본 발명의 발명강이 매우 우수하다는 것을 알 수 있다.Therefore, when comparing these results with the invention steel, it turns out that the invention steel of this invention is very excellent.
한편, 도 2(a),(b),(c)는 냉각속도를 1℃/초로 한 경우에 있어서, 발명강, 비교강(1), 및 비교강(2)의 미세조직을 나타낸 사진이다.2 (a), 2 (b) and 2 (c) are photographs showing the microstructures of the inventive steel, the comparative steel 1, and the comparative steel 2 when the cooling rate was 1 ° C / sec. .
도 2(b)에 나타난 바와 같이, 비교강(1)의 경우에는, 펄라이트(검은 부분)과 페라이트(흰 부분)로 구성된 미세조직을 가지고, 도 2(c)에 나타난 바와 같이, 탄소(C)의 함량이 높은 비교강(2)의 경우에는 미세조직이 통상의 저탄소 베이나이트 조직으로 된 것을 알 수 있다.As shown in FIG. 2 (b), in the case of the comparative steel 1, the carbon (C) has a microstructure composed of pearlite (black portion) and ferrite (white portion), and as shown in FIG. 2 (c). In the case of the comparative steel (2) having a high content of), it can be seen that the microstructure is a general low carbon bainite structure.
반면에, 도 2(a)의 본 발명강은 단일조직인 극저탄소 베이나이트 조직을 나타내고 있다.On the other hand, the inventive steel of Figure 2 (a) shows a very low carbon carbon bainite structure of a single structure.
이와 같이, 본 발명의 발명강은 단일조직인 극저탄소 베이나이트 조직으로 되기 때문에, 냉각속도가 코일내부와 코일외부에서 다르다 하더라도, 냉각속도 차이에 기인하는 기계적 성질의 편차가 적은 것이다.As described above, the inventive steel of the present invention has a very low carbon bainite structure, which is a single structure, so that even if the cooling rate is different from the inside of the coil and the outside of the coil, the variation in mechanical properties due to the difference in cooling rate is small.
상술한 바와 같이 본 발명에 의하면, 냉각속도 편차에 기인한 기계적 성질 편차를 최소화 할 수 있는 선재를 제조할 수 있으므로, 이러한 선재를 사용하여 냉간압조 가공으로 최종 제품을 제작하는 경우, 생산성 향상 및 불량율 감소 등의 효과를 얻을 수 있는 것이다.As described above, according to the present invention, since a wire rod which can minimize the variation in mechanical properties caused by the variation in the cooling rate can be manufactured, when the final product is manufactured by cold pressing using such wire rod, productivity is improved and a defective rate is achieved. A reduction and the like effect can be obtained.
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
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CN100379884C (en) * | 2006-08-29 | 2008-04-09 | 武汉大学 | Method for producing ultra high temperature bainitic steel in ultralow carbon |
CN103290187A (en) * | 2013-05-06 | 2013-09-11 | 河北钢铁股份有限公司承德分公司 | Method for refining microstructure of low-carbon steel wire rods |
CN105420601A (en) * | 2015-12-11 | 2016-03-23 | 武汉钢铁(集团)公司 | Production method of high-plasticity steel wire rod for welding |
KR20160063562A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160063563A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160063564A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength, and method for manufacturing thereof |
KR20160063533A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160075924A (en) * | 2014-12-19 | 2016-06-30 | 주식회사 포스코 | Wire rod for drawing, high strength steel wire having excellent torsion property and method for manufacturing thereof |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
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JPS609086B2 (en) * | 1981-02-14 | 1985-03-07 | 川崎製鉄株式会社 | Manufacturing method of high toughness and high tensile strength steel |
JPH0730391B2 (en) * | 1986-07-15 | 1995-04-05 | 株式会社神戸製鋼所 | Method for manufacturing high strength hot coil materials with excellent hydrogen sulfide resistance and toughness |
JPH0737646B2 (en) * | 1990-11-08 | 1995-04-26 | 新日本製鐵株式会社 | Manufacturing method of refractory high strength steel with excellent low temperature toughness of weld zone |
US5766381A (en) * | 1994-09-20 | 1998-06-16 | Kawasaki Steel Corporation | Method of producing bainitic steel materials having a less scattering of properties |
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Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
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CN100379884C (en) * | 2006-08-29 | 2008-04-09 | 武汉大学 | Method for producing ultra high temperature bainitic steel in ultralow carbon |
CN103290187A (en) * | 2013-05-06 | 2013-09-11 | 河北钢铁股份有限公司承德分公司 | Method for refining microstructure of low-carbon steel wire rods |
CN103290187B (en) * | 2013-05-06 | 2014-10-29 | 河北钢铁股份有限公司承德分公司 | Method for refining microstructure of low-carbon steel wire rods |
KR20160063562A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160063563A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160063564A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength, and method for manufacturing thereof |
KR20160063533A (en) | 2014-11-26 | 2016-06-07 | 주식회사 포스코 | Wire rod having high strength and impact toughness, and method for manufacturing thereof |
KR20160075924A (en) * | 2014-12-19 | 2016-06-30 | 주식회사 포스코 | Wire rod for drawing, high strength steel wire having excellent torsion property and method for manufacturing thereof |
CN105420601A (en) * | 2015-12-11 | 2016-03-23 | 武汉钢铁(集团)公司 | Production method of high-plasticity steel wire rod for welding |
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