KR101316320B1 - Steel sheet having excellent yield strength and elongation and method foe mafufacturing the same - Google Patents
Steel sheet having excellent yield strength and elongation and method foe mafufacturing the same Download PDFInfo
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- KR101316320B1 KR101316320B1 KR1020110129505A KR20110129505A KR101316320B1 KR 101316320 B1 KR101316320 B1 KR 101316320B1 KR 1020110129505 A KR1020110129505 A KR 1020110129505A KR 20110129505 A KR20110129505 A KR 20110129505A KR 101316320 B1 KR101316320 B1 KR 101316320B1
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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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
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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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0436—Cold rolling
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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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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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
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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
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
본 발명은 항복강도 및 연신율이 우수한 강판 및 그 제조방법에 관한 것으로서, 중량%로, C: 0.005%이하(0은 제외), B: 0.003~0.015%, Si: 0.03%이하(0은 제외), S: 0.015%이하(0은 제외), P: 0.01%이하(0은 제외), N: 0.005%이하(0은 제외), 잔부 Fe 및 기타 불가피한 불순물을 포함하는 항복강도 및 연신율이 우수한 강판 및 그 제조방법을 제공한다.
본 발명의 강판은 2차가공취성이나 표면결함이 발생하지 않을 뿐 아니라, 우수한 항복강도와 연신율을 가지며, 경제적으로도 유리하게 제조될 수 있다.The present invention relates to a steel sheet excellent in yield strength and elongation and a method for manufacturing the same, in weight%, C: 0.005% or less (excluding 0), B: 0.003-0.015%, Si: 0.03% or less (excluding 0) , S: 0.015% or less (excluding 0), P: 0.01% or less (excluding 0), N: 0.005% or less (excluding 0), balance yield strength and elongation including residual Fe and other unavoidable impurities And a method for producing the same.
The steel sheet of the present invention not only does not produce secondary work brittleness or surface defects, but also has excellent yield strength and elongation, and can be advantageously manufactured economically.
Description
본 발명은 항복강도 및 연신율이 우수한 강판 및 그 제조방법에 관한 것이다.
The present invention relates to a steel sheet excellent in yield strength and elongation and a method of manufacturing the same.
가공성 및 내덴트성이 요구되는 가전제품 또는 자동차용 부품에 사용되기 위해서는 높은 연신율과 항복강도가 요구된다. 이러한 요구에 대응하기 위해 주로 극저탄소강(이하 IF강이고도 함)에 Ti, Nb, P 등과 같은 원소들을 첨가한 강판이 제조되고 있다. Ti와 Nb는 강력한 탄, 질화물 원소로서 가공성을 향상시키고, P는 강중에 고용되어 강도를 향상시키는 역할을 한다. 이와 같이, 심가공용 냉연강판을 제조함에 있어서, 양호한 성형성의 확보를 위하여 통상의 제강공정에서 C, N과 같은 침입형 고용원소의 양을 수십 ppm이하로 낮추고 탄질화물 형성원소인 Ti, Nb 등을 단독 또는 복합첨가한 IF강을 이용하여 제조하는 것이 일반적이다.
High elongation and yield strength are required for use in home appliances or automotive parts that require workability and dent resistance. In order to cope with such demands, steel sheets are mainly manufactured by adding elements such as Ti, Nb, and P to ultra low carbon steel (hereinafter, referred to as IF steel). Ti and Nb are strong carbon and nitride elements, which improves workability, and P is dissolved in steel to improve strength. As described above, in manufacturing the cold rolled steel sheet for deep processing, in order to secure good formability, the amount of invasive solid solution such as C and N is lowered to several tens of ppm or less in the general steelmaking process, and the carbon nitride forming elements Ti, Nb and the like are reduced. It is common to manufacture using IF steel added alone or in combination.
이와 같은 대표적인 기술로는 일본공개특허공보 소57-041349호가 있다. 상기 기술은 Ti가 첨가된 IF강에 P를 0.04~0.12% 첨가하여 강도를 확보하는 기술이다. 그러나, IF강에서의 P의 첨가는 입계편석에 의한 2차가공취성의 문제점을 발생시키는 문제점이 있다.
As a representative technique of this, there is a Japanese Laid-Open Patent Publication No. 57-041349. The above technique is a technique for securing strength by adding 0.04 to 0.12% of P to the IF steel added with Ti. However, the addition of P in the IF steel has a problem of causing secondary work brittleness due to grain boundary segregation.
다른 기술로는 한국 공개특허공보 제2003-0052248호가 있는데, 상기 기술은 P 첨가 대신 0.5~2.0%의 Mn과 함께 Al, B 등을 첨가하여 가공성과 2차가공취성을 개선하는 기술이다. 그러나, 극저탄소강에서 사용하는 Mn은 고품위이기 때문에 Mn을 2.0% 수준까지 다량 첨가하게 되면 제조원가가 상승하게 되고, 특히 도금특성에도 좋지 않다.
Another technique is Korean Laid-Open Patent Publication No. 2003-0052248, which is a technique for improving processability and secondary processing brittleness by adding Al, B, etc. together with 0.5 to 2.0% of Mn instead of P. However, since Mn used in the ultra low carbon steel is high quality, when Mn is added in a large amount up to a level of 2.0%, manufacturing cost increases, and in particular, the plating property is not good.
또 다른 기술로는 일본 공개특허공보 특개평6-057336호가 있는데, 상기 기술은 IF강에 Cu를 0.5~2.5% 첨가하여 ε-Cu의 석출상을 형성하여 강도를 확보하는 기술이다. 그러나, 상기 기술은 ε-Cu의 석출상에 의해 고강도는 확보할 수 있으나, 가공특성이 좋지 않다는 단점이 있다. 이러한 문제점을 해결하기 위한 기술로는 한국 공개특허공보 제2002-0053295호가 있는데, 상기 특허에서 제안하는 강판은 항복강도가 낮고 연신율이 떨어지는 문제점이 있다.
Another technique is Japanese Patent Laid-Open No. Hei 6-057336, which is a technique of securing strength by adding 0.5 to 2.5% of Cu to IF steel to form a precipitated phase of ε-Cu. However, the above technique can secure high strength by the precipitated phase of ε-Cu, but has a disadvantage in that the processing characteristics are not good. As a technique for solving this problem, there is a Korean Patent Publication No. 2002-0053295, the steel sheet proposed in the patent has a problem that the yield strength is low and elongation is low.
본 발명은 2차가공취성이 발생하지 않으면서도, 우수한 항복강도 및 연신율을 갖고, 제조 비용도 저감될 수 있는 강판과 그 제조방법을 제공하고자 하는 것이다.
It is an object of the present invention to provide a steel sheet and a method of manufacturing the same, which have excellent yield strength and elongation and can also reduce manufacturing cost without generating secondary work brittleness.
본 발명의 일태양은 중량%로, C: 0.005%이하(0은 제외), B: 0.003~0.015%, Si: 0.03%이하(0은 제외), S: 0.015%이하(0은 제외), P: 0.01%이하(0은 제외), N: 0.005%이하(0은 제외), 잔부 Fe 및 기타 불가피한 불순물을 포함하는 항복강도 및 연신율이 우수한 강판을 제공한다.
One embodiment of the present invention is by weight, C: 0.005% or less (excluding 0), B: 0.003 to 0.015%, Si: 0.03% or less (excluding 0), S: 0.015% or less (excluding 0), P: 0.01% or less (except for 0), N: 0.005% or less (except for 0), and provide a steel sheet excellent in yield strength and elongation including residual Fe and other unavoidable impurities.
본 발명의 다른 태양은 중량%로, C: 0.005%이하(0은 제외), B: 0.003~0.015%, Si: 0.03%이하(0은 제외), S: 0.015%이하(0은 제외), P: 0.01%이하(0은 제외), N: 0.005%이하(0은 제외), 잔부 Fe 및 기타 불가피한 불순물을 포함하는 슬라브를 1100~1200℃에서 재가열하는 단계; 재가열된 상기 슬라브를 Ar3~920℃에서 마무리 열간압연하여 강판을 얻는 단계; 상기 강판을 500~750℃에서 권취하는 단계; 귄취된 상기 강판을 50~90%의 압하율로 냉간압연하는 단계; 냉간압연된 상기 강판을 800~900℃에서 연속소둔하는 단계; 및 연속소둔된 상기 강판을 1~3%의 압하율로 스킨패스압연하는 단계를 포함하는 항복강도 및 연신율이 우수한 강판의 제조방법을 제공한다.
Another aspect of the invention is by weight, C: 0.005% or less (excluding 0), B: 0.003 to 0.015%, Si: 0.03% or less (excluding 0), S: 0.015% or less (excluding 0), Reheating the slab containing P: 0.01% or less (excluding 0), N: 0.005% or less (excluding 0), residual Fe and other unavoidable impurities at 1100 to 1200 ° C; Finishing hot rolling of the reheated slab at Ar 3 to 920 ° C. to obtain a steel sheet; Winding the steel sheet at 500˜750 ° C .; Cold rolling the rolled steel sheet at a reduction ratio of 50 to 90%; Continuously annealing the cold rolled steel sheet at 800 to 900 ° C; And it provides a method for producing a steel sheet excellent in yield strength and elongation comprising the step of skin pass rolling the steel sheet continuously annealed at a reduction rate of 1 to 3%.
본 발명의 강판은 2차가공취성이나 표면결함이 발생하지 않을 뿐 아니라, 우수한 항복강도와 연신율을 가지며, 경제적으로도 유리하게 제조될 수 있다.
The steel sheet of the present invention not only does not produce secondary work brittleness or surface defects, but also has excellent yield strength and elongation, and can be advantageously manufactured economically.
일반적으로 IF강을 제조할 때에는 강력한 탄,질화물 형성원소인 Ti, Nb등을 첨가하는데 이들 원소는 재결정온도를 상승시키므로 고온에서 소둔해야 한다. 이 때문에 생산성이 낮아지고 에너지를 많이 사용하여 원가가 상승할 뿐만 아니라 많은 공해를 유발한다. 또한 고온에서 소둔을 하면 파인흠, 형상결함 등 여러가지 결함이 발생하기 쉬운 단점이 있다. 또한, Ti, Nb는 산화성이 강하기 때문에 제강중 많은 비금속 개재물을 생성하여 강판의 표면결함을 유발시키는 문제점이 있다.
In general, when manufacturing IF steel, strong carbon and nitride forming elements such as Ti and Nb are added. These elements increase the recrystallization temperature, so they must be annealed at high temperature. This leads to lower productivity, higher energy costs, and more pollution. In addition, annealing at a high temperature has a disadvantage in that various defects such as fine defects and shape defects are likely to occur. In addition, since Ti and Nb are strong in oxidizing property, many non-metallic inclusions are generated in steelmaking to cause surface defects of the steel sheet.
따라서, 본 발명자들은 Ti나 Nb를 첨가하지 않고도 우수한 항복강도와 연신율을 갖는 강판을 제조하기 위해 연구를 하던 중, B을 적정량 첨가하게 되면 가공성과 항복강도가 향상된다는 사실을 인지하고, 본 발명을 완성하게 되었다.
Therefore, the present inventors are aware of the fact that the workability and yield strength are improved by adding an appropriate amount of B during the study for producing a steel sheet having excellent yield strength and elongation without adding Ti or Nb. It was completed.
이하, 본 발명을 상세히 설명한다.
Hereinafter, the present invention will be described in detail.
C : 0.005중량%이하(0은 제외)C: 0.005% by weight or less (excluding 0)
강 중 탄소는 강도 확보에 유리한 원소지만, 과다하게 첨가될 경우, 침입형 고용원소로 작용하여 냉연 및 소둔시 강판의 집합조직 형성 과정에서 가공성에 유리한 {111} 집합조직의 형성을 저해한다. 마무리 열간 압연시에도 다량의 고용원소에 의해 가공성에 좋지 않다고 알려진 {100} 및 {110} 집합조직이 형성되고, 이 조직이 소둔 후까지도 잔존하게 되어 가공성 향상에 불리하므로, 상기 탄소는 0.005%이하로 첨가하는 것이 바람직하다.
Carbon in steel is an element that is advantageous for securing strength, but when excessively added, it acts as an invasive solid solution element and inhibits formation of {111} texture structure which is advantageous for workability during the formation of the texture structure of the steel sheet during cold rolling and annealing. Even during finishing hot rolling, {100} and {110} aggregates, which are known to be poor in workability, are formed by a large amount of solid elements, and these structures remain even after annealing, which is disadvantageous in improving workability, so the carbon is less than 0.005%. It is preferable to add by.
B : 0.003~0.015중량%B: 0.003-0.015 wt%
B는 입계를 강화시키고 Fe와 석출물을 형성시키는 역할을 한다. 즉, B의 첨가를 통해 결정립계간 결합력을 강화시켜 기존강에 대비 동일한 소성변형을 가하더라고 균열이 잘 발생하지 않게 된다. 그러나, 상기 B의 함량이 0.003%미만일 경우에는 상기 효과가 떨어질 뿐만 아니라 항복강도를 확보하기 곤란하며, 0.015%를 초과하는 경우에는 항복강도는 향상되나 연신율이 감소할 수 있다.
B serves to strengthen the grain boundary and to form precipitates with Fe. That is, the addition of B strengthens the bonding strength between grain boundaries, so that even if the same plastic deformation is applied to the existing steel, cracking does not occur well. However, when the content of B is less than 0.003%, not only the effect is lowered but also it is difficult to secure yield strength, and when it exceeds 0.015%, the yield strength is improved but the elongation may be decreased.
Si: 0.03중량%이하(0은 제외)Si: 0.03% by weight or less (excluding 0)
Si는 적스케일을 유발하는 원소일 뿐만 아니라, 강 중 함유량이 0.03%를 초과하는 경우에는 표면에 산화물을 형성시켜 도금젖음성을 저하시키므로, 0.03%이하로 포함되는 것이 바람직하다.
Si is not only an element causing red scale, but when the content in steel exceeds 0.03%, an oxide is formed on the surface to lower the plating wettability, and therefore it is preferably included below 0.03%.
S: 0.015중량%이하(0은 제외)S: 0.015 wt% or less (excluding 0)
S는 고온취성을 유발하는 원소이므로, 가능한 적게 함유되는 것이 바람직하다. 공정상 불가피하게 포함되는 양을 고려하여 그 상한을 0.015%로 제어하는 것이 바람직하다.
Since S is an element causing high temperature brittleness, it is preferable to contain S as little as possible. It is preferable to control the upper limit to 0.015% in consideration of the amount inevitably included in the process.
P:0.01중량%이하(0은 제외)P: 0.01% by weight or less (excluding 0)
P는 입계취성 결함을 유발하는 원소이므로, 가능한 적게 함유되는 것이 바람직하다. 공정상 불가피하게 포함되는 양을 고려하여 그 상한을 0.01%로 제어하는 것이 바람직하다.
Since P is an element causing grain boundary brittle defects, it is preferable to contain P as little as possible. It is preferable to control the upper limit to 0.01% in consideration of the amount inevitably included in the process.
N: 0.005중량%이하(0은 제외)N: 0.005 wt% or less (excluding 0)
N은 그 양이 0.005%를 초과하는 경우에는 가공성이 크게 저하하므로, 그 함유량이 0.005%이하인 것이 바람직하다.
When the amount exceeds N, the workability greatly decreases, so the content thereof is preferably 0.005% or less.
상기와 같은 조성성분 및 범위를 만족하는 강종은 0.25이상의 가공경화지수가를 만족하게 된다. 기존의 IF강은 Ti 또는 Nb나 그 외 합금원소를 추가로 포함하고 있지만, 이 경우라도 본 발명의 강과 같이 우수한 가공경화지수를 얻기는 곤란하며, 통상 0.16 수준의 가공경화지수를 확보하고 있다. 즉, 본 발명에서 제공하고 있는 강판은 기존 강판 대비 동일한 응력을 가하더라도 가공경화 효과가 우수하며, 가공시 균열이 발생할 확률이 감소한다.
Steel grades satisfying the compositional components and ranges as described above satisfy a work hardening index of 0.25 or more. Existing IF steel further includes Ti or Nb or other alloying elements, but even in this case, it is difficult to obtain an excellent work hardening index like the steel of the present invention, and usually has a work hardening index of 0.16. In other words, the steel sheet provided in the present invention is excellent in the work hardening effect even if the same stress applied to the existing steel sheet, the probability of occurrence of cracking during processing is reduced.
이하, 본 발명의 제조방법의 일태양에 대하여 설명한다.
EMBODIMENT OF THE INVENTION Hereinafter, one aspect of the manufacturing method of this invention is demonstrated.
상기와 같은 조성을 갖는 슬라브를 1100~1200℃에서 재가열한다. 재가열 온도가 1100℃ 미만인 경우에는 재가열온도가 낮아 연속주조 중에 생성된 조대한 석출물들이 완전히 용해되지 않은 상태로 남아 있어, 열간압연후에도 조대한 석출물이 많이 남게되기 때문이다. 한편, 1200℃를 초과하는 경우에는 과도한 열량 사용으로 인하여 제조 비용이 증가할 수 있다.
The slab having the composition as described above is reheated at 1100 ~ 1200 ℃. If the reheating temperature is less than 1100 ℃, the reheating temperature is low, the coarse precipitates produced during the continuous casting is not completely dissolved, so the coarse precipitates remain even after hot rolling. On the other hand, when it exceeds 1200 ℃ may be increased due to the excessive use of calories manufacturing costs.
상기와 같이, 재가열된 상기 슬라브를 Ar3~920℃에서 마무리 열간압연하여 강판을 얻는다. 마무리 열간압연온도가 Ar3변태온도 미만인 경우에는 압연립의 생성으로 인해 가공성이 저하할 뿐만 아니라 강도도 낮아지기 때문이다. 한편, 상기 마무리 열간압연온도가 920℃를 초과할 경우에는 스케일층이 다량 발생하여 산세가 어려울 수 있다.
As described above, the reheated slab is finished hot rolled at Ar 3 to 920 ° C. to obtain a steel sheet. If the finish hot rolling temperature is less than the Ar3 transformation temperature, not only the workability is degraded due to the formation of the rolled grain, but also the strength is lowered. On the other hand, when the finishing hot rolling temperature exceeds 920 ° C, a large amount of scale layer may be generated and pickling may be difficult.
이후, 상기 강판을 500~750℃에서 권취하는 것이 바람직하다. 상기 권취온도가 500℃미만인 경우에는 권취시 형상불량의 위험성이 증대되며, 750℃를 초과하는 경우에는 스케일 결함이 발생할 가능성이 크다. 보다 바람직한 권취온도 범위는 650~700℃이다.
Thereafter, the steel sheet is preferably wound at 500 to 750 ° C. If the coiling temperature is less than 500 ° C, the risk of shape defects during the winding is increased, and if the coiling temperature exceeds 750 ° C, scale defects are likely to occur. The more preferable winding temperature range is 650-700 degreeC.
이후, 냉간압연을 행하는데, 상기 귄취된 강판을 50~90%의 압하율로 냉간압연하는 것이 바람직하다. 냉간압하율이 50%미만일 경우에는 소둔재결정 핵생성 양이 적기 때문에 소둔시 결정립이 너무 크게 성장하여 강도 및 성형성이 저하될 수 있다. 한편, 냉간압하율이 90%를 초과하는 경우에는 성형성은 향상되지만 핵생성 양이 너무 많아 오히려 소둔 재결정립이 너무 미세하게 되어 연성이 저하할 수 있다. 보다 바람직한 냉간압하율 범위는 60~80%이다.
Thereafter, cold rolling is performed, and it is preferable that the cold rolled steel sheet is cold rolled at a reduction ratio of 50 to 90%. If the cold reduction rate is less than 50%, since the amount of nucleation of the annealing material crystal is small, the grains may grow too large during annealing, thereby deteriorating strength and formability. On the other hand, when the cold reduction rate exceeds 90%, the moldability is improved, but the amount of nucleation is too large, rather the annealed recrystallized grain becomes too fine and ductility may be reduced. The more preferable cold reduction rate range is 60 to 80%.
이어서, 상기 냉간압연된 강판을 800~900℃에서 연속소둔한다. 연속소둔 온도는 제품의 재질을 결정하는 중요한 역할을 한다. 상기 연속소둔 온도가 800℃미만일 경우에는 재결정이 완료되지 않아 목표로 하는 연성 값을 확보할 수 없으며, 소둔온도가 900℃를 초과하는 경우에는 재결정립의 조대화로 강도가 저하된다. 한편, 상기 연속소둔을 행하는 시간은 10초~10분의 범위를 갖는 것이 바람직한데, 재결정의 완료를 위해서는 10초 이상 소둔을 행하여야 하기 때문이다. 생산성과 제조비용을 고려할 때, 상기 소둔시간은 10분을 초과하지 않는 것이 바람직하다.
Subsequently, the cold rolled steel sheet is continuously annealed at 800 to 900 ° C. The continuous annealing temperature plays an important role in determining the material of the product. If the continuous annealing temperature is less than 800 ° C., recrystallization is not completed and a target ductility value cannot be secured. If the annealing temperature exceeds 900 ° C., the strength decreases due to coarsening of recrystallized grains. On the other hand, the time for performing the continuous annealing is preferably in the range of 10 seconds to 10 minutes, because annealing must be performed for 10 seconds or more to complete the recrystallization. In consideration of productivity and manufacturing cost, the annealing time is preferably not more than 10 minutes.
이후, 상기 연속소둔된 강판을 1~3%의 압하율로 스킨패스압연(Skin Pass Mill, SPM)한다. 본 발명에서는 Ti나 Nb와 같은 탄질화물을 첨가하지 않음에 따라 발생할 수 있는 항복점 현상을 방지하기 위하여, 상기와 같이, 적정 수준의 스킨 패스 압연을 행하는 것을 주요지로 한다. 기존 IF강에서는 Ti, Nb 등과 같은 합금 원소 첨가에 따라 항복점 현상이 발생하지 않았고, 이로 인해 스킨패스압연을 행하지 않아도 되었다. 만약, 스킨패스압연을 실시하더라도 단지 형상 불량 제어를 위한 것일 뿐, 본 발명에서와 같이 가동전위를 형성시키거나 활성화시켜 항복점 현상을 방지하고자 하는 것은 아니었다. 그러나, 본 발명에서는 스킨패스압연을 통해 가동전위를 형성시켜 항복점 현상이 일어나는 것을 방지하고자 하는 것이며, 이를 위해 1~3%의 압하율을 적용하는 것이 바람직하다. 압하율이 1%미만일 경우에는 가동전위가 충분히 활성화되지 않아 항복점 연신현상이 없어지지 않고, 3%를 초과할 경우에는 항복점 연신은 없어지지만 연신율이 저하될 수 있다.
Thereafter, the continuously annealed steel sheet is subjected to skin pass rolling (Skin Pass Mill, SPM) at a rolling rate of 1 to 3%. In the present invention, in order to prevent the yield point phenomenon caused by not adding a carbonitride such as Ti or Nb, as described above, the main subject is to perform the appropriate level of skin pass rolling. In the conventional IF steel, the yield point phenomenon did not occur due to the addition of alloying elements such as Ti and Nb, thereby eliminating the need for skin pass rolling. If skin pass rolling is carried out, it is merely for shape defect control, and it is not intended to prevent a yield point phenomenon by forming or activating a movable potential as in the present invention. However, the present invention is to prevent the yield point phenomenon occurs by forming the movable potential through the skin pass rolling, it is preferable to apply a reduction ratio of 1 to 3% for this purpose. If the rolling reduction is less than 1%, the operating potential is not sufficiently activated so that the yield point stretching does not disappear. If the rolling reduction exceeds 3%, the yield point stretching disappears, but the elongation may decrease.
이렇게 얻어진 강판은 이후 용융아연도금 또는 합금화 용융아연도금을 행할 수 있으며, 양호한 표면품질과 기계적 특성을 얻을 수 있다.
The steel sheet thus obtained can then be subjected to hot dip galvanizing or alloyed hot dip galvanizing, and obtain good surface quality and mechanical properties.
이하, 실시예를 통해 본 발명을 보다 상세히 설명한다. 다만, 하기 실시예는 본 발명을 보다 상세하게 설명하기 위한 예시일 뿐, 본 발명의 권리범위를 한정하지 않는다.
Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only illustrative of the present invention in more detail and do not limit the scope of the present invention.
(실시예)(Example)
하기 표 1에 나타난 바와 같은 합금성분 및 조성범위를 갖는 슬라브를 1200℃에서 재가열한 뒤, 910℃에서 마무리 열간압연하고, 680℃에서 권취하였다. 이렇게 얻어진 강판을 77%의 압하율로 냉간압연한 뒤, 840℃에서 연속소둔을 행하고, 이후, 스킨패스압연을 실시하여 강판을 제조하였다. 상기와 같이 제조된 강판의 기계적 특성을 조사하기 위해 JIS 규격에 의한 표준시편으로 가공한 뒤, 인장시험기를 이용하여 항복강도, 인장강도, 가공경화지수, 연신율 등을 측정하였으며, 그 결과를 하기 표 2 내지 7에 나타내었다.
The slabs having the alloying components and composition ranges as shown in Table 1 were reheated at 1200 ° C., finished hot rolled at 910 ° C., and wound up at 680 ° C. The steel sheet thus obtained was cold rolled at a reduction ratio of 77%, then subjected to continuous annealing at 840 ° C., and then subjected to skin pass rolling to prepare a steel sheet. In order to investigate the mechanical properties of the steel sheet manufactured as described above was processed to a standard specimen according to JIS standards, using a tensile tester measured the yield strength, tensile strength, work hardening index, elongation, etc. 2 to 7 are shown.
상기 표 1 내지 7에서 알 수 있듯이, 본 발명이 제안하는 합금성분 및 조성범위와 스킨패스시 압하율을 만족하는 발명예들의 경우에는 185MPa이상의 우수한 항복강도와 55%이상의 우수한 연신율을 확보하고 있는 것을 알 수 있다.
As can be seen from Tables 1 to 7, in the case of the invention examples satisfying the alloy composition and composition range and the rolling reduction rate in the skin pass proposed by the present invention is to ensure excellent yield strength of 185MPa or more and excellent elongation of 55% or more Able to know.
그러나, B이 첨가되지 않거나 적게 첨가된 비교강 1 및 2의 경우에는 항복강도가 약 140MPa 이하로서, 본 발명예들에 비하여 항보강도가 낮은 수준임을 알 수 있다. 또한, B이 많이 첨가된 비교강 3의 경우, 항복강도는 우수한 수준을 확보하고는 있으나, 연신율이 55%미만임을 알 수 있고, 결국 본 발명예들에 비하여 연신율이 저하되었음을 알 수 있다.
However, in the case of Comparative steels 1 and 2, in which B is not added or less, the yield strength is about 140 MPa or less, which indicates that the anti-reinforcement level is lower than that of the present invention examples. In addition, in the case of Comparative Steel 3 to which B is added a lot, the yield strength is excellent, but it can be seen that the elongation is less than 55%, and as a result, the elongation is lowered compared to the present examples.
한편, 본 발명의 합금성분 및 조성범위를 만족하더라도, 스킨패스압연을 행하지 않거나, 행하더라도 본 발명의 압하율 범위 미만인 경우에는 항복점 현상이 발생하였음을 알 수 있으며, 과도한 압하율의 스킨패스압연을 행한 경우에는 본 발명예들에 비하여 연신율이 전반적으로 떨어졌음을 알 수 있다.
On the other hand, even if it satisfies the alloy composition and composition range of the present invention, even if the skin pass rolling is not performed, even if it is less than the reduction rate range of the present invention, it can be seen that the yield point phenomenon occurs, the skin pass rolling of excessive reduction rate In this case, it can be seen that the elongation is generally lower than the examples of the present invention.
즉, 본 발명이 제안하는 성분계와 스킨패스압연시 압하율을 만족하는 경우에는 우수한 항복강도와 인장강도를 확보할 수 있음을 알 수 있다.In other words, it can be seen that excellent yield strength and tensile strength can be secured when the component system proposed by the present invention and the rolling reduction rate during skin pass rolling are satisfied.
Claims (5)
55%이상의 연신율을 가지며, 0.25이상의 가공경화지수를 갖는 강판.
By weight%, C: 0.005% or less (excluding 0), B: 0.007 ~ 0.015%, Si: 0.03% or less (excluding 0), S: 0.015% or less (excluding 0), P: 0.01% or less ( 0), N: 0.005% or less (excluding 0), balance Fe and other unavoidable impurities,
Steel sheet having an elongation of 55% or more and a work hardening index of 0.25 or more.
상기 강판은 냉연강판, 용융아연도금강판 및 합금화 용융아연도금강판으로 이루어지는 그룹으로부터 선택된 1종인 것을 특징으로 하는 강판.
The method of claim 1,
The steel sheet is one kind selected from the group consisting of a cold rolled steel sheet, a hot dip galvanized steel sheet and an alloyed hot dip galvanized steel sheet.
재가열된 상기 슬라브를 Ar3~920℃에서 마무리 열간압연하여 강판을 얻는 단계;
상기 강판을 500~750℃에서 권취하는 단계;
귄취된 상기 강판을 50~90%의 압하율로 냉간압연하는 단계;
냉간압연된 상기 강판을 800~900℃에서 연속소둔하는 단계; 및
연속소둔된 상기 강판을 1~3%의 압하율로 스킨패스압연하는 단계를 포함하여,
55%이상의 연신율을 가지며, 0.25이상의 가공경화지수를 갖는 강판을 얻는 강판의 제조방법.
By weight%, C: 0.005% or less (excluding 0), B: 0.007 ~ 0.015%, Si: 0.03% or less (excluding 0), S: 0.015% or less (excluding 0), P: 0.01% or less ( Reheating the slab comprising N: 0.005% or less (excluding 0), residual Fe and other unavoidable impurities at 1100 to 1200 ° C;
Finishing hot rolling of the reheated slab at Ar 3 to 920 ° C. to obtain a steel sheet;
Winding the steel sheet at 500˜750 ° C .;
Cold rolling the rolled steel sheet at a reduction ratio of 50 to 90%;
Continuously annealing the cold rolled steel sheet at 800 to 900 ° C; And
Including the step of skin pass rolling the steel sheet continuously annealed at a rolling rate of 1 to 3%,
A method for producing a steel sheet having an elongation of 55% or more and obtaining a steel sheet having a work hardening index of 0.25 or more.
상기 연속소둔은 10초~10분간 행하는 것을 특징으로 하는 강판의 제조방법.5. The method of claim 4,
The continuous annealing is performed for 10 seconds to 10 minutes.
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| JPH05171287A (en) * | 1991-12-20 | 1993-07-09 | Nippon Steel Corp | Production of cold rolled steel sheet having stretcher strain resistance and extremely excellent in baking hardenability |
| KR20010112947A (en) * | 2000-02-29 | 2001-12-22 | 에모또 간지 | High tensile cold-rolled steel sheet having excellent strain aging hardening properties |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH05171287A (en) * | 1991-12-20 | 1993-07-09 | Nippon Steel Corp | Production of cold rolled steel sheet having stretcher strain resistance and extremely excellent in baking hardenability |
| KR20010112947A (en) * | 2000-02-29 | 2001-12-22 | 에모또 간지 | High tensile cold-rolled steel sheet having excellent strain aging hardening properties |
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