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%
• • 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

Definitions

• a powder mixture for manufacturing of alloy steel wherein the metal powder portion consists of a mixture of two powders, viz. a first atomized prealloyed steel powder and a second non atomized alloy powder comminuted from a solidified melt.
• the alloying elements are distributed in such a way that elements, the oxides of whichare easily reducible preferably nickel, copper, molybdenum and/or cobalt substantially enter into the atomized prealloyed steel powder and the oxidation sensitive elements especially chromium and manganese enter into the finely communited powder.
• the present invention relates to metal powders for the manufacture of alloy steel and especially low alloy steel. Such manufacturing can be carried out by means of the conventional powder metallurgical method (pressing and sintering) or by means of the developing hot forging method.
• oxide impurities present in the powder have a much more damaging influence on the mechanical properties than they have in products compressed and sintered in conventional manner.
• Powders for the production of such alloy steel products can be divided into two principally different groups. First. it is possible to mix different powders each consisting of one or more but not all of the alloying elements of the finished product.
• each powder particle is homoge neously alloyed with the same proportions of alloying elements as desired in the end product.
• this alloying method has some disadvantages which in some cases make it directly unsuitable.
• the heating of green compacts in reducing atmosphere before the forging offers a further possibility of reducing remaining oxides in the powder. since this heating is carried out to a higher temperature than the one used for the annealing of the powder.
• the present technique it is possible to produce substantially oxide free forged materials provided that the steel powder only contains alloying elements. the oxides of which are relatively easily reduced. i.e. have a free energy of formation with an absolute value lower than 120 kcaI/mole O (502 kJ/mole 0 at IO0U C.,Values of the free energy of formation for oxides of some of the alloying elements most commonly present in steel calculated according to Kubaschewsky, O. & Evan. L. I... Metallurgical Thermochemistry, London I956. are given in the table below.
• these oxides then cause a strong impairment of ductility and toughness. These properties. however, are also dependent of the size of the oxide inclusions as shown by experiments. At predetermined total oxygen content in the end product the material obtains considerably impaired mechanical prop erties when the oxygen is present in the form of coarse impurities in comparison with material where the oxide impurities are small but therefore more numerous. This critical size of the oxide inclusions, above which they cause a strong impairment of the properties of the material is between 20 um and 100 am.
• the present invention provides for a solution of the problem of avoiding the above mentioned difficulties by means of a suitable powder mixture.
• the metal powder portion consists of a mixture of two powders. viz.. a first atomized prealloyed steel powder and a second non atomized alloy powder comminuted from a solidified melt.
• the alloying elements are distributed in such a way that elements. the oxides of which are easily reducible (preferably nickel. copper. molybdenum and- /or cobalt) substantially enter into the atomized prealloyed steel powder and the oxidation sensitive elements (especially chromium and manganese) enter into the finely comminuted powder.
• the atomized prealloyed powder is produced by melting iron and ().2l ()7: of alloying elements. the oxides of which have an absolute value of the free energy of formation below 120 kcal/mole O 502 kJ/mole O- at 1000 C. water atomization of the melt and finally annealing in a reducing atmosphere (suitably cracked ammonia).
• the atomized prealloyed powder can contain up to 0.4% accessory elements. the oxides of which have an absolute value of the free energy of formation above 120 kcal/mole O (502 kJ/mole at 1000 C. The content of such accessory elements.
• the oxides of which have an absolute value of the free energy of formation above 150 kcal/mole O- (627 kJ/mole O- at 1000 C, should not exceed 0.1%.
• the contents of silicon. titanium and aluminum should not exceed 0.04%. 0.03% and 0.03%. respectively.
• the powder should have such a particle size distribution that more than 90% and preferably more than 97% of the powder passes a sieve having a mesh opening of 175 .1.m (80 Tyler mesh; Method for sieve analysis ofgranu lar metal powders. MPlF Standard 5-46. Metal Powder Industries Federation. New York. USA).
• alloying elements the oxides of which have an absolute value of the free energy of formation exceeding 120 kcal/mole O (502 kJ/mole 0 at 1000 C, are molten possibly under addition of at most 75% preferably at most 50% iron and/or other metals with easily re ducible oxides and carbon. and is cast. The ingot is crushed and comminuted to a fine alloy powder. The total content of elements. the oxides of which have an absolute value of the free energy of formation exceeding 150 kcal/mole O (627 kJ/mole 0 at 1000 C. should not be higher than 1% in the finely comminuted alloy powder.
• the two components are now mixed in the proportions 80-99% atomized prealloyed powder and l% finely comminuted alloy powder.
• a powder mixture produced in this way provides a material having small and few oxide particles which is shown by the following example.
• EXAMPLE l Two powders were produced. one by atomizing by means of water and subsequent annealing in cracked ammonia (A). the other by mixing finely ground ferro alloy powder and water atomized. molybdenumalloyed steel powder (B).
• the two powders (A) and (B) had the composition of 1% Mn. 1% Cr. 0.5% Mo. balance Fe.
• the ferroalloy powder used in powder (B) had the composition Mn. 25% Cr. 7% C. balance Fe. and an average particle size of 4 am according to Fischer (Methods for determination of average particle size of metal powder by the Fischer sub-sieve sizer. MPlF Standard 32-60. Metal Powder Industries Feder ation. New York. USA). In both cases graphite was added in such an amount that the carbon content of the powders amounted to 0.5%.
• Green compacts in the form of cylinders with 25 mm diameter and mm length were pressed from both powders.
• the compacts were heated, one group at 1 120 C in hydrogen gas atmosphere with a dew point of 20 C and maintained at these temperatures for 30 minutes. From the furnace the compacts were ripidly brought to a die where the cylinders at the elevated temperature were compressed to full density.
• the alloying elements are to a large extent homogeneously distributed in the finished product.
• the component of the mixture containing the oxidation sensitive alloying elements according to the invention must be comminuted to a small particle size. This is illustrated in the followmg example.
• EXAMPLE 2 Three powder mixtures were produced. all of them with the composition 1% chromium. 2% nickel and 0.5% molybdenum. balance iron. in all of the mixtures the components consisted of water atomized prealloyed steel powder comprising 2% nickel and 0.5% molybdenum. and ferro-chromium powder comprising chromium and 0.3% carbon.
• the ferrochromium powder had an average particle size according to Fischer of 33 ,um.
• D 20 um
• E third case
• 0.5% graphite powder and 0.8% zinc stearate were mixed into the three powders.
• a further improvement in this respect is obtained if the mixture is subjected to a heat treatment at 65()900 C for a period of minutes to 2 hours in reducing atmosphere with subsequent cautious disintegration of the cake formed.
• this treatment the finely comminuted alloy powder particles are sintercd to the steel powder particles which effectively counteracts segregation.
• This cautious sintering treatment can be carried out on powder to which the above mentioned oil has been added as well as on powder without the addition of such oil.
• this finely comminuted powder can advantageously be mixed with only part of the steel powder to form a concentrate.
• This concentrate is then subjected to one of the above described processes for diminishing the risk of segregation. Finally this concentrate is mixed with such a quantity of steel powder that the desired composition is obtained.
• the mixtures according to the above specification can contain a suitable lubricant. c.g. zinc stearate.
• a suitable lubricant c.g. zinc stearate.
• the addition of lubricant should not exceed 1%.
• a powder mixture for manufacturing of alloy steel articles having small and few oxide inclusions comprising a metal powder portion which consists of a mixture of two powders. viz. an atomized prealloyed steel powder and a finely comminuted powder containing alloying elements. wherein alloying elements. the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole O (502 kJ/molc 0 at 1()O() C substantially are contained in the atomized prealloyed powder while all alloying elements. the oxides of which have a free energy of formation with an absolute value exceeding 120 kcal/mole O (502 kJ/mole 0 at 1()0O C. are completely contained in the finely comminuted powder.
• a powder mixture according to claim 1. consisting of to 99% of an atomized prealloyed powder of iron and (1.2 to 10% of said alloying elements, the oxides of which have a free energy of formation with an absolute value of less than kcal/mole O (502 kJ/mole 0 at 10()() C. and ofa finely comminuted powder consisting of a total of at least 25% and preferably at least 50% of said alloying elements.
• a powder mixture according to claim I in which that the finely comminuted powder consists of a ferro alloy with a total of at least 25% and preferably at least 50% of said alloying elements.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=20319234

Family Applications (1)

Country Status (9)

Cited By (9)

Families Citing this family (6)

Citations (3)

• 1973
  • 1973-11-29 SE SE7316117A patent/SE378260B/xx unknown
• 1974
  • 1974-10-29 US US518474A patent/US3899319A/en not_active Expired - Lifetime
  • 1974-11-12 IT IT54010/74A patent/IT1023230B/it active
  • 1974-11-13 AT AT908974A patent/AT344763B/de not_active IP Right Cessation
  • 1974-11-26 DE DE2455850A patent/DE2455850C3/de not_active Expired
  • 1974-11-26 CA CA214,618A patent/CA1036389A/en not_active Expired
  • 1974-11-28 GB GB51685/74A patent/GB1491726A/en not_active Expired
  • 1974-11-29 JP JP13637974A patent/JPS5429171B2/ja not_active Expired
  • 1974-12-20 FR FR7442361A patent/FR2253101B1/fr not_active Expired

Patent Citations (3)

Also Published As

Similar Documents