KR100276290B1 - The manufacturing method for 60kg grade high strength steel with tensile strength 60kg/mm2 up - Google Patents
The manufacturing method for 60kg grade high strength steel with tensile strength 60kg/mm2 up Download PDFInfo
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- KR100276290B1 KR100276290B1 KR1019960046466A KR19960046466A KR100276290B1 KR 100276290 B1 KR100276290 B1 KR 100276290B1 KR 1019960046466 A KR1019960046466 A KR 1019960046466A KR 19960046466 A KR19960046466 A KR 19960046466A KR 100276290 B1 KR100276290 B1 KR 100276290B1
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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
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0037—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 by injecting powdered material
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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Abstract
Description
본 발명은 철탑용 소재 등에 사용되는 60Kg/㎟급 고장력강을 제조하는 방법에 관한것으로써, 보다 상세하게는 후판제어압연에 의해 60Kg/㎟급 고장력강을 제조하는 방법에 관한 것이다.The present invention relates to a method for producing a 60 kg / mm < 2 > class high tensile steel used for a steel tower material, and more particularly, to a method for producing a high tensile steel having a 60 kg /
산업이 발전함에 따라 전력사용량의 증가는 필연적이며, 원만한 전력수급을 위해서 새로운 전력수급체계 즉 송전전력의 향상이 요구된다. 이러한 관점에서 송전전압 향상과 철탑거리 확대를 목적으로 기존의 형강형 철탑은 강관형 철탑으로 교체되고 있는 실정이다.As the industry develops, the increase in power consumption is inevitable, and a new power supply and demand system, that is, the improvement of transmission power, is required for smooth power supply and demand. From this point of view, existing steel-frame steel towers have been replaced with steel-pipe towers for the purpose of improving transmission voltage and increasing the distance of steel towers.
송전압 향상을 위한 송전시 지름의 확대와 철탑거리 확대로 인해 철탑에 가해지는 장력이 급격히 증가하므로 기존의 형강형 철탑으로는 이런하중을 지탱하기에는 무리가 있으므로, 형강대비 굽힘강도와 굴곡강도가 우수한 강관형 철탑으로의 교체는 필수적이라 할 수 있다.Since the tension applied to the steel tower increases sharply due to the enlargement of the diameter of the steel tower and the increase of the diameter during the transmission to improve the transmission voltage, it is difficult to support such a load in the existing steel tower. Therefore, It is necessary to replace it with steel pipe type steel tower.
한편, 철탑 제작용 강재는 방청처리를 위해 실시하는 Zn도금시 강재의 용융 Zn속침적에 따른 열응력과 용접시 발생한 잔류응력 등의 영향으로 용접열영향부의 결정입계에 용융아연이 확산하여 균열이 발생하게 된다.On the other hand, due to the thermal stress due to deposition of molten Zn in the steel during the Zn plating, which is performed for the anti-rust treatment, and the residual stress generated during welding, the molten zinc diffuses into the grain boundaries of the weld heat affected portion, .
대부분의 송전용 철탑은 산간지역에 설치됨에 따라 지형특성상 철탑간의 거리를 가급적 크게 하여 철탑수를 최소화 할 필요가 있으며, 이로 인해 철탑에 가해지는 하중을 견딜수 있는 강재가 요구된다.Most of the transmission towers are installed in mountainous areas. Therefore, it is necessary to minimize the number of towers by increasing the distance between towers as much as possible due to the characteristics of the terrain. Therefore, a steel material capable of withstanding the load applied to the towers is required.
또한, 초고압(Ultra High Voltage, UHV)송전탑 제작용 강재는 용융아연도금시 액상 금속취화(Liquid Metal Embrittlement)현상에 의해 발생하는 균열에 대한 저항성이 우수한 강재가 요구된다.In addition, a steel material for manufacturing ultra high voltage (UHV) transmission towers is required to have excellent resistance to cracking caused by liquid metal embrittlement phenomenon during hot dip galvanizing.
종래 강관철탑 제작용 강재로 일반구조용강(SS400, SM490, STK490)이 사용되고 있으나, 이런강재는 강도부족으로 철탑간거리 확대가 불가하며, 용융아연취성에 따른 균열발생 등의 문제점을 내포하고 있다.Although general structure molten steel (SS400, SM490, STK490) is used as a steel material for manufacturing a conventional steel pipe tower, such a steel material can not expand the distance between the steel pavers due to lack of strength, and has problems such as cracking due to molten zinc embrittlement.
또한, 일반압연법을 적용하여 강재를 제조하려면 적정강도 확보를 위해 다량의 합금원소 첨가는 불가피하며, 이로인해 강재는 대입열 적용불가, 용접부저온인성 발생등 용접성이 현저히 떨어지는 문제점이 있다.In addition, in order to obtain steels by applying the general rolling method, it is inevitable to add a large amount of alloying elements in order to secure an appropriate strength. As a result, there is a problem that weldability is remarkably decreased due to the inability to apply heat to the steel and low temperature toughness of the weld.
이에, 본 발명자는 상기한 종래방법들의 제반 문제점을 해결하기 위하여 연구 및, 실험을 행하고, 그 결과에 근거하여 본 발명을 제안하게 된 것으로써, 본 발명은 강성분을 적절히 조절함과 동시에 제어 압연 및 가속냉각을 적절히 행하므로써, 내용융아연취성, 용접성 및 파이프 조관성이 우수한 60Kg/㎟급 고장력 강을 제조할수 있는 방법을 제공하고자 하는데, 그 목적이 있다.Accordingly, the present inventors conducted research and experiment to solve all the problems of the conventional methods described above, and propose the present invention based on the results. The present invention has been made in view of the above circumstances, And a method of producing high strength steel of 60 kg / mm < 2 > class which is excellent in brittle zinc embrittlement, weldability and pipe toughness by suitably accelerating and cooling the steel.
본 발명은 60Kg/㎟급 고장력강을 제조하는 방법에 있어서, 중량%로, C:0.08-0.11%, Si:0.10-0.25%, Mn:0.9-1.6%, P:0.023%이하, S:0.008%이하, Nb:0.02-0.05%, V:0.02-0.05%, Ti:0.005-0.02%, B:2ppm이하, 잔부 Fe 및 기타 불가피한 불순물로 조성되는 용강을 제조한 후, 이 용강으로 강 슬라브를 제조한 다음, 강 슬라브를 1100-1200℃의 온도범위로 가열하여 1000-1100℃의 압연개시온도 및 950-1000℃의 압연종료온도 조건으로 재결정영역에서 압연을 한후, 860-900℃의 압연개시온도, 70-80%의 압하율 및 710-750℃의 압연종료온도 조건으로 미재 결정영역에서 압연한 다음, 480-520℃까지 가속냉각한 후 공냉하여 60Kg/㎟급 고장력강을 제조하는 방법에 관한 것이다.The present invention relates to a method for producing high strength steel of 60 Kg / mm < 2 >. A method for producing high strength steel of 60 kg / mm < 2 >, comprising the steps of: C: 0.08-0.11%; Si: 0.10-0.25%; Mn: 0.9-1.6%; P: The steel slab is produced with the molten steel after the molten steel having the composition of Nb: 0.02-0.05%, V: 0.02-0.05%, Ti: 0.005-0.02%, B: 2ppm or less and the balance Fe and other unavoidable impurities The steel slab is heated in the temperature range of 1100-1200 占 폚 and rolled in the recrystallization region at the rolling start temperature of 1000-1100 占 폚 and the rolling finish temperature of 950-1000 占 폚, , A rolling reduction of 70 to 80% and a rolling finish temperature of 710 to 750 캜, followed by accelerated cooling to 480 - 520 캜, followed by air cooling to produce a high tensile steel of 60 kg / .
이하, 본 발명에 대하여 상세히 설명한다.Hereinafter, the present invention will be described in detail.
상기 C는 강도를 확보하는데 필요한 원소로서 60Kg/㎟ 이상의 인장 강도를 확보하기 위해서는 0.08%이상이 요구되며, 0.11%을 초과하는 경우에는 용접부영향부(HAZ)에 균열이 발생되고, 또한 연속주조시 표면의 크랙 발생이 민감해지기 때문에 상기 C의 함량은 0.08-0.11%로 제한하는 것이 바람직하다.C is an element necessary for ensuring strength, and 0.08% or more is required in order to secure a tensile strength of 60 kg / mm < 2 > or more. When it exceeds 0.11%, cracks are generated in the welded zone affected zone (HAZ) It is preferable to limit the content of C to 0.08-0.11%.
상기 Mn은 C와 같이 강재의 강도를 확보하는 원소로서 강재의 강도를 60Kg/㎟ 이상 확보하기 위해서는 0.9% 이상이 필요하며, 첨가량이 증가함에 따라 강도와 인성이 향상되지만, 함량이 증가할수록 베이나이트 및 마르텐사이트등 경화조직이 생성되어 충격인성을 해칠 우려가 있으므로, 그 상한은 1.6%로 제한하는 것이 바람직하다.Mn is an element which secures the strength of the steel as C, which is required to secure the strength of the steel to 60 kg / mm 2 or more. As the amount of Mn increases, the strength and toughness are improved as the amount of Mn is increased. However, And martensite may be generated to deteriorate the impact toughness. Therefore, the upper limit is preferably limited to 1.6%.
상기 Si은 강도 향상에 부분적인 기여를 하지만, 첨가주목적은 강종의 탈산제로서 이용되므로 최저 0.1%가 요구되지만, HAZ부의 용융아연 취하를 방지하기 위하여 그 상한은 0.25%로 제한하는 것이 바람직하다.Although the Si contributes a partial contribution to the strength improvement, the addition is mainly used as a deoxidizing agent of the steel grade, so a minimum of 0.1% is required. However, the upper limit of the Si content is preferably limited to 0.25% in order to prevent the removal of molten zinc from the HAZ.
상기 P의 함량은 0.023% 이하로 제한하는 것이 바람직한데, 그 이유는 강의 불순물로서 연속주조시 중심편석부에 집적하여 내부품질을 열화시키기 때문이다.The content of P is preferably limited to 0.023% or less because the impurities of the steel accumulate in the central segregation portion during continuous casting to deteriorate the internal quality.
상기 S의 함량은 0.008%이하로 제한하는 것이 바람직한데, 그 이유는 P 성분과 같이 강의 내부 품질에 유해한 원소로서 연속주소시 내부 크랙 및 중심편석을 유발할 수 있기 때문이다.The content of S is preferably limited to 0.008% or less because it is an element harmful to the internal quality of steel such as P component, which can cause internal cracks and center segregation at continuous addressing.
상기 Nb은 후판 압연시 입계에 편석된 Nb(C,N)석출물이 결정립 성장을 억제하여 결정립 미세화에 의해 강도를 확보하기 위해 첨가되는 성분으로써, 60Kg/㎟급 이상의 강도를 확보하기 위해 첨가되는 성분으로써 60Kg/㎟ 이상의 강도를 확보하기 위해서는 0.02%이상이 요구되지만, 과다함유시 용접부 충격인성을 저해하기 때문에 그 상한값은 0.05%로 제한 하는 것이 바람직하다.The Nb is a component added to the Nb (C, N) precipitate segregated in the grain boundary during the rolling process to secure the strength by crystal grain refinement by suppressing the grain growth, and the component added to secure the strength of 60 kg / 0.02% or more is required in order to secure a strength of 60 kg / mm 2 or more, but it is preferable to limit the upper limit value to 0.05% in order to inhibit the impact toughness of the weld portion in the case of excessive content.
상기 V은 V(C,N)을 석출시키는 원소로서 함유량증가에 따라 인장강도가 증가되는데, 특히 Ti와 동시에 첨가될때에 HAZ 부 내 크랙성이 향상되며, V함량이 0.02% 미만일때는 Ti 복합효과가 없으므로 0.02%이상의 첨가가 요구된다.The V is an element which precipitates V (C, N). As the content increases, the tensile strength increases. Particularly, when C is added simultaneously with Ti, the crackability of the HAZ is improved. When the V content is less than 0.02% 0.02% or more is required.
그러나, 다량 함유시 강도확보는 가능하지만, 모재 및 용접부 충격 인성을 저해하므로, 그 상한은 0.05%로 제한하는 것이 바람직하다.However, the strength can be secured when a large amount is contained, but the impact strength of the base material and the welded part is deteriorated. Therefore, the upper limit is preferably limited to 0.05%.
상기 Ti은 고온에서 TiN 석출물이 입계에 미세분산되어 초기 오스테나이트 결정립성장을 억제함으로서 강도의 부분적인 증가와 함게 인성의 대폭적인 개선효과가 있고, 또한, V과 복합첨가시 내 HAZ 부 균열성이 개선되는데, 복합첨가 효과를 얻기 위해서는 0.005%이상이 필요하지만, 0.02%이상 첨가시에는 산화물 형성 또는 과잉 고용 Ti가 조대 석출물을 형성하여 인성을 저해시키므로, 상기 Ti의 함량은 0.005-0.02%로 제한하는 것이 바람직하다.The above-mentioned Ti has a tendency to partially increase the strength and to significantly improve the toughness by suppressing the growth of the initial austenite grains by finely dispersing the TiN precipitates at the high temperature. In addition, In order to obtain the effect of compound addition, 0.005% or more is required. When Ti is added in an amount of 0.02% or more, oxide formation or excessive use Ti forms coarse precipitates to inhibit toughness. Therefore, the content of Ti is limited to 0.005-0.02% .
상기 B의 함량이 2ppm 이상인 경우에는 도금시 용융아연에 의한 균열발생정도 커지므로, B의 함량은 2ppm 이하로 제한하는 것이 바람직하다.When the content of B is 2 ppm or more, the degree of cracking due to hot zinc is increased during plating, so the content of B is preferably limited to 2 ppm or less.
상기와 같이 조성되는 용강 제조시 CaSi 분말 등의 분말 취입(powder injection) 및 RH 처리를 행하는 것이 바람직하다.It is preferable to perform powder injection and RH treatment of CaSi powder or the like in the production of the molten steel as described above.
상기 분말취입시 Ar가스와 같은 불활성가스와 함께 취입되는 분말은 용강중에서 Al2O3계, SiO2계 및 MnS계 개재물 등의 핵 생성자리로서 작용을 하여 개재물의 부상분리를 촉진하므로써, 재재물을 저감시키는 역할을 하게 된다. 상기 분말로서 CaSi 분말을 사용하는 경우에는 200-400Kg/300ton-용강을 투입하는 것이 바람직한데, 그 이유는 투입량이 너무적은 경우에는 투입효과가 없고, 너무 많은 경우에는 오히려 산화물계 개재물의 양이 증가되기 때문이다.The powder blown together with the inert gas such as Ar gas during the powder blowing acts as nucleation sites of the Al 2 O 3 system, SiO 2 system and MnS system inclusions in the molten steel to promote the floating separation of the inclusions, As shown in FIG. When CaSi powder is used as the powder, it is preferable to add 200-400 Kg / 300 ton-molten steel because the amount of the CaSi powder is not sufficient when the amount of the CaSi powder is too small and the amount of the oxide inclusion is increased .
상기 RH처리시 진공도는 2.0torr 이하가 바람직하고, 처리시간은 20분 이상이 바람직하다.The degree of vacuum during the RH treatment is preferably 2.0 torr or less, and the treatment time is preferably 20 minutes or more.
본 발명에서는 상기와 같이 조성되는 용강으로 강슬라브를 제조한후 강 슬라브를 제어압연법에 의해 제어압연한다.In the present invention, a steel slab is produced from molten steel as described above, and the steel slab is controlled and controlled by a control rolling method.
즉, 상변태전의 조직인 오스테타이트 조직을 미세화시키기 위하여 재결정 영역에서 압연을 행한 다음, 오스테타이트 입내에 변형대(deformation band)를 생성시켜 오스테나이트 페라이트 변태시 페라이트 결정립의 핵 생성을 조장하기 위한 미재결정 영역에서의 압연을 행하게 된다.That is, in order to miniaturize the osteite structure that is the structure before the phase transformation, rolling is performed in the recrystallization region, and then a deformation band is generated in the austenite grain to form a non-recrystallization region for promoting nucleation of the ferrite grains in the austenite ferrite transformation. Rolling is performed.
그리고, 상기 제어압연 후, 오스테나이트→ 페라이트 변대에 필요한 구동력을 크게 하고, 또한, 상변태시 페라이트 핵생성 자리로 작용할 수 있는 유효 핵생성자리(effective nucleation site)수를 증가시키기 위하여 가속냉각한다.After the controlled rolling, accelerated cooling is performed in order to increase the driving force required for the austenite-to-ferrite zone and to increase the number of effective nucleation sites capable of acting as a ferrite nucleation site at the time of phase transformation.
상기 강 슬라브는 제어 압연하기 위하여 가열되며, 가열온도는 1100-1200℃로 선정하는 것이 바람직한데, 그 이유는 가열온도가 1100℃이하인 경우에는 압연이 곤란하게 되고, 1200℃ 이상인 경우에는 오스테나이트 입도가 커져 결정립 미세화에 의한 강도 향상 정도가 미흡하기 때문이다.The steel slab is heated for controlled rolling and the heating temperature is preferably selected from 1100 to 1200 ° C. This is because when the heating temperature is less than 1100 ° C., rolling becomes difficult and when the temperature is 1200 ° C. or more, The degree of strength improvement due to grain refinement is insufficient.
상기와 같이 가열된 강 슬라브는 1000-1100℃의 압연개시온도 및 950-1000℃의 압연종료온도 조건으로 재결정영역에서 압연된다.The steel slab thus heated is rolled in the recrystallization zone at a rolling start temperature of 1000-1100 ° C and a rolling finish temperature of 950-1000 ° C.
상기 재결정영역에서의 압연시 압연온도가 1100℃이상인 경우에는 고온영역에서의 압연으로 누적압하효과가 적어 초기 오스테나이트 결정립 미세화 효과가 미흡하고, 950℃미만의 온도영역에서 압연을 행하면, 결정립 미세화 효과는 달성할 수 있지만, 재결정 온도범위 및 압하량을 고려하여, 상기와 같이 압연개시온도 및 압연종료온도를 제한하는 것이 바람직하다.When the rolling temperature in rolling in the recrystallization region is 1100 ° C or higher, the effect of rolling down in the high temperature region is small and the effect of miniaturizing the initial austenite grain is insufficient. When the rolling is performed in the temperature region below 950 ° C, It is preferable to limit the rolling start temperature and the rolling finish temperature as described above in consideration of the recrystallization temperature range and the rolling reduction amount.
상기 재결정영역에서의 압연시 압하율은 특별히 제한되는 것은 아니지만, 30-50%의 압하율이 바람직하다.The reduction rate in rolling in the recrystallized region is not particularly limited, but a reduction ratio of 30 to 50% is preferable.
상기와 같이 재결정영역에서 압연한 후, 860-900℃의 압연개시온도, 70-80%의 압하율 및 710-750℃의 압연종료온도조건으로 미재결정 영역에서 압연한다.After rolling in the recrystallization region as described above, the steel is rolled in the non-recrystallized region at a rolling start temperature of 860-900 ° C, a rolling reduction of 70-80%, and a rolling finish temperature of 710-750 ° C.
상기 미재결정영역에서의 압연시 압하율이 70%이하인 경우에는 압연시간이 길어져 결정립이 커지게 되므로, 목적하는 항복강도를 얻을 수 없을 뿐만 아니라 생산성이 떨어지고, 80%이상인 경우에는 압연롤 부하가 커지게 되므로, 압하율은 70-80%로 선정하는 것이 바람직하다.When the rolling reduction rate in the non-recrystallized region is 70% or less, the rolling time becomes long and the grain size becomes large. Therefore, the desired yield strength is not obtained and the productivity is decreased. It is desirable to select the reduction ratio at 70 to 80%.
상기와 같이 제어압연후 수냉에 의한 가속냉각시 냉각종료온도가 520℃이상인 경우에는 오스테나이트→ 페라이트 변태가 완료되지 않아 밴드조직이 형성됨으로써 강재의 저온균열 기점으로 작용할 수 있고, 480℃이하의 저온까지 냉각을 실시하면 마르텐사이트등 저온변태조직을 형성하여 강도확보는 유리하지만, 충격인성을 저해하므로, 상기 가속냉각시 냉각종료온도는 480-520℃로 제한하는 것이 바람직하다.When the cooling end temperature is 520 ° C or more during the accelerated cooling by water cooling after the control rolling as described above, the austenite-to-ferrite transformation is not completed and the band structure is formed, so that it can act as a low temperature crack starting point of the steel, , A low temperature transformation structure such as martensite is formed to secure the strength, but the impact toughness is deteriorated. Therefore, the cooling termination temperature during the accelerated cooling is preferably limited to 480 - 520 占 폚.
한편, 가속냉각시 냉각속도가 8℃/sec 미만인 경우에는 약냉에 의해 오스테나이트→페라이트 변태 미완료로 충격인성 및 인장강도 향상에 적합한 베이나이트 확보가 어려우며, 14℃/sec 이상인 경우에는 높은 냉각속도에 의해 인장강도는 향상되나 제품형상이 불량해지므로, 상기 냉각속도는 8-14℃/sec 로 제한하는 것이 바람직하다.On the other hand, when the cooling rate is less than 8 ° C / sec during the accelerated cooling, it is difficult to secure bainite suitable for improving the impact toughness and tensile strength due to the austenite → ferrite transformation unfinished by cold cooling. The tensile strength is improved but the product shape becomes poor. Therefore, the cooling rate is preferably limited to 8-14 DEG C / sec.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다.Hereinafter, the present invention will be described more specifically by way of examples.
[실시예][Example]
하기표 1과 같이 조성되는 강 슬라브를 하기표 2와 같이 열간압연한 후, 기계적 특성, 및 Zn 도금시 크랙발생유무를 조사하고, 그 결과를 하기표 3에 나타내었다.The steel slabs formed as shown in the following Table 1 were hot rolled as shown in the following Table 2, and then the mechanical properties and the occurrence of cracks during Zn plating were examined. The results are shown in Table 3 below.
상기 강 슬라브 제조를 위한 용강제조시 인성을 해치고 중심편석을 조장시키는 불순물인 [P][S]를 극저관리하기 위해 밀 스케일(mil1 sca1e)투입후 교반처리로 탈[P]작업을 실시한 다음, 슬래그를 배제한 후, 카바이드(carbide)투입에 의한 탈류작업을 실시하였다. 그리고 전로 조업이후 용강 노외 정련공정에서 분말취입(powder injection)작업시 Ca-Si 분말 210kg/300ton-용강을 투입하고 진공 탈개스처리를 실시하였다.In order to control the impurity [P] [S], which impairs the toughness and induces center segregation during molten steel production for the steel slab, the mill scale (mil1 sca1e) is added, followed by agitation to remove the [P] After the slag was excluded, a desulfurization operation was carried out by the addition of carbide. In the process of powder injection in the process of refining the molten steel after the converter process, 210kg / 300ton of Ca-Si powder was injected and subjected to vacuum degassing treatment.
제강에서 용선 탈[P], 탈[S]처리, 분말취입 처리 및 진공탈 가스중 처리(처리시간:26분,진공도:1torr)를 실시하였으며, 연주시 중심편석을 최소화하기 위해 전자교반처리를 실시하였다.In order to minimize center segregation during the performance, the steel was subjected to electromagnetic stirring (P), de-S treatment, powder blowing treatment and vacuum degassing treatment (treatment time: 26 minutes, vacuum degree: Respectively.
또한, 슬라브 냉각은 열간주편 상태에서 내부잔존 개스의 확산방출을 위해 상온까지 다단적치 공냉(72시간 이상)을 실시하였다.In addition, the slab cooling was performed by multi-stage compact air cooling (72 hours or more) to room temperature for diffusive discharge of the remaining residual gas in the heat trapped state.
발명강의 압연 공정에서는 슬라브를 1150℃로 가열하였으며, 제어 압연시에는 단계별로 온도 및 압하율을 제어하여 상변태전의 조직인 오스테나이트 미세화 및 오스테나이트 입내에 변형대(deformation band)를 생성시켜 오스테나이트 → 페라이트 변태시 페라이트 입의 핵생성에 의한 입자 미세화 효과로 강도를 확보하는 미재결정 영역 압연으로 나누어 실시하였다.In the rolling process of the inventive steel, the slab was heated to 1150 ° C. During the control rolling, the temperature and the reduction rate were controlled stepwise to form a deformation band in the austenite grain and austenite structure before the phase transformation, And non - recrystallized zone rolling to secure strength by grain refining effect by nucleation of ferrite ingot at transformation.
즉, 강도 및 인성확보를 위해 980℃ 재결정 영역에서 압하율 50%를 적용하여 부분적인 압연을 실시함으로써, 초기오스테나이트 결정립의 미세화를 유도하였고, 미재결정 압연은 880℃에서 잔 압하율 75%를 적용하였으며, 압연종료온도는 730-760℃였다.That is, in order to secure the strength and toughness, partial reduction of the austenite grains was induced by applying a reduction ratio of 50% in the 980 ° C. recrystallization region, and the non-recrystallization rolling resulted in a reduction of the residual reduction of 75% at 880 ° C. And the rolling finish temperature was 730-760 ° C.
또한, 제어압연후 730-760℃에서 가속냉각을 행하고, 500-550℃에서 냉각을 종료했으며, 이때의 냉각속도는 10-14℃/sec였다.After the controlled rolling, accelerated cooling was performed at 730 - 760 캜, and cooling at 500 - 550 캜 was completed. The cooling rate at this time was 10 - 14 캜 / sec.
발명재(A-C)의 경우 결정립 크기는 5-10pm 정도였다.In case of invention material (A-C), the grain size was about 5-10 pm.
한편, 종래강의 경우에는 1030℃에서 압연을 개시하여 950℃에서 종료한 후 공냉하였다.On the other hand, in the case of the conventional steel, rolling was started at 1030 캜, followed by termination at 950 캜, followed by air cooling.
[표 1][Table 1]
[표 2][Table 2]
[표 3][Table 3]
상기 표 3에 나타난 바와같이, 본 발명에 따라 제조된 본 발명재(A-C)는 강관철탑용 6Okg/㎟급 고장력강의 수요가 요구를 만족하고 있음을 알 수 있다.As shown in Table 3, it can be seen that the present invention material (A-C) produced according to the present invention satisfies the demand of 60 kg / mm 2 high tensile strength steel for a steel pipe tower.
상술한 바와 같이, 본 발명은 높은 장력에 견딜수 있고, 또한 용융 Zn에 의한 액상금속취성에 강한 60Kg/㎟급 고장력강을 제공하므로써, 높은 장력에 견디고 또한 액상 금속 취성에 강한 재질이 요구되는 철탑제조용 강재 분야에 효과적으로 적용될수 있는 것이다.INDUSTRIAL APPLICABILITY As described above, the present invention provides a high strength steel of 60 kg / mm < 2 > grade which is resistant to high tensile force and resistant to brittle liquid metal by molten Zn, It can be effectively applied to the field.
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