EP0481481B1 - Process for production of austenitic stainless steel thin cast strip and strip obtained thereby - Google Patents

Process for production of austenitic stainless steel thin cast strip and strip obtained thereby Download PDF

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Publication number
EP0481481B1
EP0481481B1 EP91117741A EP91117741A EP0481481B1 EP 0481481 B1 EP0481481 B1 EP 0481481B1 EP 91117741 A EP91117741 A EP 91117741A EP 91117741 A EP91117741 A EP 91117741A EP 0481481 B1 EP0481481 B1 EP 0481481B1
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EP
European Patent Office
Prior art keywords
cast strip
thin cast
strip
solidification structure
stainless steel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP91117741A
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German (de)
English (en)
French (fr)
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EP0481481A1 (en
Inventor
Toshiyuki C/O Nippon Steel Corporation Suehiro
Masanori C/O Nippon Steel Corporation Ueda
Isao C/O Nippon Steel Corporation Suichi
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Nippon Steel Corp
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Nippon Steel Corp
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Publication of EP0481481A1 publication Critical patent/EP0481481A1/en
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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
    • B22D11/0637—Accessories therefor
    • B22D11/0648—Casting surfaces
    • B22D11/0651—Casting wheels
    • 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 thin cast strip having a thickness close to the thickness of a product by a synchronous continuous casting process wherein there is no difference in the relative speed of the thin cast strip and the inner wall surface of a casting mold, a process for the production of this thin cast strip, and a process for the production of an austenitic stainless steel strip and sheet by cold rolling this thin cast strip.
  • a cast slab having a thickness larger than 100 mm is formed by casting while shaking a casting mold in the casting direction, the surface of the formed cast slab is finished, the cast slab is heated at a temperature higher than 1000°C in a heating furnace, and hot-rolled by a hot strip mill comprising rows of rough mills and finish mills to form a hot strip having a thickness of several millimeters, and according to need, the thin cast strip is then annealed, descaled, cold-rolled and subjected to a final annealing.
  • a process for preparing a thin cast strip having a thickness equal or substantially equal to the thickness of a hot strip, by the continuous casting process has recently been investigated.
  • a twin-roll method, a twin-belt method and other synchronous continuous casting processes wherein there is no difference in the relative speed of a thin cast strip and the inner wall surface of a casting mold as introduced in lectures given in the Special Edition, Iron and Steel, ′85-A197-′85-A-256.
  • This process for the continuous production of thin cast strip is different from the conventional process for producing slabs by continuous casting equipment in that a formation of a thin cast strip having a high-grade surface is intended even if the reduction of cold rolling at subsequent steps is lowered. Accordingly, if surface cracking appears in a thin cast strip, surface defects appear in the product, resulting in drastic reduction of the commercial value thereof, and thus the intended object cannot be attained.
  • the formation of surface defects such as surface cracks can be prevented if casting is carried out in the presence of dimples formed on the circumferential face of the cooling drum, as a rapidly cooled area and a slowly cooled area are formed on the surface of the thin cast strip by an air gap generated by the dimples, with the result that, the residual amount of ⁇ -ferrite in these areas is made different and a solidification structure unevenness occurs on the surface of the thin cast strip.
  • This solidification structure unevenness becomes obvious as a gloss unevenness on the surface of cold rolled strip and sheet product.
  • the present invention specifies chemical compositions of stainless steel and conditions of dimples arranged on the surface of the cooling drum for attaining the above-mentioned object.
  • the present invention is characterized in that ⁇ - Fe cal. (%) defined by 3(Cr + 1.5Si + Mo) - 2.8(Ni + 0.5Mn + 0.5Cu) - 84(C + N) - 19.8 is controlled to 5 to 9%, and a melted steel having a high ⁇ -ferrite steel composition readily giving a primary ⁇ -ferrite solidification structure is continuously cast by a cooling drum, many dimples having diameter of 0.1 to 1.2 mm and a depth of 50 to 100 »m and having a circular or ellipsoidal opening being distributed on the cooling drum so that the distance between every two adjacent dimple edges is smaller than 0.35 mm , while controlling the initial solidification cooling rate to a uniformly slow speed.
  • a ⁇ -ferrite solidification structure having no solidification structure unevenness can be imparted to the surface portion of the thin cast strip, and even if a strip and sheet product is prepared by cold-rolling the obtained thin cast strip, no gloss unevenness occurs on the surface of the product, and thus the quality of the product can be improved.
  • This solidification structure unevenness is brought about because the ⁇ -ferrite content is high in the slowly cooled area and is low in the rapidly cooled area, as shown in Fig. 1. If the thin cast strip having this solidification structure unevenness is cold-rolled and subjected to final annealing, the growth of recrystallization grains is inhibited in the area having a high ⁇ -ferrite content to form a fine grain structure while recrystallization grains grow in the area having a low ⁇ -ferrite content to form a relatively coarse structure, whereby the grain size becomes uneven and this results in the appearance of a gloss unevenness on the surface of a product.
  • Fig. 2 is a sectional diagram of the portion corresponding to Cr eq. +Ni eq. ⁇ 30% in the Fe-Cr- Ni ternary equilibrium phase diagram, which is quoted from Transaction of JWRI, vol. 14, No. 1, 1985, page 125.
  • the region of small Cr eq. is a region of complete ⁇ solidification structure (zone I), but it is expected that as the Cr eq. increases, the solidification state will be changed to a primary ⁇ ⁇ ⁇ + ⁇ solidification structure (zone I) or primary ⁇ ⁇ ⁇ + ⁇ solidification structure (zone III), or to a complete ⁇ solidification structure (zone IV).
  • the area (zone I) where [ ⁇ - Fe cal. (%)] is - 2.3% is the area of complete ⁇ solidification structure, and unevenness of the solidification structure due to the ⁇ -ferrite content is not observed.
  • the area (zone II) where [ ⁇ ⁇ Fe cal. (%)] is 2.3% is the area of primary ⁇ ⁇ ⁇ + ⁇ solidification structure, and remaining ⁇ -ferrite amount state is apparently different at the slowly cooled portion and at the rapidly cooled portion due to the presence of dimples, and the solidification structure unevenness is conspicuous.
  • Many circular or ellipsoidal dimples are formed on the surface of the cooling drum used in the present invention.
  • the dimples form independent air gaps not interconnected to one another.
  • a slowly cooled portion is formed by these air gaps and a portion contiguous to the surface of the cooling drum is rapidly cooled, the ⁇ -ferrite content is reduced in the rapidly cooled portion below the ⁇ -ferrite content in the slowly cooled portion, with the result that a solidification structure unevenness occurs due to the difference of the ⁇ -ferrite content of these portions.
  • Figure 4 illustrates the relationship between the distance between the edges of every two adjacent dimples on the surface of the cooling drum and the solidification structure. From Fig. 4 it is understood that, if the distance between the edges is smaller than 0.35 mm, the solidification structure observed in the shell solidificated contiguously to the face between the edges is an ordinary ( ⁇ + ⁇ ) solidification structure where the ⁇ -ferrite content is uniform, but if the distance between the dimple edges is larger than 0.35 mm, not only an ordinary ( ⁇ + ⁇ ) solidification structure but also a solidification structure where the ⁇ -ferrite content is low (“ ⁇ "-solidification structure) is observed. The reason for this is considered to be as follows.
  • the diameter of the opening of the dimple is smaller than 0.1 mm, the gradual cooling effect by the air gap is small, and the dimple-forming operation and brush cleaning operation of removing dust or the like are difficult. If the diameter of the opening of the dimple exceeds 1.2 mm, a fine crack often grows from the dimple.
  • the depth of the dimple is smaller than 50 »m, the gradual cooling effect by the cooling drum as a whole is insufficient, and if the dimple depth exceeds 100 »m, the convex dimple transferred onto the thin cast strip has a large height, and therefore, grinding by a coil grinder or other treatment becomes necessary before the cold rolling, and thus the productivity is reduced.
  • the ratio of the projection height of the convex dimple transferred onto the thin cast strip to the depth of the dimple is 80 to 100%.
  • the surface projection of the thin cast strip of the present invention has a circular or ellipsoidal shape, a diameter of 1.0 to 1.2 mm, and a height of 40 to 100 »m. A great number of such projections are distributed while the minimum distance is maintained smaller than 0.35 mm between every two adjacent projection edges.
  • the surface of the obtained cast strip is subjected to ordinary descaling, and the cast strip is cold-rolled at rolling reduction of 50 to 85% and annealed at 1050 to 1200°C for 0.5 to 2 minutes and is then cooled and subjected to pickling.
  • a thin cast strip in which an occurrence of solidification structure unevenness, as shown in Fig. 1, is controlled is prepared, whereby a gloss unevenness can be prevented in a strip and sheet product after cold rolling.
  • Thin cast strips were formed by casting various melted stainless steels differing in ⁇ -Fe cal. (%) by a twin-drum continuous casting machine comprising a cooling drum having dimples arranged uniformly or randomly on the surface thereof.
  • the surface of each thin cast strip was polished to a thickness of about 100 »m, and the solidification structure was manifested by electrolytic etching with nitric acid to examine the solidification structure unevenness.
  • the thin cast strip was descaled, cold-rolled at a thickness reduction ratio of 50 to 90% and annealed at 1050 to 1200°C. Then the cold-rolled sheet was subjected to a salt treatment and pickled with a nitric fluoric mixed acid, and the occurrence of gloss unevenness on the surface of the finished sheet was observed. Then the obtained sheet was formed into a cylinder having a diameter of 32 mm from a disc having a diameter of 80 mm (the draw ratio was 2.5), and after 48 hours, the occurrence of delayed cracking was checked. The results are shown
  • the solidification structure of the thin cast strip prepared according to the process of the present invention had no unevenness, and the cold rolled sheet prepared form this thin cast strip had no gloss unevenness and had a good quality.
  • the ⁇ -ferrite content was appropriate, because the dimple distance was too wide, the solidification structure unevenness and the gloss unevenness of cold rolled sheet occurred.
  • comparative runs 9 and 10 since the ⁇ -ferrite content was not correct, the solidification structure unevenness and gloss unevenness occurred.
  • the product obtained in comparative run 11 had a controlled solidification structure unevenness and gloss unevenness of cold rolled sheet, but since the ⁇ -Fe cal. content was higher than 9%, delayed cracking occurred.
  • Figure 6(a) shows an appearance and microstructure of the thin cast strip of run 4 of the present invention and the cold rolled sheet thereof. It is seen that no unevenness occurred.
  • Figure 6(b) shows the solidification structure unevenness of the thin cast strip obtained in comparative run 9, and it is seen that the unevenness of the thin cast strip depended on the difference of content of ⁇ -ferrite, and that gloss unevenness of cold rolled sheet occurred due to the difference of the size of recrystallization grains.
  • the growth of recrystallization grains in the cold rolled sheet is controlled by the difference of ⁇ -ferrite content after the casting, and therefore, the difference in the grain size resulting in an occurrence of gloss unevenness.
  • the present invention since there is no difference in the ⁇ -ferrite content after the casting, no gloss unevenness occurred in the cold rolled sheet.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Continuous Casting (AREA)
  • Heat Treatment Of Articles (AREA)
EP91117741A 1990-10-19 1991-10-17 Process for production of austenitic stainless steel thin cast strip and strip obtained thereby Expired - Lifetime EP0481481B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP279097/90 1990-10-19
JP2279097A JPH082484B2 (ja) 1990-10-19 1990-10-19 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

Publications (2)

Publication Number Publication Date
EP0481481A1 EP0481481A1 (en) 1992-04-22
EP0481481B1 true EP0481481B1 (en) 1994-06-08

Family

ID=17606374

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91117741A Expired - Lifetime EP0481481B1 (en) 1990-10-19 1991-10-17 Process for production of austenitic stainless steel thin cast strip and strip obtained thereby

Country Status (5)

Country Link
EP (1) EP0481481B1 (ko)
JP (1) JPH082484B2 (ko)
KR (1) KR950014485B1 (ko)
DE (1) DE69102388T2 (ko)
ES (1) ES2056553T3 (ko)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0679114B2 (en) * 1993-11-18 2004-11-03 Castrip, LLC Casting stainless steel strip on surface with specified roughness
BR9307904A (pt) * 1993-12-01 1996-08-27 Siemens Ag Instalação de laminação de fundição para fitas de aco e sistema de regulagem
US6044895A (en) * 1993-12-21 2000-04-04 Siemens Aktiengesellschaft Continuous casting and rolling system including control system
FR2726209B1 (fr) * 1994-10-31 1996-11-29 Usinor Sacilor Surface de coulee d'une lingotiere de coulee continue des metaux a paroi mobile
FR2746333B1 (fr) * 1996-03-22 1998-04-24 Usinor Sacilor Procede de coulee continue d'une bande d'acier inoxydable austenitique sur une ou entre deux parois mobiles dont les surfaces sont pourvues de fossettes, et installation de coulee pour sa mise en oeuvre
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'
KR100381523B1 (ko) * 1998-12-29 2003-07-23 주식회사 포스코 표면품질이우수한고니켈당량오스테나이트계스테인레스합금의제조방법
KR100411277B1 (ko) * 1999-09-15 2003-12-18 주식회사 포스코 쌍롤식 박판제조공정에서 균열이 없는 주편의 제조방법
AU2008100847A4 (en) 2007-10-12 2008-10-09 Bluescope Steel Limited Method of forming textured casting rolls with diamond engraving
CN113263162B (zh) * 2021-04-20 2022-12-02 广州市通上德智能装备有限公司 一种铅合金挂浆式铸带机
CN113741337B (zh) * 2021-09-10 2023-02-03 哈尔滨工业大学 一种薄壁球壳类微小构件全表面均布微坑结构加工轨迹的规划方法及装置

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3877675T2 (de) * 1987-09-24 1993-06-09 Mitsubishi Heavy Ind Ltd Kuehltrommel fuer stranggussmaschinen zur herstellung duenner metallischer baender.
JPS6483342A (en) * 1987-09-24 1989-03-29 Nippon Steel Corp Cooling drum for continuous casting apparatus for cast thin slab
JPH0252152A (ja) * 1988-08-15 1990-02-21 Nippon Steel Corp 薄帯連続鋳造装置用冷却ドラム
JPH0730407B2 (ja) * 1988-07-08 1995-04-05 新日本製鐵株式会社 表面品質が優れたＣｒ―Ｎｉ系ステンレス鋼薄板の製造方法
EP0378705B2 (en) * 1988-07-08 1999-09-15 Nippon Steel Corporation PROCESS FOR PRODUCING THIN Cr-Ni STAINLESS STEEL SHEET EXCELLENT IN BOTH SURFACE QUALITY AND QUALITY OF MATERIAL

Also Published As

Publication number Publication date
ES2056553T3 (es) 1994-10-01
JPH04158957A (ja) 1992-06-02
EP0481481A1 (en) 1992-04-22
KR920007716A (ko) 1992-05-27
DE69102388T2 (de) 1995-01-19
JPH082484B2 (ja) 1996-01-17
DE69102388D1 (de) 1994-07-14
KR950014485B1 (ko) 1995-12-02

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