EP0378705A1 - PROCEDE DE FABRICATION DE TOLES MINCES EN ACIER INOXYDABLE Cr-Ni, DE QUALITE ET FINITION EXCELLENTES - Google Patents

PROCEDE DE FABRICATION DE TOLES MINCES EN ACIER INOXYDABLE Cr-Ni, DE QUALITE ET FINITION EXCELLENTES Download PDF

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Publication number
EP0378705A1
EP0378705A1 EP89908266A EP89908266A EP0378705A1 EP 0378705 A1 EP0378705 A1 EP 0378705A1 EP 89908266 A EP89908266 A EP 89908266A EP 89908266 A EP89908266 A EP 89908266A EP 0378705 A1 EP0378705 A1 EP 0378705A1
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Prior art keywords
cast strip
cooling
temperature
sec
grains
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EP89908266A
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German (de)
English (en)
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EP0378705B2 (fr
EP0378705B1 (fr
EP0378705A4 (en
Inventor
Masanori Nippon Steel Corporation R&D Ueda
Shinichi Nippon Steel Corporation R&D Teraoka
Hidehiko Nippon Steel Corporation Sumitomo
Toshiyuki Nippon Steel Corporation Suehiro
Masayuki Nippon Steel Corporation R&D Abe
Shigeru Nippon Steel Corporation Minamino
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Nippon Steel Corp
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Nippon Steel Corp
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Priority claimed from JP63169095A external-priority patent/JPH0730405B2/ja
Priority claimed from JP22147188A external-priority patent/JPH0730406B2/ja
Priority claimed from JP63221472A external-priority patent/JPH0730407B2/ja
Priority claimed from PCT/JP1989/000692 external-priority patent/WO1990000454A1/fr
Application filed by Nippon Steel Corp filed Critical Nippon Steel Corp
Publication of EP0378705A1 publication Critical patent/EP0378705A1/fr
Publication of EP0378705A4 publication Critical patent/EP0378705A4/en
Publication of EP0378705B1 publication Critical patent/EP0378705B1/fr
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys

Definitions

  • the present invention relates to a process for the production of a Cr-Ni type stainless steel sheet, by which the thickness of a cast strip is made almost the same as the product thickness by a synchronous continuous casting process in which the relative speed of the.cast strip to the inner wall surface of a casting mold is the same.
  • it relates to a process by which the microstructure is made finer from the cast strip stage to form a Cr-Ni type stainless steel sheet having excellent surface properties.
  • a slab having a thickness of more than 100 mm is formed by casting while vibrating a casting mold in the casting direction, the obtained slab is surface-finished, the slab is heated at a temperature higher than 1000°C in a heating furnace, and the slab is hot-rolled by a hot strip mill comprising rows of rough rolling machines and finish rolling machines, to form a hot strip having a thickness of several mm.
  • an object of the present invention is to provide a continuous casting process for the production of a stainless steel cast strip having a thickness of less than 10 mm, in which an excellent cast strip capable of providing a product having excellent surface properties and quality can be prepared.
  • the object of the present invention is to provide a simple process capable of forming a Cr-Ni type stainless steel sheet which does not have an uneven gloss and surface defect called a "roping phenomenon" inherently observed in stainless steel sheets prepared by the thin continuous casting apparatus.
  • the inventors succeeded in preventing the occurrence of roping on the surface of a product by making the austenite ( ⁇ ) grain size of a cast strip finer by controlling the cooling of the strip cast in a high temperature zone (zone of temperature is higher than 1100°C) and preventing the occurrence of an uneven gloss by controlling the cooling in a low temperature zone (zone of temperatures of 900 to 550°C).
  • the inventors engaged in further research and found that, if the above-mentioned 7 grain size is kept below 50 p m, a high degree of a prevention of roping can be attained and developed rapid cooling methods for a high-temperature cast strip, cold-rolling methods, and hot rolling methods as the means for the above-mentioned adjustment of the 7 grain size.
  • the present invention was completed based on the foregoing findings.
  • a molten steel comprising SUS 304 steel as the main component was cast by a twin-roll (twin-drum) continuous casting machine of the internal water-cooling type to form a cast strip having a thickness of 2 to 4 mm, and the cast strip was cooled and wound.
  • the obtained cast strip (thin band) was subjected to descaling, directly cold-rolled, finally annealed, and pickled to obtain a 2B product.
  • the surface properties of the obtained product were examined and compared with those of a conventional product obtained by heating a slab having a thickness larger than 100 mm, hot-rolling the ingot by a hot strip mill, and cold-rolling the hot-rolled strip.
  • the inventors examined the cause of this problem of the surface properties of the product in detail and, as a result found that, where the ⁇ grain size of the cast strip before cold-rolling is larger or cooling in the Cr carbide-precipitating temperature range is insufficient, the above-mentioned surface defects become prominent.
  • the composition of the molten steel comprises 0.01 to 0.08% of C, 0.25 to 1.50% of Si, 0.15 to 3.0% of Mn, 0.015 to 0.040% of P, 0.001 to 0.008% of S, 16.0 to 28.0% of Cr, 6.0 to 24.0% of Ni, 0.015 to 0.33% of N, 0.001 to 0.050% of Al, 0.01 to 3.0% of Mo, 0.01 to 2.0% of Cu, 0.01 to 0.60% of Ti, and 0.01 to 0.80% of Nb, with the balance being Fe and unavoidable impurities.
  • a molten steel having the above-mentioned composition is cast into a strip, that is, a cast strip having a thickness smaller than 10 mm, at a cooling speed of at least 100°C/sec by a twin-roll or single-roll continuous casting machine. If the thickness of the cast strip exceeds 10 mm, it becomes difficult to make the 7 grains finer, and becomes difficult to obtain the product by a direct cold-rolling.
  • a method is adopted in which cooling of the cast strip is initiated at a temperature as high as possible just below the casting machine, to prevent reheating of the cast strip at the outlet of the continuous casting machine, and cooling is effected to 1100°C while maintaining the cooling rate in the ⁇ grain-growing temperature range at a level of at least 100°C/sec and as high as possible, whereby the grain growth of 7 is inhibited.
  • the phase is crystallized at a temperature higher than 1450°C, just below the liquidus, and the ⁇ phase then grows.
  • Creq increases and is 19.5% or higher
  • solidification of the primary crystal is completed in the 5 phase, and precipitation of the ⁇ phase begins at about 1370°C as the result of solid phase reaction, and the 7 phase then grows.
  • the grain growth of ⁇ is greatly controlled, compared with the above-mentioned case where Creq is small. This can be understood from the fact that the grain growth of ⁇ is influenced by the high temperature range just after solidification.
  • Creq is an intermediate value
  • a peritectic reaction is added and the system becomes complicated, but in this case, a composition causing 6 solidification is advantageous to depress the grain growth of 7 .
  • the combination of selection of the composition retarding initiation of precipitation of ⁇ grains by utilizing 6 solidification and rapid cooling in the high temperature range is especially effective for controlling the grain growth of and making ⁇ grains finer.
  • Figures 2(a), 2(b), and 2(c) are metallographic microscope photos of microstructure of cast strip obtained by casting compositions differing in ⁇ -Fe.cal (%) into 2-mm cast strip and cooling them.
  • ⁇ -Fe.cal (%) is -2.3%
  • ⁇ solidification is caused and grains grow.
  • ⁇ -Fe.cal (%) is -1.1%
  • ⁇ ferrite is left and the size of ⁇ grains is reduced.
  • ⁇ -Fe.cal (%) is 3.0%, ⁇ solidification is apparently caused and the size of ⁇ grains is kept small. If ⁇ -Fe.cal (%) is larger, both of the sizes of ⁇ grains and 5 grains are kept small.
  • the combination of the above-mentioned cooling of the cast strip and selection of the composition in the Cr-Ni system has large influences on the reduction of the size of 7 grains, and it is very important to control ⁇ -Fe.cal (%) from -2 to 10%. Even if ⁇ -Fe.cal (%) exceeds 10%, the above-mentioned effect becomes saturated, and the 6 phase is left in the product and bad influences are imposed on the product quality.
  • the cast strip must be cooled in the temperature range of 900 to 550°C at an average cooling rate of at least 50°C/sec and the cast strip wound at a temperature lower than 650°C. If this requirement is not satisfied, carbides are precipitated in the grain boundary of the cast strip and intergranular corrosion is caused at the process of pickling the cast strip, resulting in degradation of the gloss of the final product.
  • the above-mentioned basic technique is very effective for making 7 grain finer, and to reduce the average grain size of 7 grains below 50 ⁇ n, an addition of the following means is especially effective.
  • the cooling in order to reduce the size of ⁇ grains of the cast strip by the twin-roll or single-roll continuous casting, the cooling must be started at a high temperature.
  • a method is advantageously adopted in which a roll of the internal cooling type is used and roll cooling is carried out at a certain reduction for example, a reduction lower than 5%.
  • a pair or a plurality of pairs of rolls for the roll cooling, it is possible to perform the cooling effectively while preventing reheating, and the cooling can be effected to 1200°C at an average cooling speed of at least 200°C/sec.
  • uniform cooling can be effectively accomplished by the combination of this roll cooling with gas cooling under a high pressure with air or nitrogen or mist cooling using a small amount of a liquid incorporated in such as gas.
  • these cooling methods can be adopted singly.
  • the as-cast strip is subjected to hot-processing to advance recrystallization and reduce the size of 7 grains.
  • the cast strip is rapidly cooled from the high-temperature range just below the casting machine to depress the grain growth of ⁇ in the cast strip, and then, hot-rolling is carried out to obtain finer 7 grains.
  • Figure 4 shows the temperature history of the cast strip formed by continuously casting a molten steel by the twin-roll method and winding the cast strip.
  • the cast strip is cast and is then air-cooled.
  • the cast strip is rapidly cooled by a casting drum in a casting machine, the cast strip is reheated after the outlet of the casing machine, and therefore, cooling is slower than in the case where cooling is started just below the drum and if the cast strip is directly wound, the grain growth offis advanced during cooling after winding, with the result that problems concerning the surface properties, such as roping, sensitization by precipitation of Cr carbide, and uneven gloss arise.
  • hot-rolling is carried out after casting to cause recrystallization in the cast strip and make 7 grains finer, and after hot-rolling, sensitization by precipitation of Cr carbide is prevented by rapid cooling.
  • Figure 5 illustrates influences of the reduction on the roping height in the cold-rolled sheet, observed when a cooled cast strip having 6-Fe.cal (%) adjusted to about 1% is hot-rolled at 1100°C.
  • the average grain size of the 7 grains is reduced below 50 ⁇ n.
  • Hot-rolling is carried out in the region where the surface temperature of the cast strip is higher than 900°C, and recrystallization in the center of the cast strip is promoted by this hot-rolling. Especially, it is sufficient if the cast strip is subjected to hot-rolling at a reduction of up to 60% while the interior of the cast strip is still in the high-temperature region (within 10 seconds after the casting). If the reduction exceeds 60%, the effect is saturated. If hot-rolling is started after the elapse of more than 10 seconds from the point of termination of the casting, the temperature difference between the surface layer portion of the cast strip and the interior of the cast strip becomes small and the effect of making 7 grains finer is reduced.
  • Annealing of the hot-rolled sheet is carried out at a temperature higher than 950°C to advance recrystallization. Especially, annealing is conducted while controlling the temperature and time so that the average grain size of 7 does not exceed 50 ⁇ n.
  • the amount of 6-Fe is reduced as compared with the amount of 6-Fe at the stage of the cast strip, and precipitation of Cr carbide in the ⁇ / ⁇ interface is delayed and hence, it is permissible to adopt a lower cooling rate than the cooling rate adopted for cooling the cast strip or hot-rolled sheet. Accordingly, the cooling rate after annealing is adjusted to at least 10°C/sec in the Cr carbide-precipitating region.
  • cooling of the cast strip obtained by the above-mentioned continuous casting machine of the twin-roll type is started just below the casting machine at a temperature as high as possible, and cooling to 1100°C is conducted at a cooling rate of at least 100°C/sec to inhibit the grain growth of 7 . Then, cooling is conducted at a cooling rate of at least 50°C/sec in the temperature range of 900 to 550°C and the cast strip is wound in the region of temperature s lower than 650°C.
  • the obtained cast strip is subjected to preliminary cold-working such as cold-rolling, and then subjected to high-temperature short-time annealing to effect recrystallization in the cast strip.
  • Cast strips were subjected to preliminary cold rolling and then to short-time annealing at 1080°C, and cold-rolling (main cold-rolling) to the final sheet thickness was carried out.
  • the relationship between the reduction and the roping height in the product is shown in Fig. 6, relative to the reduction at the preliminary cold-rolling.
  • ⁇ -Fe.cal (%) in the composition of the cast strip is adjusted from -2 to 10%, 7 grains can easily be made finer cojointly with cooling in the high-temperature region.
  • the compositions of the stainless steels were as shown in Table 1, and ⁇ -Fe.cal (%) was changed in the range of from -3.6 to 7.8%.
  • cooling methods for blowing high-pressure nitrogen gas was disposed, and cooling methods including a roll of the internal cooling type.was,subsequently arranged.
  • the cast strips were cooled while preventing reheating.
  • mist cooling methods was arranged after the roll-cooling methods.
  • The.average cooling rate to 1200°C. was adjusted to 400 to 220°C/sec according to the thickness of the cast strip, that is, the casting rate.
  • water cooling was carried out in the temperature region of 900 to 550°C at a cooling rate of at least 50°C/sec, followed by winding.
  • the cast strips were hot-rolled in the temperature region of 1100 to 950°C within 8 seconds from the point of termination of casting.
  • the reduction at this hot-rolling was in the range of from about 10% to about 60% (Table 4).
  • the cast strips were cooled at a cooling rate of at least 60°C/sec in the temperature region of 900 to 550°C and the cast strips were wound at a temperature lower than 600°C.
  • the cast strips were subjected to pickling, descaling, cold-rolling, and ordinary annealing or bright annealing.
  • the compositions of the steels were as shown in Table 5. Air cooling and spray cooling were carried out just below the outlet of the twin-drum casting machine. Cooling to 1100°C was conducted at an average cooling rate of at least 100°C/sec, and water cooling was conducted in the temperature region of 900 to 550°C at an average cooling rate of at least 70°C/sec. Winding was then carried out at temperatures of 650 to 600°C.
  • the cast strips were descaled by mechanical descaling and pickling and were preliminarily rolled by cold-rolling. Both the cast strips having a thickness of 3 mm and the cast strips having a thickness of 4.5 mm were preliminarily cold-rolled at a reduction of 10 to 40%, annealed for less than 20 seconds at a temperature higher than 1000°C, and rapidly cooled. Thus, the cast strips were recrystallized and the grain size of was controlled below 50 ⁇ m.
  • the cast strips were subjected to the main drawing at a reduction of 30, 50, 80, or 95% or a reduction higher than 95%, and final annealing was carried out according to customary procedures to obtain 2B and BA products. As shown in Table 6, these products were excellent in surface properties and mechanical properties.
  • molten steels having the same compositions as described above were cast according to the twin-drum method, and cooling to 1100°C was carried out at a cooling rate lower than 100°C/sec and cooling to 550°C was carried out at a cooling rate of 70°C/sec.
  • the cast strips were wound at a temperature of 650 to 600°C, descaled, and cold-rolled to obtain products. If the reduction at the cold-rolling was increased, the surface properties were improved, but fine roping was left on the surface and the effect of preventing roping was insufficient.
  • the present invention has the above-mentioned structure and exerts the above-mentioned function, a simple process in which a thin band having a thickness close to the product thickness can be directly obtained by continuous casting can be provided, and a Cr-Ni type stainless steel sheet having excellent surface property and material quality can be obtained.

Abstract

Procédé de fabrication d'une pièce coulée mince sous forme d'une tôle d'acier inoxydable Cr-Ni ayant sensiblement la même épaisseur que celle d'un produit final, par coulage en continu synchronisé, procédé comprenant: la trempe à haute température de la pièce immédiatement après coulage, la transformation à chaud ou à froid de ladite pièce, le recuit, etc. destinés à réduire la taille des grains gamma et le refroidissement à une température plus basse, égale ou inférieure à 900°C, afin d'empêcher la précipitation de carbure de chrome à la limite des grains. Ce procédé permet de réduire la tendance au vrillage ou l'irrégularité du brillant sur la surface de la tôle en acier inoxydable.
EP89908266A 1988-07-08 1989-07-10 PROCEDE DE FABRICATION DE TOLES MINCES EN ACIER INOXYDABLE Cr-Ni, DE QUALITE ET FINITION EXCELLENTES Expired - Lifetime EP0378705B2 (fr)

Applications Claiming Priority (12)

Application Number Priority Date Filing Date Title
JP169095/88 1988-07-08
JP63169095A JPH0730405B2 (ja) 1988-07-08 1988-07-08 表面品質が優れたＣｒ―Ｎｉ系ステンレス鋼薄板の製造方法
JP16909688 1988-07-08
JP16909488 1988-07-08
JP16909588 1988-07-08
JP221471/88 1988-09-06
JP221472/88 1988-09-06
JP22147288 1988-09-06
JP22147188 1988-09-06
JP63221472A JPH0730407B2 (ja) 1988-07-08 1988-09-06 表面品質が優れたＣｒ―Ｎｉ系ステンレス鋼薄板の製造方法
JP22147188A JPH0730406B2 (ja) 1988-07-08 1988-09-06 表面品質と材質が優れたＣｒ−Ｎｉ系ステンレス薄鋼板の製造法
PCT/JP1989/000692 WO1990000454A1 (fr) 1988-07-08 1989-07-10 PROCEDE DE FABRICATION DE TOLES MINCES EN ACIER INOXYDABLE Cr-Ni, DE QUALITE ET FINITION EXCELLENTES

Publications (4)

Publication Number Publication Date
EP0378705A1 true EP0378705A1 (fr) 1990-07-25
EP0378705A4 EP0378705A4 (en) 1991-09-04
EP0378705B1 EP0378705B1 (fr) 1996-01-31
EP0378705B2 EP0378705B2 (fr) 1999-09-15

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EP89908266A Expired - Lifetime EP0378705B2 (fr) 1988-07-08 1989-07-10 PROCEDE DE FABRICATION DE TOLES MINCES EN ACIER INOXYDABLE Cr-Ni, DE QUALITE ET FINITION EXCELLENTES

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0530675A3 (en) * 1991-08-28 1996-04-24 Nippon Steel Corp Process for producing thin sheet of cr-ni-baced stainless steel having excellent surface quality and workability
EP0679114B2 (fr) † 1993-11-18 2004-11-03 Castrip, LLC Coulee d'une bande d'acier inoxydable sur une surface a rugosite predeterminee

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0463182B2 (fr) * 1990-01-17 2001-08-22 Nippon Steel Corporation PROCEDE POUR FABRIQUER DE LA TOLE EN ACIER INOXYDABLE Cr-Ni PRESENTANT UNE EXCELLENTE QUALITE DE SURFACE, ET MATERIAU AINSI OBTENU
JPH082484B2 (ja) * 1990-10-19 1996-01-17 新日本製鐵株式会社 表面品質の優れたオーステナイト系ステンレス鋼薄帯状鋳片、薄板の製造方法および薄帯状鋳片
IT1294228B1 (it) * 1997-08-01 1999-03-24 Acciai Speciali Terni Spa Procedimento per la produzione di nastri di acciaio inossidabile austenitico, nastri di acciaio inossidabile austenitico cosi'

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57155322A (en) * 1981-03-18 1982-09-25 Nippon Steel Corp Treatment of continuous cast strip of austenite-based stainless steel
JPS62124220A (ja) * 1985-07-17 1987-06-05 Nippon Steel Corp ステンレス厚鋼板の製造方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57155322A (en) * 1981-03-18 1982-09-25 Nippon Steel Corp Treatment of continuous cast strip of austenite-based stainless steel
JPS62124220A (ja) * 1985-07-17 1987-06-05 Nippon Steel Corp ステンレス厚鋼板の製造方法

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, vol. 11, no. 353 (C-457)[2800], 18th November 1987; & JP-A-62 124 220 (NIPPON STEEL) 05-07-1987 *
PATENT ABSTRACTS OF JAPAN, vol. 6, no. 261 (C-141)[1139], 21st December 1982; & JP-A-57 155 322 (SHIN NIPPON SEITETSU) 25-09-1982 *
See also references of WO9000454A1 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0530675A3 (en) * 1991-08-28 1996-04-24 Nippon Steel Corp Process for producing thin sheet of cr-ni-baced stainless steel having excellent surface quality and workability
EP0679114B2 (fr) † 1993-11-18 2004-11-03 Castrip, LLC Coulee d'une bande d'acier inoxydable sur une surface a rugosite predeterminee

Also Published As

Publication number Publication date
EP0378705B2 (fr) 1999-09-15
EP0378705B1 (fr) 1996-01-31
EP0378705A4 (en) 1991-09-04

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