KR100417520B1 - Reheating method for tungsten containing duplex stainless steel - Google Patents
Reheating method for tungsten containing duplex stainless steelInfo
- Publication number
- KR100417520B1 KR100417520B1 KR10-1999-0057665A KR19990057665A KR100417520B1 KR 100417520 B1 KR100417520 B1 KR 100417520B1 KR 19990057665 A KR19990057665 A KR 19990057665A KR 100417520 B1 KR100417520 B1 KR 100417520B1
- Authority
- KR
- South Korea
- Prior art keywords
- heating
- stainless steel
- tungsten
- phase stainless
- oxidation
- Prior art date
Links
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 title claims abstract description 29
- 239000010937 tungsten Substances 0.000 title claims abstract description 29
- 229910052721 tungsten Inorganic materials 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims abstract description 15
- 229910001039 duplex stainless steel Inorganic materials 0.000 title 1
- 238000003303 reheating Methods 0.000 title 1
- 238000010438 heat treatment Methods 0.000 claims abstract description 58
- 229910001220 stainless steel Inorganic materials 0.000 claims abstract description 30
- 239000010935 stainless steel Substances 0.000 claims abstract description 28
- 230000007547 defect Effects 0.000 claims abstract description 15
- 239000002344 surface layer Substances 0.000 claims abstract description 15
- 238000005098 hot rolling Methods 0.000 claims abstract description 10
- 230000003647 oxidation Effects 0.000 abstract description 38
- 238000007254 oxidation reaction Methods 0.000 abstract description 38
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 20
- 239000001301 oxygen Substances 0.000 abstract description 20
- 229910052760 oxygen Inorganic materials 0.000 abstract description 20
- 239000007789 gas Substances 0.000 abstract description 9
- 238000009749 continuous casting Methods 0.000 abstract description 3
- 229910000831 Steel Inorganic materials 0.000 description 25
- 239000010959 steel Substances 0.000 description 25
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 13
- 229910052750 molybdenum Inorganic materials 0.000 description 13
- 239000011733 molybdenum Substances 0.000 description 13
- 238000005096 rolling process Methods 0.000 description 10
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 230000007797 corrosion Effects 0.000 description 7
- 238000005260 corrosion Methods 0.000 description 7
- 239000010410 layer Substances 0.000 description 7
- 239000011651 chromium Substances 0.000 description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005461 lubrication Methods 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000005501 phase interface Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
- B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- 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
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2201/00—Special rolling modes
- B21B2201/16—Two-phase or mixed-phase rolling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2261/00—Product parameters
- B21B2261/20—Temperature
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
본 발명은 텅스텐을 1%이상 함유하는 2상 스테인레스강의 연속주조 슬라브의 열간압연을 위하여 고온에서 가열시 표면에 형성되는 고온산화 정도를 조절하여 입계산화를 최소화함으로써 표면결함 발생을 방지하기 위한 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법을 제공하는 데 그 목적이 있다.The present invention regulates the degree of high temperature oxidation formed on the surface when heated at a high temperature for hot rolling of continuous casting slabs of two-phase stainless steel containing 1% or more of tungsten, thereby minimizing grain boundary oxidation to prevent surface defects from occurring. It is an object of the present invention to provide a heating method of a containing two-phase stainless steel slab.
위와 같은 목적을 달성하기 위한 본 발명에 따르면, 텅스텐을 1%이상 함유하는 2상 스테인레스강 슬라브를 열간압연하기 위해 가열하는 방법에 있어서, 상기 슬라브의 표층부의 결함을 방지하기 위한 최적의 조건은 분위기 가스의 과잉산소량을 3%이하로 하고, 가열온도 1250℃ 이하인 상태에서 240분 이하 동안 가열하는 것이다.According to the present invention for achieving the above object, in the heating method for hot-rolling a two-phase stainless steel slab containing tungsten 1% or more, the optimal conditions for preventing defects in the surface layer portion of the slab is atmosphere The amount of excess oxygen of the gas is 3% or less, and the heating is performed for 240 minutes or less while the heating temperature is 1250 ° C or less.
Description
본 발명은 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법에 관한 것이며, 특히, 텅스텐을 함유하는 2상 스테인레스강 연속주조 슬라브를 열간압연을 위하여 고온에서 가열시 표면에 형성되는 고온산화 정도를 조절함으로써 표면결함 발생을 방지하기 위한 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법에 관한 것이다.The present invention relates to a heating method of a tungsten-containing two-phase stainless steel slab, and in particular, by controlling the degree of high-temperature oxidation formed on the surface when heating the tungsten-containing two-phase stainless steel continuous casting slab at high temperature for hot rolling A method of heating a tungsten-containing two-phase stainless steel slab for preventing the occurrence of defects.
우수한 내식성 및 내응력부식균열성을 갖는 2상 스테인레스강은 통상적으로 크롬(Cr)을 약 21 ~ 28 중량%(이하 단지 '%'라 함), 니켈(Ni)을 3 ~ 8%, 몰리브덴(Mo)을 1 ~ 5%, 질소(N)를 0.08 ~ 0.3%, 망간(Mn)을 2% 이하 그리고 탄소(C)를 0.03% 이하로 함유하고 있으며, 물리적 특성을 극대화 시키기 위하여 합금성분을 적절히 조절하여 페라이트상과 오스테나이트상이 약 50 : 50으로 유지되게 제조되어 진다.Two-phase stainless steels with good corrosion resistance and stress corrosion cracking typically have about 21 to 28% by weight of chromium (Cr) (hereinafter referred to simply as '%'), 3 to 8% of nickel (Ni), and molybdenum ( It contains 1 ~ 5% of Mo), 0.08 ~ 0.3% of nitrogen (N), 2% or less of manganese (Mn) and 0.03% or less of carbon (C). By adjusting, the ferrite phase and the austenite phase are maintained at about 50:50.
그리고, 2상 스테인레스강의 내식성을 향상시키기 위해서 크롬, 몰리브덴, 텡스텐(W) 및 질소의 함량을 증가시키는 방법이 있으나, 질소 함량의 증가는 강 중의 질소 용해도가 한정되어 있으며, 크롬, 몰리브덴 및 텅스텐의 증가는 강의 내식성을 저해하는 시그마상과 같은 금속간화합물의 형성을 촉진시키기 때문에 제한을 받는다.And, in order to improve the corrosion resistance of two-phase stainless steel, there is a method of increasing the content of chromium, molybdenum, tungsten (W) and nitrogen, but the increase in nitrogen content is limited in nitrogen solubility in the steel, chromium, molybdenum and tungsten The increase in is limited because it promotes the formation of intermetallic compounds, such as sigma phases, which inhibit the corrosion resistance of the steel.
그리고, 2상 스테인레스강의 내식성을 향상시키기 위한 다른 방법으로는 합금성분 중 몰리브덴의 일부를 중량비로 1 : 2가 되게 텅스텐으로 치환하는 방법이 있으며, 이 경우 시그마상의 석출을 지연시키면서 내식성을 향상시키는 효과가 있어 가장 효율적인 방법이라 할 수 있다.As another method for improving the corrosion resistance of two-phase stainless steel, there is a method of replacing a part of molybdenum in the alloy component with tungsten in a weight ratio of 1: 2, in which case the effect of improving corrosion resistance while delaying sigma phase precipitation This is the most efficient way.
그러나, 2상 스테인레스강에서 내식성을 향상시키기 위하여 합금성분 중 몰리브덴의 일부를 텅스텐으로 대체하여도 고온에서의 변형저항 변화는 거의 없기 때문에, 열간압연시 압연조건의 변화없이 몰리브덴 만 단독으로 함유하고 있는 2상 스테인레스강과 동등한 조건으로 열간압연이 가능하다.However, even if a part of molybdenum is replaced with tungsten to improve corrosion resistance in two-phase stainless steel, there is almost no change in deformation resistance at high temperature. Therefore, only molybdenum alone is contained without change in rolling conditions during hot rolling. Hot rolling is possible under the same conditions as two-phase stainless steel.
그리고, 크롬 함량이 높은 2상 스테인레스강은 몰리브덴 만 함유하고 있을 때에는 표면에 치밀한 산화층을 형성하여 고온산화량이 많지 않기 때문에 압연시 표면 산화층에 의한 윤활 효과가 충분치 못할 뿐만 아니라, 압연롤과의 접촉에 의해 표층부 온도감소 정도가 커 슬라브 압연 초기에 표층부에 집중되는 응력에 의하여 표면결함이 쉽게 발생될 소지가 크다.When the two-phase stainless steel having a high chromium content contains only molybdenum, a dense oxide layer is formed on the surface, so that the high temperature oxidation amount is not large, so that the lubrication effect by the surface oxide layer during rolling is not sufficient, and the contact with the rolling roll is not sufficient. As a result, the temperature decrease of the surface layer portion is large, so that surface defects are easily generated due to the stress concentrated on the surface layer portion at the initial stage of slab rolling.
따라서, 몰리브덴 만 함유하고 있는 2상 스테인레스강을 열간 압연시에는 표층부 온도 감소를 최소화하기 위하여 디스케일링(descaling)을 생략하고 롤 냉각수의 유량을 최소화하여 압연을 행하는 방법을 택하고 있어 대량생산에 제약을 받는다. 반면에, 텅스텐이 첨가된 2상 스테인레스강은 몰리브덴 만 첨가된 강에 비하여 고온 산화량이 최소한 5배 이상으로 많기 때문에 충분한 윤활효과를 얻을 수 있을 뿐만 아니라, 디스케일링(descaling)을 생략하거나 롤 냉각수의 유량을 최소화 해 줄 필요가 없어 매우 유리하다. 그러나, 텅스텐이 함유한 2상 스테인레스강은 가열온도가 높거나, 가열시간이 길어질수록 고온산화량이 급격히 증가하여 입계산화를 유발시키기 때문에 고온 입계산화에 의한 표면결함 발생을 억제할 수 있는 적정 가열조건을 설정할 필요가 있다.Therefore, when hot-rolling two-phase stainless steel containing only molybdenum, in order to minimize the decrease in surface layer temperature, descaling is omitted and rolling is performed by minimizing the flow rate of roll cooling water. Receive. On the other hand, tungsten-added two-phase stainless steels have at least five times more high-temperature oxidation compared to molybdenum-only steels, which not only provides sufficient lubrication, but also eliminates descaling or It is very advantageous because there is no need to minimize the flow rate. However, since tungsten-containing two-phase stainless steel has a high heating temperature or a long heating time, the amount of high temperature oxidation rapidly increases and causes grain boundary oxidation, so that it is possible to suppress surface defects caused by high temperature grain boundary oxidation. It is necessary to set the heating conditions.
그리고, 페라이트상과 오스테나이트상이 혼재되어 있는 2상 스테인레스강에서 압연시 표면결함의 발생 원인은 상간의 고온 유동응력의 차이가 크기 때문이다. 특히, 슬라브 상태에서는 상 계면이 압연방향과 수직으로 존재하는 상 계면이 많아 표면결함이 쉽게 발생되기 때문에, 압연시 표층부의 응력집중에 따른 결함 발생을 억제하기 위해서는 가열조건을 변화시켜 표층부에 충분한 산화층을 형성해 주어야 하며 입계산화 정도를 줄여주어야 한다.In the two-phase stainless steel in which the ferrite phase and the austenite phase are mixed, the cause of surface defects during rolling is due to the large difference in high temperature flow stress between the phases. Particularly, in the slab state, since the phase interface exists in the vertical direction perpendicular to the rolling direction, surface defects are easily generated. Therefore, in order to suppress defects caused by stress concentration at the surface layer part during rolling, an oxide layer sufficient for the surface layer part is changed by changing heating conditions. Should be formed and the degree of grain boundary oxidation should be reduced.
따라서, 본 발명은 텅스텐을 1%이상 함유하는 2상 스테인레스강의 연속주조 슬라브의 열간압연을 위하여 고온에서 가열시 표면에 형성되는 고온산화 정도를 조절하여 입계산화를 최소화함으로써 표면결함 발생을 방지하기 위한 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법을 제공하는 데 그 목적이 있다.Accordingly, the present invention controls the degree of high temperature oxidation formed on the surface when heated at high temperature for hot rolling of continuous casting slabs of two-phase stainless steel containing 1% or more of tungsten to prevent surface defects by minimizing grain boundary oxidation. It is an object of the present invention to provide a heating method of a tungsten-containing two-phase stainless steel slab.
도 1은 본 발명의 실험에 사용된 강들의 화학 조성표(중량비)이고,1 is a chemical composition table (weight ratio) of steels used in the experiment of the present invention,
도 2는 과잉산소 3%의 혼합가스 분위기에서 1230 ~ 1290℃로 가열시 가열시간에 따른 실험강 들의 고온산화 증량를 나타낸 그래프이고,Figure 2 is a graph showing the high-temperature oxidation of the experimental steels according to the heating time when heated to 1230 ~ 1290 ℃ in a mixed gas atmosphere of excess oxygen 3%,
도 3은 과잉산소 3%의 혼합가스 분위기에서 가열온도 1230 ~ 1290℃에서 210분 가열 후 몰리브덴 만 함유한 2상 스테인레스강의 표면 산화층을 보여주는 사진이고,3 is a photograph showing the surface oxide layer of the two-phase stainless steel containing only molybdenum after heating for 210 minutes at a heating temperature of 1230 ~ 1290 ℃ in a mixed gas atmosphere of 3% excess oxygen,
도 4는 과잉산소 3%의 혼합가스 분위기에서 가열온도 1230 ~ 1290℃에서 210분 가열 후 텅스텐을 함유한 2상 스테인레스강의 표면 산화층을 보여주는 사진이고,4 is a photograph showing the surface oxide layer of tungsten-containing two-phase stainless steel after 210 minutes of heating at 1230 ~ 1290 ℃ heating temperature in a mixed gas atmosphere of excess oxygen 3%,
도 5는 과잉산소 4.7%의 혼합가스 분위기에서 1230 ~ 1250℃로 가열시 가열시간에 따른 실험강 들의 고온산화 증량을 나타낸 그래프이고,5 is a graph showing the high-temperature oxidation increase of the experimental steels according to the heating time when heated to 1230 ~ 1250 ℃ in a mixed gas atmosphere of excess oxygen 4.7%,
도 6은 과잉산소 4.7%의 혼합가스 분위기에서 1250℃에서 210분 가열 후 텅스텐을 함유한 2상 스테인레스강의 입계산화 정도를 보이는 사진이며,6 is a photograph showing the degree of grain boundary oxidation of tungsten-containing two-phase stainless steel after heating for 210 minutes at 1250 ° C. in a mixed gas atmosphere of 4.7% excess oxygen.
도 7은 텅스텐을 함유한 강들을 1230 ~ 1290℃의 가열온도구간에서 과잉산소량을 3 ~ 4.7% 변화시켜 210 ~ 300분까지 가열 후 모사압연을 실시하여 표층부 크랙발생의 경향을 관찰한 표이다.FIG. 7 is a table observing the tendency of surface crack generation by performing simulated rolling after heating the steel containing tungsten by changing the amount of excess oxygen by 3 to 4.7% in a heating temperature section of 1230 to 1290 ° C for 210 to 300 minutes.
위와 같은 목적을 달성하기 위한 본 발명에 따르면, 텅스텐을 1%이상 함유하는 2상 스테인레스강 슬라브를 열간압연하기 위해 가열하는 방법에 있어서, 상기 슬라브의 표층부의 결함을 방지하기 위한 최적의 조건은 분위기 가스의 과잉산소량을 3%이하로 하고, 가열온도 1250℃ 이하인 상태에서 240분 이하 동안 가열하는 것이다.According to the present invention for achieving the above object, in the heating method for hot-rolling a two-phase stainless steel slab containing tungsten 1% or more, the optimal conditions for preventing defects in the surface layer portion of the slab is atmosphere The amount of excess oxygen of the gas is 3% or less, and the heating is performed for 240 minutes or less while the heating temperature is 1250 ° C or less.
아래에서, 본 발명에 따른 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법의 양호한 실시예를 첨부한 도면을 참조로 하여 상세히 설명하겠다.Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the heating method of the tungsten-containing two-phase stainless steel slab according to the present invention will be described in detail.
도 1에는 본 발명에서 사용한 강의 화학 조성이 나타나 있다. 통상, 2상 스테인레스강의 열간 압연은 슬라브를 1200℃이상의 고온으로 가열된 가열로에 장입하여 충분히 숙열을 시킨 후 행한다. 따라서, 고온 산화 실험에 있어서, 시편의 가열은 가열로내에서 슬라브 표층부 승온속도를 측정한 결과를 기초하여 과잉산소량 3% 및 4.7%인 혼합가스 분위기 내에서 상온에서 600℃까지는 60℃/min로 10분간 가열하고 이후 균일한 속도로 가열하여 가열온도 1230℃, 1250℃, 1270℃ 및 1290℃까지 전체 승온 소요시간이 120분되게 한 다음 가열온도에서 90분간 유지하는 방법을 사용하고 있다.1 shows the chemical composition of the steel used in the present invention. Usually, hot rolling of two-phase stainless steel is performed after charging a slab to the heating furnace heated at the high temperature of 1200 degreeC or more, and letting it fully warm. Therefore, in the high temperature oxidation experiment, the heating of the specimen was performed at a temperature of 60 ° C./min from 600 ° C. to 600 ° C. in a mixed gas atmosphere of 3% and 4.7% excess oxygen based on the result of measuring the heating rate of the slab surface layer in the furnace. After heating for 10 minutes and then heating at a uniform rate to the heating temperature of 1230 ℃, 1250 ℃, 1270 ℃ and 1290 ℃ total heating time required 120 minutes and then maintained at the heating temperature for 90 minutes.
그리고, 도 2는 과잉산소 3% 분위기에서 각 강들의 가열온도에 따른 산화 증량을 보이고 있다. 도 2에 보이듯이, 몰리브텐 만 함유한 A강 및 J강은 초기산화 후 고온에서 유지시 산화량이 완만히 증가하여 210분 가열 후에도 산화증량이 3 ~ 4㎎/㎠ 수준으로 매우 작으며, 가열온도가 증가하여도 큰 변화를 보이지 않는다. 반면, 텅스텐을 함유한 N강 및 O강은 120분간 가열 후 고온에서 유지시 산화증량이 직선적으로 증가하여 210분 후에는 산화증량이 17㎎/㎠ 이상으로 A강 및 J강의 5배 이상의 산화량을 보이고 있으며, 가열온도가 높을수록 산화량이 급격히 증가하는 경향을 보이고 있다.And, Figure 2 shows the oxidation increase according to the heating temperature of each steel in the atmosphere of 3% excess oxygen. As shown in Fig. 2, A and J steels containing only molybdenum have a moderately increased oxidation amount when maintained at a high temperature after initial oxidation, and thus the oxidation increase is very small, even after 210 minutes of heating, at a level of 3 to 4 mg / cm 2. There is no big change even if the temperature increases. On the other hand, the N and O steels containing tungsten increased linearly after 120 minutes of heating and maintained at high temperature. After 210 minutes, the oxidation increase was 17 mg / cm 2 or more, which was 5 times higher than that of A and J steels. And, the higher the heating temperature is showing a tendency to rapidly increase the amount of oxidation.
도 3은 과잉산소 3% 분위기에서 산화실험 후 A강 및 J강의 표층부에 형성된 산화 스케일의 형상을 보여주는 사진으로, 몰리브덴 만 함유하는 강은 가열시간에 상관없이 표층부에 두께가 10㎛이하로 얇고 매우 치밀한 산화 스케일이 형성됨을보여주고 있다. 이에 반해, 도 4는 과잉산소 3% 분위기에서 산화실험 후 N강 및 O강의 표층부에 형성된 산화 스케일의 형상을 보여주는 사진으로, 텅스텐을 함유한 강의 경우는 표층부에 두께가 25 ~ 50㎛ 수준이며, 매우 취약(brittle)하여 쉽게 제거가 가능한 상태의 산화 스케일이 형성되며, 가열온도가 높을수록 산화층의 두께가 두꺼워지며, 내부의 입계산화의 경향도 심해짐을 알 수 있다.Figure 3 is a photograph showing the shape of the oxidation scale formed on the surface layer of A steel and J steel after the oxidation experiment in the atmosphere of 3% excess oxygen, the steel containing only molybdenum is thin and very thin with a thickness of less than 10㎛ in the surface layer irrespective of the heating time It has been shown that a dense oxidation scale is formed. On the other hand, Figure 4 is a photograph showing the shape of the oxidation scale formed on the surface layer of the N steel and O steel after the oxidation experiment in the atmosphere of 3% excess oxygen, the thickness of the tungsten-containing steel is 25 ~ 50㎛ level, It is very brittle to form an oxidized scale that can be easily removed, and as the heating temperature is higher, the thickness of the oxidized layer becomes thicker, and it can be seen that the tendency of internal grain boundary oxidation is also increased.
도 5는 과잉산소 4.7% 분위기에서 각 강들의 가열온도에 따른 산화 증량을 보이고 있다. 도 5에 보이듯이, 몰리브덴 만 함유한 A강 및 J강은 과잉산소량이 변하여도 큰 차이점을 보이지 않지만, 텅스텐을 함유한 N강 및 O강은 산화량이 급격히 증가하여 210분간 가열 후 상대적으로 저온인 1230℃와 1250℃의 가열온도에서도 산화 증량이 거의 30㎎/㎠ 수준을 보이고 있다.Figure 5 shows the oxidation increase according to the heating temperature of each steel in the atmosphere of excess oxygen 4.7%. As shown in FIG. 5, the A steel and the J steel containing only molybdenum do not show a significant difference even when the excess oxygen is changed, but the N and O steels containing tungsten rapidly increase in oxidation and relatively low temperature after heating for 210 minutes. Oxidation gain was almost 30mg / cm2 even at heating temperature of 1230 ℃ and 1250 ℃.
도 6은 과잉산소 4.7%의 혼합가스 분위기에서 1250℃에서 210분 가열 후 텅스텐을 함유한 2상 스테인레스강 O강의 표층부 사진으로, 입계산화 정도가 매우 심함을 보이고 있다. 따라서, 고온산화량이 큰 텅스텐 함유강은 가열로 분위기내의 과잉산소량 및 가열시간에 매우 민감하며, 고온산화량이 커지면 입계산화의 정도도 매우 커지기 때문에 표면에 결함을 유발할 확률도 높아진다. 따라서, 텡스텐을 함유한 강은 고온산화 증량이 25㎎/㎠이하가 되게 가열온도를 1250℃이하로 하고 분위내의 과잉산소량을 3%이하로 하며, 가열시간을 240분 이하로 하면 윤활 효과를 도모할 수 있는 정도의 표층부 산화층의 두께를 확보할 수 있을 뿐만 아니라 입계산화에 의한 표층부의 결함발생을 억제할 수 있다.6 is a surface photograph of a tungsten-containing two-phase stainless steel O steel after heating at 1250 ° C. for 210 minutes in a mixed gas atmosphere of 4.7% excess oxygen, showing that the degree of grain boundary oxidation is very severe. Therefore, tungsten-containing steel having a large amount of high temperature oxidation is very sensitive to excess oxygen and heating time in a heating atmosphere. As the amount of high temperature oxidation increases, the degree of grain boundary oxidation becomes very large, and thus the probability of causing defects on the surface increases. Therefore, the steel containing tungsten has a heating temperature of 1250 ℃ or less, the excess oxygen content in the atmosphere of 3% or less, and the heating time of 240 minutes or less so that the high temperature oxidation increase is 25 mg / cm 2 or less. Not only can the thickness of the surface layer oxide layer be achieved, but also the occurrence of defects in the surface layer portion due to grain boundary oxidation can be suppressed.
도 7은 텅스텐을 함유한 2상 스테인레스강을 1230 ~ 1290℃의 가열온도구간에서 과잉산소량을 3 ~ 4.7% 변화시켜 210 ~ 300분까지 가열 후 모사압연을 실시하여 표층부 크랙 발생의 경향을 관찰한 것이다. 도 7에서 알 수 있듯이, 과잉산소량을 3%이하로, 가열온도는 1250℃이하로 그리고 가열시간을 240분이하로 해 줌으로써 표층부 결함이 발생되지 않음을 알 수 있다.FIG. 7 shows the tendency of surface crack generation by performing simulated rolling after heating tungsten-containing two-phase stainless steel by changing the excess oxygen amount by 3 to 4.7% at a heating temperature range of 1230 to 1290 ° C for 210 to 300 minutes. will be. As can be seen in Figure 7, it can be seen that the surface layer defects do not occur by setting the excess oxygen amount to 3% or less, the heating temperature to 1250 ° C or less and the heating time to 240 minutes or less.
앞서 상세히 설명한 바와 같이 본 발명의 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법은 과잉산소량을 3%이하로, 가열온도는 1250℃이하로 그리고 가열시간을 240분이하로 하여 고온산화 정도를 조절하여 입계 산화를 최소화함으로써 표면결함 발생을 방지할 수 있다.As described in detail above, the heating method of the tungsten-containing two-phase stainless steel slab according to the present invention regulates the intergranular oxidation by adjusting the degree of high temperature oxidation with the amount of excess oxygen 3% or less, the heating temperature of 1250 ° C or less and the heating time of 240 minutes or less. By minimizing the surface defects can be prevented.
이상에서 본 발명의 텅스텐 함유 2상 스테인레스강 슬라브의 가열방법에 대한 기술사상을 첨부도면과 함께 서술하였지만 이는 본 발명의 가장 양호한 실시예를 예시적으로 설명한 것이지 본 발명을 한정하는 것은 아니다.The technical idea of the method for heating the tungsten-containing two-phase stainless steel slab of the present invention has been described above with the accompanying drawings, but this is by way of example and not by way of limitation.
또한, 이 기술분야의 통상의 지식을 가진 자이면 누구나 본 발명의 기술사상의 범주를 이탈하지 않는 범위내에서 다양한 변형 및 모방이 가능함은 명백한 사실이다.In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.
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| JPH03229839A (en) * | 1990-02-02 | 1991-10-11 | Sumitomo Metal Ind Ltd | Manufacture of duplex stainless steel and its steel material |
| JPH0681037A (en) * | 1992-08-31 | 1994-03-22 | Sumitomo Metal Ind Ltd | Production of hot rolled strip of dual phase stainless steel |
| KR0143481B1 (en) * | 1995-06-05 | 1998-08-17 | 김만제 | The making method and same product of duplex stainless steel plate |
| KR0146784B1 (en) * | 1995-06-01 | 1998-11-02 | 김만제 | Method for heating 2-phase stainless steel slab containing molybdenum and tungsten |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH03229839A (en) * | 1990-02-02 | 1991-10-11 | Sumitomo Metal Ind Ltd | Manufacture of duplex stainless steel and its steel material |
| JPH0681037A (en) * | 1992-08-31 | 1994-03-22 | Sumitomo Metal Ind Ltd | Production of hot rolled strip of dual phase stainless steel |
| KR0146784B1 (en) * | 1995-06-01 | 1998-11-02 | 김만제 | Method for heating 2-phase stainless steel slab containing molybdenum and tungsten |
| KR0143481B1 (en) * | 1995-06-05 | 1998-08-17 | 김만제 | The making method and same product of duplex stainless steel plate |
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