KR19980073737A - High toughness chromium-molybdenum steel for pressure vessels - Google Patents
High toughness chromium-molybdenum steel for pressure vessels Download PDFInfo
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Abstract
본 발명은 화학적 조성이 중량%로 탄소(C) 0.10%∼0.17%, 규소(Si) 0.10%∼0.30%, 망간(Mn) 0.25%∼0.50%, 니켈(Ni) 0%∼ 0.25%, 크롬(Cr) 1.8%∼2.7%, 몰리브덴(Mo) 0.90%∼1.30%, 바나디움(V) 0%∼0.10%, 티타늄(Ti) 0.008%∼0.030%, 보론(B) 0.0008%∼0.0030%, 알루미늄(Al) 0.005%∼0.030%, 인(P) 0%∼ 0.020%, 황(S) 0%∼0.010%이고, 잔부는 철(Fe) 및 제강정련에 의하여 제거할 수 없는 불가피한 불순원소로 구성된 압력용기용 고인성 강에 관한 것이다.In the present invention, the chemical composition is 0.1% to 0.17% of carbon (C), 0.10% to 0.30% of silicon (Si), 0.25% to 0.50% of manganese (Mn), 0% to 0.25% of nickel (Ni), and chromium. (Cr) 1.8% to 2.7%, molybdenum (Mo) 0.90% to 1.30%, vanadium (V) 0% to 0.10%, titanium (Ti) 0.008% to 0.030%, boron (B) 0.0008% to 0.0030%, aluminum (Al) 0.005% to 0.030%, phosphorus (P) 0% to 0.020%, sulfur (S) 0% to 0.010%, and the balance consists of inevitable impurity elements that cannot be removed by iron (Fe) and steelmaking A high toughness steel for pressure vessels.
본 발명강은 고온에서 인장강도가 높고 뛰어난 파괴인성과 뜨임취성에 대한 높은 저항성을 갖는다.The inventive steel has high tensile strength at high temperatures and has excellent resistance to fracture toughness and temper brittleness.
Description
제1도는 냉각속도와 강의 충격인성과의 일반적인 관계를 나타낸 그래프이다.1 is a graph showing a general relationship between cooling rate and impact toughness of steel.
제2도는 본 발명강의 제강 및 조괴공정을 나타낸 도면이다.2 is a view showing the steelmaking and ingot process of the present invention steel.
제3도는 본 발명강의 단조공정을 나타낸 도면이다.3 is a view showing a forging process of the present invention steel.
제4도는 본 발명의 실험예에 따라 시험된 본 발명강과 비교강의 미세조직을 나타낸 사진이다.4 is a photograph showing the microstructure of the inventive steel and the comparative steel tested according to the experimental example of the present invention.
제5도는 본 발명의 실험예에 따라 시험된 본 발명강과 비교강의 충격인성을 나타낸 그래프이다.5 is a graph showing the impact toughness of the inventive steel and the comparative steel tested according to the experimental example of the present invention.
본 발명은 고온에서 인장강도가 높고, 뛰어난 파괴인성과 더불어 고온 고압에서 장시간 운전하는 조건에서도 뜨임취성에 대한 높은 저항성이 요구되는 압력용기를 제작하는 데 사용되는 크롬-몰리브덴이 함유된 특수강에 관한 것이다.The present invention relates to a special steel containing chromium-molybdenum which is used to manufacture a pressure vessel having high tensile strength at high temperature, high fracture resistance and high resistance to temper brittleness even under long-term operation at high temperature and high pressure. .
용기제작에 필요한 링과 경판의 두께는 120∼350mm에 달하는 극후재이므로 압력용기 제작에 요구되는 위의 성질을 얻기 위하여는 소재의 표면에서 중심부까지 열처리에 의하여 균질한 베이나이트 미세조직이 얻어져야 한다. 또 소재생산에 소요되는 기간을 단축시키고 극후 두께의 링을 단조상태로 열처리 하더라도 이러한 요구성질을 달성할 수 있도록 담금질성의 획기적인 개선이 요구된다.Since the thickness of the ring and the slab required for the production of the container is 120 ~ 350mm thick, it is necessary to obtain a homogeneous bainite microstructure by heat treatment from the surface to the center of the material to obtain the above properties required for the production of pressure vessels. . In addition, shortening the time required for the production of the material and heat treatment of the extremely thick ring in the forged state is required to drastically improve the hardenability to achieve this requirement.
그러나, 티타늄과 보론이 첨가되지 않은 종래 합금성분으로 제작한 압력용기용 소재의 경우 다음과 같은 문제점이 대두되었다.However, the following problems have arisen in the case of a pressure vessel material made of a conventional alloy without addition of titanium and boron.
첫째, 담금질성이 낮아 하기 공정도에 나타낸 공정으로 극후 두께의 단조링을 제조하였다. 즉, 단조후에 예비열처리인 불림처리를 수행하고, 소재를 담금질처리하는 동안에 열전달효과를 개선시키고, 소재의 두께를 얇게 하여 중심부에서도 요구되는 성질을 얻기 위하여 황삭 기계가공 후에 품질열처리인 담금질과 뜨임처리를 수행하였다.First, the forging ring having a very thick thickness was manufactured by the process shown in the following process chart with low hardenability. That is, after forging, preliminary heat treatment is performed, quenching and tempering treatment, which is a quality heat treatment after rough machining, to improve the heat transfer effect during the quenching of the material, and to obtain the required properties in the center by thinning the material thickness. Was performed.
종래의 합금성분을 이용한 극후 압력용기용 소재의 제조공정Manufacturing process of material for ultra-thick pressure vessel using conventional alloy components
이러한 제조공정에 따라 소재를 생산하면 두차례의 기계가공을 하므로써 소재의 제조공정이 복잡하고, 대형의 중량물을 취급하는 데 많은 어려움이 수반되어 소재생산에 소요되는 기간이 길어져 생산성이 낮다.If the material is produced according to such a manufacturing process, the machining process of the material is complicated by two times of machining, and a lot of difficulties are involved in handling a large weight, resulting in a long period of time required for producing the material, resulting in low productivity.
둘째, 제1도에 도시한 바와 같이 링의 중심부에서 높은 충격인성을 얻기 위하여 요구되는 최소 냉각속도는 분당 섭씨 7도 이상이어야 된다고 알려져 있다. 따라서 종래의 강은 합금성분의 구성 등 상변태 특성 때문에 이러한 조건을 만족시킬 수 있는 최대한의 두께는 400mm로 제한된다. 그러나 상기한 조건으로 담금질을 하더라도 극후 압력용기 제작에 필요한 두께의 링 중심부에서 충격인성을 저해시키는 페라이트 미세조직이 생성되는 사례가 보고되어 있다. 즉 고온강도, 파괴인성 및 뜨임취성에 대한 저항성이 높은 극후 압력용기 제작용 링 소재의 두께가 350mm 이상일 경우 링의 가공전의 두께는 약 450mm이므로 단조상태에서 열처리할 수 없는 문제점을 안고 있다.Second, as shown in FIG. 1, it is known that the minimum cooling rate required to obtain high impact toughness at the center of the ring should be at least 7 degrees Celsius per minute. Therefore, the conventional steel is limited to the maximum thickness that can satisfy these conditions due to the phase transformation properties such as the composition of the alloy component is 400mm. However, even when quenched under the above conditions, a case has been reported in which a ferrite microstructure is produced that impairs impact toughness at the center of a ring having a thickness required for manufacturing a pressure vessel. In other words, if the thickness of the ring material for the manufacture of the ultra-thick pressure vessel having high resistance to high temperature strength, fracture toughness and temper brittleness is 350 mm or more, the thickness before processing of the ring is about 450 mm, and thus, it cannot be heat-treated in a forged state.
따라서 본 발명자들은 기존강종(ASME SA336 F22)의 재질적인 문제점을 해결한 강종으로서 열처리과정 동안의 담금질성이 우수하고, 높은 충격파괴인성과 뜨임취성에 대한 저항성을 갖는 극후 압력용기 소재를 제공하기 위하여, 화학조성이 중량%로 탄소(C) 0.10% 내지 0.17%, 규소(Si) 0.10% 내지 0.30%, 망간(Mn)이 0.25% 내지 0.50%, 니켈(Ni) 0% 내지 0.25%, 크롬(Cr) 1.80% 내지 2.70%, 몰리브덴(Mo) 0.90% 내지 1.30%, 바나디움(V) 0% 내지 0.10%, 티타늄(Ti) 0.008% 내지 0.030%, 보론(B) 0.0008% 내지 0.0030%, 알루미늄(Al) 0.005% 내지 0.030%, 인(P) 0% 내지 0.020%, 황(S) 0% 내지 0.010%이고, 잔부는 철(Fe) 및 제강정련에 의하여 제거할 수 없는 불가피한 불순원소로 구성된 소재를 제작하였다.Therefore, the inventors of the present invention solve the material problems of the existing steel grade (ASME SA336 F22) to provide an extreme pressure vessel material having excellent hardenability during the heat treatment process, high impact fracture toughness and resistance to temper brittleness , Chemical composition by weight 0.1% to 0.17% of carbon (C), 0.10% to 0.30% of silicon (Si), 0.25% to 0.50% of manganese (Mn), 0% to 0.25% of nickel (Ni), chromium ( Cr) 1.80% to 2.70%, molybdenum (Mo) 0.90% to 1.30%, vanadium (V) 0% to 0.10%, titanium (Ti) 0.008% to 0.030%, boron (B) 0.0008% to 0.0030%, aluminum ( Al) 0.005% to 0.030%, phosphorus (P) 0% to 0.020%, sulfur (S) 0% to 0.010%, and the balance is composed of inevitable impurities that cannot be removed by iron (Fe) and steelmaking Was produced.
본 발명을 상세히 설명하면 다음과 같다.The present invention is described in detail as follows.
본 발명 강의 화학성분을 다음 표 1에 나타내었다.The chemical composition of the inventive steel is shown in Table 1 below.
[표 1]. 본 발명강의 화학성분TABLE 1 Chemical composition of the present invention steel
탄소(C)는 열처리 과정에 탄화물을 석출시켜 소재의 강도와 경도를 결정하는 중요한 원소로 0.10% 이하의 경우는 고온강도를 요구하는 값으로 유지할 수 없고, 0.17% 이상 함유되면 용접성을 저해시키므로 압력용기 제작이 어렵게 된다. 따라서 요구되는 강도를 유지하고, 용접성이 우수한 조건이 되기 위하여는 0.10% 내지 0.17%의 범위로 한정하는 것이 바람직하다.Carbon (C) is an important element that determines the strength and hardness of the material by depositing carbide during the heat treatment process. If it is 0.10% or less, it cannot be maintained at a value that requires high temperature strength. The container becomes difficult to make. Therefore, in order to maintain the required strength and become a condition excellent in weldability, it is preferable to limit to 0.10%-0.17% of range.
규소(Si)는 제강정련 동안에 용강중의 산소를 제거하는 탈산제 역할을 하며 함량이 0.10% 이하일 경우는 불안정한 탈산효과를 나타내고, 0.30% 이상 함유되면 탄화물의 안정성을 해치게 되어 강도를 낮추거나 뜨임취성을 조장시키기 때문에 적정함유량은 0.10% 내지 0.30%로 한정시키는 것이 바람직하다.Silicon (Si) acts as a deoxidizer that removes oxygen from molten steel during steelmaking, and if the content is less than 0.10%, it shows an unstable deoxidizing effect. If it contains more than 0.30%, silicon deteriorates the stability of the carbide and promotes temper brittleness. For this reason, the proper content is preferably limited to 0.10% to 0.30%.
망간(Mn)은 강도유지와 열처리 과정에 담금질성을 향상시키는 합금원소로 중요한 역할을 한다. 0.25% 이하로 함유되면 강도 값이 낮아지고, 담금질성을 해치게 된다. 또 0.50% 이상 함유되면 규소와 함께 뜨임취성에 대한 저항성을 해치게 되므로 0.25% 내지 0.50% 범위가 바람직하다.Manganese (Mn) plays an important role as an alloying element to improve the hardenability during the maintenance of strength and heat treatment. If the content is 0.25% or less, the strength value is lowered and the hardenability is impaired. In addition, since the content of 0.50% or more impairs resistance to temper brittleness with silicon, the range of 0.25% to 0.50% is preferable.
인(P)은 소재를 열처리하는 과정과 고온에서 사용하는 소재의 뜨임취성을 일으키는 역할을 하기 때문에 가능한 낮은 함량으로 제거하는 것이 바람직하다.Phosphorus (P) is preferably removed at a low content because it plays a role in causing heat treatment of the material and tempering brittleness of the material used at a high temperature.
유황(S)은 소재에 함유된 망간(Mn)과 작용하여 충격인성을 저해하고, 소재의 기계적 성질의 이방성을 일으킬 뿐만 아니라 고온강도를 해치는 유해한 원소이므로 가능한 낮은 함량으로 제거하는 것이 바람직하다.Sulfur (S) acts with manganese (Mn) contained in the material to inhibit the impact toughness, not only cause anisotropy of the mechanical properties of the material but also harmful elements that harm the high temperature strength, it is desirable to remove as low as possible.
니켈(Ni)은 열처리 과정에 담금질성을 향사시키고, 인성을 높이는 효과가 있으나 고온 강도를 저해시키는 작용을 하므로 0.25% 이하로 함유량을 제한하는 것이 바람직하다.Nickel (Ni) is preferred to limit the content to 0.25% or less because it enhances the hardenability during the heat treatment process, and has the effect of increasing the toughness but inhibits the high temperature strength.
크롬(Cr)은 고온강도 및 수소에 의한 침식 작용을 억제하는데 중요한 역할을 한다. 함유량이 1.8% 이하로 낮은 경우는 고온강도가 얻어지지 않고, 2.7% 이상 함유되면 수소에 의한 침식 저항성을 향상시키나 고온 강도를 급격하게 떨어지게 한다. 따라서 1.8% 내지 2.7%로 제한하는 것이 바람직하다.Chromium (Cr) plays an important role in suppressing erosion by high temperature strength and hydrogen. If the content is lower than 1.8%, the high temperature strength is not obtained. If the content is more than 2.7%, the erosion resistance by hydrogen is improved, but the high temperature strength is sharply dropped. Therefore, it is desirable to limit to 1.8% to 2.7%.
몰리브덴(Mo)은 고온강도를 높이고, 뜨임취성에 대한 저항성을 높이는데 효과적이다. 그러나 함량이 0.9% 이하로 되면 섭씨 500도 근처에서 강도를 저하시키고, 1.30% 이상되면 용접성을 저해시키는 작용을 한다. 따라서 함유량을 0.9% 내지 1.30%로 제한하는 것이 바람직하다.Molybdenum (Mo) is effective in increasing the high temperature strength and resistance to temper brittleness. However, if the content is less than 0.9%, the strength is lowered near 500 degrees Celsius, and if more than 1.30%, it serves to inhibit the weldability. Therefore, it is preferable to limit the content to 0.9% to 1.30%.
바나디움(V)은 미세한 탄화물을 석출시켜 고온 강도를 높이지만 다량 함유되면 용접균열 생성을 촉진시키므로 0.1% 이하로 제한하는 것이 바람직하다.Vanadium (V) is precipitated fine carbide to increase the high-temperature strength, but if contained in a large amount to promote the generation of weld cracks, it is preferable to limit to 0.1% or less.
티타늄(Ti)은 용강중에 포함된 질소(N)와 반응하여 질화물을 생성시켜 보론(B)에 의한 소재의 담금질성을 향상시키는데 효과적이다. 함유량이 0.008% 이하이고, 질소함량이 0.003% 이상이면 보론(B)과 반응하여 보론질화물(BN)이 생성되어 담금질성이 저하되고, 티타늄의 함유량이 0.030% 이상이면 비금속개재물이 생성되어 충격인성을 나쁘게 하므로 0.008% 내지 0.030%로 제한하는 것이 바람직하다.Titanium (Ti) is effective in improving the hardenability of the material by boron (B) by generating nitride by reacting with nitrogen (N) contained in molten steel. If the content is 0.008% or less, and the nitrogen content is 0.003% or more, boron nitride (B) is reacted to form boron nitride (BN), and the hardenability is lowered. If the titanium content is 0.030% or more, nonmetallic inclusions are formed to give impact toughness. It is preferable to limit the amount to 0.008% to 0.030% because of deterioration.
알루미늄(Al)은 용강중의 산소와 친화력이 강하므로 티타늄(Ti)과 보론(B) 첨가효과를 극대화하기 위하여 0.005% 내지 0.030%로 한정하는 것이 바람직하다.Since aluminum (Al) has a strong affinity with oxygen in molten steel, it is preferable to limit the amount to 0.005% to 0.030% in order to maximize the effect of adding titanium (Ti) and boron (B).
보론(B)은 미량 첨가하여 소재를 열처리하는 과정에 담금질성을 획기적으로 개선시킬 수 있는 합금원소이다. 그러나 용강중에 보론(B)의 함량이 0.0005% 이하일 경우는 담금질성 향상에 미치는 효과를 얻을 수 없고, 0.0030% 이상 함유되면 열간가공성과 용접성을 해치게 되므로 0.0008% 내지 0.0030%로 한정하는 것이 바람직하다.Boron (B) is an alloy element that can significantly improve the hardenability in the process of heat-treating the material by adding a trace amount. However, when the content of boron (B) in the molten steel is less than 0.0005%, it is not possible to obtain an effect on improving hardenability, and if it is contained in more than 0.0030%, the hot workability and weldability are deteriorated, so it is preferable to limit it to 0.0008% to 0.0030%.
따라서 미량의 보론(B) 첨가에 의한 소재의 담금질성을 효과적으로 개선하기 위하여는 용강중의 산소(O), 질소(N)와의 반응성이 매우 강한 보론(B) 첨가 전에 알루미늄(Al)과 티타늄(Ti)을 첨가하여 유해한 산소(O)와 질소(N)를 제거하거나 질화물(TiN)을 생성시키도록 하는 것이 중요하다.Therefore, in order to effectively improve the hardenability of the material by adding a small amount of boron (B), aluminum (Al) and titanium (Ti) before the addition of boron (B), which is highly reactive with oxygen (O) and nitrogen (N), in molten steel It is important to add) to remove harmful oxygen (O) and nitrogen (N) or to produce nitride (TiN).
본 발명강을 이용한 극후 압력용기용 소재의 제조공정을 요약하면 다음과 같다.Summarizing the manufacturing process of the material for the ultra-thick pressure vessel using the present invention steel is as follows.
본 발명강을 이용한 극후 압력용기용 소재의 제조공정Manufacturing process of material for extreme pressure vessel using steel of the present invention
이하 본 발명의 제조공정을 단계별로 상세히 설명한다.Hereinafter, the manufacturing process of the present invention will be described in detail step by step.
가. 제강 및 조괴end. Steelmaking and Ingot
제강의 공정은 제2도에 나타낸 바와 같이, 염기성전기로(EAF)-2차 정련로(ASEA-SKF LRF)-진공 강괴 주입(VSD)의 공정을 거치며, 염기성전기로에서는 불순물의 원소(Cu, As, Sb, Sn)가 적은 고품질의 고철을 엄선하여, 전기로에서 용해작업, 탈인(P) 작업 산화정련을 거쳐 불순물을 제거한 후 레이들(Ladle)에 수강하여 ASEA-SKF 2차 정련로에서 비금속개재물의 부상 제거, 균일한 화학성분 및 온도를 조절하여 환원정련하고, 진공 탈가스 처리에 의하여 유해한 가스(H, N, O) 성분을 최대한 낮추어 진공분위기 상태에서 용강을 주입하여 강괴를 제조한다. 이때의 화학성분 요구값은 상기 표 1과 같다.As shown in FIG. 2, the steelmaking process is carried out in the basic furnace (EAF) -secondary refinery (ASEA-SKF LRF) -vacuum ingot injection (VSD) process, and in the basic furnace, the impurities (Cu, Selected high-quality scrap steel with low As, Sb, Sn), dissolved in electric furnace, dephosphorized (P) work, removed impurities, and then taken to ladle to take base metal in ASEA-SKF secondary refinery Reduction and refining of the inclusions, uniform chemical composition and temperature control to reduce and refining, by reducing the harmful gas (H, N, O) components by vacuum degassing as much as possible injecting molten steel in a vacuum atmosphere to produce a steel ingot. At this time, the required chemical component values are shown in Table 1 above.
특히 ASEA-SKF 2차 정련로에서 진공탈가스 처리에 의하여 소재의 열처리 과정에 담금설정을 저해시키는 질소(N) 함량을 최대한 낮추기 위하여 질소와 친화력이 강한 티타늄(Ti)을 탈가스 처리후에 첨가하며, 산화물 계열의 비금속개재물의 생성을 억제하기 위하여 산소(O) 함량을 낮출 수 있는 알루미늄(Al)과 규소(Si)를 상한 값에 가깝게 맞춘다. 보론(B)은 용강을 주입하기 전에 상한 값에 가깝게 조절한다.Particularly, in order to minimize nitrogen (N) content, which inhibits immersion setting in the heat treatment process of the material by vacuum degassing treatment in ASEA-SKF secondary refining furnace, titanium (Ti) having strong affinity with nitrogen is added after degassing treatment. In order to suppress the generation of oxide-based nonmetallic inclusions, aluminum (Al) and silicon (Si) that can lower the oxygen (O) content are set close to the upper limit. Boron (B) is adjusted close to the upper limit before the molten steel is injected.
이와 같이 진공 탈가스처리를 하고, 진공상태에서 강괴를 제조하면 극후 압력용기 제조용 소재는 재질의 청정도가 높고, 기공, 성분편석 및 기계적 성질에 유해한 결함을 최대한으로 감소시킬 수 있다.In this way, if the vacuum degassing treatment and the steel ingot is manufactured in a vacuum state, the material for the production of the ultra-high pressure vessel may have high cleanliness of material, and may reduce defects harmful to pores, component segregation and mechanical properties to the maximum.
나. 단조I. minor
품질의 균일성과 내부 결함이 없는 대형 무계목 링을 제조하기 위하여 강괴를 제3도에 나타낸 바와 같이 가열하여 1차로 강괴에서 주조결함이 포함된 강괴의 밑부분(Bottom)과 상부(Hot Top)를 소정의 양만큼 나이프(Knife)로 절단하고, 소정의 크기로 엎세팅한 다음 중심공을 만들기 위하여 천공작업을 한다. 다음에 천공된 제품의 중심부에 링 단조용 다이를 끼워 확관 및 길이를 요구하는 제품크기로 단조하여 대형 무계목 링을 제작한다.In order to manufacture large sized tree rings without quality uniformity and internal defects, the ingots are heated as shown in FIG. 3 and the bottom and top of the ingots containing casting defects are first A predetermined amount is cut with a knife, set to a predetermined size, and then drilled to make a central hole. Next, a ring forging die is inserted into the center of the perforated product to forge the product size requiring expansion and length to produce a large tree-less ring.
다. 열처리All. Heat treatment
본 발명강은 고온강도, 파괴인성, 충격인성 및 뜨임취성에 대한 저항성이 우수한 성질을 얻기 위해 단조후 불균질한 미세조직을 균질하게 조절하고, 극후 압력용기용 소재의 요구되는 특성을 얻기 위하여 예비열처리인 불림(Normalizing), 품질열처리(Quality Heat Treatment)인 담금질과 뜨임(Tempering) 열처리순으로 열처리된다.The steel of the present invention homogeneously controls the heterogeneous microstructure after forging in order to obtain properties excellent in resistance to high temperature strength, fracture toughness, impact toughness and temper brittleness, and preliminary to obtain the required characteristics of the material for pressure vessels Heat treatment is performed in order of heat treatment, quenching and tempering heat treatment.
불림처리는 880∼1000℃의 일정온도까지 소재두께 25mm당 1시간의 비율로 유지한 후 공기중에서 냉각시킨 다음 뜨임처리로서 660∼690℃의 일정온도에서 소재두께 25mm당 1시간의 비율로 유지한 후 공기중에서 냉각시켜 수행된다. 불림처리는 단조상태에서 얻어진 불균질한 미세조직을 균질하게 하고, 결정립을 미세화하여 기계적 성질을 개선시키기 위하여 오스테나이트 온도 영역에서 적당한 시간 유지한 후 공기중에서 냉각시켜 수행된다.The soaking treatment is maintained at a rate of 1 hour per 25mm of material thickness up to a constant temperature of 880-1000 ℃, then cooled in air and then tempered at a rate of 1 hour per 25mm of material thickness at a constant temperature of 660-690 ℃. It is then carried out by cooling in air. The soaking treatment is carried out by homogenizing the heterogeneous microstructure obtained in the forged state, cooling it in air after maintaining a suitable time in the austenite temperature range in order to refine the crystal grains and improve the mechanical properties.
요구되는 물성을 얻기 위해 수행되는 품질열처리인 담금질은 910℃ 이상 1050℃ 이하의 일정온도에서 적당한 시간 유지한 후 수냉(Water Quenching)시킨 다음 뜨임처리로서 660∼690℃의 일정온도에서 적정시간 유지한 후 공기중에서 냉각시켜 수행된다. 담금질은 오스테나이트 온도로부터 소재를 적당한 속도로 냉각하는 처리로, 소재를 강화시키기 위하여 요구되는 베이나이트 미세조직으로 상변태 시키기 위한 조치이다. 본 발명에서는 요구되는 베이나이트 미세조직을 얻기 위하여 극후 압력용기 소재의 중심부에서 냉각속도가 분당 최저 섭씨 3도이상되도록 하여 안정한 소재를 생산할 수 있었다(표 2). 이러한 결과는 종래 소재에서 요구되는 냉각속도인 분당 최저 섭씨 7도 보다 훨씬 느린 냉각속도로 담금질처리할 수 있으므로 압력용기벽의 두께가 두꺼운 소재를 제작할 수 있음을 의미한다.Quenching, a quality heat treatment performed to obtain the required physical properties, is maintained at a constant temperature of 910 ° C or higher and 1050 ° C or lower for a suitable time, followed by water quenching, followed by tempering to maintain a proper time at a constant temperature of 660-690 ° C. It is then carried out by cooling in air. Quenching is a process that cools the material from the austenite temperature at an appropriate rate, and is a step for phase transformation into the bainite microstructure required to strengthen the material. In the present invention, in order to obtain the required bainite microstructure, the cooling rate at the center of the extreme pressure vessel material was allowed to produce a stable material by at least 3 degrees Celsius per minute (Table 2). These results indicate that the thickening of the pressure vessel wall can be made because it can be quenched at a cooling rate much slower than the minimum 7 degrees Celsius per minute, which is required for conventional materials.
뜨임처리는 담금질한 소재를 상변태점이하의 온도로 가열하는 열처리이며, 불안정한 담금질상태의 금속조직을 안정화시켜 소재의 인성을 부여하기 위한 목적으로 수행한다. 뜨임처리의 온도와 유지시간 등의 조건은 요구되는 기계적 성질에 따라 다르며, 열처리중에 발생하는 잔류응력을 해소하여 용접중에 발생할 수 있는 균열생성 등을 최소화하는 목적도 있다.Tempering is a heat treatment that heats a quenched material to a temperature below the phase transformation point, and is performed for the purpose of stabilizing the metal structure in an unstable quenched state to impart toughness of the material. Conditions such as temperature and holding time of the tempering treatment depend on the required mechanical properties, and also have the purpose of minimizing crack formation that may occur during welding by eliminating residual stresses generated during heat treatment.
상기에서와 같은 조성 및 제조공정에 의해 제조된 본 발명강은 아래에서 설명하는 실험예에서 보는 바와 같이 종래 강의 문제점인 충격인성, 뜨임취성에 대한 저항성이 개선되었으며, 열처리 과정에서 담금질성을 개선하여 중심부까지 균질한 베이나이트 미세조직을 생성함으로써 균일한 기계적 성질을 얻는 등 품질적인 문제를 효과적으로 해결하였고, 특히 두께 450mm의 극후 무계목 링을 황삭가공하지 않고 단조상태에서 열처리를 수행하더라도 높은 충격인성, 고온강성, 파괴인성이 얻어지는 베이나이트 미세조직을 표면에서부터 중심부까지 얻을 수 있어, 정유공장의 중질유분해 및 수소 첨가에 의한 정련에 사용되는 핵심 고온 고압 반응기 제조용 소재에 적용될 수 있다.Steel according to the present invention manufactured by the composition and manufacturing process as described above has improved the resistance to impact toughness and temper brittleness of the problems of the conventional steel, as shown in the experimental example described below, by improving the hardenability during the heat treatment process By creating a homogeneous bainite microstructure up to the center, it has effectively solved the quality problems such as obtaining uniform mechanical properties.In particular, high impact toughness, The bainite microstructure obtained at high temperature stiffness and fracture toughness can be obtained from the surface to the center, and can be applied to materials for manufacturing core high temperature and high pressure reactors used for refining by heavy oil decomposition and hydrogenation in refineries.
이하 실험예를 통하여 본 발명을 설명한다.Hereinafter, the present invention will be described through experimental examples.
[실험예]Experimental Example
종래의 티타늄과 보론이 함유되지 않은 압력용기 소재용 강으로 사용되었던 ASME SA 387 Cl. 2, SA 336 F22 계열과 같은 계열의 실제 생산된 비교 재료의 화학성분을 표 2에 나타내었다. 종래에 사용되었던 수입소재(K-1)와 본 발명강의 성질을 비교하기 위하여 동일하게 열처리한 시험편으로 미세조직 및 충격인성 시험을 수행하여 그 각각의 결과를 표 3과 제4도 및 제5도에 나타내었다. 본 발명강의 담금질성, 충격인성등이 비교강에 비하여 안정하고 훨씬 우수함을 알 수 있다.ASME SA 387 Cl. Used as a steel for conventional pressure vessel materials without titanium and boron. 2, the chemical composition of the actual production of the comparative material of the same series as the SA 336 F22 series is shown in Table 2. In order to compare the properties of the imported material (K-1) and steel of the present invention, which were used in the past, the microstructure and impact toughness test were carried out with the same heat treated test specimens. Shown in It can be seen that the hardenability, impact toughness, and the like of the present invention are more stable and much better than those of the comparative steel.
[표 2]. 본 발명강 비교강의 화학성분TABLE 2 Chemical Compositions of Comparative Steels of the Invention
[표 3]. 본 발명강과 비교강의 충격인성TABLE 3 Impact Toughness of Invented Steels and Comparative Steels
본 발명강의 특징을 표 3과 제4도 및 제5도에 나타낸 시험 결과로써 설명하면 다음과 같다.The characteristics of the steel of the present invention will be described with the test results shown in Tables 3 and 4 and 5 as follows.
(1) 담금질성(1) hardenability
담금처리 과정에서 냉각속도에 따른 미세조직을 비교하면 본 발명강은 비교강에 비하여 담금질성이 우수하고, 미세조직이 층상을 이루는 방향성이 없는 것을 알 수 있다. 냉각속도가 비교강의 5.3℃/min. 보다 느린 3.5℃/min. 조건에서도 본 발명강은 충격인성을 저해하는 페라이트가 생성되지 않고 중심부까지 베이나이트 미세 조직으로 상변태하고 있음을 제4도로 부터 알 수 있다.Comparing the microstructure according to the cooling rate in the quenching process, it can be seen that the inventive steel has superior hardenability and no direction in which the microstructures are layered compared to the comparative steel. Cooling rate is 5.3 ℃ / min. Slower 3.5 ° C / min. It can be seen from FIG. 4 that even in the conditions of the present invention, the steel of the present invention phase-transforms to the bainite microstructure without the formation of ferrite that impairs impact toughness.
(2) 충격인성(2) impact toughness
비교강의 충격인성은 동일한 냉각조건으로 준비한 시험편을 이용하여 시험하였다. 비교강이 본 발명강에 비하여 시험온도에 따라 매우 불안정한 상태로 취성파괴 양상을 나타내는 파단면의 비율이 심하게 산포되는 것을 제5도로 부터 알 수 있다. 반면에 본 발명강의 충격인성은 동일한 시험 온도에서 취성파괴 파단면 비율의 산포가 안정되어 있음을 알 수 있다. 충격파괴에 견디는 충격파괴 흡수 에너지 값도 비교강에 비하여 높을 뿐만 아니라 시험온도에 따라 산포되는 정도가 안정함을 알 수 있다(제5도). 40ft-1bf천이온도(vTr40) 및 연성-취성 천이온도(FATT50)의 값도 비교강에 비하여 낮은 것으로 보다 본 발명강이 우수한 충격인성을 나타내고 있음을 제5도와 표 3으로부터 알 수 있다.The impact toughness of the comparative steels was tested using test pieces prepared under the same cooling conditions. It can be seen from FIG. 5 that the comparative steel is more unstable depending on the test temperature than the steel of the present invention, and the ratio of the fracture surface exhibiting brittle fracture is severely distributed. On the other hand, the impact toughness of the inventive steel can be seen that the scatter of brittle fracture fracture rate is stable at the same test temperature. It can be seen that the shock absorption energy value that withstands impact fracture is not only higher than that of the comparative steel, but also stable in accordance with the test temperature (FIG. 5). The values of the 40 ft-1bf transition temperature (vTr 40 ) and the ductile-brittle transition temperature (FATT 50 ) are also lower than those of the comparative steel, and it can be seen from FIG. 5 and Table 3 that the inventive steel exhibits excellent impact toughness.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100330453B1 (en) * | 1999-10-28 | 2002-04-01 | 윤영석 | Cr-Mo-V Alloy Steel for Pressure Vessel |
| KR100470670B1 (en) * | 2000-10-04 | 2005-03-07 | 주식회사 포스코 | Method for Manufacturing Steel Plate for Pressure Vessel with Superior Workability and High Tensile Strength and Method for Manufacturing Pressure Vessel with High Tensile Strength Using the Steel Plate |
| KR100605679B1 (en) * | 1999-11-11 | 2006-07-31 | 주식회사 포스코 | Slag Pot Steel with Excellent High Temperature Strength |
| WO2009061073A1 (en) * | 2007-11-07 | 2009-05-14 | Posco | High tensile steel for deep drawing and manufacturing method thereof |
| CN113981176A (en) * | 2021-10-26 | 2022-01-28 | 舞阳钢铁有限责任公司 | Quenching method for improving long-time die-welding low-temperature impact toughness of chromium-molybdenum steel plate |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103740912A (en) * | 2013-12-28 | 2014-04-23 | 首钢总公司 | Processing method for improving temper embrittlement resistance of steel plate for pressure vessels |
| CN115029623B (en) * | 2022-05-07 | 2023-08-25 | 兰州兰石集团有限公司铸锻分公司 | Smelting and forging heat treatment process method of 12Cr2Mo1 steel for pressure vessel |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0250910A (en) * | 1988-08-15 | 1990-02-20 | Nippon Steel Corp | Manufacturing method of mold steel plate with good thermal fatigue properties |
-
1997
- 1997-03-18 KR KR1019970009222A patent/KR100209450B1/en not_active Expired - Lifetime
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100330453B1 (en) * | 1999-10-28 | 2002-04-01 | 윤영석 | Cr-Mo-V Alloy Steel for Pressure Vessel |
| KR100605679B1 (en) * | 1999-11-11 | 2006-07-31 | 주식회사 포스코 | Slag Pot Steel with Excellent High Temperature Strength |
| KR100470670B1 (en) * | 2000-10-04 | 2005-03-07 | 주식회사 포스코 | Method for Manufacturing Steel Plate for Pressure Vessel with Superior Workability and High Tensile Strength and Method for Manufacturing Pressure Vessel with High Tensile Strength Using the Steel Plate |
| WO2009061073A1 (en) * | 2007-11-07 | 2009-05-14 | Posco | High tensile steel for deep drawing and manufacturing method thereof |
| US8652273B2 (en) | 2007-11-07 | 2014-02-18 | Posco | High tensile steel for deep drawing and manufacturing method thereof and high-pressure container produced thereof |
| CN113981176A (en) * | 2021-10-26 | 2022-01-28 | 舞阳钢铁有限责任公司 | Quenching method for improving long-time die-welding low-temperature impact toughness of chromium-molybdenum steel plate |
Also Published As
| Publication number | Publication date |
|---|---|
| KR100209450B1 (en) | 1999-07-15 |
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