WO1994026942A1 - Produits de metaux ferreux industriels et procede de raffinage de fabrication sous laitier electroconducteur - Google Patents

Produits de metaux ferreux industriels et procede de raffinage de fabrication sous laitier electroconducteur Download PDF

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Publication number
WO1994026942A1
WO1994026942A1 PCT/GB1994/001017 GB9401017W WO9426942A1 WO 1994026942 A1 WO1994026942 A1 WO 1994026942A1 GB 9401017 W GB9401017 W GB 9401017W WO 9426942 A1 WO9426942 A1 WO 9426942A1
Authority
WO
WIPO (PCT)
Prior art keywords
composition
titanium
roll
metal
consumable electrode
Prior art date
Application number
PCT/GB1994/001017
Other languages
English (en)
Inventor
David Wragg
Paul Herbert Hewitt
Jack Nutting
Original Assignee
Sheffield Forgemasters Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from GB939309737A external-priority patent/GB9309737D0/en
Priority claimed from GB939315359A external-priority patent/GB9315359D0/en
Priority claimed from PCT/GB1993/002380 external-priority patent/WO1994011541A1/fr
Application filed by Sheffield Forgemasters Limited filed Critical Sheffield Forgemasters Limited
Priority to AU66611/94A priority Critical patent/AU6661194A/en
Publication of WO1994026942A1 publication Critical patent/WO1994026942A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/18—Electroslag remelting
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D23/00—Casting processes not provided for in groups B22D1/00 - B22D21/00
    • B22D23/06—Melting-down metal, e.g. metal particles, in the mould
    • B22D23/10—Electroslag casting

Definitions

  • This invention relates to an engineering ferrous metal product and to a method of making such a product. More particularly, but not exclusively, the product is a roll for use in rolling mills.
  • the rolling mill may be, for example, used for rolling strip or sheet metal or maybe a calendering mill for paper.
  • An object of the invention is to provide a new and improved engineering ferrous metal product and a new and improved method of making such a product.
  • an engineering ferrous metal product comprising performing an electroslag remelting operation on a consumable electrode element comprising engineering ferrous metal and in which an ingredient, additional to said consumable electrode element, is added to the melt pool.
  • the consumable electrode element may comprise a complete consumable electrode and said additional ingredient may be added to the melt pool separately from the electrode.
  • the consumable electrode element may comprise a first part of a consumable electrode, the consumable electrode having a second part of a different composition to the first part and the second part providing said additional ingredient.
  • the first part of the consumable electrode may comprise an inner part of the electrode and the second part of the consumable electrode may comprise an outer part of the electrode.
  • the invention relates to a roll for use in rolling mills and to a method of making such a roll.
  • the first more specific facet of the invention is particularly, but not exclusively, concerned with roughing work rolls of a hot strip rolling mill for rolling steel strip or sheet.
  • bimetallic rolls have generally been used for hot rolling because of the inability to produce monoblock rolls of metal providing the surface properties desired for hot rolling.
  • Such bi-metallic rolls comprise a shell providing a surface layer of the roll made of metal of a composition to provide the desired surface properties and a core made of different metal to provide the desired core properties.
  • the shell metal comprises high alloy steel or high alloy cast iron and the core metal comprises nodular cast iron or plain steel.
  • Centrifugal Casting in which metal of shell composition is poured into a spinning mould and allowed at least substantially wholly to solidify followed by pouring of metal of core composition into the mould and allowing the core metal then to solidify.
  • Bimetallic Electroslag Remelting in which a water cooled mould is disposed concentrically around a solid metal arbour made of metal of core composition and at least one consumable electrode of shell composition is inserted into the gap between the core and the mould and melted by electroslag remelting and the mould moved upwardly as the shell metal solidifies at the bottom of the mould. If desired, the arbour and the mould may be rotated.
  • Bimetallic Hot Isostatic Pressing in which a solid arbour of core composition is coated with metal powder, heated in a furnace and then pressed using a high isostatic pressure pressing operation such as explosive forming.
  • the metal powder is normally produced as an extruded cylindrical shell and slid onto the arbour prior to the heating and hot isostatic pressing operation.
  • Weld Cladding in which a submerged arc welding operation is performed to weld a wire of shell composition spirally around an arbour of core composition whilst rotating the arbour.
  • Bimetallic rolls whether made by one of the methods described hereinbefore or by any other method all have a distinct chemical interface between the core metal and the shell metal and a consequent distinct physical interface.
  • monoblock rolls have been heat treated to improve the surface properties of the roll, for example by heating to austenitising temperature and then quenching to produce a martensitic/bainitic shell which is then tempered and a pearlitic/ferritic core.
  • heat treatment operation there is a sharp interface between the shell and the core although there may be a transition zone of relatively steep physical gradient of relatively short radial width, for example, of the order of 5mm to 10mm.
  • An object of the first more specific facet of the present invention is to provide a roll for use in rolling mills whereby the above mentioned problems of spalling is overcome or is reduced.
  • a further object of the first more specific facet of the invention is to provide a method of making such an improved roll.
  • a method of making a roll for use in a rolling mill comprising performing an electroslag remelting operation on a consumable electrode which comprises an inner part of a core composition and an outer part of a shell composition.
  • the electroslag remelting operation may produce an ingot comprising an inner part of a first composition and a surface part of a second composition, the second composition being different to the first composition and the metal of the roll between the inner part and the surface layer having a composition which changes without discontinuity.
  • the consumable electrode may comprise an inner body provided with an external cladding.
  • the external cladding may comprise a plurality of discrete elements, which may be elongate elements, such as slats, fixed by welding or otherwise to an external surface of the inner body.
  • the discrete elements may extend longitudinally of the inner body or may be wound helically around the body or may extend circumferentially around the body or may be in the form of a loop or part loop which lies in a plane which is inclined to the longitudinal axis of the body at less than a right angle.
  • the external cladding may comprise a sleeve which may be fixed, by welding or otherwise, to the external surface of the body.
  • the discrete elements or the sleeve may be solid and may be of constant composition throughout their cross-section and length, or they may vary in composition across their cross-section and/or along their length.
  • the discrete elements or the sleeve may comprise a composite element of different composition at different positions across the cross- section of the element and/or along the length of the element.
  • Each discrete element or the sleeve may comprise a hollow element containing material of different composition to the material of the hollow element.
  • each discrete element may comprise a tube to provide said hollow element.
  • the material inside the or each hollow element may be a powder.
  • the additional ingredient comprises powder
  • means may be provided to release the powder in controlled manner. For example by reducing the cross-section of a hollow component in which the powder is contained to divide the powder into discrete amounts for release into the melt pool sequentially as the component and electrode element are melted.
  • the powder may have a mesh size of less than 3mm, but may have a mesh size up to 5mm and may lie in the range 2 - 5mm.
  • the powder may comprise at least one or chromium, tungsten, titanium, molybdenum, niobium and vanadium combined with carbon as an inter- metallic compound or compounds or as a solid solution or solutions.
  • Each discrete hollow element or hollow sleeve may comprise steel, such as mild steel or stainless steel.
  • the external cladding may comprise a shell part of a bimetallic rolling mill roll the core of which provides the inner body.
  • the bimetallic rolling mill roll may have been made in any desired manner including, for example, Centrifugal Casting, Bimetallic Electroslag Remelting, Continuous Pouring of a Cladding, and Bimetallic Hot Isostatic Pressing or Weld Cladding.
  • the cladding comprises discrete elements
  • at least one of the elements may be of different composition to the other elements.
  • the inner body may be of constant composition throughout its cross- section or it may be of varying composition across at least part of its cross-section.
  • the consumable electrode may comprise a body having an inner part having a first composition and an outer part having a second composition, which is different from the first composition and the metal of the body between the inner part and the outer part having a composition which changes from the first composition to the second composition without discontinuity.
  • the consumable electrode may comprise a scrap roll according to the first aspect of the invention.
  • the electroslag remelting operation may be performed at a relatively slow rate or a relatively high rate.
  • variable rates may be achieved by using a relatively high voltage and a relatively low current, or vice versa.
  • the slag may have a relatively high melting point.
  • the ratio of the diameter of the electrode to the diameter of the mould cavity may be relatively high, for example, greater than 0.8.
  • the melting point of the outer part of the consumable electrode may be higher than the melting point of the inner part of the consumable electrode and the melting point of the inner part may be higher than the melting point of the slag.
  • the melting point of the inner part of the consumable electrode may be higher than the melting point of the outer part of the consumable electrode and the melting point of the outer part may be higher than the melting point of the slag.
  • the droplets of metal from the outer part of the consumable electrode because of their spatial proximity to the wall of the mould, solidify relatively rapidly at or adjacent to the mould wall so that the ingot is provided with a surface part of a composition similar to that of the outer part of the consumable electrode.
  • the droplets of metal from the outer part of the electrode are made of a metal of higher alloy content than the metal of the inner part of the electrode, they are denser and they drop relatively rapidly and directly downwardly from the outer part of the electrode and hence are disposed adjacent to the mould wall and hence they solidify relatively rapidly to provide the ingot with a surface layer having a composition similar to that of the outer part of the consumable electrode.
  • the external cladding is hollow and contains an alloy and/or alloy-carbide
  • the melting point of the alloy and of the alloy carbides may be greater than the melting point of the slag and of the inner part of the consumable electrode.
  • the outer part of the ingot may be hardened by at least one of a dispersion hardening effect of the alloy carbides, phase transformation, or cell size transformation.
  • the outer part of the rolled ingot may be hardened, additionally, or alternatively, by a secondary hardening heat treatment operation.
  • the electroslag remelting operation is performed so that the floor of the molten bath is relatively flat. This may be achieved by inter-relating the voltage, current and the slag composition of the electroslag remelting operation.
  • the cooling rate of the mould may be adjusted as may be the rate of movement of the mould.
  • the additional ingredient may comprise a high alloy steel or cast iron.
  • the additional ingredient may comprise a powder comprising at least one of chromium, tungsten, titanium, molybdenum, niobium and vanadium combined with carbon as an inter-metallic compound or compounds or as a solid solution or solutions or ferro-titanium.
  • the additional ingredient may comprise a powder having a mesh size of less than 5mm.
  • a second more specific facet of the invention relates to an engineering ferrous metal product and to a method of making such a product. More particularly, but not exclusively, the product comprises a roll for use in rolling mills such as roughing work rolls of a hot strip rolling mill for rolling steel strip or sheet, or a calendering mill for paper.
  • An object of the second more specific facet of the present invention is to provide an engineering ferrous metal product having a relatively hard and tough surface layer.
  • a further object of the second more specific facet of the invention is to provide a method of making such a product.
  • an engineering ferrous metal product comprising performing an electroslag remelting operation on a consumable electrode element comprising engineering ferrous metal and in which an addition to form sub-microscopic carbides, nitrides and/or carbo-nitrides is made to the melt pool.
  • the second more specific facet of the invention may be provided together with or without the first more specific facet of the invention.
  • the addition forms sub-microscopic titanium and/or niobium carbides, nitrides and/or carbo-nitrides.
  • the additions may comprise at least one of titanium carbide, niobium carbide, mixed carbides of titanium and tungsten, mixed carbides of any of the above mentioned carbides or ferro titanium.
  • the carbide may be a mixed tungsten titanium carbide of the kind (TiW)C where the ratio of titanium to tungsten is about 1:1 by weight.
  • the alloy carbide may comprise Ti and W in the ratio range:
  • the alloy carbide may contain nitrogen, for example up to about 0.1% nitrogen.
  • the alloy carbide preferably comprises:-
  • the alloy carbide particles preferably have a density which matches that of the engineering ferrous metal.
  • matches we mean a density preferably lying in the range 6 - 8 gms per cc. This is to be compared with a typical density of 7 gms per cc. for cast iron and steel. More preferably, the alloy carbide particles have a density of ⁇ 5% of the density of the engineering ferrous metal to which they are added.
  • the alloy carbide particles have a very low co-efficient of thermal expansion compared to the co-efficient of thermal expansion of engineering ferrous metals. Accordingly, if relatively large alloy carbide particles were present in the engineering ferrous metals this would give rise to high stresses on cooling, and leading to thermal fatigue.
  • the alloy carbide particles preferably have a maximum dimension of up to 10 microns and preferably 0.1 - 5 microns and more preferably 0.1 - 2 microns.
  • the amount of alloy carbide particles added is such as to achieve up to 20% by volume of alloy carbide particles in the solid metal.
  • the alloy carbide content may be in the range 0.1 to 20% by volume, and may be in the range 1 to 20% and more preferably 3 to 10% when a hardening effect based on the law of mixtures is provided.
  • the alloy carbide content may be lower, e.g. down, for example from about 1%, to about 0.5% or 0.1% or less when a hardening effect based on a modification of the transformation of the microstructure is provided.
  • the engineering ferrous metals are preferably steel or cast iron having a carbon content lying in the range 0.3 - 3.8%.
  • the engineering ferrous metals may contain chromium and may have a chromium content which is greater than or equal to 1%.
  • the engineering ferrous metal and/or the additions may contain nitrogen, for example up to 0.1% nitrogen in total in the as cast product.
  • the solid carbide particles may be coated with a metal which allows wetting to occur between the particles and the liquid engineering ferrous metal.
  • wetting we mean the ability of the liquid engineering ferrous metal to wet the coating metal. More particularly, for example, where the interfacial tension between the liquid engineering ferrous metal and the solid coating metal is such that the contact angle therebetween is 0° - 90°C.
  • the wettability of the coated particles and the density of the alloy carbide particles each promote a uniform distribution of the carbide particles in the liquid engineering ferrous metal which is retained when the metal solidifies.
  • uniform distribution we mean an even distribution throughout the section of a casting made of the engineering ferrous metal with no significant segregation.
  • the solid carbide particles are not orientated in any direction and are distributed across all phases of the micro-structure.
  • the coating metal preferably comprises iron or an iron carbon alloy, but may comprise an alloy of two or more elements selected from the group comprising iron, nickel, copper, titanium and carbon, or may be nickel or copper and usual incidentals.
  • the coating metal may comprise nitrogen, for example up to about 0.1% nitrogen.
  • the coating is iron, then because iron has a higher melting point than the engineering ferrous metal to which it is to be added, which would inhibit wettability, it is preferred to add an appropriate amount of at least one alloying element such as carbon, nickel, copper or titanium to the iron to produce an alloy having a melting point which matches the operating temperature of the ferrous metal.
  • alloying element such as carbon, nickel, copper or titanium
  • operating temperature we mean the temperature of the engineering ferrous metal whilst the coated carbide particles are added.
  • the iron coating may contain up to 3.5% carbon.
  • the additions to provide the sub-microscopic carbide, nitride or carbide-nitride particles may be made into the melt pool separately from the electrode.
  • the electroslag remelting operation may be performed so as to achieve or aim to achieve a uniform composition throughout the cross-section of the ingot.
  • the coating metal, and/or the alloy carbide and/or the engineering ferrous metal contains nitrogen it is considered that titanium carbo- nitrides may be precipitated in the microstructure of the engineering ferrous metal.
  • the total nitrogen content of all the components may be limited to about 0.1% nitrogen.
  • an engineering ferrous metal product when made by performing an electroslag remelting operation on a consumable electrode element comprising engineering ferrous metal in which an ingredient, additional to said consumable electrode element, was added to the melt pool.
  • a roll for use in a rolling mill comprising an inner part having a first composition and a surface part having a second composition, which is different from the first composition and the metal of the roll between the inner pan and the surface part having a composition which changes from the first composition to the second composition without discontinuity.
  • the composition may change continuously between the surface part and the inner part and the change in composition may be relatively uniform.
  • the roll may have a composition gradient between the surface part and the inner part of less than 40% per 100mm in the radial direction at any position along the longitudinal extent of the roll.
  • the roll may have a relatively uniform transition region between the surface part and the inner part and the roll may have substantially the same elastic modulus throughout its cross-section.
  • the total alloying elements may reduce from about 15% in the surface pan to less than 3% at the middle of the inner part.
  • the carbon content may be less than 0.9 throughout and the ratio of molybdenum to carbon in the surface part may be greater than 2.0 such that M7C3 type carbides are formed.
  • the presence of such M7C3 carbide permits secondary hardening of the roll to be achieved, with suitable heat treatment.
  • the surface part may comprise carbides of at least one of chromium, tungsten, titanium, molybdenum, niobium and vanadium combined with carbon as an inter-metallic compound or compounds and/or as a solid solution or solutions.
  • the surface part may have a relatively high distribution of alloy and/or alloy carbides.
  • the roll may have a relatively uniform transition region between the surface part and the inner part.
  • the roll may have the same elastic modulus throughout its cross- section.
  • the roll may have an elastic modulus that increases in proportion to the amount of the alloy and/or alloy carbide through the roll cross- section.
  • an as-cast engineering ferrous metal product at least a surface region of which has a microstructure comprising feathery or a sheath-like bainite with sub-microscopic carbide, nitride and/or carbo-nitride particles distributed in the bainite and/or bainitic ferrite matrix.
  • the sub-microscopic particles are of titanium and/or niobium carbide and/or carbo-nitride.
  • electroslag remelting we mean a process in which a consumable electrode is melted beneath an electrical conductive slag to form a melt pool in a moving mould from the lower end of which a continuously cast ingot emerges; the electrode is heated by thermal conduction from the slag and the slag is heated by electrical conduction from the electrode through the slag and melt pool to a counter-electrode provided by the ingot.
  • engineing ferrous metals we mean cast iron and steel.
  • sub-microscopic we mean a particle size of less than 1 micron.
  • FIGURE 1 is a diagrammatic side elevation of an electroslag remelting apparatus for use in a method embodying the present invention
  • FIGURE 2 is a transverse cross-section through a consumable electrode for use in the apparatus of Figure 1;
  • FIGURE 3 is a diagrammatic fragmentary cross-section through the apparatus of Figure 1 when in use;
  • FIGURE 4 is a graph showing the variation in composition in a transverse section of roll made according to the present invention
  • FIGURES 5a and 5b are graphs showing the variation in composition in a transverse section of prior art bimetallic rolls made by hot isostatic pressing and centrifugal casting, respectively,
  • FIGURE 6 is a diagrammatic side elevation of another embodiment of an electroslag remelting apparatus when in use in a method embodying the present invention.
  • FIGURE 7 is a transverse cross-section through a consumable electrode for use in the apparatus of Figure 6.
  • FIGURE 8 is a photomicrograph of an outer part of a roll embodying the invention at a magnification of x 100, and
  • FIGURE 9 is a photomicrograph of an outer part of a roll of a similar base composition to the roll shown in Figure 8 but not embodying the invention at a magnification of x 100.
  • an electroslag remelting apparatus is shown in Figure 1 and is of essentially conventional kind comprising a cylindrical water cooled mould 10 which is movable vertically upwardly or downwardly.
  • An electrode holder 11 holds, for example by being welded thereto, the upper end of a consumable electrode 12. Initially, the bottom end of the consumable electrode is immersed in molten slag contained between a bottom plate 13 and the wall of the mould 10. Electric current is then passed to cause the lower end of the electrode to melt and as the droplets of metal fall from the lower end of the electrode 12 they pass through the slag and are refined and then solidify to form an ingot 14.
  • the consumable electrode 12 comprises an electrode element which comprises a first part of the electrode and comprises an inner body 20 of cylindrical configuration having welded to its external surface 21 a second, outer, part of the electrode 12 which comprises a cladding 22 which comprises a plurality of discrete elements 23 in the form of slats and which provides an ingredient, additional to the material of the electrode element 20, which is added to the melt pool during the electroslag remelting operation.
  • the inner body 20 is made of low alloy steel, cast iron or mild steel such as 0.2%C steel, whilst the cladding is made of high alloy steel or cast iron or material of any desired suitable composition.
  • the cladding may have a composition lying in the range:-
  • the cladding has a composition lying in the range:-
  • the slats have the following composition:
  • the inner body may comprise a low alloy steel which may comprise:
  • the cladding may comprise other relatively high alloy engineering ferrous metal such as:-
  • the inner body may comprise other relatively low alloy ferrous engineering metal such as:-
  • the cladding may comprise a sleeve, for example, a cylindrical sleeve mounted, for example, by welding or by virtue of being a push fit, on an inner cylindrical body.
  • the consumable electrode may comprise a bimetallic body, that is to say a body having a core and a shell bonded together by, for example, Centrifugal Casting, Bimetallic Electroslag Remelting, Continuous Pouring of Cladding, Weld Cladding or in any other way and the bimetallic body may comprise a scrap bimetallic roll.
  • a bimetallic body that is to say a body having a core and a shell bonded together by, for example, Centrifugal Casting, Bimetallic Electroslag Remelting, Continuous Pouring of Cladding, Weld Cladding or in any other way and the bimetallic body may comprise a scrap bimetallic roll.
  • the electrode may comprise a scrap roll made in accordance with the present invention may comprise another body comprising an inner part having a first composition and an outer part having a second composition, the second composition being different from the first composition and the metal of the body between the inner part and the surface layer having a composition which changes without discontinuity.
  • the electrode may comprise an E.S.R. or other spray coated composite electrode.
  • the lower end of the disposable electrode 12 is immersed in a bath 30 of slag and beneath the slag bath 30 is a bath 31 of molten metal from which the metal solidifies in normal dendritic structure as shown at 32 to form an ingot 33.
  • the metal of the cladding 22 has a melting point which is 40°C below the melting point of the inner part 20 and 60°C above the melting point of the slag 30.
  • the melting point of the cladding 22 is, in the present example, 1530°C.
  • the inner part may have a melting point lying in the range 1160°C to 1600°C and the cladding may have a melting point lying in the range 1160°C to 1600°C.
  • the melting point of the inner and outer parts may differ by 20°C to 60°C.
  • the slag may have a melting point which differs from the lower of the melting point of the inner part and the cladding by 20°C to 60°C.
  • the mould is water cooled to a temperature lying in the range of 15°C to 65°C and the molten metal pool 31 has a temperature lying in the range 1400°C to 1600°C may be in the range 1160°C to 1600°C.
  • droplets of liquid metal from the cladding fall generally vertically downwardly and because of the relatively close proximity to the wall of the mould 10 and the relative low melting point of the metal from the cladding it is cooled and begins to solidify at and adjacent to the wall of the mould 10 so that the metal at the surface of the ingot 33 has a composition substantially similar to the composition of the metal of the cladding.
  • the metal droplets falling from the middle of the bottom of the inner part fall vertically downwardly and thus the metal solidifying at the centre of the ingot has a composition substantially similar to the composition of the inner part of the electrode.
  • composition at the centre of the ingot is:-
  • composition gradient does not exceed 40% per 100mm in the radial direction and this condition applies at any position along the longitudinal extent of the roll although only one such position is illustrated in Figure 4.
  • the resultant ingot has a uniform transition between the outer layer and the inner part and has substantially the same elastic modulus throughout its cross- section with the absence of any definite boundary or discontinuity between parts of different composition.
  • the total alloying elements reduced from about 15 wt.% in the surface part to less than 3% at the middle of the inner part.
  • the carbon content is less than 0.9 throughout and the molybdenum to carbon ratio in the surface part is greater than 2.0 such that M7C3 carbides are formed in the ingot to permit of secondary hardening of a roll made from the ingot when suitably heat treated in known manner.
  • the resultant ingot has uniform axial chemical and physical properties, has superior oxidation, wear and mechanical properties compared with known rolls which all suffer from the interface problems described hereinbefore.
  • the voltage and current used in the electroslag remelting operation are manipulated so that there is a relatively high voltage and a relatively low current, or vice versa and in addition the composition of the slag is adjusted so as to provide a relatively viscous slag. As a result turbulence in the slag and the melt pool are minimised so that the desired composition gradient explained above is achieved.
  • the voltage and current used are manipulated so that the floor of the melt pool is relatively flat.
  • the metal droplets leaving the cladding of the electrode are more dense than the metal droplets leaving the inner body of the electrode because they are more highly alloyed. This results in the droplets from the cladding of the electrode falling downwardly adjacent to the wall of the mould and, because the floor of the melt pool is relatively flat, there is relatively little tendency for these droplets to run towards the middle of the melt pool before they have solidified as a result of their spatial and temperature proximity to the mould wall.
  • the composition of the slag is adjusted to reduce the ionic capacity of the slag by adjusting the balance of the silicon, calcium and aluminium in the slag to reduce the tendency for electromagnetic stirring as well as the composition of the slag being adjusted to provide a relatively higher viscosity.
  • the slag has the following composition:- 33V3% CaO, 33V3% CaF 2 , 33Vs% A1,0 3 .
  • the slag may have a composition, for example, lying in the range to 20% CaO, 80%o CaF 2 , 0% A1 2 0 3 or 45% CaF, 45% A1 2 0 3 , 10% SiO 2 .
  • the cooling rate provided by the water cooling to the mould may be adjusted by adjusting the raw temperature of the mould to lie in the range 15°C to 65°C. In addition, the rate of movement of the mould may also be adjusted.
  • the electrode has a diameter which is about 0.9% of the diameter of the mould cavity.
  • the electrode is arranged so that approximately 20%, by weight, of the electrode comprises cladding and the balance is provided by the inner body. This ratio may lie in the range 10 to 40%.
  • the melting point of the cladding has been described as being lower than the melting point of the metal of the inner body, if desired this may be reversed.
  • metal droplets falling from the cladding of the electrode will still solidify out adjacent to the mould wall without significant mixing but other metal from the inner body, because of the greater density of the metal from the cladding, causes the droplets to fall downwardly adjacent to the mould wall together with the hereinbefore mentioned precautions to avoid mixing of low slag viscosity, low slag electromagnetic stirring and relatively flat melt pool base.
  • the rolling mill roll may be used for any desired purpose depending upon the selected composition but in the present example it is intended as a roughing work roll for the reducing stands of a hot strip rolling mill for rolling steel strip. Other typical applications are rolls for a cold rolling mill or back-up rolls for hot or cold rolling mills.
  • the modulus of elasticity of the ingot and hence of the resultant rolling mill roll varies in accordance with the composition change across the cross-section of the ingot but there is a relatively uniform change of modulus across the cross- section substantially proportional to the change of composition equivalent to less than 10% per 100mm of cross-section.
  • the consumable electrode 12 comprises an inner body 120 having welded to its external surface 121 a hollow cladding 122 which comprises a plurality of discrete tubular elements 123 in the form of tubes 124 containing powder 125.
  • the tubes and the powder provide an ingredient, additional to the tube of the inner body 120, which is added to the melt pool during electroslag remelting.
  • the inner body 120 is made of low alloy steel, cast iron or mild steel such as 0.2% carbon steel or any other suitable engineering ferrous metal.
  • the tubes 124 are made of mild steel in the present example but may be made of stainless steel and, if desired, the tubes may be made of high alloy steel or cast iron or indeed in any material of the composition described for the slats of the first embodiment.
  • the tubes may be provided solely to hold the powder or other alloying addition and so could be composed of material of the same composition as the inner body or indeed may be made of suitable non-metallic material, such as silica, of a melting point so as to melt in the bath at a desired rate to release the alloying addition.
  • suitable non-metallic material such as silica
  • the tubes have the following composition:
  • the powder has a mesh size of less than 3mm, but may have a mesh size up to 5mm and may lie in the range 2 - 5mm.
  • the powder may comprise any desired alloying additions such as one or more elements, intermetallic compound, or alloy.
  • the powder may comprise 0-100% of any one or more of the following elements:-
  • the powder may be made of a powdered alloy of any one of the compositions or range of compositions described as being suitable for the cladding in connection with the first embodiment or may be made of alloy of other compositions or of components which provide such compositions.
  • the powder may comprise alternatively or in addition metallic carbide(s) such as carbides of at least one of chromium, molybdenum, tungsten, titanium and vanadium and niobium.
  • metallic carbide(s) such as carbides of at least one of chromium, molybdenum, tungsten, titanium and vanadium and niobium.
  • the powder may comprise:-
  • Some of the carbon is combined with the Tungsten and the Titanium as intermetallic compound but the Tungsten and Titanium are combined as a solid solution and a proportion of the Carbon present is as free graphite.
  • the powder has the following composition:
  • the powder mixture has the following composition:- Chromium 2%
  • One or more of the above mentioned alloying elements may be present in the powder, either combined with the carbon as an inter-metallic compound or compounds, or as a solid solution or solid solutions.
  • the powder may comprise solid carbide particles coated with metal which allows wetting to occur between the particles and the metal of the melt pool.
  • the coating metal is preferably iron or iron carbon alloy or may be nickel or copper.
  • the coating is iron, because iron has a higher melting point than the melt pool metal to which it is to be added, which would inhibit wettability, it is preferred to add an appropriate amount of carbon or other alloying element such as nickel to the iron to produce an alloy having a melting point which matches that of the melt pool metal.
  • matches we mean that the melting points are preferably within approximately 20°C-30°C of each other.
  • the iron coating contains 3-3.5% carbon.
  • the particles may be coated with iron or with an iron carbon alloy having a lower carbon content where the particles dwell in the melt sufficiently long for the carbon to diffuse into the iron of the coating and so produce a composition which has a melting point which matches that of the metal of the melt pool.
  • the coated carbide particles preferably have a density which matches that of the melt pool.
  • matches we mean a density preferably lying in the range 6-8 grams per cc.
  • the carbides are preferably selected from the group comprising chromium, molybdenum, titanium, tungsten, niobium, vanadium or are mixed carbides thereof such as Cr7C3, (CrMo)7C3 and/or carbo-nitrides or mixed carbo-nitrides.
  • the carbides preferably have a composition so that the above mentioned matching density is achieved.
  • the amount of carbide particles added is such as to achieve up to 0.5 - 20% by weight of carbide particles in the surface part.
  • the tubes 124 in the present example are 16mm OD, 13mm ID but may lie in the range from 6mm ID to 28mm ID with appropriate OD.
  • the tubes are provided with restrictions at intervals along their length so as to hold discrete amounts of powder at positions along the length of the tubes, for example, such restrictions may be provided every 10cm.
  • restrictions are provided by crimping the tubes so as to close or substantially to close their bore but, of course, such restrictions may be provided in any other desired way.
  • the tubes 124 are attached to the inner body 120 so as to extend longitudinally thereof parallel to the longitudinal axis of the inner body but, if desired, a single tube or tubes may be wound helically around the inner body or one or more tubes may extend circumferentially around the body so as to lie in a plane which is perpendicular to the longitudinal axis of the inner body so long as the tubes are of the correct size to hold the correct amount of powder to be released into the melt at the longitudinal position of the body.
  • one or more tubes may be arranged to extend around the inner body in a plane or respective plane which is inclined to the longitudinal axis of the inner body at less than a right angle.
  • the cladding may comprise a hollow sleeve, for example, a sleeve comprising inner and outer generally cylindrical walls inter-connected by generally annular shaped walls with the space between the walls containing powder such as that described hereinbefore and the sleeve being mounted, for example, by welding or by virtue of being a push fit on the inner body.
  • the hollow sleeve is provided with restrictions in its wall at suitable positions along the length of the sleeve so as to divide the powder into discrete amounts for release into the melt pool sequentially as the sleeve and inner body are melted.
  • the consumable electrode 12 is melted in the electroslag remelting apparatus shown in Figure 3 and as in the case of the first embodiment, the lower end of the electrode 12 is immersed in a bath 30 of slag and beneath the slag bath 30 is a bath 31 of molten metal from which the metal solidifies in normal dendritic structure, as shown at 32 to form an ingot 14.
  • the melting point of the additional ingredient for example Tungsten, Titanium solid solution which can at least partly melt in the melt bath and the alloy carbides is greater than the melting point of the slag 30 and of the inner body 120 of the consumable electrode 12.
  • the melting point of the slag, the inner body and cladding tube/sleeve may be related as described in connection with the first embodiment and the mould may be similarly water cooled whilst the molten melt pool may have a temperature lying in a similar range to the first embodiment.
  • droplets of liquid metal and metal carbide from the tubes 124 and powder 125 fall generally vertically downwardly and because of the relatively close spacial and temperature proximity to the wall of the mould 110 the droplets solidify relatively rapidly at or adjacent to the mould wall so that the metal at the surface of the ingot 14 has a relatively high uniform distribution of alloy and alloy carbides as well as having a composition of matrix substantially similar to the composition of the metal of the tubes 124. Where the carbide is solid it is trapped by the solidifying metal adjacent the mould wall.
  • the metal droplets falling from the middle of the bottom of the inner part fall vertically downwardly and thus the metal solidifying at the centre of the ingot has a composition substantially similar to the composition of the inner part of the electrode.
  • the ingot has a relatively uniform transition region between the inner part and the surface part.
  • the ingot, and hence any resulting product such as a roll as described hereinbefore, has an elastic modulus which increases in direct proportion to the amount of the distribution of the alloy/alloy carbide through the ingot cross-section.
  • composition at the surface of the ingot is:
  • composition at the centre of the ingot is:
  • the variation in composition is believed to arise due to the relatively higher diffusion of chromium and carbon compared with the relatively lower diffusion and more dense tungsten and titanium.
  • the composition gradient does not exceed 40% per 100mm in the radial direction and this condition applies with any position along the longitudinal extent of the roll.
  • Other features of the method and apparatus of this embodiment are similar to those of the first described embodiment and hence further discussion is not required.
  • a third embodiment will now be described, which is a modification of the second embodiment.
  • the structure and composition of the consumable electrode and the hollow elements are as described in connection with the second embodiment except that the inner body 120, or the tubular elements 123 or the additional ingredient, hereinafter to be described, individually or together, contain nitrogen in an amount or amounts to provide a total of 0.001 to 0.1% nitrogen and, in addition, may provide a total of 0.001 to 0.5% niobium. If desired, such amounts of nitrogen and niobium may be provided in the first and second embodiments.
  • the powder in the tubular elements comprises at least one of, titanium carbide, a mixed carbide of titanium and at least one other element, such as a mixed carbide of titanium and tungsten such as previously described, niobium carbide, or mixed carbides of any of the above mentioned carbides, and/or ferro-titanium.
  • a mixed carbide of titanium and tungsten such as previously described, niobium carbide, or mixed carbides of any of the above mentioned carbides, and/or ferro-titanium.
  • ferro-titanium ferro-titanium
  • the particles of the additional ingredient powder have a mesh size lying in the range up to 5 mm.
  • the additional ingredient may include other components such as those described in connection with the second embodiment.
  • the amount of such powder lies in the range 0.5% - 2% by weight.
  • the ESR operation may be performed in a manner in which mixing occurs in the melt pool so that there is little or no variation in composition across the cross-section of the resultant ingot.
  • the addition comprises titanium carbide or a mixed carbide of titanium and other elements such as tungsten
  • the carbide particles fall from the ends of the tube through the slag into the melt pool they are heated and caused to wholly or substantially go into solution in the metal in the melt pool.
  • titanium carbo-nitrides TiCN
  • titanium nitride sub-microscopic particles are precipitated in the interdendritic pools occurring on solidification.
  • the titanium carbo-nitride typically contains about 90% titanium and less than 10% carbon and nitrogen.
  • the tungsten carbide when present in the initial carbide, is believed to go into solid solution with the matrix metal, but some precipitation of very fine sub-microscopic particles of tungsten carbide or tungsten oxy-carbide may take place.
  • the ferro-titanium particles go into solution in the melt pool and there are precipitated sub-microscopic titanium carbo-nitride particles and/or titanium nitride particles and/or titanium carbide particles are precipitated, again in the interdendritic pools.
  • sub-microscopic particles of a respective carbide or carbides may also be precipitated and/or some of the added ingredient particles may not go into solution, but so long as they are sufficient titatium containing sub-microscopic particles the effects on microstructure hereinafter to be described are obtained.
  • the titanium of the sub-microscopic titanium carbo- nitride or other titanium or niobium containing sub-microscopic particles which are precipitated during the ESR operation pin the austenite grain boundaries, which interferes with the normal pearlite precipitation to give the above described bainitic/ferritic structure.
  • the titanium of the sub-microscopic titanium carbo- nitride etc. particles are made in the second or first embodiments, then a similar microstructure is obtained, although in such cases the effect will be concentrated at the surface due to the composition gradient.
  • additional ingredient to produce such sub-microscopic particles of titanium carbo-nitride etc. may be added to the melt pool in other ways to that described hereinbefore. For example, by adding particles in any desired manner, for example through a lance or in discrete amounts from a suitable dispensing means. Alternatively, the particles may be contained in a hollow container separate from the electrode and which is fed into the melt pool as a desired rate.
  • the appropriate ingredient may be fed into the melt pool in other than powder form either in the form of slats or other solid elements fixed to the electrode element or separately therefrom.
  • the consumable electrode comprises an inner body part with tubes containing powder mounted thereon.
  • the body part has the following composition:-
  • the tubes have the following composition:-
  • the powder has the following composition:-
  • the particle has a mesh size of less than 2mm.
  • the wt.% of powder addition was 1% of the finished ingot.
  • the ESR operation was carried out under standard operating conditions without any attempt being made to obtain the composition gradient. In fact, some composition gradient was noted, in particular with regard to tungsten and titanium.
  • the resulting ingot has a microstructure in a surface region as shown in Figure 8 and has the following composition:-
  • Figure 9 is a microstructure of a similar surface region of another ingot cast in the same way as in the above described example using an electrode of the same composition as the body part described above but without the tubes or powder addition.
  • the resultant ingot, shown in Figure 9 has a composition which corresponds to that of the electrode which was remelted.
  • the low carbon steel of this example contained about 0.1% nitrogen it is considered that at least some of this nitrogen has formed titanium carbo-nitride particles and hence that at least some of the above mentioned carbide particles comprise such titanium carbo-nitride particles which may also contain tungsten.
  • the composite electrode may comprise first and second parts which are not inner and outer parts respectively.
  • the second part may comprise a bore or bores or other hollow or hollows provided within the first part.
  • the composite electrode may comprise a plurality of individual components, such as a plurality of rods, slats or the like, of the same composition range as described above for the first part and assembled with a plurality of individual other components, such as tubes or other hollow elements containing powder or solid additional ingredient, or assembled with tubes and/or rods, slats or the like of solid metal and, of the same composition ranges as described above for the additional ingredient.
  • residuals includes nitrogen when present.
  • nitrogen When nitrogen is present it is typically present up to 0.1% and generally when present, is present in the range 0.001-0.1%.
  • compositions are expressed in % by weight.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

Procédé de fabrication d'un produit d'un métal ferreux industriel comprenant une opération de refusion sous laitier électroconducteur effectuée sur un élément d'électrode fusible comportant ledit métal ferreux industriel et où on a ajouté un ingrédient au bain de fusion, en plus dudit élément d'électrode fusible.
PCT/GB1994/001017 1993-05-12 1994-05-12 Produits de metaux ferreux industriels et procede de raffinage de fabrication sous laitier electroconducteur WO1994026942A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU66611/94A AU6661194A (en) 1993-05-12 1994-05-12 Engineering ferrous metal products and electroslag refining method of making such products

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
GB9309737.6 1993-05-12
GB939309737A GB9309737D0 (en) 1993-05-12 1993-05-12 Roll for use in rolling mills and method of making such a roll
GB9315359.1 1993-07-23
GB939315359A GB9315359D0 (en) 1993-07-23 1993-07-23 Roll for use in rolling mills and method of making such a roll
PCT/GB1993/002380 WO1994011541A1 (fr) 1992-11-19 1993-11-19 Metaux ferreux industriels, en particulier fonte et acier
GBPCTGB93/02380 1993-11-19

Publications (1)

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WO1994026942A1 true WO1994026942A1 (fr) 1994-11-24

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WO (1) WO1994026942A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102189247A (zh) * 2011-03-29 2011-09-21 沈阳东大兴科冶金技术有限公司 大电流短网直连式气体保护三相电渣炉
JP2012236212A (ja) * 2011-05-12 2012-12-06 Japan Steel Works Ltd:The エレクトロスラグ再溶解用消耗電極およびその製造方法
US10173395B2 (en) 2013-10-31 2019-01-08 Vermeer Manufacturing Company Hardfacing incorporating carbide particles

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1181663A (en) * 1966-05-05 1970-02-18 Foseco Int Production of Ingots by Electroslag Remelting Processes
LU61904A1 (fr) * 1970-10-21 1971-08-10
FR2086965A5 (en) * 1970-04-15 1971-12-31 Usinor Prodn of rolling mill rolls
LU65293A1 (fr) * 1971-10-26 1972-08-23
DE2450830A1 (de) * 1973-10-29 1975-06-05 Mitsubishi Heavy Ind Ltd Verfahren zur herstellung einer rohrfoermigen metallkonstruktion nach dem elektroschlackeumschmelz-verfahren
US3975577A (en) * 1974-06-04 1976-08-17 Centro Sperimentale Metallurgico S.P.A. Compound meltable electrode for manufacturing metal articles by remelting under electroslag
FR2306037A1 (fr) * 1975-04-01 1976-10-29 Usinor Procede de fabrication de cylindres de laminoir bimetalliques
EP0291922A2 (fr) * 1987-05-22 1988-11-23 Fried. Krupp Gesellschaft mit beschränkter Haftung Procédé de fabrication d'un rouleau composé
EP0386515A2 (fr) * 1989-03-04 1990-09-12 Fried. Krupp Gesellschaft mit beschränkter Haftung Procédé pour la production d'un composite métallique qui a une région présentant une résistance élevée à l'usure et dispositif pour la mise en oeuvre du procédé

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1181663A (en) * 1966-05-05 1970-02-18 Foseco Int Production of Ingots by Electroslag Remelting Processes
FR2086965A5 (en) * 1970-04-15 1971-12-31 Usinor Prodn of rolling mill rolls
LU61904A1 (fr) * 1970-10-21 1971-08-10
LU65293A1 (fr) * 1971-10-26 1972-08-23
DE2450830A1 (de) * 1973-10-29 1975-06-05 Mitsubishi Heavy Ind Ltd Verfahren zur herstellung einer rohrfoermigen metallkonstruktion nach dem elektroschlackeumschmelz-verfahren
US3975577A (en) * 1974-06-04 1976-08-17 Centro Sperimentale Metallurgico S.P.A. Compound meltable electrode for manufacturing metal articles by remelting under electroslag
FR2306037A1 (fr) * 1975-04-01 1976-10-29 Usinor Procede de fabrication de cylindres de laminoir bimetalliques
EP0291922A2 (fr) * 1987-05-22 1988-11-23 Fried. Krupp Gesellschaft mit beschränkter Haftung Procédé de fabrication d'un rouleau composé
EP0386515A2 (fr) * 1989-03-04 1990-09-12 Fried. Krupp Gesellschaft mit beschränkter Haftung Procédé pour la production d'un composite métallique qui a une région présentant une résistance élevée à l'usure et dispositif pour la mise en oeuvre du procédé

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102189247A (zh) * 2011-03-29 2011-09-21 沈阳东大兴科冶金技术有限公司 大电流短网直连式气体保护三相电渣炉
CN102189247B (zh) * 2011-03-29 2013-09-18 沈阳东大兴科冶金技术有限公司 大电流短网直连式气体保护三相电渣炉
JP2012236212A (ja) * 2011-05-12 2012-12-06 Japan Steel Works Ltd:The エレクトロスラグ再溶解用消耗電極およびその製造方法
US10173395B2 (en) 2013-10-31 2019-01-08 Vermeer Manufacturing Company Hardfacing incorporating carbide particles

Also Published As

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