Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/008—Using a protective surface layer
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
  • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching

Definitions

• ABSTRACT OF THE DISCLOSURE A method of treating metal surfaces to protect the surfaces against scale formation during heat treatment such as annealing including applying to the surface a composition of a vitreous material such as powdered glass, a refactory filler such as silica and ferrosilicon.
• This invention relates to the treatment of metals and more particularly to means for preventing or reducing oxidation of the surface of metal objects such as billets, slabs and castings during heat treatment operations applied thereto.
• Furnaces in which the atmosphere may be controlled are suitable for heating small objects such as tools but it is impractical to make use of such apparatus to heat large objects such as billets and slabs which may weigh several tons. Moreover, if the metal object is required to be removed from the furnace whilst still in a heated condition (e.g., a steel billet or Patented Dec. 10, 1968 slab for rolling), fairly severe oxidation can still take place on exposure to the atmosphere.
• a heated condition e.g., a steel billet or Patented Dec. 10, 1968 slab for rolling
• paints may include materials which are preferentially oxidised (e.g., powdered aluminium, ferrosilicon or silicon and are thus intended to function in a sacrificial manner.
• Other types of paint depend upon the physical exclusion of the atmosphere from the surface by the ability of their constituents to form a glaze when heated. Materials used in such paints are mixtures of various refractory oxides, slags, silica and ground glass. The preferentially oxidised materials mentioned above have also been included in the glaze-forming perparations.
• Varying degrees of success may be achieved by the use of these known paints which are generally applied to the metal surface as a layer of the order of A2.
• none of them has been found to be capable of consistently reducing oxidation losses to a satisfactory degree although, in some instances, the amount of metal lost as oxide scale has been reduced by as much as 70%.
• a reduction in losses even of this magnitude is however considered unsatisfactory in that the degree of oxidation still suffered is inevitably accompanied, in the case of steels, by surface decarburisation, thus necessitating a machining operation to remove the decarburised layer.
• It is an object of the present invention to provide a method of protecting metal surfaces which comprises applying a composition thereto which, when applied to metal articles to be treated, affords a substantially improved measure of protection against surface oxidation and surface decarburisation during heat treatment, so that the extent of residual metal oxide formation is at most 20% by weight of that which occurs when no preventive measures are taken, i.e., at least four fifths of the normal loss is avoided.
• the residual oxidation is then at so low a level that it may be wholly unnecessary to carry out any machining of the surface for removal of oxidised or decarburised strata.
• a protective layer in order to be capable of achieving this degree of success, must be able to form a continuous film on the surface of the metal article which is imperivious to gases, and must adhere firmly to the metal surface.
• the coating composition must be formulated such that the applied coating does not completely fuse to form a glaze since, in such acase, the film acts as an oxide ion carrier and scaling can become very severe indeed; worse, in fact than on a similar, untreated specimen.
• the composition used to apply the layer should have such fluidity that it may be applied by spraying, dipping, brushing or any other conventional method.
• a method for the treatment of slabs, billets and other articles of metal, to reduce or inhibit surface oxidation during heat treatment thereof which comprises applying to the surface thereof a layer of a composition containing ferrosilicon, finely divided refractory material and a fusible glaze-forming material.
• compositions in the form of dispersions, suspensions or slurries and for that reason it is desirable to include with the composition as applied, in addition to a liquid carrier for the solid ingredients, a dispersing agent (i.e., an agent which will aid in holding the particulate ingredients in suspension in the carrier liquid). It is also frequently desirable to include an adhesive substance which will aid in anchoring the applied layer to the metal surface.
• a dispersing agent i.e., an agent which will aid in holding the particulate ingredients in suspension in the carrier liquid.
• adhesive substance which will aid in anchoring the applied layer to the metal surface.
• the composition further includes ingredients which when the coated metal is heated react with one another exothermically. It is found that in this way the fusing of the glaze-forming material is facilitated and improved results may be obtained.
• the ingredient ferrosilicon is well known and requires no further comment.
• the finely divided refractory material may be, for example, alumina, silica, magnesia or any other refractory oxide or a mixture of any of these, or any other refractory material such as a refractory silicate.
• the fusible glaze-forming material may be powdered glass or any material known per se for use as a ceramic glazing material. These are usually mixtures of silicates, borates or phosphates with metal oxides, e.g., iron oxide, or lead oxide. Slagging agents known for use in the iron and steel industry may also be employed.
• the composition is in the form of a suspension, dispersion or slurry in a liquid carrier
• any liquid carrier can be used. Water is generally preferred from the standpoint of convenience and cheapness. Any other volatile or inflammable liquid can be employed, e.g., an alcohol, but the latter are generally less preferable as introducing fire and explosion hazards.
• the dispersing agent may be any such compound known per se, e.g., a montmorillonite gel.
• Adhesives present in the composition may be gums or resins, r bentonite clay or mixture of these.
• the composition should contain exothermically reacting ingredients, these will usually consist of an oxidisable substance and an oxidising agent.
• the former may be the ferrosilicon which is in any event present in the composition but there may additionally be present a proportion of finely divided aluminium.
• the oxidising agent may be most conveniently an alkali metal or alkaline earth metal nitrate or chlorate, iron oxide (Fe O or Fe O manganese dioxide and mixtures of any of these.
• aluminium and an oxidising agent it is usually preferable also to include a proportion of a fluoride, e.g., alkali metal or alkaline earth metal fluoride, aluminium fluoride or a mixed fluoride such as sodium aluminium fluoride or potassium aluminium fluoride or a complex fluoride such as a silica fluoride, boro fluoride or titano fluoride.
• a fluoride e.g., alkali metal or alkaline earth metal fluoride, aluminium fluoride or a mixed fluoride such as sodium aluminium fluoride or potassium aluminium fluoride or a complex fluoride such as a silica fluoride, boro fluoride or titano fluoride.
• a fluoride e.g., alkali metal or alkaline earth metal fluoride, aluminium fluoride or a mixed fluoride such as sodium aluminium fluoride or potassium aluminium fluoride or a complex fluoride such as a silic
• Example 1 Parts by weight Refractory (e.g. alumina or silica) (l00 mesh B.S.S.) Ground glass (-200 mesh B.S.S.) 3 Ferrosilicon (200 mesh B.S.S.) 34 Aluminium powder (100 mesh B.S.S.) 14 Fluoride (60 mesh B.S.S.) 4 Oxidising agent (60 mesh B.S.S.) 15 Bentonite 7 Rosin pitch 3 Alkyl ammonium montmorillonite gel The whole of the foregoing ingredients are mixed to a paste and diluted with isopropyl alcohol in the proportions 100 gm. paste: 100 cc. isopropyl alcohol.
• Refractory e.g. alumina or silica
• the gel referred to is prepared by thorough kneading together 8.7 parts by weight of alkyl ammonium montmorillonite and 4.3 parts by weight of methyl alcohol. The dough thus formed is added to 87 parts by weight toluene whilst stirring gently. Finally the whole mixture is stirred vigorously for about three minutes, after which it is transferred to an air tight container and allowed to stand for 24 hours before use.
• Example 2 Parts by weight Refractory material (eg. alumina or silica) (-l00 mesh B.S.S.) 3O Powdered glass (-200 mesh B.S.S.) 2 /2 Ferrosilicon (200 mesh B.S.S.) 6 Sodium fluoride (-l0() mesh B.S.S.) 2 /2 Bentonite 2 Vinsol resin 2 /2 Alkyl ammonium montmorillonite gel 11
• Refractory material eg. alumina or silica
• 3O Powdered glass -200 mesh B.S.S.
• Ferrosilicon 200 mesh B.S.S.
• Sodium fluoride -l0() mesh B.S.S.
• Bentonite 2 Vinsol resin 2 Alkyl ammonium montmorillonite gel 11
• the gel is prepared in the same way as in Example 1. The 11 parts of the prepared gel were mixed with 66 parts by weight of isopropyl alcohol until all lumps were removed and the remaining dry ingredients were added in
• Example 3 Parts by weight Refractory material (eg. alumina or silica) (-lO0 mesh B.S.S.) 18 Powdered glass (60 mesh B.S.S.) 2 Ferrosilicon (200 mesh B.S.S.) 28 Powdered aluminium (l00 mesh B.S.S.) l2 Fluoride 100 mesh B.S.S.) 5 Oxidising agent (nitrate, iron oxide or the like (60 mesh B.S.S.) l2 Bentonite 7 Water soluble resin binder (e.g. urea formaldehyde, phenol formaldehyde resin) Aqueous suspension agent (e.g. a gum) 4 Sodium silicate solution (4.8% solids) 4 Buffer (eg. boric acid or mono sodium orthophosphate) All the ingredients except sodium silicate, resin and the suspension agent are mixed together in the proportions stated (88 parts by weight) and added to parts weight of water. The remaining ingredients are then stirred into the mixture.
• Refractory material
• Example 4 Parts by weight parts of above mixture are mixed with 25 parts of isopropyl alcohol exactly as in Example 1.
• compositions thus produced are in the form of slurries which may be applied, preferably by spraying, to the surfaces of the metal to be subjected to heat treatment. Adherence of the resulting layers to metal surfaces is very good, cohesion being given to the applied coating by the resin and bentonite content.
• the gel is included in the composition as a suspension agent and, even though some settling of the solid constituents may occur, redispersion is effected very readily.
• Example 3 employs boric acid and monosodium orthophosphate as buffering agents. Corrosion of such ingredients as ferrosilicon may be further inhibited by precoating them, e.g., with insoluble resins.
• the novel method of this invention is suitable, therefore, for protecting metal billets and slabs which are to be heated before hot working operations.
• the method is also useful for protecting the surface of finished metal articles which are to undergo heat treatment, e.g., tools which have been formed and machined to size but which must then be annealed, tempered or otherwise heat treated.
• a composition cousitsing essentially of vitreous material a refractory filler selected from the group consisting of aluminia, silica, magnesia, refractory silicates and mixtures thereof, and ferrosilicon, in proportions, per one part by weight vitreous material, of from about 5 to about 30 parts by weight refractory filler, and from about 1 to about parts by weight ferrosilicon.
• vitreous material of the composition is a glass.
• composition contains up to about 10% by weight of an oxidising agent selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates, alkali metal chlorates, alkaline earth metal chlorates, iron oxide, manganese Oxide and mixtures thereof.
• an oxidising agent selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates, alkali metal chlorates, alkaline earth metal chlorates, iron oxide, manganese Oxide and mixtures thereof.
• composition contains up to about 10% by weight of a fluoride.
• composition contains up to about 10% by weight a fluoride.
• composition contains up to about 10% by weight finely divided aluminium.
• composition is in the form of a suspension of the ingredients in a liquid carrier.
• composition contains up to about 10% by weight of a suspending agent 11.
• composition contains up to about 10% by weight of an adhesive substance.
• composition contains up to about 10% by weight of an oxidising agent selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates, alkali metal chlorates, alkaline earth metal chlorates, iron oxide, manganese oxide and mixture thereof.
• an oxidising agent selected from the group consisting of alkali metal nitrates, alkaline earth metal nitrates, alkali metal chlorates, alkaline earth metal chlorates, iron oxide, manganese oxide and mixture thereof.
• composition contains up to about 10% by weight finely divided aluminium.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Paints Or Removers (AREA)
• Coating By Spraying Or Casting (AREA)

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Publications (1)

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Family Applications (1)

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Cited By (4)

Citations (11)

• 1963
  • 1963-11-07 GB GB44025/63A patent/GB1021374A/en not_active Expired
• 1964
  • 1964-11-03 US US408672A patent/US3415691A/en not_active Expired - Lifetime
  • 1964-11-05 BE BE655345A patent/BE655345A/xx unknown
  • 1964-11-06 ES ES0305715A patent/ES305715A1/es not_active Expired
  • 1964-11-06 AT AT943364A patent/AT250756B/de active
  • 1964-11-06 DE DE19641496513 patent/DE1496513B2/de active Pending

Patent Citations (11)

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