Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/10—Making spheroidal graphite cast-iron
  • C21C1/105—Nodularising additive agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/17—Metallic particles coated with metal
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12181—Composite powder [e.g., coated, etc.]

Definitions

• nickel and magnesium afford certain advantages, and in particular nickel is extremely effective in moderating the violence of the reaction between magnesium and molten iron. Moreover it is often a very useful constituent of the cast iron formed.
• the standard nickel-containing alloy in use contains from 14 to 16% magnesium. This alloy has many advantages. In particular, its reaction with molten iron, though spectacular, is not violent; and its density is greater than that of the molten iron so that it sinks into the melt and remains submerged during reaction.
• Nickel-magnesium alloys containing a higher proportion of magnesium have lower densities than the 15% magnesium alloy, and to avoid excessive losses of magnesium they need to be held below the surface of the melt by a plunger while they react with the molten iron.
• the efficiency of such nickelnited States Paten magnesium alloys is high, and generally higher than that obtained by a direct addition of the standard 15 magnesium alloy. Nevertheless these high-magnesium alloys are not used to any great extent, largely because they are very difficult to produce commercially by melting techniques. Melting losses are high, and segregation of magnesium in the cast nickel-magnesium ingots readily occurs.
• Still another object of the present invention is to provide by powder metallurgy nickel-magnesium bodies having improved addition characteristics when employed to introduce magnesium into molten cast iron.
• nickel-magnesium addition agents can be prepared without melting from particles of magnesium coated with nickel.
• Our invention comprises compacting together particles of nickel-coated magnesium powder with or without other particles in a proportion such that the magnesium constitutes from 10 to 50% of the compacts by weight.
• Higher proportions of magnesium lead to undesirably violent reaction with molten iron and low recoveries of magnesium, while if the magnesium content is less than 10% such a large proportion of the addition agent must be added to the iron to introduce a given amount of magnesium as undesirably to lower the temperature of the molten iron, and also unnecessarily to increase the cost.
• the compacts may either be used as such or may be sintered before addition to molten iron.
• the nickel coating on the particles serves to restrain the reaction of the magnesium with the molten iron, while in the sintered compacts it reacts with the magnesium during sintering to form intermetallic compounds and solid solutions that react with only moderate vigor with the molten iron.
• the intimate association of the magnesium and the nickel of the coating provide very favorable conditions for their interdiifusion and alloying during sintering without loss of magnesium.
• the thickness of the coating is thus of importance both in green (unsintered) compacts and when they are sintered.
• the nickel-coated magnesium powder may be admixed with powder of other constituents such as nickel, iron, silicon and copper commonly used as diluents in magnesium addition agents in order to moderate their reaction with molten iron.
• the use of any such diluent powder gives rise to risk of segregation in the compacts to the extent that the size and shape of the particles differ from those of the nickel-coated magnesium particles, but on the other hand a diluent powder may assist in moderating the reaction and thereby permit the nickel coating to be thinner than is otherwise required.
• the compacts may contain substantial additional amounts of nickel powder, to bring the total nickel content of the compacts up to as much as 90% of the weight of the compacts, the maximum amount of added nickel being set by the need for an adequate coating of nickel on the magnesium particles while maintaining a sufiicient magnesium content in the compact.
• the resulting compacts have the advantage of having no other constituents than nickel and magnesium. Iron, which is not as effective as nickel in moderating the violence of the reaction, may be present in amounts up to 30% of the weight of the compacts.
• Silicon which has a moderating power between that of nickel and iron, and which is also useful as a graphitizing agent, may be present up to 70% of the weight of the compacts. Iron and silicon in the compacts may, if desired, be alloyed together as ferro-silicon powder.
• Copper the other common diluent metal, is an excellent moderator of the violence of the reaction, but in large amounts adversely affects the formation of spheroidal graphite in cast iron, and for this reason the proportion of any copper in the compacts should not exceed 30%.
• the nickel coatings on the particles may be formed by any convenient method, but we prefer to deposit the nickel by the thermal decomposition of nickel carbonyl. In this way a continuous layer of nickel is formed over the particle surface and may be built up to any desired thickness, thus enabling the proportion of nickel to magnesium in the coated particles to be varied over a very wide range.
• the green strength of the compacts is also afiected by the particle size, decreasing as the particles become coarser, and for this reason in unsintered compacts the coated powder is preferably not larger than 72 mesh BS8 (0.2 mm), and most advantageously not larger than mesh (0.18 mm).
• the strength of unsintered compacts may be increased, though at the expense of some loss in efiiciency, by incorporating a small proportion of binder, e.g. a synthetic resin, either throughout the mix or as a surface layer.
• the compacts may be enclosed in bags or coverings, e.g. of polythene, to facilitate their handling. The highest efliciency is obtained when the coated powder does not contain any substantial proportion of particles smaller than mesh (0.1 mm.).
• coarser particles e.g. from 10 to 60 mesh 1388 (1.7 to 0.25 mm.)
• sintering introduces a further processing operation with attendant increase in cost, and we prefer to employ the unsintered compacts.
• the magnesium may be alloyed with small amounts of elements, e.g. up to 1% of silicon, added before it is coated to render it brittle and aid in the production of magnesium powder by pulverization of a cast ingot of magnesium. Care must however be taken to avoid any additions that have a deleterious effect on the formation of spheroidal graphite in cast iron.
• elements e.g. up to 1% of silicon
• the addition agents of the invention have many advantages compared with materials of similar composition prepared by melting, casting and crushing to size. Thus they can readily be made by standard powdermetallurgical procedures without appreciable loss of nickel or magnesium, whereas in preparing nickel-magnesium alloys by melting substantial losses are encountered. This is particularly advantageous in the case of addition agents of high magnesium content, e.g. about 30% or 40% to about 50%. For example, in melting a nickel-magnesium alloy containing 15% by weight of magnesium about 7% of the materials charged is lost as dross or otherwise during the melting process, and the losses in melting such alloys of higher magnesium content are still greater.
• the compacts are readily made of regular and uniform shape and size, are easily packed, and have a reliably reproducible composition. Thus, they can be made to contain an accurately predetermined amount of magnesium, so that a given magnesium addition may readily be calculated by simply counting out the number of compacts to be added to a given metal.
• magnesium recoveries and efficiencies similar to or even better than those for melted alloys of the same composition are obtainable.
• Example I Magnesium powders of commercial purity having particle sizes of about 60 mesh BSS, in the range minus 85 to plus 120 mesh and in the range minus 100 to plus 150 mesh respectively, were coated with nickel by the thermal decomposition of nickel carbonyl to provide coated powders containing, by weight, about 60% nickel, the balance being magnesium.
• the initial powders were elongated in particle shape, some angular particles being present in the 60 mesh powder.
• the powders were briquetted at a pressure of about 30 long tons per square inch to produce strong cylindrical pellets having a diameter of about one inch and a height of about 0.75 inch.
• Magnesium powder containing about 0.5% silicon was coated with nickel by the thermal decomposition of nickel carbonyl to provide coated particles containing about 60% nickel, the balance being magnesium.
• the magnesium powder had a particle size of about 36 mesh and had a regular, angular shape. Portions of the coated powder were coni'pacted at a pressure of about 30 long tons per square inch to provide cylindrical pellets having a diameter of about one inch and a height of about 0.75 inch.
• About 0.4% by weight of the as-pressed compacts were plunged into two other portions of the molten iron at 1500 C. as in Example I. Residual magnesium contents of 0.043% and 0.051%, representing an average magnesium recovery of about 33.7% and an average efficiency of about 13.5%, respectively, were obtained.
• the compacts obtained in this instance were noticeably more friable than those obtained using finer powders as set forth in Example I and the lower magnesium recovery obtained was attributed to this factor.
• Example III Atomised magnesium powder having a particle size range of 22 to 44 mesh BSS was coated with nickel by thermal decomposition of nickel carbonyl.
• the magnesium powder particles were rounded in shape, with a few re-entrants and the nickel coatings were from 20 to 30 microns thick and covered the whole surface fairly uniformly and filled the irregularities.
• the analysed nickel content of the powder was 58.8%.
• Portions of the coated powder were compacted under a pressure of 30 tons per square inch to form cylindrical pellets about one inch in diameter and about 0.75 inch high. These had fair green strength, but tended to crumble at the edges. Their strength was not significantly improved by heating at temperatures below 400 C., above which interdiffusion began to occur between the nickel and the magnesium as a preliminary to sintering.
• Example IV Pellets prepared as described in Example III were heated for 30 minutes at 650 C. in an atmosphere of dry hydrogen. Under these conditions the magnesium center of the particles just melted, and the nickel and magnesium reacted to form the intermetallic compound Mg Ni and the eutectic Mg/Mg Ni. Substantial amounts of the nickel coating remained unreacted and leakage of the molten metal through the nickel coating sintered the particles together and greatly increased the strength of the bodies.
• Example V Further compacted pellets prepared as described in Example III were heated for one hour in dry hydrogen at 725 C. i.e., below the temperature (760 C.) of peritectic formation of the intermetallic compound Mg Ni. Substantially all the nickel reacted with the magnesium to form Mg Ni and Mg/Mg Ni eutectic and the identity of the individual particles was almost lost in the sintered mass. Sintered pellets formed in this way, added in an amount of 0.5 to a further portion of the molten iron described in Example III at 1500" C. by plunging, reacted in a similar manner to the unsintered pellets to give an iron which, when cast, contained 0.059% magnesium and has a satisfactory spheroidal graphite structure.
• Example VI A mixture of 36.4 parts by weight of the nickel-coated magnesium powder used in Example III with 63.6 parts by weight of carbonyl nickel powder was compacted at 30 tons per square inch as in Example 111 to pellets having the composition nickel-15% magnesium and the pellets were sintered by heating at 850 C. for 15 minutes.
• the resulting sintered bodies had a duplex structure consisting of nickel and the intermetallic compound MgNi Despite the high temperature employed for sintering, the presence of the nickel powder substantially prevented loss of magnesium. When 1.0% of these bodies were added to molten iron at 1450 C. by tapping the iron on to the addition bodies, the reaction was not violent.
• Castings poured from the treated melt had a magnesium content of 0.073% and had a satisfactory spheroidal graphite structure.
• a standard alloy of 85% nickell5% magnesium made by adding magnesium to molten nickel was similarly added to another portion of the same iron melt.
• the vigor of the reaction was similar to that occurring with the sintered material, and the resulting iron contained about 0.052% magnesium, and had a satisfactory spheroidal graphite structure.
• Table II The results of Examples III to VI are summarised in the following Table II:
• magnesium-containing addition agent according to the invention is also useful for treating molten metals with magnesium for purposes other than the production of ductile iron. Such purposes include the desulphurisation of cast iron and of steel.
• the improvement which comprises introducing magnesium into molten cast iron as a briquetted agent containing about 10% to about 50% magnesium, with the balance essentially nickel made from an initial powder mix comprising magnesium particles coated with nickel.
• the improvement which comprises introducing magnesium into molten cast iron as a powder metallurgical compact containing about 10% to about 50% magnesium, with the balance essentially nickel, said compact being made from an initial powder mix comprising magnesium particles coated with nickel and having a particle size of not more than about 72 mesh BSS.
• the improvement which comprises introducing magnesium into molten cast iron as a ower metallurgical compact containing about 40% magnesium particles coated with nickel and having a particle size of not more than about 85 mesh B85.
• the improvement which comprises introducing magnesium into molten cast iron as a sintered powder metallurgical compact containing about 10% to about magnesium, with the balance essentially nickel, said compact being made from an initial powder mix comprising magnesium particles coated with nickel and having a particle size from about 10 mesh to about mesh B85.
• An addition agent for adding magnesium to molten metals consisting of compacts in which the magnesium is present as nickel-coated magnesium powder having a particle size not greater than 60 mesh BSS, and said magnesium amounts to from 10 to 50% by weight of the compacts, with the balance essentially nickel.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Treatment Of Steel In Its Molten State (AREA)

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Cited By (11)

Citations (12)

• 1964
  • 1964-05-13 GB GB20019/64A patent/GB1033358A/en not_active Expired
• 1965
  • 1965-05-10 US US454652A patent/US3385696A/en not_active Expired - Lifetime
  • 1965-05-13 CH CH672265A patent/CH439761A/fr unknown
  • 1965-05-13 BE BE663907A patent/BE663907A/xx unknown
  • 1965-05-13 NL NL6506104A patent/NL6506104A/xx unknown

Patent Citations (12)

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