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
  • 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
  • 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
  • B22D11/12—Accessories for subsequent treating or working cast stock in situ
  • B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
• • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
• • 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
  • B21B3/003—Rolling non-ferrous metals immediately subsequent to continuous casting, i.e. in-line rolling

Definitions

• the present invention relates to the hot forming of metals, and more particularly relates to the continuous casting and hot forming of the as-cast bars of certain impure or alloyed steels which may be prone to crack during hot-rolling.
• metals such as copper and aluminum
• metals may be continuously cast, either in stationary vertical molds or in a rotating casting wheel, to obtain a cast bar which is then immediately hot formed, while in a substantially as-cast condition, by passing the cast bar exiting the mold to and through the roll stands of a rolling mill while the cast bar is still at a hot-forming temperature.
• the as-cast structure of the metal bar is such that cracking of the cast bar during hot forming may be a problem if the cast bar is required to be directly hot formed into a semi-finished product, such as redraw rod, during which the initially large cross-sectional area of the cast bar is substantially reduced by a plurality of deformations along different axes to provide a much small-er cross-sectional area in the product.
• the prior art has not, however, provided a solution to the cracking problem described above for metals, such as steel, containing a relatively high percentage of alloying elements. This is because the large amounts of alloying elements, often in the grain boundaries of the as-cast structure, cause the cast bar to crack when an attempt is made to substantially destroy the as-cast structure with the same large initial reduction of the cross-sectional area of the cast bar that is known to be effective with relatively pure non-ferrous metal. Moreover, the greater the percentage of alloying elements in the cast bar, the more likely it is that cracks will occur during hot forming.
• the present invention solves the above-described cracking problem of the prior art by providing a method of continuously casting and hot forming both low and high alloy steels without substantial cracking of the cast bar occurring during the hot rolling process.
• the invention provides, in a method of continuously casting molten metal to obtain a cast bar with a relatively large cross-sectional area, and hot forming the cast bar at a hot-forming temperature into a product having a relatively small cross-sectional area by a substantial reduction of the cross-sectional area of the cast bar which would be such that the as-cast structure of the cast bar would be expected to cause the cast bar to crack, the additional step of first forming a substantially uniform subgrain structure at least in the surface layers of the cast bar prior to later substantial reduction of the cross- sectional area of the cast bar, said substantially uniform subgrain structure being formed by relatively light deformations of the cast bar while at a hot-forming temperature.
• the light deformations are of magnitude (preferably 5 to 25%) which will not cause the cast bar to crack, but which in combination with the hot-forming temperature of the cast bar will cause the cast bar to have a substantially uniform subgrain or cell structure of a thickness sufficient (about 10% of total area) to produce a bar of increased ductility when compared to a bar produced by the prior art process, which substantially inhibits the initiation of micro and macro cracking that normally begin at the as-cast grain boundaries, thus preventing cracking of the cast bar (even when having relatively high percentage alloying elements) during the subsequent substantial deformations.
• the substantially uniform subgrain structure of the surface provided by this invention allows substantial reduction of the cross-sectional area of the bar in a subsequent pass, even in excess of 30%, without cracking occurring a.nd even though the cast bar has a relatively high amount of impurities or alloying elements.
• the present invention allows a steel alloy cast bar having a cross-sectional area of 5 square inches, or more, and containing alloying elements, to be continuously hot formed into wrought rod having a cross- section area of 1/2 square inch, or less, without cracking.
• the invention has wide general utility since it can also be used with certain other relatively impure or alloyed metals as an alternative to the solution to the problem of cracking described in U.S. Patent No. 3,317,994, and U.S. Patent No. 3,672,430.
• Fig. 1 is a schematic representation of casting and forming apparatus for practicing the method of the present invention.
• Fig. 2 is a representation cross-section of a cast bar in substantially an as-cast condition (in this case columnar) .
• Fig. 2A is a representation cross-section of a cast bar in substantially an as-cast condition (in this case equiaxed) .
• Fig. 3 is a representation cross-section of the cast bar shown in Fig. 2 following one light reduction of the cross- section.
• Fig. 3A is a representation of a magnification of 2000x of the subgrain (cell or recrystallized) structure, a portion of which is shown in Fig. 3.)
• Fig. 4 is a representation cross-section of the cast bar shown in Fig. 2 following two perpendicular light compressions to form a complete shell of fine or equiaxed grains near the surface of the bar.
• Fig. 5 is a representation cross-section of the cast bar shown in Fig. 2 following two light compressions and one severe hot-forming compression.
• Fig. 1 schematically depicts an apparatus for practicing the method of the present invention.
• the continuous casting and hot-forming system (10) includes a casting machine (12) which includes a casting wheel (14) having a peripheral groove therein, a flexible band (16) carried by a plurality of guide wheels (17) which bias the flexible band (16) against the casting wheel (14) for a portion of the circumference of the casting wheel (14) to cover the peripheral groove and
• OMPI form a mold between the band (16) and the casting wheel (14).
• the casting wheel (14) is rotated and the band (16) moves with the casting wheel (14) to form a moving mold.
• a cooling system (not shown) within the casting machine (12) causes the molten metal to solidify in the mold and to exit the casting wheel (14) as a solid cast bar (20).
• the cast bar (20) passes through a conditioning means (21) , which includes roll stands (22) and (23).
• the conditioning roll stands (22) and (23) lightly compress the bar to form a shell of substantially uniform fine or equiaxed grain structure at the surface of the bar (20).
• the bar (20) is passed through a conventional rolling mill (24), which includes roll stands (25), (26), (27) and (28).
• the roll stands of the rolling mill (24) provide the primary hot forming of the cast bar by compressing the conditioned bar sequentially until the bar is reduced to a desired cross- sectional size and shape.
• the grain structure of the cast bar (20) as it exits from the casting machine (12) is shown in Fig. 2.
• the molten metal solidifies in the casting machine in a fashion that can be columnar, or equiaxed, or both, depending on the super heat and cooling rate.
• This as-cast structure can be characterized by grains (30) extending radially from the surfaces of the bar (if columnar) and separated from each other by grain boundaries (31). Most of the alloying elements present in the cast bar are located along the grain and dendrite boundaries (31).
• the conditioning means (21) prevents such cracking by providing a sequence of preliminary light compressions as shown in Fig. 3 and Fig. 4, wherein the result of a compression is shown and the previous shape of the cast bar is shown in broken lines.
• Fig. 3 shows the result of a 7% reduction provided by the roll stand (22) along a horizontal axis of compression (33).
• the columnar and/or equiaxed as- cast grain structure of the cast metal has been formed into a layer of substantially uniform fine grained, equiaxed or cell structure (35) covering a portion of the surface of the cast bar (20).
• the interior of the bar may still have an as-cast structure.
• Fig. 4 the bar (20) has been subjected to a second 7% reduction by the roll stand (23) along a vertical axis of compresion (33) perpendicular to the axis of compression, of roll stand (22).
• the volume of substantially uniform fine grained, equiaxed or cell structure (35) now forms a shell (36) around the entire surface of the bar (20), although the interior of the bar retains some as-cast structure.
• the formation of the shell may be accomplished by a conditioning means comprising any number of roll stands, preferably at least two, or any other type of forming tools, such as extrusion dies, multiple forging hammers, etc., .so long as the preliminary light deformation of the metal results in a substantially uniform fine grained, equiaxed or cell structure covering substan ⁇ tially the entire surface of the bar, or at least the areas subject to cracking.
• a conditioning means comprising any number of roll stands, preferably at least two, or any other type of forming tools, such as extrusion dies, multiple forging hammers, etc., .so long as the preliminary light deformation of the metal results in a substantially uniform fine grained, equiaxed or cell structure covering substan ⁇ tially the entire surface of the bar, or at least the areas subject to cracking.
• the individual light deformations should be between 5-25% reduction so as not to crack the bar during conditioning.
• the total deformation provided by the conditioning means (21) must provide a shell (36) of sufficient depth (at least about 10%) to prevent cracking of the bar during subsequent deformation of the bar when passing through the roll stands (25-28) of the rolling mill (24).
• the shape of the bar in its as-cast condition includes prominent corners such as those of the bar shown in Fig. 2, the shape of the compressing surfaces in the roll stands (22) and (23) may be designed to avoid excessive compression of the corner areas as compared to the other surfaces of the cast bar, so that cracking will not result at the corners.
• Fig. 5 shows a cross-section (20) following a substantial reduction of the cross-sectional area by the first roll stand (25) of the rolling mill (24).
• the remaining as-cast structure in the interior of the bar (20) has been transformed into a uniform fine grained, equiaxed or cell structure (35).
• the method of the present invention allows continuous casting and rolling of relatively high percentage alloy steel, such as molybdum and tungsten containing steels and austeuitic steel alloys without cracking the bar. Furthermore, cracking is. prevented throughout the hot- forming temperature range of the metal.
• the same casting and hot-forming apparatus may be used to produce steel alloys of varying purities and alloying elements depending on the standards which must be met for a particular product.
• elliptically shaped rolling channels may be provided for all of the roll stands (22), (23), and (25-28) in order to provide optimal tangential velocities of the rolls in the roll stands with respect to the cast metal, as disclosed in U.S. Patent No. 3,317,994.
• measures are usually not needed to avoid cracking if the present invention is practiced as described herein on metals having alloy levels as described above.
• the roll stands of the conditioning means (21) may be either a separate component of the system or may be constructed as an integral part of a rolling mill.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Metal Rolling (AREA)
• Forging (AREA)

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• 1983
  • 1983-02-04 GB GB08326523A patent/GB2124939B/en not_active Expired
  • 1983-02-04 EP EP83902518A patent/EP0105368B1/de not_active Expired
  • 1983-02-04 WO PCT/US1983/000194 patent/WO1983002783A1/en active IP Right Grant

Patent Citations (6)

Non-Patent Citations (1)

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