Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0264—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 5%
  • C22C33/0271—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 5% with only C, Mn, Si, P, S, As as alloying elements, e.g. carbon steel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0207—Using a mixture of prealloyed powders or a master alloy
  • C22C33/0214—Using a mixture of prealloyed powders or a master alloy comprising P or a phosphorus compound

Definitions

• the present invention is related to steel powder compositions containing phosphorus, which in addition to iron and phosphorus may contain one or several other alloying constituents, either alloyed or mixed with iron powder, to a total concentration of percent.
• High compressibility means that the powder when exposed to a relatively moderate pressure achieves such a high density that the subsequent sintering results in components with satisfactory strength. This must be done without great dimensional changes during sintering (growth or shrinkage) because otherwise one may loose the greatest advantage with ferrous powder metallurgy, viz. the posssibility to produce precision components to final tolerances without machining operations.
• the inventors have set themselves the problem of finding a phosphorus-rich composition, which would be sufficiently brittle so that it could be comminuted to a fine powder and at the same time give rise to a minimum of tool wear during compaction. They found that the solution to this problem is to use an ironphosphorus alloy with a composition corresponding to the compound Fe P, i.e., containing 15.6 percent by weight of phosphorus.
• steel powder containing phosphorus to be used for the production of precision machinecomponents without excessive tool wear during compaction is characterized by consisting of an essentially phosphorus-free steel powder with good compressibility and with a maximum particle size of 100 500um, and intimately mixed therewith an ironphosphorus alloy powder with a maximum particle size of 75pm at the most, preferably 45pm at the most, and with a phosphorus centent of between 13 and 17 percent, appropriately between 14 and 16 percent, i.e., preferably about the compsition of Fe P which contains 15.6 percent P and in addition thereto, if necessary, a suitable pressing lubricant such as zinc stearate in the usual proportion, the relative proportions of ironphosphorus alloy powder and steel powder being adjusted in such a way that the phosphorus content of the mixture is between 0.2 and 3 percent, preferably between 0.3 and 1.5 percent.
• the percentages above are in weight percent.
• a further improvement in this respect is obtained if the powder mixture is exposed to a heat treatment at 650 to 900 C for 15 minutes to 2 hours in a reducing atmosphere and subsequently the lightly sintered cake formed during the heat treatment is broken up by gentle comminution.
• the small iron-phosphorus alloy particles which before this treatment were loosely attached to the steel particles are now solidly bonded to the latter, which effectively prevents segregation without affecting the compressibility to any appreciable degree.
• EXAMPLE 1 Three powder mixtures A, B, and C, were prepared.
• the sponge iron powder with a maximum particle size of 147p.m was used for all these mixtures.
• the mixtures consisted of the following components:
• Cylindrical compacts with a height of 8 mm, a diameter of 8 mm and a density of 6.75 g/cm were pressed.
• the pressing was done in an automatic press at a rate of 35 pieces per minute.
• the die had been made from high speed steel which had been hardened to a Rockwell C hardness of 63.
• the die wear was determined by measuring the diameter of the compacts at regular intervals. It was found that the diameter increased by 0.6;zm per 10,000 pieces when mixture A was used, whereas mixture B which had been made according to the invention gave an increase of 0.3;.tm per 10,000 pieces.
• the pure sponge iron powder C gave an increase of 0.25 pm for the same number of pieces. Mixture B thus wore the die insignificantly more than the pure sponge iron powder (C), whereas the die wear was doubled with mixture A.
• the three powder mixtures were compacted into tensile test bars in a special die for this purpose using a compacting pressure of 400 MN /m
• the density in the green (unsintered) state was about 6.5 g/cm in all cases which shows that iron-phosphorus alloy addition did not lower the compressibility of the mixtures.
• the tensile test bars were sintered at a temperature of 1,l20 C for 1 hour in an atmosphere of dissociated ammonia. When they had cooled to room temperature they were tested for density, dimensional change during sintering, tensile strength and elongation. The results are given in the table below.
• mixtures E and F were filled into a funnel and the powder was then allowed to run out freely. The last tenth of each mixture to run out was collected and analyzed for phosphorus.
• the sample from mixture E contained 0.35 percent P and from mixture F 0.57 percent P.
• mixture E, but not mixture F contained oil, it can be concluded that the risk of segregation can be diminished by oil addition.
• the average phosphorus content of each of the mixtures D to F was 0.30 percent.
• EXAMPLE 4 A mixture H was prepared in the following manner. 20 kg of an iron-phosphorus alloy powder with a phosphorus content of 15 percent and with a maximum particle size of 45pm was first mixed with kg of a sponge iron powder with a maximum particle size of l49p.m and 15 g ofa thin mineral oil. This mixture was heated to 850 C for 30 minutes in an atmosphere of dissociated ammonia. A sintered cake was formed as a result of the heat treatment, and this was comminuted to a powder with a maximum particle size of l77p.m. This powder consisted mainly of iron powder particles to the surfaces of which iron-phosphorus alloy particles were bonded. This powder was mixed with 900 kg of sponge iron powder and 8 kg of zinc stearate powder.
• Phosphorus containing steel powder for the production of sintered precision components with a low tool wear during the compacting step characterized in that it essentially consists of powdery steel substantially free of phosphorus and intimately mixed therewith an iron-phosphorus alloy powder with such a particle size that all of the powder passes a screen with an opening of at the most 75pm, said iron-phosphorus alloy powder having a phosphorus content of between about 12 and 16 percent by weight, the relative proportions of said iron-phosphorus alloy powder and said powdery steel being adjusted in such a way that the phosphorus content of the mixture is between about 0.2 and 3 percent by weight.
• Phosphorus containing steel powder according to claim 1 characterized in that it also contains at the most 1.5 percent by weight of a solid lubricant powder.
• Phosphorus containing steel powder according to claim 1 characterized in that it also contains 0.005 to 0.02 percent by weight of a thin mineral oil for the prevention of segregation.
• Phosphorus containing steel powder according to claim 1 characterized in that the iron-phosphorus alloy particles are bonded to particles of said powdery steel by sintering and subsequent comminution for the prevention of segregation.
• Phosphorus containing steel powder as claimed in claim 1 wherein the particle size of said ironphosphorus alloy powder is such that it passes a screen with an opening of at the most 45pm.
• Phosphorus containing steel powder as claimed in claim 1 wherein the phosphorus content of said ironphosphorus alloy powder is between about 14-16 percent by weight.
• Phosphorus containing steel powder as claimed in claim 1 wherein the composition of said ironphosphorus alloy powder corresponds to that of Fe P, the relative proportions of said iron-phosphorus alloy powder and said powdery steel being such that the phosphorus content of the mixture is between about 0.3 and 1.5 percent by weight.
• Phosphorus containing steel powder as claimed in claim 2 characterized in that it also contains 0.005 to 0.02 percent by weight ofa thin mineral oil for the prevention of segregation.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)
• Lubricants (AREA)

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• 1972
  • 1972-05-02 SE SE7205754A patent/SE372293B/xx unknown
• 1973
  • 1973-04-10 CA CA168,354A patent/CA1004507A/en not_active Expired
  • 1973-04-11 US US00349918A patent/US3836355A/en not_active Expired - Lifetime
  • 1973-04-13 IT IT23019/73A patent/IT983889B/it active
  • 1973-04-16 GB GB1827773A patent/GB1427070A/en not_active Expired
  • 1973-04-26 AU AU54841/73A patent/AU464376B2/en not_active Expired
  • 1973-04-26 DE DE2321103A patent/DE2321103C3/de not_active Expired
  • 1973-04-26 JP JP4752973A patent/JPS5421803B2/ja not_active Expired
  • 1973-04-27 FR FR7315379A patent/FR2183069B1/fr not_active Expired
  • 1973-04-30 ES ES414239A patent/ES414239A1/es not_active Expired
  • 1973-05-02 BE BE130643A patent/BE798981A/fr not_active IP Right Cessation

Patent Citations (3)

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