Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/067—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds comprising a particular metallic binder

Definitions

• This invention relates to cemented chromium carbide alloys having considerably enhanced strength and to a process for preparing such alloys.
• Cemented carbides are well known for their unique combination of hardness, strength and abrasion resistance and are accordingly extensively used in industry as cutting tools, drawing dies and wear parts.
• the most extensively used cemented carbide alloys are composed of tungsten carbide and cobalt because of their unexcelled combination of hardness and strength or toughness.
• the tungsten carbide-cobalt alloys have certain deficiencies, such as their relatively low oxidation resistance and their susceptibility to corrosion in media such as aqueous acids. Moreover, they have a very low coeflicient of thermal expansion relative to that of steel.
• Chromium carbide-nickel cemented carbide alloys possess a number of very desirable properties. They are characterized by a higher coefiicient of thermal expansion than the other cemented carbidescloser to that of steela low density, they are nonmagnetic, and they are generally more resistant to oxidation and to corrosion in aqueous acid media. They possess high hardness, like the other cemented carbide alloys. However, the chromium carbidenickel alloy systems heretofore available have displayed a very serious deficiency relative to the other cemented carbides that has considerably restricted their usage. They are significantly lower than the other cemented carbide systems in strength or specifically transverse rupture strength.
• the foregoing and other objects of this invention may be achieved by the addition of certain small but critical amounts of phosphorus to the composition from which the cemented carbide alloy is prepared. More specifically, the addition of amounts ranging from a trace to about 0.4% by weight, based on the total weight of the composition, of phosphorus to a chromium carbidenickel powder mixture produces a cemented carbide alloy having a strength which is enhanced as much as 100% over a comparable chromium carbide-nickel composition prepared without the phosphorus addition.
• the alloys of the invention are prepared by pressing a mixture of the aforementioned powders and sintering the pressed mixture into a compact.
• the phosphorus is preferably added to the starting mixture in the form of a nickel-phosphorus alloy in amounts adjusted so as to contain the necessary phosphorus quantity.
• compositions of this invention contain chromium carbide essentially in the form of Cr C and a binder of nickel, the binder ranging from about 1, and preferably 3, to about 35% by weight.
• Other metals may be added to the nickel binder and specifically up to one-third of the nickel may be replaced by molybdenum or tungsten.
• the present compositions have very excellent resistance to oxidation relative to that of cemented carbide alloys in general. They also display good resistance to corrosion in media such as aqueous acids. They have low density, approximately one-half that of tungsten carbide-cobalt alloys. They are nonmagnetic unlike the cobalt-containing alloys. They have a high coeflicient of thermal expansion, more nearly that of steel or about double that of tungsten carbide, titanium carbide and tantalum carbide base alloys. They are of high hardness. Unlike the chromium carbide-nickel base alloys heretofore available, the compositions of this invention are of high strength, having up to approximately twice the strength of the chromium carbide-nickel base alloys heretofore available.
• the compositions of the present invention are suificiently strong such that compromises may be made between strength and hardness.
• the tungsten carbideFcobalt alloys vary in tungsten carbide content from about to 97% by weight, and in cobalt content from about 25% to about 3% by weight. Maximum strength is achieved in alloys of high cobalt content. Maximum hardness is achieved in alloys of high tungsten carbide content but some sacrifice in strength must be made to accomplish the latter.
• the improvements provided by the present invention are such that similar compromises between strength and hardness can now be made within useful limits in chromium carbide base alloys.
• compositions of the present invention may vary in chromium carbide content from about 65% to about 99% by weight.
• Strength is greatest in alloys of high nickel content, being about double that of the chromium carbide base alloys heretofore available.
• Hardness is greatest in alloys of high chromium carbide content, and these have hardness values as high as about 91 R considerably higher than that of existing chromium carbide commercial alloys, which generally run from 8789 R even though their strengths are equal.
• alloys containing more than about 35% nickel, or other nickelbase binder such as nickel-molybdenum or nickeltungsten do not have the requisite hardness, whereas alloys containing less than 1% nickel are low in strength. If more than about 0.4% phosphorus by weight is employed, the hardness of the resulting alloys suffers substantially. It is difficult to define in absolute terms the exact minimum amount of phosphorus that is required. The strength improvement has, however, been achieved with extremely small amounts. On the one hand, it is of course encessary that a definite amount of phosphorus be present. On the other hand, the few parts per million that may be present in starting materials of usual purity is not suflicient.
• the carbon content of the starting chromium carbide Cr C should normally be between 13.0% and 13.3% by weight, preferably between 13.2% and 13.3%. It is believed that the carbon of the chromium carbide powder employed herein is essentially all combined. Again, this is not known with certainty because the analysis of carbon in chromium carbide is very difiicult and the results subject to some doubt, even utilizing the best analytical techniques available.
• the process of the invention is carried out by first intimately mixing the chromium carbide powder, nickel metal powder and a source of phosphorus, the latter preferably being in the form of a mixture of a transition metal such as nickel and phosphorus.
• a nickel-phosphorus alloy may be made, for example, by reacting ammonium phosphates with nickel metal powders at elevated temperatures, and subsequently crushing and pulverizing the solidified melt.
• Phosphorus may also be added directly as ammonium phosphate or as an anhydride of phosphorus but the oxygen present in combined form must be carefully expelled by reduction or dissociation prior to sintering.
• the above-mentioned powders are intimately mixed by ball-milling in a liquid medium such as acetone.
• the milled powder is then dried in a protec tive atmosphere, and a small amount of parafiin is added to facilitate pressing of the powder.
• the pressed compacts are heated to about 450 C. in a protective atmosphere to expel the paraffin.
• the compacts are then sintered in a protective atmosphere at about 1200-1300 C.
• Example #1 An alloy containing 17% nickel, 83% chromium carbide, and about .04% phosphorus was prepared as follows:
• chromium carbide powder of 13.1% carbon was adjusted to the desired carbon level in 10 kilo lots.
• 86 grams of chromium powder were added as a carburization promoter together with 33 grams of carbon (lamp black) such that the carbon content of the total mix was about 13.3%.
• These powders were intimately mixed and heated in carbon boats in a hydrogen atmosphere at a temperature of 1400 to 1500" C. for a period of approximately one hour. The resulting mass was crushed and pulverized to -325 mesh powder.
• a nickel-phosphorus alloy was prepared by reacting diammonium phosphate and nickel powder in quantities sufiicient to provide a 17% phosphorus alloy. For this purpose, the mixture was melted in carbon boats in a hydrogen atmosphere at a temperature of approximately 1250 C. The cooled mass was quite friable and easily converted to 200 mesh powder.
• the resulting pieces had a hardness of 88.5 R 2. density of 7.03 gm./cc., and a transverse rupture strength of 250,000 p.s.i. This is approximately twice the strength of heretofore available chromium carbide-nickel alloys.
• Example #2 An alloy containing 8% nickel, 92% chromium carbide and about .04% phosphorus was prepared as described above, from 276 grams of chromium carbide powder, 24 grams of nickel powder, and one gram of the nickelphosphorus alloy. In this case, the sintering temperature was 1275 C. This alloy had a hardness of 90.3 R a density of 6.87 gm./cc., and a strength of about 200,000 p.s.i., over 50% greater that that (about 120,000 p.s.i.) of heretofore available alloys.
• Example #3 An alloy containing 83% chromium carbide, 13.6% nickel, 3.4% molybdenum and about .04% phosphorus was processed as indicated in Example #1, from 249 grams of chromium carbide powder, 40.8 grams of nickel powder, 10.2 grams of molybdenum powder, and about one gram of nickel-phosphorus alloy. The sintering temperature in this case was 1275 C. This alloy had a hardness of 89.2 R a density of 7.1 gm./cc., and a strength of about 210,000-220,000 p.s.i., about more than the heretofore available alloys.
• a composition for the production of a cemented carbide alloy consisting essentially of chromium carbide and from 1-35 by weight of a binder containing nickel, said composition containing phosphorus in an amount ranging from a trace to about 0.4% by weight based on the total weight of the composition.
• composition of claim 1 in which the binder is present in percentages of 3-35 3.
• composition of claim 1 in which up to one-third of the total binder by weight is molybdenum or tungsten.
• composition of claim 1 in which the chromium carbide contains from 13.0 to 13.3% carbon by weight.
• a hard cemented carbide alloy of enhanced strength consisting essentially of chromium carbide and from 135% by weight of a nickel binder, said alloy containing consisting essentially of chromium carbide in the form 5 of Cr C and from 15-35% by Weight of a nickel binder, said alloy containing phosphorus added in an amount ranging from a trace to about 0.4% by Weight based on the total weight of the alloy.

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• 1968
  • 1968-05-01 US US725929A patent/US3445203A/en not_active Expired - Lifetime
• 1969
  • 1969-04-25 GB GB21258/69A patent/GB1267992A/en not_active Expired
  • 1969-04-29 DE DE1921756A patent/DE1921756C3/de not_active Expired
  • 1969-04-30 SE SE06193/69*A patent/SE351438B/xx unknown
  • 1969-05-02 FR FR6914046A patent/FR2007618A1/fr not_active Withdrawn

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