KR100419654B1 - Method for plate rolling dual phase stainless steel - Google Patents
Method for plate rolling dual phase stainless steel Download PDFInfo
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- KR100419654B1 KR100419654B1 KR10-1999-0052408A KR19990052408A KR100419654B1 KR 100419654 B1 KR100419654 B1 KR 100419654B1 KR 19990052408 A KR19990052408 A KR 19990052408A KR 100419654 B1 KR100419654 B1 KR 100419654B1
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- Prior art keywords
- rolling
- stainless steel
- amount
- phase stainless
- cumulative
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- 238000005096 rolling process Methods 0.000 title claims abstract description 150
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 29
- 239000010935 stainless steel Substances 0.000 title claims abstract description 28
- 238000000034 method Methods 0.000 title claims abstract description 17
- 230000009977 dual effect Effects 0.000 title 1
- 230000001186 cumulative effect Effects 0.000 claims abstract description 37
- 238000005098 hot rolling Methods 0.000 claims abstract description 11
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 8
- 239000010959 steel Substances 0.000 claims abstract description 8
- 239000000498 cooling water Substances 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 abstract description 8
- 239000000463 material Substances 0.000 abstract description 6
- 230000007423 decrease Effects 0.000 abstract description 5
- 229910001039 duplex stainless steel Inorganic materials 0.000 abstract 1
- 229910001566 austenite Inorganic materials 0.000 description 18
- 229910000859 α-Fe Inorganic materials 0.000 description 10
- 238000005336 cracking Methods 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 239000012535 impurity Substances 0.000 description 5
- 239000010410 layer Substances 0.000 description 4
- 229910001208 Crucible steel Inorganic materials 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000005501 phase interface Effects 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- -1 and 0.08 N. -0.3% Inorganic materials 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000010405 reoxidation reaction Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 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
- 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
- B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
- B21B27/06—Lubricating, cooling or heating rolls
-
- 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
- B21B37/16—Control of thickness, width, diameter or other transverse dimensions
-
- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- 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
- B21B2265/00—Forming parameters
- B21B2265/14—Reduction rate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2275/00—Mill drive parameters
- B21B2275/02—Speed
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 2상 스테인레스 후강판을 제조하는 방법에 관한 것으로, 그 목적은 압연 도중에 소재의 온도감소에 따른 압연 각 패스간 압연롤 직경, 압연속도 및 압연량에 의하여 결정되어지는 변형속도, 누적압연량 등을 적절히 설정함으로써 표면 균열이 없는 광폭 2상 스테인레스 후판의 열간압연방법을 제공함에 있다.The present invention relates to a method for manufacturing a two-phase stainless thick steel sheet, the object of which is the deformation rate, cumulative rolling is determined by the rolling roll diameter, rolling speed and rolling amount between each pass of the rolling in accordance with the temperature decrease of the material during the rolling By appropriately setting the amount and the like, there is provided a hot rolling method for wide two-phase stainless steel plates without surface cracks.
상기 목적을 달성하기 위한 본 발명은, 2상 스테인레스강 슬라브를 10%이하의 압연량과 3sec-1이하의 변형속도로 첫패스 압연한 다음, 누적압연량의 65%까지 압연변형속도를 5sec-1이하로 하여 폭내기압연과 길이내기 압연하는 것을 포함하여 이루어지는 2상 스테인레스 후강판의 압연방법에 관한 것을 그 기술적요지로 한다.The present invention for achieving the above object, a first-pass rolling, the duplex stainless steel slab to a rolling amount and the deformation rate of 3sec -1 or less in less than 10% 5sec the following, the rolling strain rate up to 65% of the cumulative amount of rolling - The technical gist of the rolling method of the two-phase stainless steel thick steel plate which consists of rolling less than 1 width | variety and length rolling is made into the technical summary.
Description
본 발명은 2상 스테인레스 후강판으로 제조하는 방법에 관한 것으로, 보다 상세하게는 열간 가공성이 상이한 오스테나이트상과 페라이트상이 혼재되어 있는 2상 스테인레스강의 표면 균열 결함을 방지하기 위한 열간압연방법에 관한 것이다.The present invention relates to a method for manufacturing a two-phase stainless thick steel sheet, and more particularly, to a hot rolling method for preventing surface cracking defects of two-phase stainless steel in which austenite and ferrite phases having different hot workability are mixed. .
우수한 내식성 및 내응력 부식균열성을 갖는 2상 스테인레스강은 Cr을 약 21∼28중량%(이하 단지 "%" 라 함), Ni을 3-8%, Mo을 2-5%, N를 0.08-0.3%, Mn을 2%이하, C를 0.03% 이하를 포함하여 조성되는 강으로, 그 물리적 특성을 극대화시키기 위하여 합금성분을 적절히 조절하여 페라이트상과 오스테나이트상이 약 50:50 으로 유지되게 제조된다. 고온에서 페라이트상은 쉽게 변형이 되고 오스테나이트상은 변형이 잘 되지 않아 페라이트와 오스테나이트 상간의 유동응력 차이가 크기 때문에, 압연조건이 적절하지 못하면 압연중 오스테나이트와 페라이트의 상(Phase) 계면에서 크랙이 쉽게 발생되어 표면크랙으로 발전된다. 이러한 경우에는 제품의 표면품질 확보를 위해 표면연마 등의 후처리가 별도로 필요하게 된다. 압연조건이 불량하여 표면균열이 심하게 발생되는 경우는 에지(Edge) 크랙의 발생정도 역시 커지기 때문에 에지부 절단에 따른 실수율의 급격한 감소를 초래한다.Two-phase stainless steels with excellent corrosion and stress corrosion cracking properties are about 21-28 wt% Cr (hereinafter referred to as "%"), 3-8% Ni, 2-5% Mo, and 0.08 N. -0.3%, Mn is less than 2%, C is less than 0.03% of the composition is made of steel, the alloy composition is properly adjusted to maximize the physical properties of the ferrite phase and austenite phase is maintained at about 50:50 do. At high temperatures, the ferrite phase deforms easily and the austenite phase does not deform well, so the difference in flow stress between the ferrite and austenite phase is large. If the rolling conditions are not appropriate, the cracks at the phase interface of the austenitic and ferrite phases during rolling Easily generated and developed into surface cracks. In this case, post-treatment such as surface polishing is required separately to secure the surface quality of the product. If the surface conditions are severely cracked due to poor rolling conditions, the generation of edge cracks also increases, resulting in a sharp decrease in the error rate due to edge cutting.
연속주조된 주편에 존재하는 오스테나이트상은 페라이트상 모재 내부에 위드멘스테턴(Widmanstatten) 형태로 주편 내부에 무질서하게 존재한다. 열간압연시 가해지는 응력은 오스테나이트상의 재결정을 위해 사용되지 못하고 페라이트상 모재의 동적 회복(Dynamic recovery)에 의한 연화(Softening)에 소요되므로, 오스테나이트 상은 압연량이 증가함에 따라 재결정이 이루어지지 않고 압연방향으로 점차정렬되어 페라이트상 모재 내부에 층상 형태로 존재한다. 이렇듯, 열가압연도중 주편내부에 존재하는 오스테나이트상의 형상이 변하게 되므로, 오스테나이트상과 페라이트상의 계면에서 균열이 발생하여 제품의 표면에 크랙(Crack)을 유발하게 되는 문제점이 있다.The austenite phase present in the continuously cast slab is disordered in the cast steel in the form of Widmanstatten in the ferritic base material. Since the stress applied during hot rolling is not used for recrystallization of the austenitic phase and is required for softening by dynamic recovery of the ferritic substrate, the austenitic phase is rolled without recrystallization as the rolling amount increases. It is gradually aligned in the direction and exists in a layered form inside the ferrite matrix. As described above, since the shape of the austenite phase present in the cast steel is changed during the hot rolling, cracks are generated at the interface between the austenite phase and the ferrite phase, thereby causing cracks on the surface of the product.
2상 스테인레스강을 압연시 표면결함을 줄이는 방안으로 상간의 계면 취하를 발생시키는 S, P 등의 불순물 함량을 최소화하는 방법이 최선으로 여겨지고 있으나, 불순물의 함량을 최소화하기 위해서는 정련에 장시간이 소요되므로 상업적 대량 생산을 위한 방법으로는 적합하지 않다.In order to reduce surface defects when rolling two-phase stainless steel, the method of minimizing the impurity content such as S and P, which causes interfacial withdrawal between phases, is considered the best, but it takes a long time to refine the impurities to minimize the content of impurities. It is not suitable as a method for commercial mass production.
본 발명은 2상 스테인레스강 광폭 후판을 제조할때 상간의 열간가공성의 차이에 따른 균열이 발생되는 단점을 해결하기 위하여 연구와 실험을 거듭하여 그 결과에 근거하여 제안하게 된 것으로, 압연 도중에 소재의 온도감소에 따른 압연 각 패스간 압연롤 직경, 압연속도 및 압연량에 의하여 결정되어지는 변형속도, 누적압연량 등을 적절히 설정함으로써 표면 균열이 없는 광폭 2상 스테인레스 후판의 제조방법을 제공하고자 하는데, 그 목적이 있다.The present invention was proposed based on the results of repeated studies and experiments to solve the disadvantage that the crack occurs due to the difference in the hot workability between phases when manufacturing a wide two-phase stainless steel thick plate, To reduce the surface cracks by providing a method of manufacturing a wide two-phase stainless steel plate without surface cracks by appropriately setting the deformation rate, cumulative rolling amount, etc., which are determined by the rolling roll diameter, rolling speed and rolling amount between each pass. The purpose is.
도 1은 누적압연량별 고온연성을 나타내는 그래프1 is a graph showing the high temperature ductility according to the cumulative rolling amount
도 2는 실제압연중에 온도감소와 누적압연량을 고려한 고온연성의 변화를 나타내는 그래프2 is a graph showing the change in high temperature ductility considering the temperature decrease and the cumulative rolling amount during actual rolling;
도 3은 표면균열 발생부의 조직사진3 is a tissue photograph of the surface crack generation portion
도 4는 누적압하율과 변형속도의 관계를 나타내는 그래프4 is a graph showing the relationship between cumulative reduction ratio and strain rate
상기 목적을 달성하기 위한 본 발명의 2상 스테인레스 후강판의 압연방법은,누적압연량 40~65%에서의 압연온도가 1050~1100℃인 2상스테인레스강 슬라브의 열간압연방법에 있어서, 2상 스테인레스강 슬라브를 10%이하의 압연량과 3sec-1이하의 변형속도로 첫패스 압연한 다음, 누적압연량의 65%까지 압연변형속도를 5sec-1이하로 하여 폭내기압연과 길이내기 압연하는 것을 포함하여 구성된다.Rolling method of the two-phase stainless thick steel sheet of the present invention for achieving the above object, in the hot rolling method of the two-phase stainless steel slab having a rolling temperature of 1050 ~ 1100 ℃ in the cumulative rolling amount 40 ~ 65%, two phase First pass rolling of stainless steel slab with rolling amount of less than 10% and strain rate of 3sec -1 or less, then rolling width and length rolling with a rolling strain rate of 5sec -1 or less to 65% of cumulative rolling amount. It is configured to include.
이하, 본 발명을 설명한다.Hereinafter, the present invention will be described.
본 발명은 2상 스테인레스후강판의 압연과정에서 오스테나이트상의 압연방향으로의 정렬상태에 따라 압연량, 롤의 직경, 압연속도 등으로 결정되는 패스간 변형속도를 적절히 설정해주어서 오스테나이트상과 페라이트상의 계면에서 균열을 방지하는데, 그 특징이 있다.In the present invention, the austenite phase and the ferrite phase are appropriately set by setting the deformation rate between passes determined by the rolling amount, the diameter of the roll, the rolling speed, etc. according to the alignment state of the austenitic phase in the rolling process of the two-phase stainless thick steel sheet. It is characterized by preventing cracks at the interface.
2상 스테인레스강의 열간압연시 균열이 발생되는 가장 취약한 부위는 오스테나이트상과 페라이트상의 계면이며, 압연방향과 수직으로 존재하는 계면의 존재 확율이 높으면 쉽게 크랙이 발생되는데, 이 계면은 페라이트상 내부에 존재하는 오스테나이트상의 형상에 의하여 결정된다. 따라서, 본 발명에서는 먼저 열간압연과정에서 오스테나이트상의 압연방향으로의 정렬정도가 증가하여 압연방향 수직으로 존재하는 계면의 존재확율이 작아져서 충분한 열간가공성을 확보할 수 있는 임계 누적 압연량을 설정하는데 촛점을 맞추었다.The most vulnerable site of cracking during hot rolling of two-phase stainless steel is the interface between austenite and ferrite phases, and cracks are easily generated when the probability of existence of the interface perpendicular to the rolling direction is high. It is determined by the shape of the austenite phase present. Therefore, in the present invention, first, in the hot rolling process, the degree of alignment of the austenite phase in the rolling direction is increased, so that the existence probability of the interface existing perpendicular to the rolling direction is reduced, thereby setting a critical cumulative rolling amount that can secure sufficient hot workability. Focused.
일반적으로 주조상태의 2상 스테인레스강 슬라브에는 오스테나이트상이 페라이트상 모재 내부에 위드멘스테턴(Widmanstatten) 형태로 방향성 없이 무질서하게 존재하므로, 압연방향과 수직으로 존재하는 상계면의 존재 확율이 높기 때문에, 근원적으로 크랙 발생 민감도가 매우 커 열간가공성이 나쁘다. 도 1에 나타난 바와 같이, 2상 스테인레스강의 슬라브는 온도가 떨어짐에 따라 열간가공성이 급격히 감소하는 결과를 보이고 있다. 그러나, 압연이 어느 정도 진행된 61% 압연재의 경우는 주조상태보다는 다소 양호한 열간가공성을 보이나 계면이 압연방향으로의 정렬 정도가 충분치 못하여 여전히 열간가공성이 나쁜 상태로 비교적 고온인 1100℃ 까지 열간가공성이 급격히 떨어지는 경향을 보인다. 오스테나이트상이 페라이트상 모재내에 압연방향으로 길게 늘어져 층상으로 존재하는 86% 압연재의 경우는 800∼1100℃ 의 온도구간에서 매우 양호한 열간 가공성을 보이고 있다. 이와 같이, 2상 스테인레스강은 누적압연량의 차이에 따라 열간가공성의 차이가 매우 크며 압연량이 증가함에 따라 열간가공성이 증가하나 압연량 약 63% 부근에서는 열가간공성이 온도변화에 매우 민감함을 잘 알 수 있으며, 충분히 압연된 약 86% 부근에서는 온도변화에 대한 민감도가 작아져 온도가 비교적 낮아도 충분한 열간가공성이 확보됨을 알 수 있다. 즉, 도 1에서 보인 바와같이, 2상 스테인레스강의 열간가공성은 압연량의 정도 및 압연시점의 온도에 따라 차이가 매우 크게 나타나기 때문에 압연조건이 맞지 않으면 오스테나이트상과 페라이트상의 계면에서 쉽게 균열이 발생하게 됨을 알 수 있다.In general, in the two-phase stainless steel slab in the cast state, because the austenite phase is disorderly without orientation in the form of a Widmanstatten in the ferritic base material, the probability of existence of the phase interface existing perpendicular to the rolling direction is high. As a result, cracking sensitivity is very high, resulting in poor hot workability. As shown in Figure 1, the slab of two-phase stainless steel is showing a result that the hot workability is rapidly reduced as the temperature drops. However, in the case of 61% rolled material which has been rolled to some degree, the hot workability is somewhat better than the casting state, but the interface is not sufficiently aligned in the rolling direction, and the hot workability is still high at 1100 ° C. with the hot workability being poor. It tends to fall sharply. The 86% rolled material in which the austenite phase is stretched in the rolling direction in the ferrite-like base material and is present in the form of layers shows very good hot workability at a temperature range of 800 to 1100 ° C. As described above, the two-phase stainless steel has a very large difference in hot workability according to the difference in the cumulative rolling amount, and the hot workability increases as the rolling amount increases, but the hot workability is very sensitive to the temperature change at about 63% of the rolling amount. It can be seen that, in the vicinity of about 86% sufficiently rolled, the sensitivity to temperature change is small, so that even if the temperature is relatively low, sufficient hot workability can be obtained. That is, as shown in Figure 1, the hot workability of the two-phase stainless steel is very different depending on the degree of rolling amount and the temperature of the rolling time, so if the rolling conditions are not matched, cracks easily occur at the interface between the austenitic and ferritic phases. It can be seen that.
상기 도 1의 결과를 토대로 실제 후판 압연시 누적 압연량의 변화를 고려하여 2상 스테인레스강의 온도에 따른 열간 가공성의 변화를 도시하면 도 2와 같다. 도 2에서 알 수 있듯이, 압연을 하기 위하여 슬라브를 고온에서 가열한 직후는 열간가공성이 양호한 상태이나, 압연량이 증가하면서 온도가 떨어지기 때문에 열간가공성이 떨어지다가 약 1050℃ 부근에서 열간가공성이 최소로 나타나고, 다시 점차적으로 열간가공성이 향상됨을 알 수 있다.Based on the result of FIG. 1, the change in hot workability according to the temperature of the two-phase stainless steel in consideration of the change in the cumulative rolling amount during the actual thick plate rolling is as shown in FIG. 2. As can be seen in Figure 2, the hot workability is good immediately after heating the slab at a high temperature for rolling, but since the temperature decreases as the rolling amount increases, the hot workability is lowered and the hot workability is about 1050 ° C. It can be seen that the hot workability is gradually improved.
2상 스테인레스강 후판을 제조하기 위해서는 연속주조된 주편을 약 1200∼1250℃ 로 가열된 가열로에 장입하여 충분히 숙열을 시킨 후 압연을 행한다. 후판 압연은 열연코일 제조와는 달리 비교적 저속 압연이기 때문에 압연중 온도가 떨어지는 정도가 심하며 누적압연량이 약 40∼65% 정도에서의 온도는 통상적으로 약 1050∼1100℃ 이다. 따라서, 2상 스테인레스 후강판의 열간압연에서는 누적압연량이 65%까지는 압연을 매우 신중히 해야함을 알 수 있다. 연속주조 슬라브의 폭은 약 1580mm 정도인데, 이를 폭 약 3500mm 까지로 광폭의 압연판을 제조하기 위해서는 폭내기 압연 후 길이내기 압연을 하게 된다. 최종제품의 폭에 따라 폭내기 압연량이 달라지나, 통상적으로 누적압연량 약 30∼50% 수준에서 폭내기 압연이 마무리되므로, 폭내기 압연 과정이나 폭내기 압연 완료후 길이내기 압연 초기 단계 사이의 압연을 매우 신중히 행하여야 함을 알 수 있다.In order to manufacture a two-phase stainless steel thick plate, continuous cast steel is charged into a heating furnace heated to about 1200 to 1250 ° C., sufficiently heated, and then rolled. Since hot plate rolling is relatively slow rolling unlike hot rolled coil production, the temperature during rolling is severely reduced, and the temperature at a cumulative rolling amount of about 40 to 65% is usually about 1050 to 1100 ° C. Therefore, it can be seen that in the hot rolling of the two-phase stainless thick steel sheet, rolling must be performed very carefully up to 65% of the cumulative rolling amount. The width of the continuous casting slab is about 1580mm, which is about 3,500mm in width to produce a wide rolled plate to the width-roller after the width rolling. Depending on the width of the final product, the rolling width of the width changer varies, but usually, the width reduction rolling is finished at the cumulative rolling amount of about 30 to 50%. It can be seen that this must be done very carefully.
한편, 도 3은 실제로 압연판 표면에 관찰된 크랙 단면을 보여주는 미세조직 사진으로 압연중 발생된 크랙은 압연이 진행되면서 압연방향으로 페라이트와 오스테나이트상(Phase) 계면을 따라 진행됨을 보여주고 있다. 표면크랙의 상층부는 압연 초기 단계의 조직을 보이고 있어, 압연초기의 표면크랙을 방지할 수 있는 압연조건도 중요함을 알 수 있다. 슬라브를 가열한 직후는 고온으로 열간가공성이 매우 양호한 상태이나 압연 롤(Roll)과의 접촉에 의한 표층부의 온도는 급격히 감소하게 된다. 위드멘스테턴(Widmanstatten) 형태로 존재하는 오스테나이트상은 온도가 떨어짐에 따라 열간가공성이 급격히 감소되기 때문에 이를 고려하여 압연조건을 설정하여야 한다. 본 발명에서는 수회의 실험결과를 통하여, 압연 첫 패스의 압연량이 10%를 초과하거나 변형속도가 3sec-1를 초과하는 경우 표면 크랙이 발생되는 것을 확인하였다. 압연 첫패스는 고르기 압연 개념으로 압연량을 10% 이하로, 변형속도는 3sec-1이하로 행함이 바람직하다.On the other hand, Figure 3 is actually a microstructure photograph showing the crack cross section observed on the surface of the rolling plate shows that the cracks generated during the rolling progresses along the ferrite and austenite phase (Phase) interface in the rolling direction. The upper layer part of the surface crack shows the structure of the initial stage of rolling, it can be seen that the rolling conditions that can prevent the surface crack of the initial rolling is also important. Immediately after the slab is heated, the hot workability is very good at high temperatures, but the temperature of the surface layer portion due to contact with the rolling rolls decreases rapidly. The austenite phase in the form of Widmanstatten is rapidly reduced in hot workability as the temperature drops, so the rolling conditions should be set in consideration of this. In the present invention, the results of several experiments, it was confirmed that the surface crack occurs when the rolling amount of the first pass of the rolling exceeds 10% or the strain rate exceeds 3sec -1 . In the first pass of rolling, the rolling amount is preferably 10% or less, and the deformation rate is 3 sec −1 or less.
또한, 본 발명에 따른 실험결과에 따르면, 후판 압연시 폭내기 압연 단계까지의 누적 압연량은 오스테나이트상의 압연방향으로의 정렬정도를 크게 변화시키지 못하며 압연온도 역시 열간가공성이 열위한 구간에 속하게 되므로, 폭내기 압연시 압연 변형속도를 작게 해주어야 하며, 압연변형속도가 5sec-1를 넘지 않음이 바람직하다는 것을 확인하였다. 더우기 폭내기 압연 후에는 길이내기 압연을 하여야 하며 이 경우 압연판의 압연 방향이 90°바뀌기 때문에 상당량의 오스테나이트 상이 압연방향과 직각으로 정렬하게 되어 폭내기 압연 후 길이내기 압연 초기는 크랙 발생 민감도가 매우 큰 상태이므로, 후판 압연시 폭내기 압연후 본격적인 길이내기 압연전 오스테나이트상의 압연방향으로의 정렬정도가 충분할 때까지 계속적으로 변형속도를 낮게 해주어야 한다. 따라서, 최소한 누적 압연량 65% 정도까지는 변형속도가 5sec-1를 넘지 않아야 하며, 바람직하게는 폭내기 압연 후 길이내기 압연시 압연방향과 수직으로 존재하는 계면에 의한 균열발생을 억제하기 위하여 추가적으로 누적 압연량 25% 정도까지는 변형속도가 5sec-1를 넘지 않도록 하면, 열간가공성을 크게 개선할 수 있다.In addition, according to the experimental results according to the present invention, the cumulative rolling amount up to the rolling step during thick plate rolling does not significantly change the degree of alignment in the rolling direction of the austenite phase, so the rolling temperature also belongs to the section for hot workability It should be noted that the rolling strain rate should be made small during rolling, and the rolling strain rate should not exceed 5 sec −1 . In addition, lengthening rolling should be carried out after the rolling process. In this case, since the rolling direction of the rolling plate is changed by 90 °, a considerable amount of austenite phase is aligned at right angles to the rolling direction. Since it is a very large condition, the deformation rate must be continuously lowered until the degree of alignment in the rolling direction of the austenite phase is sufficient before the full length rolling after full width rolling in thick plate rolling. Therefore, the strain rate should not exceed 5sec -1 at least up to 65% of the cumulative rolling amount, and preferably cumulatively to suppress cracking caused by the interface perpendicular to the rolling direction during the lengthening rolling after the widthwise rolling. If the deformation rate is not more than 5 sec −1 up to about 25% of the rolling amount, hot workability can be greatly improved.
나아가, 본 발명에서는 2상 스테인레스강의 S, P의 함량에 따라 탈스케일공정과 압연롤의 냉각수유량을 제어하여 열간가공성이 더욱 개선한다. 2상 스테인레스강에서 S 및 P의 불순물은 계면취하에 영향을 미칠 정도로 많이 포함되면(S: 15ppm이상, P:200ppm이상) 열간가공성이 더욱 악화된다. 이 경우에는 열간압연전후 탈스케일을 생략하여 표면을 얇은 산화스케일(Scale)로 보호하여 압연시 윤활작용 효과를 도모함과 동시에, 냉각수의 유량을 가능한 최소화하여 표면의 온도 저하를 억제하여, 표면 크랙 발생의 억제한다. 압연롤의 냉각수 유량은 기존에 약 4000ℓ/min로 하였는데, 본 발명에서는 냉각수의 유량을 최소화하는 측면에서 3500ℓ/min이하로 한다.Furthermore, the present invention further improves the hot workability by controlling the descaling process and the cooling water flow rate of the rolling roll according to the S and P content of the two-phase stainless steel. In the two-phase stainless steel, when the impurities of S and P are contained in such a way as to affect the interface odor (S: 15 ppm or more, P: 200 ppm or more), the hot workability is further deteriorated. In this case, eliminating the descaling before and after hot rolling protects the surface with a thin scale of scale to achieve lubrication effect during rolling, and minimizes the flow rate of the cooling water to suppress the temperature drop on the surface, resulting in surface cracking. Suppress. The cooling water flow rate of the rolling roll was conventionally about 4000 L / min, but in the present invention, the cooling water flow rate is set to 3500 L / min or less in terms of minimizing the flow rate of the cooling water.
본 발명에 따라 탈스케일을 생략하더라도 2상 스테인레스강에서는 별 다른 문제가 되지 않는다. 통상, 스테인레스강의 압연시 압연롤의 보호를 위하여 초기 압연전후에 고압수를 분사하여 탈스케일(descaling)하고 압연도중에는 압연롤 부위에 냉각수를 다량 분사하게 되어 있다. 그런데, 2상 스테인레스강은 크롬의 함량이 높아 표면에 얇고 치밀한 Cr-Rich 산화층을 형성하여 고온 산화량이 매우 작기 때문에 표층부에 형성되는 산화스케일량이 매우 작을 뿐 아니라 압연중에 생기는 재산화층도 매우 얇다.Even if the descaling is omitted according to the present invention, the two-phase stainless steel is not a problem. In general, in order to protect the rolling rolls during the rolling of stainless steel, high-pressure water is sprayed and descaled before and after the initial rolling, and a large amount of cooling water is sprayed onto the rolling rolls during rolling. However, since the two-phase stainless steel has a high chromium content and forms a thin and dense Cr-Rich oxide layer on the surface, the amount of high-temperature oxidation is very small, so the amount of scale formed on the surface layer is very small and the reoxidation layer formed during rolling is also very thin.
이하, 본 발명을 실시예를 통하여 구체적으로 설명한다.Hereinafter, the present invention will be described in detail through examples.
[실시예]EXAMPLE
두께 150mm의 연속주조 슬라브를 1200~1250℃로 가열하여 누적압연량 40~65%에서의 압연온도가 1050~1100℃로 압연할 때, 누적압연량 40% 까지 폭내기 압연한 후 길이내기 압연을 하여 두께 8∼9mm로 압연하였는데, 이때 각 단계별 압연조건을 표 1에 나타내었고, 누적압연량과 변형속도의 관계를 도 4에 나타내었다. 도 4에서 누적압연량 40~65%에서 압연온도는 1050~1100℃였다.When the continuous casting slab with the thickness of 150mm is heated to 1200 ~ 1250 ℃ and the rolling temperature of 40 ~ 65% of the cumulative rolling is rolled to 1050 ~ 1100 ℃, it is rolled to 40% of the cumulative rolling and then rolled The thickness was rolled to 8 ~ 9mm, the rolling conditions of each step are shown in Table 1, the relationship between the cumulative rolling amount and the deformation rate is shown in FIG. In FIG. 4, the rolling temperature was 1050 to 1100 ° C. at a cumulative rolling amount of 40 to 65%.
표 1에 나타난 바와 같이, 발명예의 경우는 폭내기 압연 후 길이내기 압연시 누적압연량 65% 까지 변형속도를 5sec-1이하를 유지하여 표면에 크랙이 발생하지 않은 양호한 제품을 제조할 수 있었다. 그러나, 상기 발명예와 같이 하더라도 초기 첫 패스에서 압연량이 10% 를 초과하거나, 변형속도가 3sec-1를 넘을 경우 미세크랙이 발생되었다(비교예C).As shown in Table 1, in the case of the invention example, it was possible to manufacture a good product without cracks on the surface by maintaining the strain rate of 5sec -1 or less up to the cumulative rolling amount of 65% in the length rolling after the blasting rolling. However, even in the case of the invention example, when the amount of rolling in the initial first pass exceeded 10% or the strain rate exceeded 3sec -1 , fine cracks were generated (Comparative Example C).
한편, 비교예A의 경우는 폭내기 압연후 누적압연량 57% 까지는 변형속도를 5sec-1이하의 양호한 상태를 유지하였으나, 그후 65% 시점까지에서 변형속도를 8sec-1수준 이상으로 급격히 증가함에 따라 표면에 미세 크랙이 발생되었다.On the other hand, as Comparative Example A, but in good condition the following cumulative rolling amounts to 57% strain rate 5sec -1 until after rolling bet width, then to 65% dramatically increased the strain rate and the time at a high level for the case of 8sec -1 As a result, fine cracks were generated on the surface.
또한, 비교예B의 경우는 폭내기 압연시에는 변형속도가 5/sec 를 초과한 경우로 표면에 대형 크랙이 다량 발생되었다. 따라서, 누적압연량과 변형속도가 2상 스테인레스강의 표면 크랙 발생에 결정적인 영향을 미침은 분명하게 확인할 수 있었다.In Comparative Example B, a large amount of large cracks were generated on the surface when the strain rate exceeded 5 / sec during the baking process. Therefore, it was clearly confirmed that the cumulative rolling amount and the deformation rate had a decisive influence on the surface crack generation of the two-phase stainless steel.
상술한 바와 같이, 본 발명에 따라 압연조건을 제어하여 열간 후판압연하면 S, P등의 불순물의 함량을 낮추기 최대한 낮추기 위한 정련부하 없이도 표면 크랙이 없는 2상 스테인레스강을 제조할 수 있는 유용한 효과가 있는 것이다.As described above, according to the present invention, when controlling the rolling conditions and hot rolling the hot plate, it is useful to produce two-phase stainless steel without surface cracking without refining load to lower the content of impurities such as S and P as much as possible. It is.
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| KR100961353B1 (en) | 2003-08-28 | 2010-06-04 | 주식회사 포스코 | Method for Manufacturing Steel Plate with Different Width |
| KR101356946B1 (en) * | 2012-03-27 | 2014-01-29 | 주식회사 포스코 | Manufacturing method of duplex stainless steel |
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| KR101239560B1 (en) * | 2010-12-28 | 2013-03-05 | 주식회사 포스코 | Duplex stainless steel and method for manufacturing the same with good surface quality |
| KR101239517B1 (en) * | 2010-12-28 | 2013-03-05 | 주식회사 포스코 | Duplex stainless steel and method for manufacturing the same with good surface quality |
| CN113996657B (en) * | 2021-10-18 | 2023-10-24 | 山西太钢不锈钢股份有限公司 | Hot rolling process for preventing edge crack of low-chromium ferrite stainless steel |
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| JPS59179714A (en) * | 1983-03-30 | 1984-10-12 | Sumitomo Metal Ind Ltd | Hot working method of two-phase stainless steel |
| JPH03215625A (en) * | 1990-01-18 | 1991-09-20 | Sumitomo Metal Ind Ltd | Production of superplastic duplex stainless steel and hot working method therefor |
| KR20000045507A (en) * | 1998-12-30 | 2000-07-15 | 이구택 | Method of hot rolling two-phase stainless steel of austenite-ferrite |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59179714A (en) * | 1983-03-30 | 1984-10-12 | Sumitomo Metal Ind Ltd | Hot working method of two-phase stainless steel |
| JPH03215625A (en) * | 1990-01-18 | 1991-09-20 | Sumitomo Metal Ind Ltd | Production of superplastic duplex stainless steel and hot working method therefor |
| KR20000045507A (en) * | 1998-12-30 | 2000-07-15 | 이구택 | Method of hot rolling two-phase stainless steel of austenite-ferrite |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100961353B1 (en) | 2003-08-28 | 2010-06-04 | 주식회사 포스코 | Method for Manufacturing Steel Plate with Different Width |
| KR101356946B1 (en) * | 2012-03-27 | 2014-01-29 | 주식회사 포스코 | Manufacturing method of duplex stainless steel |
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