Classifications

• • 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
  • B21B1/46—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 metal immediately subsequent to continuous casting
• • 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
  • B21B1/40—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 foils which present special problems, e.g. because of thinness
• • 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
  • B21B1/46—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 metal immediately subsequent to continuous casting
  • B21B1/463—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 metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
• • 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
  • B21B1/46—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 metal immediately subsequent to continuous casting
  • B21B1/466—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 metal immediately subsequent to continuous casting in a non-continuous process, i.e. the cast being cut before rolling
• • 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

Definitions

• the invention relates to the manufacture of thin strips of stainless steel, directly from liquid metal, by solidification inside an ingot mold consisting of two cooled walls moving at the same speed as the solidified strip, such as the outer walls of two rotating cylinders with horizontal axes.
• the causes of the appearance of these porosities at the heart of the bands cast between cylinders can be similar to those that cause (on a dimensional scale upper) the shrinkage in the ingots and the central porosities in the products of classic continuous casting, namely the closure of pockets containing solid metal still liquid metal when the solidification of the product (which normally is substantially completed when the strip leaves the walls of the ingot mold, i.e. the core of the strip is no longer completely in the liquid state) is not carried out completely regularly.
• the cooling and solidification of the liquid metal that enclose these pockets are accompanied by a contraction of this metal, which causes a empty space. This can not be filled before the end of solidification, because this pocket closed is no longer fed by new liquid metal.
• These porosities must be distinguished from spherical faults called "blowing" which are due to a release of gas dissolved and most often occur near the surface of products.
• Document EP 0 396 862 proposes a process aimed at eliminating the porosities central, and also other internal and superficial defects, when casting strips of steel between two cylinders.
• the casting rolls have on their surfaces of the circumferential grooves precisely dimensioned, and arranged in offset on the two cylinders.
• the only prevention of these detachments is insufficient to completely avoid the appearance of central porosities.
• the object of the invention is to propose a method guaranteeing closure final of the central porosities appeared in the core of the strip after its solidification complete.
• the subject of the invention is a method for manufacturing a thin strip.
• stainless steel by direct solidification of the liquid steel in the form of a strip of thickness less than or equal to 8 mm in a casting installation comprising two cooled walls in movement and by hot rolling of said strip, the solidification is substantially completed when it leaves said walls, characterized in what hot rolling is done on a rolling mill whose working rolls have a diameter between 400 and 900 mm, in that the temperature of the strip on leaving the rolling mill is between 800 and 1100 ° C, and in that the rate of thickness reduction of the strip during hot rolling is between 15 and 50%.
• the hot rolling is carried out in line with the casting of the bandaged.
• the casting installation can be of the “casting between cylinders” type.
• the object of the invention is achieved by the combination requirements relating to the diameter of the working rolls of the hot rolling mill, the temperature of the strip at its exit from the cylinders and the rate of reduction of the thickness of the strip during hot rolling.
• the invention applies to the casting of stainless steels of all classes, which have conventionally carbon contents less than or equal to 1%, silicon contents less than or equal to 1%, manganese contents less than or equal to 15%, chromium contents between 10 and 30%, copper contents less than or equal to 5% and nitrogen contents less than or equal to 0.5% (these contents are expressed in weight percentages).
• These steels can also contain significant quantities nickel (up to 40%) or molybdenum (up to 8%).
• impurities either as alloying elements, in particular sulfur, phosphorus, titanium, niobium, zirconium. Their total must not exceed 2% by weight.
• a thin strip of stainless steel poured between cylinders is highly likely to develop porosities in its heart, during its solidification, when a liquid pocket is closed with solid metal.
• This phenomenon occurs at the end of solidification of the pasty zone, also called “equiaxial zone”, located between the two skins solidified in contact with the cylinders, also called “columnar areas”.
• the area equiaxial is very difficult to control, and its thickness can vary depending on the speed of solidification of columnar areas.
• the equiaxial zone can close locally from anticipated, at levels where the growth of columnar areas has been faster than the normal.
• the liquid bags Downstream of the closing point of the equiaxial zone, the liquid bags do not can no longer be properly replenished with liquid metal, and porosities form by contraction of the metal during the solidification of these liquid pockets. This case remains nevertheless quite rare, and in fact, generally, the isolation of a liquid pocket occurs by the grouping in the liquid of equiaxial crystals which come to form a plug obstructing the equiaxial zone.
• the porosities which form in the equiaxial zone are consisting of sets of gas-free channels and cavities, the dimension of which maximum according to the thickness of the sheet corresponds to the thickness of the equiaxial zone (i.e. 100 at 400 ⁇ m), and which can reach a length of 1 to 2 mm in the other directions. As we said, it is not a spherical blow which would originate from a evolution of gas, or an internal fault opening on the surface of the strip.
• the idea behind the invention is to create, during the hot rolling of the strip solidified, conditions such that they lead not only to a closure of central porosities as it is already known, but also a real welding of opposite walls of the porosities, which the rolling made it possible to bring together. In this way, we ensures that the porosities are not likely to open during subsequent shaping of the strip or when using the products thus produced.
• hot rolling the strip two stages follow one another. First, the internal walls of the defect are gradually approach as the thickness of the strip decreases, until brought into contact. Then, once this contact has been made, the walls are welded produced by diffusion of the constituent elements of steel through the interface. But one efficient welding of the walls must already have been obtained before the exit of the strip the grip of the rolls of the rolling mill, because otherwise the relaxation of the compression of the strip which occurs at the outlet of the cylinders leads to a partial detachment of the walls.
• the efficiency of welding essentially depends on two parameters: the duration of the forced contact of the walls in the rolling mill and the temperature at which it takes place this contact.
• This forced contact must therefore take place as soon as possible after entry of the strip in the rolling mill, and its duration depends mainly, for a speed of given rolling (which is, in the case of in-line rolling, largely conditioned by the thickness of the strip before it is rolled), the diameter of the working rolls of the rolling mill and the reduction rate of its thickness which they impose on the strip.
• the cylinders have a very large diameter, the cooling of the strip which they cause risks leading it to a temperature insufficient for that the welding of the walls of the porosities can be complete.
• the value of the temperature of the strip as it leaves the cylinders provides a good indication of the actual possibility that the walls of the porosities had to weld to each other in the grip of the cylinders.
• the temperature of the strip at the outlet of the cylinders must therefore be sufficient to allow the welding of porosities, but it must not be too high either, so avoid excessive thermal load on the cylinders. This would lead to a degradation of their surface resulting in a deterioration of the surface appearance of the strip in the form of excessive roughness.
• the objective of the invention cannot therefore be achieved without getting annoying side effects for the overall quality of the tape that if we combine the diameter of the cylinders, the reduction rate and the temperature of the strip leaving the rolling mill adequately.
• Table 1 groups together the compositions of the steels on which the tests were carried out, the results of which are given in Table 2. The contents of the various elements are given in percentages by weight. Table 1 also gives the thicknesses at the outlet of the casting rolls of the strips on which the tests were carried out, as well as the corresponding casting speeds, measured between the casting rolls and the hot rolling mill.
• compositions of types A and A 'flows correspond to those of steels classic austenitic stainless steels type AISI 304.
• Type B castings correspond to AISI 430 type ferritic stainless steels.
• Type C castings correspond to AISI 409 ferritic stainless steels stabilized with titanium.
• Table 2 shows the results of tests carried out on the strips from these castings, with the corresponding test conditions. Results of tests carried out on types A, A ', B, C Field of the invention Type of casting Diameter of rolling mill rolls (mm) Reduction rate (%) Temperature of the strip leaving the rolling mill (° C) Welding of porosities Other faults no AT 300 50 1100 no nothingness no AT 400 10 1100 no nothingness no AT 400 15 750 no nothingness Yes A, A ', B, C 400 15 800 Yes nothingness Yes A, A ', B, C 400 15 1100 Yes nothingness no AT 400 15 1150 Yes too strong roughness no AT 400 50 750 no nothingness Yes A, A ', B, C 400 50 800 Yes nothingness Yes A, A ', B, C 400 50 1100 Yes nothingness no AT 400 50 1150 Yes too strong roughness no AT 400 60 1100 Yes critics no AT 900 10 1100 no nothingness no AT 900 15 750 no nothingness Yes A, A ', B, C 900 15 800 Yes nothing
• the invention applies not only to installations for casting between rolls, but to any other type of casting installation of thin strips of stainless steel between two cooled surfaces in motion, such as moving bands.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Metal Rolling (AREA)
• Continuous Casting (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Physical Vapour Deposition (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
• Chemical Vapour Deposition (AREA)
• Chemical Treatment Of Metals (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=9530674

Family Applications (1)

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• 1998
  • 1998-09-21 FR FR9811777A patent/FR2783443B1/fr not_active Expired - Fee Related
• 1999
  • 1999-09-09 CA CA002281991A patent/CA2281991A1/fr not_active Abandoned
  • 1999-09-10 DE DE69912710T patent/DE69912710T2/de not_active Revoked
  • 1999-09-10 AT AT99402235T patent/ATE253992T1/de not_active IP Right Cessation
  • 1999-09-10 EP EP99402235A patent/EP0988901B1/fr not_active Revoked
  • 1999-09-10 SK SK1239-99A patent/SK123999A3/sk unknown
  • 1999-09-17 AU AU48778/99A patent/AU4877899A/en not_active Abandoned
  • 1999-09-18 ZA ZA9905983A patent/ZA995983B/xx unknown
  • 1999-09-20 TR TR1999/02306A patent/TR199902306A3/tr unknown
  • 1999-09-20 ID IDP990877D patent/ID25947A/id unknown
  • 1999-09-20 CN CNB991220633A patent/CN100358645C/zh not_active Expired - Fee Related
  • 1999-09-20 UA UA99095183A patent/UA63941C2/uk unknown
  • 1999-09-20 PL PL99335499A patent/PL335499A1/xx unknown
  • 1999-09-20 RU RU99120100/02A patent/RU2203749C2/ru not_active IP Right Cessation
  • 1999-09-20 KR KR1019990040351A patent/KR100573750B1/ko not_active IP Right Cessation
  • 1999-09-21 JP JP11266489A patent/JP2000094006A/ja active Pending
  • 1999-09-21 BR BR9904278-9A patent/BR9904278A/pt active Search and Examination
  • 1999-10-12 TW TW088116319A patent/TW483781B/zh not_active IP Right Cessation

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