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%

Definitions

• the invention relates to a metal powder mixture for producing martensitic through-hardened, high-strength sintered parts on the basis of a steel powder formed by atomizing a steel alloy melt, which is mixed with 0.3 to 0.7% by weight of graphite powder.
• high-strength sintered parts are understood to mean parts with a tensile strength of at least 550 N / mm2.
• a steel alloy powder for producing high-strength sintered parts is known from EP 0 136 169 B1, which consists of (% by weight) Max. 0.02% C Max. 0.1% Si 0.4-1.3% Ni 0.2-0.5% Cu 0.1-0.3% Mo Max. 0.3% Mn Max. 0.01% N Balance iron and usual impurities.
• This alloy powder should be cheap to manufacture and process, have good pressing properties and ensure high strength in the sintered finished part. This document does not specify anything about its properties with regard to the achievable dimensional accuracy in the finished part.
• Sintering a compact made from steel powder normally changes its geometry.
• martensitic hardening counteracts this effect because of the associated increase in volume as a result of the structural transformation.
• a change in volume of the finished part compared to the compact used for sintering can also be taken into account in the design of the pressing tool, ie an attempt is made to anticipate the dimensional deviations and to compensate from the outset by changing the dimensions of the compact.
• a sintered alloy is known from EP 0 042 654 in which the nickel content is at most 2.5%. This content in connection with the molybdenum content is important for the possibility of air hardening. With the maximum limit of 0.7% Mo disclosed in this document, however, this cannot be carried out. The improved strength of this alloy is achieved through a special heat treatment after sintering.
• the object of the invention is to provide a metal powder mixture which can be produced with as little effort as possible and which allows the production of high-strength and wear-resistant sintered parts, the dimensional deviations of which can be kept within a tolerance band of a maximum of +/- 0.05% without this being the case additional constructive measures on the pressing tool for the production of the compacts to be sintered are required.
• the metal powder should therefore have the property of not causing any appreciable shrinkage or waxing when sintering compacts produced therefrom with conventional compaction.
• the proportions of the individual alloy elements are kept within different limits than in the known steel powder. It is particularly important that the ratio of the proportion of Cu to the proportion of graphite also introduced in powder form as carbon in the metal powder mixture is kept in the range 1.4-2.5, preferably 2.0. If all of the provisions of claim 1 are observed, it is surprisingly possible to produce compacts by conventional pressing processes in powder metallurgy, which under normal sintering conditions have almost complete dimensional stability regardless of the wall thicknesses of the compacts. The dimensional deviations are less than +/- 0.05%.
• the sintered parts result in a completely martensitic structure, which gives the parts a high strength (over 750 N / mm2) without this a subsequent heat treatment is required.
• a steel powder was produced by water atomization of a melt with the following composition (% by weight): 0.01% C 0.02% Si 0.10% Mn 4.0% Ni 0.5% Mo 0.020% P 0.010% S Balance iron and usual impurities.
• this steel powder was dried and subjected to a reduction annealing in an H2 atmosphere at about 1000 o C. After cooling, the resulting agglomerate was ground in fine particles.
• the residual oxygen content of the steel powder was about 0.15%, its bulk density was about 3 g / cm3.
• the advantages of the metal powder mixture according to the invention can be seen in particular in the fact that dimensionally constant sintered parts can be produced which no longer require complex mechanical, shaping or thermal aftertreatment after sintering, and the steel powder can be produced inexpensively. It is namely applicable to the selected alloy of the invention, a water atomization with subsequent reduction under an H2 atmosphere. This eliminates the need for costly vacuum annealing, as is required for other fully alloyed water-atomized metal powders for the same purpose. The inexpensive production is also associated with the achievement of excellent strength and wear properties.

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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)

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Publications (2)

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• 1990
  • 1990-01-19 DE DE4001900A patent/DE4001900A1/de not_active Withdrawn
  • 1990-09-28 CA CA002074193A patent/CA2074193C/en not_active Expired - Fee Related
  • 1990-09-28 WO PCT/DE1990/000751 patent/WO1991010753A1/de active IP Right Grant
  • 1990-09-28 DE DE59009358T patent/DE59009358D1/de not_active Expired - Lifetime
  • 1990-09-28 AT AT90914132T patent/ATE124467T1/de not_active IP Right Cessation
  • 1990-09-28 EP EP90914132A patent/EP0597832B1/de not_active Expired - Lifetime
  • 1990-09-28 JP JP2513227A patent/JP2908018B2/ja not_active Expired - Fee Related

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