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
  • C22C33/0207—Using a mixture of prealloyed powders or a master alloy
• • 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
  • Y10T428/12014—All metal or with adjacent metals having metal particles
  • Y10T428/12021—All metal or with adjacent metals having metal particles having composition or density gradient or differential porosity

Definitions

• vent such as alcohol or trichlorethylene.
• the powder mixture Prior to the sintering the powder mixture can be shaped as desired by mixing it with a liquid to form a paste which is shaped in the way desired.
• the paste can for example be extruded through a nozzle to form a cylinder or a tube.
• the liquid can for example be an organic sol- It must not adversely aifect the particles of powder.
• the powder mixture shall, therefore, contain a second metallic component which alloys with the component containing the sigma-phase so that the sigma-phase in the main completely disappears.
• Metals of the iron group i.e. iron, cobalt and nickel, used either singly, or in pairs or all three, are especially suitable to be used as the second component. Even metals outside the iron group, such as copper, may be used for this purpose.
• sigmaphase does not mean only the pure sigma-phase, but also certain closely-related phases, such as mu, chi-, and xiphases.
• the terminology in the field is uncertain; certain writers call all these phases sigma-phase, while others diiferentiate between these closely-related phases.
• the sigma-phase appears in many different alloy systems.
• my patent mentioned at the beginning I have, as examples only, given a number of binary and ternary alloys in which the sigma-phase appears.
• Sigma-phase often appears in alloy systems containing chromium, as for example in the system iron-chromium-nickel and this makes the invention suitable for the production of subjects of so-called stainless steel.
• the sigma-phase is brittle and crushable and the component containing sigma-phase in the powder according to the invention can therefore easily be produced by crushing an alloy containing sigma-phase which has been produced via a molten phase, for example, as is described in United- States Patent No. 2,834,666.
• the main quantity of the powder may consist of a powder containing sigma-phase, the other component only needing to be present in such an amount as is required to make the sigma-phase disappear on sintering. In order to obtain a satisfactory density in the sintered body it is, however, sufficient if only a small part of the powder consists of a component containing sigma-phase.
• the sintering to form a body having low porosity and good chemical homogeneity is facilitated if'the powders in the powder mixture are fine grained. It is preferable if the size of grain is less than 0.074 mm. (200 mesh) and I prefer a grain size less than 0.044 mm. (325 mesh).
• the sintering is carried out, as is always the case with the powder metallurgical technique, in a protective gas, usually hydrogen, which thus fills up the pores in the powder, or in vacuum.
• a protective gas usually hydrogen
• the powder contracts during sintering, an increasing number of closed pores, filled with the protective gas and into which air cannot penetrate, are formed by the connected pore system. It is preferable to continue the sintering so long that the remaining porosity substantially consists of closed pores. Owing to the fact that these pores are filled with protective gas their walls Patented Mar. 24, 1964 are reactive and are easily welded together during the subsequent treatment.
• the body is subjected to the further treatment as soon as possible after the sintering. It can preferably be transferred from the sintering oven direct to the heat treatment (rolling, forging etc.).
• bodies can be produced which offer considerable advantages over the conventional ingots reproduced by the metallurgical smelting process.
• the structure of the body made in the powder metallurgical method will thus be very uniform; one avoids the inconventient features produced by the dendritic structure of the ingot.
• One also avoids the risk of cavities, pipes which are common with ingots, and further one can make full use of the body as a whole, whereas with ingots one cannot make use of the upper part, the socalled sink head which is often cut off at an early stage of the heat treatment.
• the powder is sintered, according to the invention, in a container of suitable shape, for example, in a ceramic crucible or an ingot mould, preferably of fireproof steel.
• the protective gas may be introduced into the heating oven in which the sintering takes place.
• the protective gas may be produced by allowing a hydride to be decomposed near the powder.
• the mould is closed by a lid and turned so that the bottom end is uppermost and then placed in a heating oven.
• the hydrogen gas which is formed by the decomposition of the hydride forces all the air out of the ingot mould and the surplus comes out between the ingot mould and the lid.
• the powder can thus easily be stamped or rammed when it is poured into the container; it will, though, he on the whole uncompressed, in contrast to the greatly compressed condition in which it is transferred for the production of pressed blanks which are to be subsequently sintered.
• a suitable sintering temperature is 1050 to 1350, preferably 1250 to 1350 C. I usually prefer to sinter at a temperature of about 1300 C.
• the sintering time will in general be longer than when sintering pressed details, because the bodies which are sintered according to the invention are, in general, considerably bigger than the pressed and sintered details, and because the crucible or the mould hinders the flow of heat and takes time to become hot itself.
• sintering small bodies /2 to two hours sintering time can be sufficient, but for large bodies, having for example a weight of hundreds of kilogrammes, a considerably longer sintering time can be called for.
• Example 1 For the production of a 200 grams body of stainless steel of the type 18/ 8/Mo, a mixture was made of 100 grams iron powder (Hogan'ais MHP 300.30) and 100 grams of a brittle alloy powder which was made by crushing and finely grinding an alloy produced by metallurgical smelting and containing 45% chromium, 20% nickel, 5% molybdenum and the rest iron. This alloy powder had a structure of more than 75% sigma-phase. The powder mixture was stamped loosely into a round ceramic tube having an inside diameter of 22 mm., with the powder body having a volume weight of 3.85 kg. dm. The tube and its contents were heated in a horizontal tube oven filled with hydrogen at a temperature of 1300" C.
• iron powder Hogan'ais MHP 300.30
• a brittle alloy powder which was made by crushing and finely grinding an alloy produced by metallurgical smelting and containing 45% chromium, 20% nickel, 5% molybdenum and the
• a pressed and sintered blank was made of the same powder mixture, weighing also about 200 grams, by pressing the powder at a pressure of 7.5 tons/cm thus producing a body having a density of about 6 kg./ dm. and sintering this body at 1310 C. for two hours, which yielded a body having a specific weight of 7.51, meaning a porosity of about 5%.
• Example 2 Analogous with Example 1 a stainless body was produced of 40% iron powder and 60% pulverized alloy having the composition:
• Example 3 Analagous with Example 1 a stainless body was produced of 50% iron powder and 50% pulverized alloy having the composition:
• Example 4 Analogous with Example 1 a body of the same chemical composition as in Example 1 was produced from the following powders containing no sigma-phase:
• the specific weight in sintered state was about 5.0 which shows that the presence of sigma-phase gives a considerably denser body.
• Example 5 Analogous with Example 1 a body was produced of the I following powders containing no sigma-phase:
• the ferromolybdenum in this example and the sigma alloy according to Example 1 had almost the same melting point (about 1430 C.). The presence of sigmaphase thus gives a higher density in the sintered body.
• Example 6 contains at least 30%, preferably 35-60% chromium. It also contains nickel, for instance 535%, preferably 30%. It may also contain alloying elements such as molybdenum and tungsten, for instance in an amount of 210%.
• the powder mixture may be further ground after having been mixed, and is placed in a mould, for instance in a ceramic tube. The mould is heated in vacuum or in a protecting gas, for instance hydrogen, at 1100-1350 C. for such a time, usually at least /2 hour and preferably one or several hours, that the porosity of the sintered body is below 10%, preferably 38%.
• the specific weight of the sintered body is more than 7.2.
• Method for the powder metallurgical manufacture of bodies adapted for further working which comprises sintering a loose, substantially uncompressed, powder mixture comprising at least 20% by weight of a first metallic component consisting of a chromium-containing ferrous alloy at least 50% of which is sigma phase and a second metallic component selected from the group consisting of iron, cobalt and nickel and mixtures thereof, said sec- 0nd metallic component being capable under the sintering conditions of alloying with said first metallic component and being present in quantity suflicient to destroy said sigma phase, the sintering being carried out at a temperature within the range from 1050 to 1350 C. and being continued until the mixture has a porosity of not more than about 10%.

Landscapes

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=20266179

Family Applications (1)

Country Status (3)

Cited By (3)

Citations (1)

• 0
  • US US3126279D patent/US3126279A/en not_active Expired - Lifetime
• 1962
  • 1962-05-14 GB GB18539/62A patent/GB941822A/en not_active Expired
  • 1962-05-18 DE DEW32287A patent/DE1258109B/de active Pending

Patent Citations (1)

Also Published As

Similar Documents