KR100270115B1 - The galvanizing coating method with hot rolled steel - Google Patents
The galvanizing coating method with hot rolled steel Download PDFInfo
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- KR100270115B1 KR100270115B1 KR1019960055338A KR19960055338A KR100270115B1 KR 100270115 B1 KR100270115 B1 KR 100270115B1 KR 1019960055338 A KR1019960055338 A KR 1019960055338A KR 19960055338 A KR19960055338 A KR 19960055338A KR 100270115 B1 KR100270115 B1 KR 100270115B1
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
Abstract
Description
본 발명은 건축물의 전기스위치박스 등에 사용되는 용융아연도금 열연강판 (Hot-rolled Galvanized Iron:이하, "HGI"라 칭함)을 제조하는 방법에 관한 것으로서, 보다 상세하게는 가공성 및 도금밀착성이 우수한 용융아연도금 열연강판을 제조하는 방법에 관한 것이다.BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hot rolled galvanized iron (hereinafter referred to as " HGI ") used in an electric switch box of a building, To a method of manufacturing a galvanized hot-rolled steel sheet.
예전에는 후물재 구조물의 경우 열연강판을 산세후 도장만을 실시하여 사용하였으나, 사용분야의 확대로 열연강판의 내식성 향상이 요구됨에 따라 용융아연도금 열연강판제품으로 개발되어 생산되고 있다. 또한, 최근에는 용융아연도금 열연강판의 주요 용도인 건축용파이프, 가드레일, 데크플레이트(deck plate) 등의 구조물 이외에 수요가의 요구에 따라 심한 가공을 필요로 하는 스위치박스 등에 사용할 수 있는 가공성이 매우 우수한 용융아연도금 열연강판제품의 개발필요성이 절실해졌다.In the past, hot-rolled steel sheets were used only after coating with acid after hot-rolled steel sheets. However, as the use of hot rolled steel sheets is required to improve corrosion resistance, hot rolled galvanized steel sheets have been developed and produced. In recent years, in addition to structures such as construction pipes, guard rails, and deck plates, which are main applications of hot-dip galvanized hot-rolled steel sheets, The need for the development of high-quality hot-dip galvanized hot-rolled steel products has become urgent.
종래, 스위치박스용 용융아연 도금강판을 제조하는 방법으로는 극저탄소강을 베이스로 하여 탄질화물 형성원소인 Ti를 첨가한 초심가공용(Extra Deep Drawing Quality:이하, "EDDQ"라 칭함)냉연강판을 연속용융 도금설비(Continuous Galvanizing Line:이하, "CGL"이라 칭함)에서 780∼820℃로 연속소둔한후 용융도금을 실시하여 제조하였다. 그러나 최근 냉간압연 공정단축에 따른 제조비용의 절감 목적으로 열연강판을 도금소재로 하여 냉연강판의 EDDQ와 동등한 고가공성 요구하는 경우가 많다.Conventionally, as a method for producing a hot-dip galvanized steel sheet for a switch box, there has been known a method of producing an extrusion steel sheet for ultra-deep drawing quality (hereinafter referred to as " EDDQ ") in which Ti, which is a carbonitride- Continuous hot-dip galvanizing line (hereinafter, referred to as "CGL") at 780 to 820 ° C., followed by hot-dip galvanizing. However, in recent years, in order to reduce the production cost due to the shortening of the cold rolling process, the hot-rolled steel sheet is often used as a plating material, requiring high porosity equivalent to the EDDQ of the cold-rolled steel sheet.
일본의 고베제강(KSC)에서는 두께 2.5mm이상의 후물재 열연강판의 경우 고연성을 확보하기 위하여 극저탄소강(C≤0.002wt%)을 이용한 0.002wt% C-0.03wt% Ti강을 Ar3이상의 온도에서 압연한후 600℃이하에서 권취함으로서 인장강도 28∼29kg/㎟, 연신율 55% 이상인 가공용 열연강판을 제조할 수 있다고 하였다. 저온권취를 선택한 가장 큰 이유는 강중에 고용 C을 적정히 잔존시켜 입계강도를 상승시킴으로서 내2차 가공취성을 개선하기 위한 것으로 알려져 있다.Kobe Steel of Japan (KSC) In the high-0.002wt% C-0.03wt% Ti steel with ultra-low carbon steel (C≤0.002wt%) to ensure ductility for muljae hot-rolled steel sheet after the thickness of at least 2.5mm or more Ar 3 Rolled at a temperature of 600 ° C or less, it is possible to produce a hot rolled steel sheet having a tensile strength of 28 to 29 kg / mm 2 and an elongation of 55% or more. The main reason for choosing low-temperature coiling is to improve the secondary workability of the steel by increasing the strength of the grain boundary by appropriately retaining the solid solution C in the steel.
또한, 일본강관(NKK)의 경우 역시 연성을 확보하기 위하여 0.002wt%C에 0.01∼0.02wt%의 Ti 또는 Nb를 단독첨가하고 650℃ 이상에서 고온권취하여 50∼53%범위의 연신율을 갖는 가공용 열연강판의 제조가 가능하다고 발표한 바 있다.In the case of NKK steel, it is also possible to add 0.01 to 0.02 wt% of Ti or Nb to 0.002 wt% C solely to secure ductility, and take up high temperature at 650 ° C. or higher, It has been announced that it is possible to manufacture hot-rolled steel sheets.
이와 같이 연성확보에 있어 재질적으로 유리한 극저탄소강임에도 불구하고 1.6mm두께이하의 박물인 용융아연 열연강판을 제조하는데는 문제가 있다.Thus, there is a problem in manufacturing a hot-dip galvanized steel sheet having a thickness of 1.6 mm or less, despite being extremely low carbon steel which is advantageous in terms of material quality in securing ductility.
열간압연시 Ar3변태점이 높기 때문에 압연온도의 확보가 어렵고, 조직적으로는 미세립과 조대립이 혼재한 혼립조직 등에 기인한 연신율의 열화가 발생하기 때문이다. 다시말하면, 이와 같은 Ti첨가 극저탄소강을 이용하여 박물 열간압연강판을 제조하는데 있어서 문제가 되는 것은 열간압연온도의 저하에 따른 혼립조직의 생성에 의한 재질열화이다. 심가공 냉연강판의 제조에 이용되는 Ti첨가 극저탄소강의 경우 통상 3.5∼4.0mm로 압연되며, 910℃ 이상에서 열간압연을 마무리한다. 그런데 열간압연 두께가 박물화될수록 압연 마무리 온도는 저하되어 1.6mm두께의 강판의 경우, 통상 열간압연 마무리 온도는 860∼880℃수준이 된다. 따라서, 극저탄소강의 경우 열간압연시의 온도저하에 의한 불균일 조직의 생성이 더욱 조장될 수 있음을 충분히 예상할 수 있다.It is difficult to secure the rolling temperature because of the high Ar 3 transformation point during hot rolling, and the elongation is deteriorated due to the mixed grain structure in which fine grains and coarse grains are mixed together in a systematic manner. In other words, material deterioration due to generation of mixed grain texture due to lowering of the hot rolling temperature is a problem in manufacturing the hot rolled steel sheet using the Ti-doped low carbon steel. In the case of Ti-doped low-carbon steels used in the manufacture of deep-drawn cold-rolled steel sheets, it is usually rolled to 3.5 to 4.0 mm and hot rolled at 910 ° C or higher. However, as the hot rolled thickness becomes thinner, the rolling finish temperature lowers. As a result, in the case of a steel sheet having a thickness of 1.6 mm, the hot rolling finish temperature is usually 860 to 880 ° C. Therefore, it can be sufficiently predicted that, in the case of ultra-low carbon steels, the generation of a non-uniform structure due to the temperature drop during hot rolling can be further promoted.
이처럼 용융아연 열연강판의 도금소재로서 연성확보에 있어 유리한 극저탄소강을 채택했음에도 불구하고 약 1.6mm두께의 박물인 용융아연 열연강판을 제조시 문제가 되는 것은, Ar3변태점(페라이트 변태온도)이 높기 때문에 압연온도의 확보가 어렵고, 조직적으로는 미세립과 조대립이 혼재한 혼립조직 등에 기인한 연신율의 현저한 감소가 발생하여 가공성이 떨어지는 문제점이 있다.In spite of adopting the extremely low carbon steel which is advantageous in securing ductility as the plating material of the hot-dip galvanized steel sheet, there is a problem in manufacturing the hot-dip galvanized steel sheet of about 1.6 mm thickness because the Ar 3 transformation point (ferrite transformation temperature) It is difficult to secure the rolling temperature, and there is a problem that the elongation rate is remarkably reduced due to the mixed grain structure in which the fine grain and the coarse grain are mixed together, resulting in poor workability.
이러한 문제점을 해결하기 위해 극저탄소강에 Ar3변태점을 저하시키는 원소인 Cr을 소량 첨가하는 방법이 있으나, 이 Cr의 첨가로 인해 가공성은 향상되나, 통상의 센지미어(Sendzimir)혹은 무산화로방식의 CGL에서 열처리시에는 Cr의 표면농화에 따른 안정한 크롬 산화물형성으로 용융도금시 미도금이 발생하거나, 가공과정에서 치명적인 도금박리가 발생하는 문제점이 있다. 또한 도금전 열처리시 고용탄소의 재고용에 따른 재질열화가 발생하는 문제점도 있다.In order to solve this problem, there is a method of adding a small amount of Cr, which is an element for lowering the Ar 3 transformation point, to an ultra-low carbon steel. However, the addition of Cr improves the workability, but the conventional Sendzimir or non- In the case of CGL, there is a problem that chromium oxide is formed due to the formation of stable chromium oxide due to the surface enrichment of Cr, and there is a problem that plating is peeled during the hot-dip coating and fatal plating peeling occurs in the processing. In addition, there is also a problem that material deterioration occurs due to the reuse of the used carbon during the pre-plating heat treatment.
이에 본 발명자들은 상기 Cr첨가에 따른 용융도금시 재질열화 및 도금밀착성 저하등의 문제점을 해결하기 위해 연구와 실험을 거듭하고, 그 결과에 근거하여 본 발명을 제안하게 된 것으로, 본 발명은 Cr함유 극저탄소강을 소지강판으로 하여 도금전의 강판온도와 도금욕의 성분을 제어함으로써, 가공성 및 도금밀착성이 우수한 용융아연도금열연강판을 제공하고자 하는데 그 목적이 있다.Accordingly, the present inventors have conducted research and experiments to solve problems such as deterioration of material and adhesion of plating during hot-dip coating due to the addition of Cr. The present invention has been made based on the results, It is an object of the present invention to provide a hot-dip galvanized hot-rolled steel sheet excellent in workability and plating adhesion by controlling the steel sheet temperature before plating and the components of the plating bath using ultra-low carbon steel as a base steel sheet.
본 발명은 용융아연도금 열연강판을 제조하는 방법에 있어서, Cr이 0.1∼ 0.5wt%범위로 함유된 극저탄소 열연강판을 소지강판으로 하고, 이 소지강판을 460∼500℃온도 범위로 가열한 후, Al:0.15∼0.20wt%, Ni:0.05∼0.15wt% 나머지 Zn 및 기타 불가피한 불순물로 구성된 용융아연도금욕에 침적하여 도금하는 가공성 및 도금밀착성이 우수한 용융아연도금 열연강판의 제조방법에 관한 것이다.The present invention relates to a method for producing a hot-dip galvanized hot-rolled steel sheet, comprising the steps of preparing an ultra low carbon hot-rolled steel sheet containing Cr in a range of 0.1 to 0.5 wt% as a base steel sheet, heating the base steel sheet to a temperature in the range of 460 to 500 , Al: 0.15 to 0.20 wt%, Ni: 0.05 to 0.15 wt%, and the balance of Zn and other unavoidable impurities, which is excellent in workability and plating adhesion, and relates to a method for producing a hot-dip galvanized hot- .
이하, 본 발명을 보다 상세히 설명한다.Hereinafter, the present invention will be described in more detail.
본 밤령에서는 Ar3변태점을 저하시키기 위해 강중에 상기 Cr을 0.1∼0.5wt%로 함유시킨다.In order to lower the Ar 3 transformation point, the steel contains 0.1 to 0.5 wt% of Cr in the steel.
일반적으로 Cr첨가는 연신율을 개선시키고, 강도의 상승효과는 매우 적다. 이는 강중 Cr원소의 고용경화능이 적고, 강중 C를 고정하는 효과가 있기 때문인 것으로 추정되고 있다. 따라서, 본 발명에서 Cr함량이 0.1wt%미만인 경우는 C를 고정하는 효과가 미미하고 Ar3변태점의 저하가 10℃미만으로 적어서 열간압연시 적정사상압연온도의 확보가 곤란하여 가공성이 불량한 문제점이 발생한다. 또한, 강중 Cr이 0.5wt%초과시는 Ar3변태점저하 및 C를 고정하는 효과는 매우 크나, Cr자체의 고용경화에 따른 가공성열화가 나타나고 경제적으로도 유리하지 못하다. 따라서, 본 발명에서는 강중의 Cr함유량을 0.1∼0.5wt%로 한정한다.In general, Cr addition improves the elongation, and the effect of increasing the strength is very small. It is presumed that this is because the effect of hardening of the solid solution of Cr element in the steel is small and the effect of fixing the steel C is low. Therefore, in the present invention, when the Cr content is less than 0.1 wt%, the effect of fixing C is insignificant and the lowering of the Ar 3 transformation point is less than 10 DEG C, which makes it difficult to ensure the proper hot rolling temperature during hot rolling, Occurs. In addition, when the Cr content exceeds 0.5 wt%, the effect of lowering the Ar 3 transformation point and fixing C is very high, but the workability deteriorates due to solidification of Cr itself and is economically unfavorable. Therefore, in the present invention, the Cr content in the steel is limited to 0.1 to 0.5 wt%.
본 발명에 있어서, 상기한 바와 같은 이유로 Cr을 함유하는 소지강판은 0.002wt%이하의 탄소와 용융아연도금 열연강판의 제조시 적용되는 통상적인 원소가 함유된 극저탄소 열연강판이다.In the present invention, the base steel sheet containing Cr is an extremely low carbon steel hot-rolled steel sheet containing 0.002 wt% or less of carbon and typical elements to be applied in manufacturing a hot-dip galvanized hot-rolled steel sheet for the reasons described above.
본 발명에서는 상기 소지강판을 도금전 열처리시 가열대에서 460∼500℃온도범위로 가열하는 과정을 거친다.In the present invention, the base steel sheet is heated in a temperature range of 460 to 500 ° C. in a heating zone during pre-plating heat treatment.
산세를 거친 열연강판은 예열대에서 강판온도를 약 150℃로 승온한 후, 간접가열로인 가열대에서 460∼500℃로 가열하고 가스냉각대를 통과하여 약 460℃의 강판입욕 온도로 도금욕에 들어가게 된다. 이때 분위기 가스의 로내에서 산세후 남아있는 강판의 산화피막을 환원제거하여 도금밀착성을 향상시킨다. 이때 용융아연 열연강판의 기계적 성질은 냉연강판을 도금소재로 하는 CGL과 달리, 제강성분과 열간압연 공정에서 거의 결정되므로 열연강판을 도금소재로 하는 CGL의 열처리 공정에서는 가능한 재질변화를 일으키지 않도록 하여야 한다. 환원열처리 로내 강판의 온도가 낮은 것이 고용탄소의 재용해에 따른 기계적 성질의 열화를 최소화하는 측면에서 유리하지만, 강판온도가 460 ℃미만으로 너무 낮으면 Fe와 Zn간의 상호확산에 따른 Fe-Zn합금층 생성이 곤란하여 도금층박리가 발생할 가능성이 높다. 반면 강판온도가 500℃초과시에는 강중 Cr이 표면으로 편석하여 치밀한 크롬산화물을 형성하여 미도금 및 도금박리가 발생할 가능성이 증가하며, 고용탄소의 재용해에 따른 강도 상승으로 가공성이 크게 열화된다. 따라서, 도금전 소지강판의 온도를 450∼500℃범위로 한정하는 것이다.The hot rolled steel sheet subjected to the pickling was heated at 460 to 500 ° C in an indirect heating furnace, heated at a temperature of about 150 ° C in a preheating zone, passed through a gas cooling zone and heated at a steel bath temperature of about 460 ° C I will enter. At this time, the oxidation film of the steel sheet remaining after pickling in the furnace of the atmospheric gas is subjected to reduction treatment to improve the plating adhesion. The mechanical properties of the hot-dip galvanized steel sheet are determined by the steelmaking process and the hot rolling process, unlike CGL, which uses cold-rolled steel sheets as the plating material, so that the CGL heat treatment process using hot- . The lower temperature of the steel sheet in the reduction annealing furnace is advantageous from the viewpoint of minimizing the deterioration of the mechanical properties due to the redissolving of the carbon. However, if the steel sheet temperature is too low to be lower than 460 ° C, the Fe- Layer formation is difficult and the possibility of peeling of the plating layer is high. On the other hand, when the steel sheet temperature exceeds 500 ° C., the Cr in the steel segregates to the surface to form dense chromium oxide, which increases the possibility of unplated and plating peeling, and the workability is greatly deteriorated due to the increase in strength due to the redissolution of the solid carbon. Therefore, the temperature of the pre-plated steel sheet is limited to the range of 450 to 500 占 폚.
본 발명에서는 상기 가열된 소지강판을 Al:0.15∼0.20wt%, Ni:0.05∼ 0.15wt%, 나머지 Zn 및 기타불가피한 불순물로 구성된 용융아연 도금욕에 침적하여 도금시키는 과정을 거친다.In the present invention, the heated ground steel sheet is subjected to plating in a hot dip galvanizing bath composed of 0.15 to 0.20 wt% of Al, 0.05 to 0.15 wt% of Ni, and the balance of Zn and other unavoidable impurities.
상기 Cr은 매우 산화되기 쉬운 원소이기 때문에 통상의 용융아연도금 열연강판의 제조공정에서 열간압연과정 및 연속소둔 열처리공정중에서 강판표면으로 확산되어 이들 원소의 농도가 모재(bulk)보다 10∼100배 정도 높게 된다. 이와같이 결정입계나 입내에 농화된 난도금성원소는 로내 분위기중의 극미량 수분이나 불순물과 반응하여 CrO2등의 산화물 피막을 형성하므로 용융아연 도금공정에서 용융아연과의 젖음성(wettability)을 크게 저하시킨다. 그 결과 젖음성 확보가 곤란하게 되어 미도금현상이 다발하게 되거나, 용융도금이 되더라도 도금밀착성을 열화시켜 가공시 도금박리가 발생하게 된다. 또한 난도금성 원소의 농화부와 비농화부에서 도금층의 불균일로 인해 용융도금후 합금화처리시 크게 영향을 미치게 되는 문제가 발생하게 된다.Since Cr is an element that is easily oxidized, it diffuses to the surface of the steel sheet during the hot rolling process and the continuous annealing heat treatment process in the process of manufacturing a hot-dip galvanized steel sheet, and the concentration of these elements is 10 to 100 times . Since the noble metal element concentrated in the crystal grain or the mouth reacts with trace moisture or impurities in the furnace atmosphere to form an oxide film such as CrO 2 , the wettability with molten zinc in the hot dip galvanizing process is greatly lowered. As a result, it becomes difficult to ensure wettability, so that the plating plating phenomenon becomes frequent or the plating adhesion is deteriorated even in the case of hot-dip coating, resulting in plating peeling at the time of processing. In addition, the unevenness of the plating layer in the enriched part and the non-enriched part of the noble metal element causes a problem that the degree of melting greatly affects the alloying treatment in the future.
이와같은 문제를 해결하기 위하여 용융아연 도금욕의 Al첨가량을 기존의 0.18%에서 0.21%이상으로 조정하여 소지철과 도금층 계면에 Zn-Fe-Al-Cr계 또는 Fe-Al-Cr의 합금층 생성량을 증가시킴으로써 합금원소의 산화층을 환원시키는 효과에 의해, 계면에서 합금원소의 산화피막으로 인한 용융도금 젖음성 저하를 방지하는 방법을 검토하였다. 그러나 도금욕내 Al농도가 0.20wt%초과시는 도금욕에 불가피하에 불순물로 첨가되는 Pb와 공존시 입계부식이 발생하기 용이하기 때문에 경시도금박리가 발생할 가능성이 높다. 또한 도금욕내 Al농도증가는 도금욕내 상부드로스(top dross)발생량을 증가시키고, 도금층 표면에 부착시 표면외관 결함을 일으키는 문제점이 있다. 반면 Al이 0.15%미만에서는 Fe와 Zn간의 반응의 확산장벽으로 작용하는 FeAl5합금층 생성을 억제하여 취약한 합금층을 형성하기 때문에 도금층박리가 발생할 확률이 증가하는 단점이 있다.To solve this problem, the amount of Al in the hot-dip galvanizing bath was adjusted from 0.18% to 0.21% or more so that the amount of Zn-Fe-Al-Cr or Fe-Al- To reduce the wettability of the molten plating due to the oxide film of the alloy element at the interface by the effect of reducing the oxide layer of the alloy element by increasing the amount of the alloy element. However, when the Al concentration in the plating bath is higher than 0.20 wt%, it is likely that the plating step is peeled with time because it is easy to generate a grain boundary condition when coexisting with Pb added as an impurity inevitably to the plating bath. Also, the increase in the Al concentration in the plating bath increases the amount of top dross generated in the plating bath, and causes surface appearance defects when adhered to the surface of the plating layer. On the other hand, when the content of Al is less than 0.15%, there is a disadvantage that the possibility of peeling of the plating layer increases due to formation of a weak alloy layer by inhibiting the formation of FeAl 5 alloy layer acting as a diffusion barrier of reaction between Fe and Zn.
이러한 이유로 본 발명에서의 용융아연 도금욕내 Al함량을 0.15∼0.20wt%로 한정하는 것이다.For this reason, the Al content in the hot-dip galvanizing bath of the present invention is limited to 0.15 to 0.20 wt%.
상기 용융아연 도금욕내 Ni의 첨가는 0.15∼0.20wt%Al을 함유한 도금욕의 표면장력을 저하시켜 Cr 등의 난도금성 원소가 함유된 강판의 도금젖음성 (Wettability) 및 도금밀착성을 향상시키기 위해서이다.The addition of Ni in the hot dip galvanizing bath reduces the surface tension of a plating bath containing 0.15 to 0.20 wt% Al to improve the plating wettability and plating adhesion of a steel sheet containing an element with an iridescent property such as Cr .
본 발명과 같이 Cr이 0.1∼0.5wt%함유한 강의 경우 통상의 아연도금욕에서 용융도금시는 표면에 치밀한 크롬산화물로 인해 국부적으로 미도금이 발생하는 문제점이 있다. 이때 도금욕내의 Ni함유량이 0.05wt%미만에서는 도금욕의 표면장력저하에 따른 도금젖음성의 향상이 미약하다. 또한, 그 함유량이 0.15wt%초과시에는 아연도금욕내 고용한계를 초과하기 때문에 도금욕중의 Al과 선택적으로 반응하여 상부 드로스(tiop dross)를 형성하여 대부분 소모되기 때문에 Fe-Zn합금화반응이 촉진되어 밀착성이 열화되고 제조원가가 상승하는 단점이 있다. 따라서, Ni첨가량은 0.05∼0.15wt%로 한정하였다. 이때 Fe, Pb 등의 불가피하게 혼입된 불순물등은 도금욕내에서 드로스발생을 증가시켜 표면품질을 열화시키므로 0.1wt%이하로 관리하는 것이 바람직하다.In the case of a steel containing 0.1 to 0.5 wt% of Cr as in the present invention, there is a problem that when the hot dip galvanizing is carried out in a conventional zinc plating bath, local uncoating occurs due to dense chromium oxide on the surface. At this time, when the Ni content in the plating bath is less than 0.05 wt%, the improvement of the plating wettability due to the lowering of the surface tension of the plating bath is weak. In addition, when the content exceeds 0.15 wt%, it exceeds the solubility limit in the zinc plating bath, so that it selectively reacts with Al in the plating bath to form an upper dross and is mostly consumed, so that the Fe-Zn alloying reaction There is a disadvantage that the adhesion is deteriorated and the manufacturing cost is increased. Therefore, the addition amount of Ni was limited to 0.05 to 0.15 wt%. At this time, inevitably mixed impurities such as Fe and Pb increase the generation of dross in the plating bath to deteriorate the surface quality. Therefore, it is preferable to control the content to 0.1 wt% or less.
이하, 실시예를 통하여 본 발명을 보다 상세히 설명한다.Hereinafter, the present invention will be described in more detail by way of examples.
[실시예 1][Example 1]
강중 Cr함량이 하기표 1과 같은 극저탄소 열연강판(0.002%C-0.14%Mn-0.006%C-0.005%S)을 연산용액에서 산세한 후 10%의 수소농도분위기에서 가열대내의 강판온도를 변경하여 열처리하고 용융아연 도금을 행한후 기계적성질을 조사하여 이를 하기표 1에 나타내었다.(0.002% C-0.14% Mn-0.006% C-0.005% S) as shown in Table 1 was subjected to pickling in the treating solution, and then the steel sheet temperature in the heating vessel was measured at a hydrogen concentration of 10% And then subjected to a heat treatment and hot dip galvanizing, and their mechanical properties were investigated. The results are shown in Table 1 below.
상기 표 1에서 알 수 있는 바와 같이 본 발명에 의해 제조된 Cr첨가 용융아연도금 열연강판은 깊이 50mm이상의 심한 가공성을 요하는 전기스위치박스 제작에 필요한 도금강판의 최소 재질규격조건인 항복강도(YS):17Kg/㎟ 이하, 연신율(E1):45%이상인 조건을 충족하여 사용이 가능하였다. 반면 Cr함량이 0.1wt%미만인 경우 혼립조직 형성에 따른 재질편차 및 고용탄소위 재고용에 따른 재질열화가 발생하였고, 0.5wt% 초과시에는 Cr자체에 의한 강도증가에 의한 연성저하가 크게 나타났다. 또한 도금전 열처리온도가 500℃를 초과하면 크롬카바이드 형태로 고용되어 있던 고용탄소가 급속히 재용해되어 항복강도가 상승하고, 항복적 연신율이 나타나서 연성이 크게 감소하여 스위치박스 가공시 대부분 파손이 발생하였다.As can be seen from the above Table 1, the Cr-added hot-dip galvanized hot-rolled steel sheet produced by the present invention had a yield strength (YS) of at least 50 mm, : 17 kg / mm 2 or less, and elongation (E 1): 45% or more. On the other hand, when the Cr content is less than 0.1wt%, the material deterioration due to the unevenness of the solid texture and the material degradation due to the employment of the carbon monoxide have occurred. When the Cr content exceeds 0.5wt% In addition, when the pre-plating heat treatment temperature is higher than 500 ° C, the solid carbon employed in the form of chromium carbide is rapidly re-dissolved, yield strength is increased, yield elongation is increased, and ductility is greatly reduced, .
[실시예 2][Example 2]
0.5%Cr을 첨가한 열연강판(0.002%C-0.14%Mn-0.006%C-0.005%S)을 도금전 열처리시 도금욕내 Al, Ni농도를 하기표 2와 같이 달리한 후 460℃도금욕에서 3초간 침적하여 도금부착량을 150g/㎡(단면기준)으로 용융아연 열연강판을 제조하였다. 여러 가지 방법으로 도금밀착성을 시험한 결과를 하기표 2에 나타내었다.Al and Ni concentrations were varied in the plating bath during the heat treatment before plating in a hot-rolled steel sheet (0.002% C-0.14% Mn-0.006% C-0.005% S) containing 0.5% Cr as shown in Table 2, And then immersed for 3 seconds to prepare a hot-rolled hot-dip galvanized steel sheet having an adhered amount of 150 g / m < 2 > Table 2 shows the results of the plating adhesion test by various methods.
상기표 2에서 알 수 있는 바와 같이, 본 발명에 의한 용융아연 도금강판의 도금밀착성은 도금전 열처리시 강판온도가 낮을수록 크롬산화물의 표면농화가 적으므로 우수하였다. 또한 도금밀착성은 도금욕내 Ni, Al농도 증가에 따라 증가하나 적정량 초과시 드로스 발생량이 증가하고 Fe-Zn반응을 촉진(Ni함량 초과시)또는 억제(Al함량 초과시)하여 도금밀착성이 열화되었다. 즉, 도금욕내 Al이 0.15∼ 0.20wt%이면서 Ni이 0.05∼0.15wt%일 때가 도금밀착성 및 드로스발생량이 가장 양호하였다.As can be seen from the above Table 2, the plating adhesion of the hot-dip galvanized steel sheet according to the present invention was excellent because the surface hardening of the chromium oxide was less as the steel sheet temperature was lowered during the pre-plating heat treatment. In addition, the plating adhesion increased with increasing Ni and Al concentration in the plating bath, but the amount of dross generated increased when the amount exceeded the proper amount, and the adhesion of the plating deteriorated due to acceleration of the Fe-Zn reaction (when the Ni content was exceeded) or inhibition (when the Al content was exceeded). That is, when Al was 0.15 to 0.20 wt% and Ni was 0.05 to 0.15 wt% in the plating bath, the plating adhesion and the amount of dross generation were the best.
또한 본 발명예의 경우 형성한계도(Forming Limit Diagram FLD)를 작성한 결과 소지철이 파단될 때까지 도금층박리가 발생하지 않았다.In addition, in the case of the present invention example, the forming limit diagram (FLD) was prepared, and as a result, the plating layer peeling did not occur until the base steel was broken.
상술한 바와 같이, 본 발명은 건축물의 전기스위치박스 등에 사용되는 심가공용 용융아연 열연강판(Hot-rolled Galvanized Iron)을 제조하는 방법에 관한 것으로서, 기존의 냉간압연에 의한 방법에 비해 공정단축에 따른 제조비용 및 에너지 절감의 잇점이 있으며, 도금전 열처리에 따른 재질변화 최소로 우수한 가공성확보 및 도금욕조성과 열처리조건을 변경하여 도금밀착성을 확보함으로써 결과적으로 경제성 및 품질을 향상시킨 것으로 산업상 이용가치가 매우큰 것이다.As described above, the present invention relates to a method of manufacturing a hot-rolled galvanized iron for deep drawing used in an electric switch box of a building and the like, It has the advantages of manufacturing cost and energy saving, securing excellent processability by minimizing material change due to pre-plating heat treatment and securing plating adhesion by changing plating bathing property and heat treatment condition, resulting in improvement of economic efficiency and quality. It is very big.
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| KR20020046709A (en) * | 2000-12-15 | 2002-06-21 | 이구택 | method of manufacturing hot-dip galvannealed steels with good anti-flaking properties |
| KR100370582B1 (en) * | 1998-12-30 | 2003-03-17 | 주식회사 포스코 | Manufacturing method of hot rolled hot dip galvanized steel sheet with excellent workability |
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| KR100370582B1 (en) * | 1998-12-30 | 2003-03-17 | 주식회사 포스코 | Manufacturing method of hot rolled hot dip galvanized steel sheet with excellent workability |
| KR20020046709A (en) * | 2000-12-15 | 2002-06-21 | 이구택 | method of manufacturing hot-dip galvannealed steels with good anti-flaking properties |
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