KR101048062B1 - Manufacturing Method of High Yield Ratio Precipitation-Reinforced Steel Sheet with Excellent Stretch Properties - Google Patents

Manufacturing Method of High Yield Ratio Precipitation-Reinforced Steel Sheet with Excellent Stretch Properties Download PDF

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KR101048062B1
KR101048062B1 KR1020030091535A KR20030091535A KR101048062B1 KR 101048062 B1 KR101048062 B1 KR 101048062B1 KR 1020030091535 A KR1020030091535 A KR 1020030091535A KR 20030091535 A KR20030091535 A KR 20030091535A KR 101048062 B1 KR101048062 B1 KR 101048062B1
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steel
steel sheet
yield ratio
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strength
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KR20050059819A (en
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한상호
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주식회사 포스코
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    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • 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
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

본 발명은 항복강도 220MPa 이상 확보 가능하며 항복비 및 연신율 특성이 우수한 자동차용 고강도 강판의 제조 방법에 관한 것이다.The present invention relates to a method of manufacturing a high strength steel sheet for automobiles that can secure a yield strength of 220 MPa or more and is excellent in yield ratio and elongation characteristics.

본 발명에 의하면, 중량 %로 C:0.02~0.04%, Mn:0.15~0.3%, P:0% 초과~0.015% 이하, S:0% 초과~0.005% 이하, N:0% 초과~0.003% 이하, Si:0% 초과~0.1%이하, 산가용 Al:0.03~0.07%, Ti:0.02~0.04%, Mo:0% 초과~0.1% 이하, B:0.0005~0.0015% 및 잔부는 Fe 와 기타 불가피한 불순물로 구성되는 강을 Ar3변태점 이상에서 열간압연을 종료하고, 550~650℃의 온도 범위에서 권취를 행하는 단계, 통상의 조건의 산세 및 압하율 55% 이상으로 냉간압연을 행하는 단계 및 연속 소둔로 또는 합금화 용융 도금 연속로에서 790~810℃의 온도 범위로 재결정 소둔을 행하는 단계로 구성되는 연신특성이 우수한 고항복비형 석출강화 강판의 제조 방법이 제공된다.According to the present invention, in weight% C: 0.02 to 0.04%, Mn: 0.15 to 0.3%, P: more than 0% to 0.015% or less, S: more than 0% to 0.005% or less, N: more than 0% to 0.003% Si: Above 0% ~ 0.1%, Acid Value Al: 0.03 ~ 0.07%, Ti: 0.02 ~ 0.04%, Mo: Above 0% ~ 0.1%, B: 0.0005 ~ 0.0015% and balance are Fe and others Performing hot rolling of the steel composed of unavoidable impurities at an Ar 3 transformation point or higher, winding in a temperature range of 550 to 650 ° C., cold rolling at a pickling rate and a reduction ratio of 55% or more under normal conditions, and continuous Provided is a method for producing a high yield ratio precipitation strengthened steel sheet having excellent stretching characteristics, comprising recrystallization annealing at a temperature range of 790 to 810 ° C. in an annealing furnace or an alloyed hot dip continuous furnace.

이러한 강판은 향상된 내충격성을 필요로 하는, 자동차의 멤버(Member), 빔(Beam) , 필라(Pillar)등의 구조 부재에 사용하기에 적합하다. Such steel sheets are suitable for use in structural members such as members, beams, pillars, and the like of automobiles, which require improved impact resistance.

연신률, 항복비, 항복강도, 석출강화강판,냉간압하율Elongation, Yield Ratio, Yield Strength, Precipitation Strengthened Steel Sheet, Cold Rolling Rate

Description

연신특성이 우수한 고항복비형 석출강화강판의 제조방법{Manufacturing Method Of Precipitation Hardened Steel Sheet Having High Ductility and High Yield Ratio}Manufacturing Method Of Precipitation Hardened Steel Sheet Having High Ductility and High Yield Ratio

본 발명은 연신특성이 우수한 고항복비형 석출강화강판의 제조방법에 관한 것으로, 보다 상세하게는 항복강도는 220MPa이상이고, 항복비는 80%이상이고,연신율은 35%이상인 자동차용 고강도 냉연강판의 제조 방법에 관한 것이다.
The present invention relates to a method for producing a high yield ratio precipitation-reinforced steel sheet having excellent stretching characteristics, more specifically, yield strength is 220MPa or more, yield ratio is 80% or more, elongation is 35% or more of the high strength cold rolled steel sheet for automotive It relates to a manufacturing method.

석출강화형 고강도강판은 최근 자동차의 충격 안전성 규제가 확산되면서 차체의 내충격성 향상을 위하여 멤버(Member), 빔(Beam), 필라(Pillar) , 내판재등의 판넬류 및 구조 부재등 다양한 용도에 사용되고 있다. 이는 자동차 사고시 충격 흡수능이 우수한 강판의 사용이 요구되기 때문이다. 석출경화형 고강도강판은 자동차의 충돌에너지를 흡수하기 위하여 설계되었기 때문에 인장강도 대비 항복강도 즉, 항복비(YS/TS)가 높은 것을 특징으로 하고 있다.
Precipitation-reinforced high-strength steel sheet has been widely used in various applications such as panels, structural members such as members, beams, pillars, inner plates, etc. to improve impact resistance of automobiles as the impact safety regulations of automobiles have spread. It is used. This is because it is required to use a steel sheet with excellent shock absorbing ability in an automobile accident. Precipitation hardening high strength steel sheet is designed to absorb the collision energy of the vehicle, characterized by high yield strength, that is, yield ratio (YS / TS).

통상 강을 강화하는 방법에는 고용강화, 석출강화, 결정립 미세화에 의한 강화 및 변태강화 방법으로 요약할 수 있다.
In general, the method of strengthening the steel can be summarized as a method of strengthening solid solution, strengthening precipitation, strengthening by transformation of grains, and transformation.

고용강화 방법으로 제조되는 고강도강으로는 P첨가 IF(interstitial free)강이 있으며, 이 강은 P첨가에 의한 강도 확보 및 침입형 원소성분을 극도로 억제하며 동시에 고정화시킴으로서 가공성을 확보하여 고가공용강으로 사용되고 있다. 이러한 고용강화강은 인장강도 대비 항복강도가 낮기 때문에 가공성을 요구하는 자동차 부품으로의 사용은 유리하지만, 앞서 언급한 내충격성을 요구하는 부품으로의 사용은 부적합하다.
High-strength steel manufactured by solid solution strengthening method includes P-added IF (interstitial free) steel, which secures workability by securing strength by P-adding, extremely inhibiting invasive elemental components, and immobilizing simultaneously. Is being used. Such solid solution reinforced steel has a lower yield strength than tensile strength, so it is advantageous to use it as an automobile part requiring workability, but it is not suitable for use as a component requiring impact resistance mentioned above.

변태 강화 방법은 강도 확보 및 변태 조직 형성을 위해 다량의 합금 성분이 필요할 뿐만 아니라 그 하부 조직이 베이나이트 혹은 마르텐사이트로 이루어져 있기 때문에 인장강도 대비 항복강도 즉 항복비가 낮아 자동차 충돌시 내충격성을 요구하는 부품에의 사용은 적절하지 못하다는 결점을 안고 있다.
Metamorphic reinforcement method requires not only a large amount of alloying elements to secure strength and formation of metamorphic structure, but also because its lower structure is made of bainite or martensite, it has low yield strength, that is, yield ratio to tensile strength. The drawback is that their use in parts is not appropriate.

석출강화형 고강도강은 주로 Cu, Nb, Ti, V등과 같은 탄,질화물 형성원소 첨가에 의한 석출 강화 효과 및 결정립 미세화 효과에 의해 강도를 향상 시킨 강으로 낮은 제조 원가로도 고강도화를 쉽게 이룰 수 있다는 장점을 가지고 있다.석출 강화 방법은 우선 강을 고온에서 용체화처리를 행한 다음 냉각 중에 미세한 석출물들을 다수 형성 시켜 석출물 주변의 응력장에 의해 강화되는 현상이다. 통상 이러한 미세 석출물들은 열간압연 후 권취 중에 다량 형성되므로 냉간압연 후 소둔시 미세 석출물들에 의한 재결정온도가 매우 급격히 상승하여 고온 소둔을 실시하여야 하는 단점을 갖고 있다. 고온 소둔시 형상 불량 뿐만 아니라 특히, 도금강판의 경우 표면에 MnO 및 SiO2등의 각종 산화물이 형성되어 도금 특성을 저해하는 요소로 작용된다.
Precipitation-reinforced high-strength steel is a steel whose strength is enhanced by the precipitation strengthening effect by the addition of carbon and nitride forming elements such as Cu, Nb, Ti, V, etc., and the grain refinement effect, making it easy to achieve high strength even at low manufacturing costs. The precipitation strengthening method is a phenomenon in which the steel is first subjected to solution treatment at high temperature, and then a large number of fine precipitates are formed during cooling to be strengthened by the stress field around the precipitate. Usually, since these fine precipitates are formed in a large amount during winding after hot rolling, the recrystallization temperature caused by the fine precipitates during annealing after cold rolling has a very high temperature annealing. In addition to poor shape during high temperature annealing, in particular, in the case of a plated steel sheet, various oxides such as MnO and SiO 2 are formed on the surface to act as a factor that inhibits plating characteristics.

석출강화형 고강도강판 제조 방법으로 공지된 기술로는 일본 공개 특허 공보 56-84422호가 있으며, 여기에서는 0.15%C이하의 저탄소강을 기본 성분계로하여 Ti, Nb, V등을 1종 혹은 2종 이상 함유하고 최종 열간압연 마무리 온도를 750~950℃의 범위로, 권취온도를 450℃ 이하로 관리하여 석출강화형 고강도강을 제조하고 있다., 이 경우 권취온도가 매우 낮다. 이는 극미세 석출물을 형성하여 강도 기여 효과는 높으나, 열연판 형상 불량 뿐만 아니라 석출물 주변의 잔류응력의 증가로 냉간압연시 과부하 현상이 종종 발생하는 결점을 가지고 있다. 일본 공개 특개평 4-221015에서는 Nb혹은 V의 석출물 형성 원소를 이용하고 열간압연 후 가속 냉각에 의해 강도 상승 효과가 우수한 석출강화강의 제조 방법을 제시하고 있으나 ,이 경우도 권취온도가 400℃ 이하로 설정되어 있어서 앞서 언급한 문제가 있으며,그외에 균일한 페라이트 조직 형성 대신 베이나이트 혹은 마르텐사이트 조직이 형성되어 항복비(항복강도/인장강도)가 저하되는 즉 항복강도가 저하되는 결점을 갖고 있다. Cu석출물을 이용한 석출강화형 고강도 강판 제조방법으로는 일본 공개 특허 공보 3-140412 및 11-241119호가 있으며, 여기에서는 Cu를 0.8wt%이상 첨가하여 제조하고 있으나 역시 Cu계 석출물에 의한 도금 강판의 합금화 불량 및 용접성에 문제가 있어 사용에 문제점을 안고 있다.
A technique known as a method of manufacturing a precipitation-reinforced high strength steel sheet is Japanese Laid-Open Patent Publication No. 56-84422, wherein one or two or more kinds of Ti, Nb, V, etc. are used based on low carbon steel of 0.15% C or less as a basic component system. Containing the final hot rolled finishing temperature in the range of 750 to 950 ° C. and winding temperature of 450 ° C. or lower to produce precipitation-reinforced high strength steel, in which case the winding temperature is very low. It has a high strength contribution effect by forming a very fine precipitate, but has the drawback that the overload phenomenon often occurs during cold rolling due to the increase in the residual stress around the precipitate as well as the shape of the hot-rolled sheet. Japanese Laid-Open Patent Publication No. 4-221015 discloses a method for producing precipitated tempered steel using Nb or V precipitate forming elements and having excellent strength synergistic effect by accelerated cooling after hot rolling. Since there is a problem described above, in addition to the formation of a uniform ferrite structure, bainite or martensite structure is formed, and thus the yield ratio (yield strength / tensile strength) is lowered, that is, the yield strength is lowered. JP-A-3-140412 and 11-241119 are methods for producing a precipitation-reinforced high strength steel sheet using Cu precipitates. In this case, Cu is added by 0.8 wt% or more, but alloying of the coated steel sheet by Cu-based precipitates is also performed. There is a problem in poor use and weldability.

본 발명의 목적은 자동차용 내,외판 판넬류, 구조부재등 내충격성 소재로 사용할 수 있도록 항복강도 220MPa 이상, 항복비 80% 이상, 연신율 35%이상이며 도금 표면특성이 매우 우수한 고강도 강판의 제조방법을 제공하는 것이다.
An object of the present invention is a method of manufacturing a high strength steel sheet having excellent plating surface properties with a yield strength of 220MPa or more, yield ratio of 80% or more, elongation of 35% or more, so as to be used as an impact resistant material for automobiles, exterior panels and structural members. To provide.

본 발명에 의하면, 중량 %로 C:0.02~0.04%, Mn:0.15~0.3%, P:0% 초과~0.015% 이하, S:0% 초과~0.005% 이하, N:0% 초과~0.003% 이하, Si:0% 초과~0.1%이하, 산가용 Al:0.03~0.07%, Ti:0.02~0.04%, Mo:0% 초과~0.1% 이하, B:0.0005~0.0015% 및 잔부는 Fe 와 기타 불가피한 불순물로 구성되는 강을 Ar3변태점 이상에서 열간압연을 종료하고, 550~650℃의 온도 범위에서 권취를 행하는 단계, 통상의 조건의 산세 및 압하율 55% 이상으로 냉간압연을 행하는 단계 및 연속 소둔로 또는 합금화 용융 도금 연속로에서 790~810℃의 온도 범위로 재결정 소둔을 행하는 단계로 구성되는 연신특성이 우수한 고항복비형 석출강화 강판의 제조 방법이 제공된다.According to the present invention, in weight% C: 0.02 to 0.04%, Mn: 0.15 to 0.3%, P: more than 0% to 0.015% or less, S: more than 0% to 0.005% or less, N: more than 0% to 0.003% Si: Above 0% ~ 0.1%, Acid Value Al: 0.03 ~ 0.07%, Ti: 0.02 ~ 0.04%, Mo: Above 0% ~ 0.1%, B: 0.0005 ~ 0.0015% and balance are Fe and others Performing hot rolling of the steel composed of unavoidable impurities at an Ar 3 transformation point or higher, winding in a temperature range of 550 to 650 ° C., cold rolling at a pickling rate and a reduction ratio of 55% or more under normal conditions, and continuous Provided is a method for producing a high yield ratio precipitation strengthened steel sheet having excellent stretching characteristics, comprising recrystallization annealing at a temperature range of 790 to 810 ° C. in an annealing furnace or an alloyed hot dip continuous furnace.

이하에서는 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail.

본 발명에서 강중 C는 석출물 형성 원소로 중요한 역할을 하나, 함량이 0.02wt% 미만의 경우 충분한 석출 효과를 얻을 수 없어 항복비가 높은 강을 제조할 수 없고, 강중 C함량이 0.04wt%를 초과하게 되면 과잉의 TiC 석출물이 제강의 연주 및 열연 단계에서 극미세 석출되어 목적 강도 이상의 강도 상승 효과를 가져오나 연신율의 급격한 저하를 동반하므로 그 함유량을 0.02~0.04wt%로 제한한다.
In the present invention, steel C plays an important role as a precipitate forming element, but if the content is less than 0.02wt%, sufficient precipitation effect cannot be obtained, and steel with high yield ratio cannot be manufactured, and the C content in steel exceeds 0.04wt%. Excess TiC precipitates are extremely fine precipitated at the stage of steelmaking and hot rolling, resulting in a strength increase effect over the target strength, but accompanied by a sharp drop in elongation, the content is limited to 0.02 to 0.04 wt%.

강 중 Mn은 고용강화 원소로 강도 상승에 기여할 뿐만 아니라 강중 S를 MnS로 석출시켜서 열간압연시 S에 의한 판파단 발생 및 고온취화를 억제시키는 중요한 역할을 한다. 그 함량이 0.15wt% 미만의 경우 제강의 연주 단계에서 Mn성분 청정화를 위한 불순물 억제 비용이 증가하여 제조 원가 상승을 가져오고, 0.3wt%를 초과하게 되면 도금 표면 특성에도 불리하게 작용하므로 그 성분함량범위를 0.15~0.3 wt%로 제한한다.
Mn in steel not only contributes to the increase in strength as a solid solution element, but also precipitates S in MnS and plays an important role in suppressing plate breakage and hot embrittlement caused by S during hot rolling. If the content is less than 0.15wt%, the impurity suppression cost for the Mn component cleanup increases during the regeneration of steelmaking, which leads to an increase in manufacturing cost. If the content exceeds 0.3wt%, it also adversely affects the surface properties of the plating. Limit the range to 0.15 to 0.3 wt%.

강 중 P는 성형성을 크게 해치지 않으면서 강도 확보에 가장 유리한 원소이지만, 과잉의 P첨가는 취성파괴 발생 가능성을 현저히 높여 열간압연 도중 슬라브의 판파단의 발생가능성이 증가될 뿐 아니라, 도금 표면 특성을 저해하는 원소로 작용하므로 그 함량을 0.015wt%로 제한한다..
Although P is the most favorable element for securing strength without significantly deteriorating formability, excessive P addition significantly increases the possibility of brittle fracture, thereby increasing the possibility of slab breakage during hot rolling, as well as plating surface characteristics. It acts as an inhibiting element, limiting its content to 0.015wt%.

S 및 N은 강중 불순물 원소들이기 때문에 가능한 한 낮게 관리하는 것이 중 요하다. 또한 우수한 용접 특성을 확보하기 위하여 그 함량을 가능한 한 낮게 관리함이 바람직하나, 이는 강의 정련 비용을 증대시킨다. 따라서, 조업조건이 가능한 범위인 S함량 0.005 wt% 이하, N함량 0.003wt% 이하로 유지되도록 한다.
It is important to manage S and N as low as possible because they are impurity elements in the steel. It is also desirable to maintain the content as low as possible to ensure good welding properties, but this increases the cost of refining the steel. Therefore, the S content is maintained at 0.005 wt% or less and the N content is 0.003 wt% or less.

강 중 Si함량은 0.1wt%이하로 제한하는데, 그 이상의 경우에는 도금표면 특성이 매우 불량해지기 때문이다.
The Si content in the steel is limited to 0.1 wt% or less, since the plating surface properties become very poor at higher levels.

산가용 Al은 강의 입도 미세화와 탈산을 위해서 첨가되는 원소이다. 함유량이 0.03Wt% 미만의 경우 통상의 안정된 상태로 killed강을 제조할 수 없고, 0.07wt%를 초과하게 되면 결정립 미세화 효과로 강도 상승에는 유리하지만 제강 연주 조업시 개재물 과다 형성으로 인한 도금 강판 표면 불량 발생 가능성이 높아질 뿐만 아니라 제조 원가 상승을 가져 오므로 그 함량을 0.03~0.07wt%로 제한한다.
Acid value Al is an element added for refinement and deoxidation of the particle size of steel. If the content is less than 0.03Wt%, the killed steel cannot be manufactured in a normal stable state. If the content exceeds 0.07wt%, it is advantageous to increase the strength due to the grain refinement effect, but the surface of the plated steel sheet is poor due to the excessive formation of the inclusions during steelmaking operation. In addition to increasing the likelihood of production, the production cost rises, so the content is limited to 0.03 ~ 0.07wt%.

Ti는 열간압연중 고용 C과 작용하여 TiC석출물을 형성하여 석출강화 원소로작용하는 중요한 원소이다. Ti함량은 C함량의 설정 범위에 따라 달라지는데 그 관계식이 (48/12×C)/4 와 같이 설정함이 바람직하다. 즉, C함량을 고려한 관계식에 의해 도출된Ti함량이 0.02t% 미만의 경우에는 강도 확보를 위한 미세 석출물들이 충분히 석출되지 못하여 목적 강도를 확보할 수 없으며 항복비가 낮아 목적으로 하는 석출강화강의 특성을 확보할 수 없고, 그 함량이 0.04wt%를 초과하게 되면 과잉의 미세 석출물로 인한 목적강도 이상의 강도가 상승하여 연신율의 급격한 저하 를 동반하고 도금 표면 특성 확보에도 불리하므로 0.02~0.04wt%로 제한한다.
Ti is an important element that acts as a precipitation strengthening element by forming TiC precipitates by working with solid solution C during hot rolling. The Ti content varies depending on the setting range of the C content, but the relational expression is preferably set as (48/12 × C) / 4. That is, if the Ti content derived by the relational expression considering the C content is less than 0.02t%, the fine precipitates for securing the strength cannot be sufficiently precipitated, so that the target strength cannot be secured, and the yield ratio is low. If the content exceeds 0.04wt%, the strength is higher than the target strength due to the excessive fine precipitates, which leads to a sharp drop in elongation, and is also disadvantageous in securing the plating surface properties, so it is limited to 0.02 ~ 0.04wt%. .

강 중 Mo는 고용 강화 효과 및 재결정 온도를 낮추는 경향있으나 그 함량을 최대 0.1wt%로 제한한다. 0.1wt% 이상에서는 제조원가 상승 부담이 있고 연신율의 감소를 수반하기 때문이다.
Mo in steel tends to lower the solid-solution strengthening effect and recrystallization temperature, but limits its content to a maximum of 0.1 wt%. Above 0.1 wt%, there is a burden of manufacturing cost increase and it is accompanied by a decrease in elongation.

강 중 B의 첨가는 Mo성분과 연계하여 도금강판의 표면 특성을 개선하는 효과가 있는 원소이다. 그함량이 0.0005wt% 미만의 경우에는 상기 효과가 미비하고 그 함량이 0.0015wt%를 초과하게 되면 재결정 온도가 급격히 상승하여 고온소둔에 의한 도금강판 결함 즉, 줄무늬가 생성되고 또한 미합금화 요인으로 작용하므로 그 함량을 제한한다.
The addition of B in the steel is an element having the effect of improving the surface properties of the plated steel sheet in connection with the Mo component. If the content is less than 0.0005wt%, the above effect is insignificant, and if the content exceeds 0.0015wt%, the recrystallization temperature rises rapidly, resulting in defects of plated steel sheet due to high temperature annealing, that is, streaks, and also acts as an unalloying factor. So limit its content.

상기와 같은 조성을 갖도록 조절된 강을 통상의 열간 압연 조건인 Ar3이상의 온도에서 열간압연을 종료하고 550~650℃ 구간에서 권취를 행한다. 550℃이하에서의 권취는 고용 C을 완전히 석출하지 못하여 석출물 효과가 떨어질 뿐만 아니라 권취시 판 형상 불량의 문제가 나타나고, 권취온도가 650℃를 초과하게 되면 석출물들이 현저하게 조대화되는 경향을 가지므로 석출물 효과가 크지 않아 항복비가 낮아지는 경향을 갖기 때문에 권취온도를 위와같이 제한한다. 또한 권취후 냉간압연을 행하되, 냉간압연의 최소 압하율을 55% 이상으로 제한 한다. 본 발명에 의하면 냉간압하율이 증가함에 따라 재결정온도는 현저하게 감소하여 낮은 재결정 소둔이 가능하므로 도금 표면 특성을 확보하는데 중요한 역할을 한다. 압하율이 55% 미만의 경우 재결정온도를 충분히 낮추는 효과가 없을 뿐만 아니라 석출물 형성을 위한 임계 핵생성 사이트의 감소로 충분한 석출물이 형성되지 않는 것으로 판단된다. 냉간압연 후에는 재결정 소둔을 한다. 본 발명 강의 경우 Mn함량이 낮아서 이에 따른 재결정 온도 저하로 낮은 온도에서도 소둔이 가능하지만, 너무 낮은 영역에서의 연속소둔은 미 재결정에 의한 연신율의 감소를 동반하므로 적정 범위의 소둔온도 영역의 설정이 중요하다. 연속소둔 또는 합금화 용융아연시 790℃미만의 소둔 조건은 미재결정 영역으로 코일내 재질 편차가 매우 높아 실용화에 문제가 발생하고, 810℃이상의 조건에서는 고온 소둔에 따른 석출물 조대화 경향으로 충분한 석출 효과가 나타나지 않을 뿐만 아니라 소둔시 표면에 농화되는 산화물 및 개재물 형성 가능성이 높아져서 도금 표면 특성에 불리하므로 온도를 790~810℃로 제한한다.
The steel adjusted to have the composition as described above is finished hot rolling at a temperature of Ar 3 or more, which is the usual hot rolling condition, and then wound in a 550 to 650 ° C section. Winding below 550 ℃ not only precipitates the solid solution C completely, but also lowers the effect of precipitates, and causes problems of plate shape during winding, and when the winding temperature exceeds 650 ℃, the precipitates tend to be significantly coarsened. Because the precipitate effect is not so large, the yield ratio tends to be lowered, so the winding temperature is limited as above. In addition, cold rolling is performed after winding, but the minimum rolling reduction rate of cold rolling is limited to 55% or more. According to the present invention, as the cold reduction rate is increased, the recrystallization temperature is remarkably reduced, so that low recrystallization annealing is possible, thereby playing an important role in securing the plating surface properties. If the reduction ratio is less than 55%, not only does it not sufficiently reduce the recrystallization temperature, but also it is judged that sufficient precipitate is not formed due to the reduction of the critical nucleation site for the formation of the precipitate. After cold rolling, recrystallization annealing is performed. In the steel of the present invention, the Mn content is low and thus annealing is possible even at low temperatures due to the lowering of the recrystallization temperature. However, the continuous annealing in the too low region is accompanied by a decrease in elongation due to unrecrystallization. Do. In case of continuous annealing or alloying molten zinc, annealing conditions of less than 790 ° C are unrecrystallized areas, so the material variation in the coil is very high, which causes problems in practical use. Not only does not appear but also the possibility of forming oxides and inclusions that are concentrated on the surface during annealing is disadvantageous to the plating surface properties, so the temperature is limited to 790 ~ 810 ℃.

이하에서는 본 발명의 실시예를 설명한다.Hereinafter, embodiments of the present invention will be described.

아래의 표 1과 같은 조성의 발명강(1-3)과 비교강(1-2)의 슬라브를 연속주조하여 제조하였다. 발명강과 비교하기위하여 비교강 1에는 Mo와 B을 첨가하지 않았으며, 비교강 2는 Mo만을 첨가하지 않았고, 비교강 1,2 모두 IF강에 해당하는 탄소함량을 갖도록 하였으며 그 외의 조성은 발명강과 유사하다. 연속주조된 슬라브를 통상의 조건으로 열간압연-산세-냉간압연을 행한다음 각각에 대해 열처리 시뮬레이터를 이용하여 소둔 열처리를 행하였다. 아래의 표 2는 표1 조성의 각 강을 권취온도, 냉간압하율, 소둔온도를 달리하였을 때의 강판 재질 특성을 나타낸 것이다. 이때 인장시험은 JIS 5호 시편을 이용하였다. 한편 도금 표면 특성은 관능검사로 하였는 바, 도금표면이 육안으로 보아 거칠은 정도가 심하면 불량(x), 도금표면이 육안으로 보아 매끄럽게 보이고 잡티가 없으면 우수( ○), 그 중간은 보통(△)으로 판단하였다.
The slab of the invention steel (1-3) and the comparative steel (1-2) of the composition shown in Table 1 below was manufactured by continuous casting. To compare with the inventive steel, Mo and B were not added to Comparative Steel 1, Comparative Steel 2 did not contain Mo only, and Comparative Steels 1 and 2 had carbon contents corresponding to IF steel. similar. The continuously cast slabs were subjected to hot rolling, pickling, and cold rolling under normal conditions, and then subjected to annealing heat treatment using a heat treatment simulator. Table 2 below shows the properties of the steel sheet when the steels of Table 1 have different winding temperatures, cold rolling rates, and annealing temperatures. At this time, the tensile test was used JIS 5 specimens. On the other hand, the surface characteristics of the plating were measured by the sensory test. If the surface of the plating is visible to the naked eye, the degree of roughness is poor (x), and the surface of the plating is visible to the naked eye. Judging by.

표 1TABLE 1

Figure 112003047871217-pat00001
Figure 112003047871217-pat00001

표 2Table 2

Figure 112003047871217-pat00002

Figure 112003047871217-pat00002

표2 에서 알 수 있는 바와같이, 항복강도≥220MPa, 항복비≥80%, 및 연신율≥35%의 조건이 만족되려면 강의 조성과 강판 제조조건(권취온도550~650℃,냉간압연의 압하율 55%이상, 재결정 소둔온도 790~810℃)이 충족되어야만 한다는 것을 알 수 있다. 즉 비교강 2의 경우 상기 제조조건이 충족되지 않는 경우는 항복강도, 항복비가 상기 조건에 도달하지 않으며 도금 특성도 우수하지 않은 것으로 나타났으며, 설사 상기 제조조건이 충족되더라도 강 조성에 문제가 있기때문에 표면도금 특성은 우수한 것으로 나타났으나 항복강도,항복비면에서 불량한 것으로 나타났다. 표2에서 비교강 및 본 발명강이 상기 제조조건 및 재질특성 조건(항복강도≥220MPa, 항복비≥80%, 연신율≥35%,및 우수한 표면도금특성)에 부적합한 경우를 ※로 표시 했으며, 발명강 중 상기 제조조건에 부적합한 경우는 어느 경우나 상기의 항복강도, 항복비, 연신률,도금표면 특성 중 어느 하나이상이 불량한 것을 보여주고 있다. 예를들면, 발명강 1의 경우 냉간압하율이 적을 경우 재질 특성 중 연신율의 급격한 저하를 볼 수 있으며, 발명강 2에서 권취온도가 매우 높을 경우 TiC석출물이 조대해 짐에 따라 연신율 특성은 다소 개선 되지만 항복비가 목표치 80%에 비해 낮아서 석출강화강으로서의 재질 특성을 확보하지 못하였다. 비교강의 경우 목표 성분 미 확보와 제조조건이 본 발명 범위에 부적합시 목표로 하는 재질 특성을 확보할 수 없음을 알 수 있다
As can be seen from Table 2, if the conditions of yield strength ≥ 220 MPa, yield ratio ≥ 80%, and elongation ≥ 35% are satisfied, the composition of steel and the manufacturing conditions of the steel sheet (coiling temperature 550-650 ° C, cold rolling rate 55) % Or more, recrystallization annealing temperature 790 ~ 810 ℃) can be seen that must be satisfied. That is, in case of Comparative Steel 2, the yield strength and yield ratio did not reach the above conditions and the plating characteristics were not excellent, even if the manufacturing conditions were not satisfied. Even if the manufacturing conditions were met, there was a problem in the steel composition. Therefore, the surface plating characteristics were excellent, but it was poor in yield strength and yield ratio. In Table 2, the case where the comparative steel and the present invention steel is inadequate to the above manufacturing conditions and material characteristic conditions (yield strength ≥ 220 MPa, yield ratio ≥ 80%, elongation ≥ 35%, and excellent surface plating characteristics) is indicated by ※, invention In any case of steel, which is not suitable for the above manufacturing conditions, any one or more of the above-described yield strength, yield ratio, elongation and plating surface properties is poor. For example, in the case of Inventive Steel 1, when the cold reduction rate is small, the elongation can be drastically decreased in the material properties.In the Invention Steel 2, when the winding temperature is very high, the elongation characteristics are slightly improved as the TiC precipitate becomes coarse. However, the yield ratio was lower than the target value of 80%, which prevented the material properties as precipitation-reinforced steel. In the case of comparative steel, it can be seen that the target material properties cannot be secured when the target component is not secured and the manufacturing conditions are not suitable for the scope of the present invention.

이상으로부터, 강 성분계의 적절한 조절 및 냉간압하율의 제어등 강판의 제조조건의 제어에 의해 790~810℃ 의 낮은 소둔온도에서도 안정된 재질이 확보되고 도금 표면 특성이 우수한 석출강화형 고강도강판을 얻을 수 있는 것으로 나타났다.
From the above, stable material can be secured even at low annealing temperature of 790 ~ 810 ℃ by controlling the steel sheet system and control of cold rolling rate, and the precipitation strengthening type high strength steel sheet with excellent plating surface characteristics can be obtained. Appeared to be.

본 발명에 의하면,강 성분계의 적절한 조절 및 냉간압하율의 제어등 강판의 제조조건의 제어에 의해 항복강도≥220MPa, 항복비≥80%,연신율≥35% 및 우수한 표면도금특성을 갖는 강판을 얻을 수 있으며, 이러한 강판은 향상된 내충격성을 필요로 하는, 자동차의 멤버(Member), 빔(Beam) , 필라(Pillar)등의 구조 부재에 사용하기에 적합하다.According to the present invention, a steel sheet having yield strength ≥ 220 MPa, yield ratio ≥ 80%, elongation ≥ 35% and excellent surface plating characteristics can be obtained by controlling steel sheet manufacturing conditions such as appropriate adjustment of steel component system and control of cold rolling ratio. Such steel sheets are suitable for use in structural members such as members, beams, pillars, etc. of automobiles, which require improved impact resistance.

Claims (2)

중량 %로 C:0.02~0.04%, Mn:0.15~0.3%, P:0% 초과~0.015% 이하, S:0% 초과~0.005% 이하, N:0% 초과~0.003% 이하, Si:0% 초과~0.1%이하, 산가용 Al:0.03~0.07%, Ti:0.02~0.04%, Mo:0% 초과~0.1% 이하, B:0.0005~0.0015% 및 잔부는 Fe 와 기타 불가피한 불순물로 구성되는 강을 Ar3변태점 이상에서 열간압연을 종료하고, 550~650℃의 온도 범위에서 권취를 행하는 단계; By weight% C: 0.02 ~ 0.04%, Mn: 0.15 ~ 0.3%, P: 0% ~ 0.015% or less, S: 0% ~ 0.005% or less, N: 0% ~ 0.003% or less, Si: 0 More than% ~ 0.1%, acid value Al: 0.03 ~ 0.07%, Ti: 0.02 ~ 0.04%, Mo: 0% ~ 0.1% or less, B: 0.0005 ~ 0.0015% and the balance consists of Fe and other unavoidable impurities Finishing the hot rolling of the steel at an Ar 3 transformation point or more, and winding the steel in a temperature range of 550 ° C. to 650 ° C .; 통상 조건의 산세 및 압하율 55% 이상으로 냉간압연을 행하는 단계; 및 Performing cold rolling at a pickling and a reduction ratio of 55% or more under ordinary conditions; And 연속 소둔로 또는 합금화 용융 도금 연속로에서 790~810℃의 온도 범위로 재결정 소둔을 행하는 단계;Performing recrystallization annealing at a temperature range of 790 ° C. to 810 ° C. in a continuous annealing furnace or an alloyed hot dip continuous furnace; 로 구성됨을 특징으로하는 연신특성이 우수한 고항복비형 석출강화 강판의 제조방법Manufacturing method of high yield ratio type precipitation strengthened steel sheet having excellent stretching characteristics 제 1항에 있어서, 상기 Ti는 C함량에 따라 (48/12 x C)/4의 관계식이 성립하도록 첨가됨을 특징으로 하는 연신특성이 우수한 고항복비형 석출강화강판의 제조방법. The method of claim 1, wherein the Ti is added to form a relationship of (48/12 x C) / 4 according to the C content.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56119732A (en) 1980-01-28 1981-09-19 Sumitomo Metal Ind Ltd Manufacture of high-strength cold rolled steel plate with superior press formability
KR930004492A (en) * 1991-08-19 1993-03-22 도사키 시노부 High tensile steel for deep drawing and its manufacturing method with excellent surface treatment

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56119732A (en) 1980-01-28 1981-09-19 Sumitomo Metal Ind Ltd Manufacture of high-strength cold rolled steel plate with superior press formability
KR930004492A (en) * 1991-08-19 1993-03-22 도사키 시노부 High tensile steel for deep drawing and its manufacturing method with excellent surface treatment

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