CA1036389A - Powder mixture for the production of alloy steel articles - Google Patents
Powder mixture for the production of alloy steel articlesInfo
- Publication number
- CA1036389A CA1036389A CA214,618A CA214618A CA1036389A CA 1036389 A CA1036389 A CA 1036389A CA 214618 A CA214618 A CA 214618A CA 1036389 A CA1036389 A CA 1036389A
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- CA
- Canada
- Prior art keywords
- powder
- alloying elements
- mixture according
- weight
- group
- Prior art date
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- 239000000843 powder Substances 0.000 title claims abstract description 118
- 239000000203 mixture Substances 0.000 title claims abstract description 36
- 229910000851 Alloy steel Inorganic materials 0.000 title claims abstract description 6
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 6
- 238000005275 alloying Methods 0.000 claims abstract description 30
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 16
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 15
- 239000010959 steel Substances 0.000 claims abstract description 15
- 229910052751 metal Inorganic materials 0.000 claims abstract description 13
- 239000002184 metal Substances 0.000 claims abstract description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 16
- 239000002245 particle Substances 0.000 claims description 15
- 229910052804 chromium Inorganic materials 0.000 claims description 13
- 239000011651 chromium Substances 0.000 claims description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 10
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 8
- 229910052742 iron Inorganic materials 0.000 claims description 7
- 239000011572 manganese Substances 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910001021 Ferroalloy Inorganic materials 0.000 claims description 4
- 239000000314 lubricant Substances 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 3
- 239000010439 graphite Substances 0.000 claims description 3
- 229910002804 graphite Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 239000011733 molybdenum Substances 0.000 claims description 3
- XOOUIPVCVHRTMJ-UHFFFAOYSA-L zinc stearate Chemical group [Zn+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O XOOUIPVCVHRTMJ-UHFFFAOYSA-L 0.000 claims description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 2
- 239000010941 cobalt Substances 0.000 claims description 2
- 229910017052 cobalt Inorganic materials 0.000 claims description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 239000010949 copper Substances 0.000 claims description 2
- 238000009826 distribution Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 description 11
- 239000000463 material Substances 0.000 description 10
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 238000005242 forging Methods 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000012298 atmosphere Substances 0.000 description 4
- 239000007795 chemical reaction product Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000012535 impurity Substances 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910021529 ammonia Inorganic materials 0.000 description 3
- 238000000137 annealing Methods 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
- 229910000604 Ferrochrome Inorganic materials 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 238000000889 atomisation Methods 0.000 description 2
- 230000006735 deficit Effects 0.000 description 2
- 230000003467 diminishing effect Effects 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- JKQOBWVOAYFWKG-UHFFFAOYSA-N molybdenum trioxide Chemical compound O=[Mo](=O)=O JKQOBWVOAYFWKG-UHFFFAOYSA-N 0.000 description 2
- 239000003921 oil Substances 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 230000002311 subsequent effect Effects 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- -1 MPIF Standard 5-46 Substances 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 229940059904 light mineral oil Drugs 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005029 sieve analysis Methods 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- 238000009692 water atomization Methods 0.000 description 1
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
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)
Abstract
A B S T R A C T
This invention relates to a powder mixture for manufacturing of alloy steel articles having small and few oxide inclusions. The mixture con-sists of a metal powder portion which consists of a mixture of two powders, viz. an atomized prealloyed steel powder and a finely comminuted powder con-taining alloying elements, wherein alloying elements, the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole O2 (502 kJ/moleO2) at 1000°C substantially are contained in the atomized pre-alloyed powder while all alloying elements, the oxides of which have a free energy of formation with an absolute value exceeding 120 kcal/moleO2 (502 kJ/mole O2) at 1000°C, are completely contained in the finely comminuted powder.
This invention relates to a powder mixture for manufacturing of alloy steel articles having small and few oxide inclusions. The mixture con-sists of a metal powder portion which consists of a mixture of two powders, viz. an atomized prealloyed steel powder and a finely comminuted powder con-taining alloying elements, wherein alloying elements, the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole O2 (502 kJ/moleO2) at 1000°C substantially are contained in the atomized pre-alloyed powder while all alloying elements, the oxides of which have a free energy of formation with an absolute value exceeding 120 kcal/moleO2 (502 kJ/mole O2) at 1000°C, are completely contained in the finely comminuted powder.
Description
lQ;~63~9 The present invention relates to metal powders for the manufacture of alloy steel and especially low alloy steel. Such m~anyfacturing can be carried out by means of the conventional powder motallurglo method (pres-sing and sintering) or by means of the developing hot forging method.
In the first case metal powder is compressed in dies to compacts which are very close to the desired shape of the finished product. The green com-paet is then subjected to a heat treatment in which the powder partieles ~inter to eaeh other and the eompaet obtains a good stren0th. Produets produeed inthis way have a eertain porosity eausing a low duetility and tou~hness. The porosity, which can vary considerably from one material to another, but usually amounts to 7 to 20 per cent by colume, can be eli-minated by using the above mentioned hot forging technique, whereby the ductility and toughness can be considerably improved. The most important step in the case of hot forging is the pressing of heated preformed com-paets in a die. The result of hot forging is a body with full density.
In the production of steel products from metal powdsr according to said latter teehnique, however, oxide impurities present in the powder have a mueh more damaaina influenee on the meehanical properties than they have in produets eompressed and sintered in eonventional manner.
Powder~ for the produetion of 5ueh alloy ~teel produet6 ean be divided ;nto two prineipally different groups. Firstly, it is possible to mix different powders eaeh eonsisting of one or more but not all of the alloying elements of the finished produet.
Seeondly, it is possible to atomize a melt having exactly the composition desired in the end product. Thus, in the latter case each powder particle is homogeneously alloyed with the same proportions of alloying elements as desired in the end product. However, this alloying method has some .. . . . , . - .. . . . .
.
. . - -: , , -.; - . . , : . - :
.
. ~ . ...
- .,~ - .
. ~- . :- . .
' ~` 1C~3Ui3 ~3 disadvantages which in some cases make it directly unsuitable.
One of the most serious disadvantages is due to oxide impurities in alloy powders. In the most common and from the economical point of view com-pletely superior of the atomizing methods, viz. atomization with water, some of the powder particles are oxidized during the atomizing process. In order to reduce the oxides thereby formed the powder is subjected to a sub-sequent heating in reducing atmosphere, e.g. cracked ammonia.
The heating of green compacts in reducing atmosphcre before the forging offers a further possibility of reducing remaining oxides in the powder, since this heatin0 i8 carried out to a hi0her temperature than the one used for the annealing of the powder, By means of the present technique it is possible to produce substantially oxide free forged materials pro-vided 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 kcal/mole 2 (502 kJ/mole 2) at 1000 Co 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,L., Metallurgical Thermochemistry, London 1956, are given in the table below, Substance Free ener0y of formation at 1000 C
kcal/mole 2 kJ/mole 2 CU2 ~ 37 _155 NiO - 57 -239 CoO - 67 -281 MoO3 - 67 -281 FeO - 86 -360 Cr203 _126 -528 MnO -140 -586 V23 _148 -619 SiO2 _156 -650 TiO2 -165 -688 Al203 -203 -846 ' ' '- ~ - .'~ .
.
,;
.. . .
'' ' ~.
Oxides having an absolute value of the ~ree energy of formation exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000C, are not at all or incompletely reduced in the present technique. This causes that oxidation sensitive elements, such as Cr and Mn, which from the economical as well as the alloying point of view are very desirable, can be used only to a very limited extent as alloying elements in atomized steel powder. This i~ due to the fact that they form oxides during atomization, which cannot 4e eliminated during further processing.
In the end product 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 properties when the oxygen is present in the form of coarse impurities in comparison with material where the oxide impurities are small but therefore more numerousO This critical size of the oxide inclusions, above which they cau9e a 9trong impairment of the properties of the material is between 20Jwn and 100 pm.
The pre9ent invention provide9 for a 901ution of the problem of avoiding the above mentioned difficulties by means of a suitable powder mixture.
Accordingly, there is provided a powder mixture for manufacturing 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 &nd a finely comminuted powder containing alloying elements, wherein a first group of alloying elements, the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole 2 (502 kJ/mole 2) at 1000C substantially are containsd in the atomized prealloyed powder while a second group of alloying elements the oxides of which have a free energy of formation with an absolute value ~ .
' " . ' . .
10363~9 exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, are completely contained in the finely comminuted powder.
Thus, the basic idea of the invention is that 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 element8~ the oxides of which are easily reducible ~preferably nickel, copper~
molybdenum and/or cobalt) substantially enter into the atomized prealloyed 9teel powder and the oxidation sensitive elements (especially chromium and manganese) enter into the finely comminuted powder. The above is not valid for carbon which is added substantially as graphite in quantities up to 1%
of the powder mixture or as an alloying element in the finely comminuted alloy powder in a content of 10% at the most of this powder. Here as well as in the continuation of the specification and claims % means percent by weight~
The atomized prealloyed powder is produced by melting iron and 0.2-10% of ~J - 3a -iC~36 3~3~ 4 alloying elements, the oxides of which have an absolute value of the free energy of formation below 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, water atomization of the melt and finally annealing in a reducing atmos-phere (suitably cracked ammonia). Depending upon the quality of the iron raw material the atomized prealloyed powder can contain up to 0.4% acces-sory elements, the oxides of which have an absolute value of the free energy of formation above 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C.
The content of such accessory elements, the oxides of which have an abso-lute value of the free energy of formation above 150 kcal/mole 2 (627 kJ/mole 2) at 1000 C, should not axceed 0,1%. Particularly the contents of silicon, titanium and aluminum should not exceed 0,04%, 0,03~ and 0.03%, respectivelyO The powder should have such a particle size distribu-tion that more than 90% and preferably more than 97~ of the powder passes a sieve having a mesh opening of 175 /um ~80 Tyler mesh; Method for sieve analysis of 0ranular metal powders, MPIF Standard 5-46, Metal Powder Industries Federation, New York, U6A).
Other alloying elements, the oxides of which have an absolute value of the free energy of formation exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, are molten possibly under addition of at most 75% preferably at most 50% iron and/or other metals with easily reducible 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 abso-lute value of the free ener0y of formation exceedin~ 150 kcal/mole 2 (627 kJ/mole 2) at 1000 C~ should not bc hi~her than 1% in the finely comminuted alloy powder.
The two components are now mixed in the proportions 80-99~ atomized pre-alloyed powder and 20-1% finely comminuted alloy powder. A powder mixture produced in this way provides a material having small and few oxide par-ticles which is shown by the following example.
Example 1 Two powders were produced, one by atomizing by means of water and subse-quent annealing in cracked ammonia (A), the other by mixing finely ground ferro-alloy powder and water atomized, molybdenum-alloyed steel powder (B) .. .. - .
;-:- ~ -...... ~ . . :, , ' ,. , ': , - , :. - .
, - .. . ~ :
: , , ?
- . . . .
-- ., ., ~ . - , , , . , .. - .. . .
10363~9 5 The two po~ders (A) and (8) had the composition ~% Mn, 1% Cr, 0.5~ Mo, balance Fe, The ferroalloy powder used in powder B had the composition 25 Mn, 25% Cr, 7~ C, balance Fe, and an average particle size of 4 lum accor-ding to Fischer (Methods for determination of average particle size of metal powder by the Fischer sub-sieve sizer, MPIF Standard 32-60, Metal Powder Industries Federation,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 30 mm length were pressed from both powders. The compacts were heated, one group to 1120 C and another to 1200 C in hydrogen gas atmosphere with a dew point of ~20 C and maintained at these temperatures for 30 minutesO
From the furnace the compacts were rapidly brought to a die where the cylinders at the elevated temperature were compressed to full density.
In order to estimate the content of oxide inclusions the cylinders were onalyzed with regard to total oxygen content. Further, the number of oxide inclusions having a linear dimension in any direction larger than 100 /um, were counted on a cross section surface of each cylinder, The results are ~hown in the following table, Temp, Material Oxygen contentNumber of oxide inclusions C % 100 /um/cm2 , 1120 A 0a54 116 t~ B 0.20 10 B 0~06 3 , .
The above example shows the advantage of the present invention, When Cr and Mn, the oxides of which have a free energy of formation of -126 and -140 kcal/mole 2 (-528 and -586 kJ/mole 2) at 1000 C respectively, were added as a finely comminuted ferroalloy (powder B) the forged product obtained a considerably lower oxygen content and lower number of large inclusions than in the case of alloying chromium and manganese already into the atomized steel powder (powder A).
, . .~i,`
. ~
~, `i~
. ' , In addition to low content of inclusions it is desired, as mentioned above, that the alloyin~ elements are to a large extent homogeneously distributed in the finished product, For this purpose the component of the mixture containing the oxidation sensitive alloying elements according to the in-vention must be comminuted to a small particle size. This s illustrated in the following 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 mix-tures the components consisted of water atomized prealloyed steel powder comprising 2~ nickel and 0,5~o lolybdenum, and ferro-chromium powder com-prising 45% chromium and 0,3% carbon. In the first case (C) the ferro-chromium powder had an average particle size according to Fischer of 33 um, in the second case (D) 20 /um and in the third case (E) 4 /um. Before compaction 0~5% graphite powder and 0.8~ zinc stearate were mixed into the three powders. They were then compacted to cylinders which were heated to 1120 C in partially combusted propane with a dew point of -3 C and then forged in the manner described in example 1. The cylinders were cut into halves, and the cut surfaces were ground and polished. The chromium con-tent was measured in several points of the cut surfaces by means of a microprobe. The coefficient of variation (CV) for these data were calcula- `
ted as the standard deviation in percent of the average concentration. CV
i9 a measure of the heterogeneity of the material. Material made from powder C had the CV-value 175%. For powder D the CV-value was 135~ and for powder E 45%. At a heterogeneity corresponding to CV 150% the harden-ability enhancing effect of chromium is almost non-existing which means that the addition of chromium in powder C is of no value whereas powder D and particularly powder E resulted in material in which the hardenabili-ty was increased by the addition of chromium.
From the above examples the advantage of adding that component which con-tains oxidation sensitive alloying elements finely in a comminuted state is obvious. The powder particles should have an average size according to Fischer below 20 /um, The example also shows that it is still more advan-tageous that the said average size is less than 5 /um.
. . .
.. . ~ - :.. ~.- .. - . . .
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~ 7 10363~g Of course it is important that the powder described obove does not segre- -- gate after the mixing operation. Possibilities for segregation occur during transportation of the powder from the mixer to the consumer and during feeding to the powder press. One way of diminishing the risk of segregation is to add 50-200 g of a light mineral oil per metric ton powder continuous-ly during the filling of the mixerO Thereby the fine constituents are brought to stick to the coarser steel particles.
A further improvement in this respect is obtained if the mixture is sub-jected to a heat treatment at 650-900 C for a period of 15 minutes to 2 hour~ in reducing atmosphere with subsequent caution~ desinte0ration of the cake formed. By this treatment the finely comminuted alloy powder particles are sintered to the steel powder particles which effectively counteracts segregation. This cautions 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.
, ~
In such cases where the powder mixture has a low content of finely commi-nuted alloy powder, 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 abcve 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, In addition to the components mentioned the mixtures according to the above specification can contain a suitable lubricant, e,g, zinc stearate, The addition of lubricant should not exceed 1%, ~., . .
`:~
, : ' .
.~' .
: : ' - .
. .
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.,. " ,,
In the first case metal powder is compressed in dies to compacts which are very close to the desired shape of the finished product. The green com-paet is then subjected to a heat treatment in which the powder partieles ~inter to eaeh other and the eompaet obtains a good stren0th. Produets produeed inthis way have a eertain porosity eausing a low duetility and tou~hness. The porosity, which can vary considerably from one material to another, but usually amounts to 7 to 20 per cent by colume, can be eli-minated by using the above mentioned hot forging technique, whereby the ductility and toughness can be considerably improved. The most important step in the case of hot forging is the pressing of heated preformed com-paets in a die. The result of hot forging is a body with full density.
In the production of steel products from metal powdsr according to said latter teehnique, however, oxide impurities present in the powder have a mueh more damaaina influenee on the meehanical properties than they have in produets eompressed and sintered in eonventional manner.
Powder~ for the produetion of 5ueh alloy ~teel produet6 ean be divided ;nto two prineipally different groups. Firstly, it is possible to mix different powders eaeh eonsisting of one or more but not all of the alloying elements of the finished produet.
Seeondly, it is possible to atomize a melt having exactly the composition desired in the end product. Thus, in the latter case each powder particle is homogeneously alloyed with the same proportions of alloying elements as desired in the end product. However, this alloying method has some .. . . . , . - .. . . . .
.
. . - -: , , -.; - . . , : . - :
.
. ~ . ...
- .,~ - .
. ~- . :- . .
' ~` 1C~3Ui3 ~3 disadvantages which in some cases make it directly unsuitable.
One of the most serious disadvantages is due to oxide impurities in alloy powders. In the most common and from the economical point of view com-pletely superior of the atomizing methods, viz. atomization with water, some of the powder particles are oxidized during the atomizing process. In order to reduce the oxides thereby formed the powder is subjected to a sub-sequent heating in reducing atmosphere, e.g. cracked ammonia.
The heating of green compacts in reducing atmosphcre before the forging offers a further possibility of reducing remaining oxides in the powder, since this heatin0 i8 carried out to a hi0her temperature than the one used for the annealing of the powder, By means of the present technique it is possible to produce substantially oxide free forged materials pro-vided 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 kcal/mole 2 (502 kJ/mole 2) at 1000 Co 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,L., Metallurgical Thermochemistry, London 1956, are given in the table below, Substance Free ener0y of formation at 1000 C
kcal/mole 2 kJ/mole 2 CU2 ~ 37 _155 NiO - 57 -239 CoO - 67 -281 MoO3 - 67 -281 FeO - 86 -360 Cr203 _126 -528 MnO -140 -586 V23 _148 -619 SiO2 _156 -650 TiO2 -165 -688 Al203 -203 -846 ' ' '- ~ - .'~ .
.
,;
.. . .
'' ' ~.
Oxides having an absolute value of the ~ree energy of formation exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000C, are not at all or incompletely reduced in the present technique. This causes that oxidation sensitive elements, such as Cr and Mn, which from the economical as well as the alloying point of view are very desirable, can be used only to a very limited extent as alloying elements in atomized steel powder. This i~ due to the fact that they form oxides during atomization, which cannot 4e eliminated during further processing.
In the end product 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 properties when the oxygen is present in the form of coarse impurities in comparison with material where the oxide impurities are small but therefore more numerousO This critical size of the oxide inclusions, above which they cau9e a 9trong impairment of the properties of the material is between 20Jwn and 100 pm.
The pre9ent invention provide9 for a 901ution of the problem of avoiding the above mentioned difficulties by means of a suitable powder mixture.
Accordingly, there is provided a powder mixture for manufacturing 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 &nd a finely comminuted powder containing alloying elements, wherein a first group of alloying elements, the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole 2 (502 kJ/mole 2) at 1000C substantially are containsd in the atomized prealloyed powder while a second group of alloying elements the oxides of which have a free energy of formation with an absolute value ~ .
' " . ' . .
10363~9 exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, are completely contained in the finely comminuted powder.
Thus, the basic idea of the invention is that 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 element8~ the oxides of which are easily reducible ~preferably nickel, copper~
molybdenum and/or cobalt) substantially enter into the atomized prealloyed 9teel powder and the oxidation sensitive elements (especially chromium and manganese) enter into the finely comminuted powder. The above is not valid for carbon which is added substantially as graphite in quantities up to 1%
of the powder mixture or as an alloying element in the finely comminuted alloy powder in a content of 10% at the most of this powder. Here as well as in the continuation of the specification and claims % means percent by weight~
The atomized prealloyed powder is produced by melting iron and 0.2-10% of ~J - 3a -iC~36 3~3~ 4 alloying elements, the oxides of which have an absolute value of the free energy of formation below 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, water atomization of the melt and finally annealing in a reducing atmos-phere (suitably cracked ammonia). Depending upon the quality of the iron raw material the atomized prealloyed powder can contain up to 0.4% acces-sory elements, the oxides of which have an absolute value of the free energy of formation above 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C.
The content of such accessory elements, the oxides of which have an abso-lute value of the free energy of formation above 150 kcal/mole 2 (627 kJ/mole 2) at 1000 C, should not axceed 0,1%. Particularly the contents of silicon, titanium and aluminum should not exceed 0,04%, 0,03~ and 0.03%, respectivelyO The powder should have such a particle size distribu-tion that more than 90% and preferably more than 97~ of the powder passes a sieve having a mesh opening of 175 /um ~80 Tyler mesh; Method for sieve analysis of 0ranular metal powders, MPIF Standard 5-46, Metal Powder Industries Federation, New York, U6A).
Other alloying elements, the oxides of which have an absolute value of the free energy of formation exceeding 120 kcal/mole 2 (502 kJ/mole 2) at 1000 C, are molten possibly under addition of at most 75% preferably at most 50% iron and/or other metals with easily reducible 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 abso-lute value of the free ener0y of formation exceedin~ 150 kcal/mole 2 (627 kJ/mole 2) at 1000 C~ should not bc hi~her than 1% in the finely comminuted alloy powder.
The two components are now mixed in the proportions 80-99~ atomized pre-alloyed powder and 20-1% finely comminuted alloy powder. A powder mixture produced in this way provides a material having small and few oxide par-ticles which is shown by the following example.
Example 1 Two powders were produced, one by atomizing by means of water and subse-quent annealing in cracked ammonia (A), the other by mixing finely ground ferro-alloy powder and water atomized, molybdenum-alloyed steel powder (B) .. .. - .
;-:- ~ -...... ~ . . :, , ' ,. , ': , - , :. - .
, - .. . ~ :
: , , ?
- . . . .
-- ., ., ~ . - , , , . , .. - .. . .
10363~9 5 The two po~ders (A) and (8) had the composition ~% Mn, 1% Cr, 0.5~ Mo, balance Fe, The ferroalloy powder used in powder B had the composition 25 Mn, 25% Cr, 7~ C, balance Fe, and an average particle size of 4 lum accor-ding to Fischer (Methods for determination of average particle size of metal powder by the Fischer sub-sieve sizer, MPIF Standard 32-60, Metal Powder Industries Federation,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 30 mm length were pressed from both powders. The compacts were heated, one group to 1120 C and another to 1200 C in hydrogen gas atmosphere with a dew point of ~20 C and maintained at these temperatures for 30 minutesO
From the furnace the compacts were rapidly brought to a die where the cylinders at the elevated temperature were compressed to full density.
In order to estimate the content of oxide inclusions the cylinders were onalyzed with regard to total oxygen content. Further, the number of oxide inclusions having a linear dimension in any direction larger than 100 /um, were counted on a cross section surface of each cylinder, The results are ~hown in the following table, Temp, Material Oxygen contentNumber of oxide inclusions C % 100 /um/cm2 , 1120 A 0a54 116 t~ B 0.20 10 B 0~06 3 , .
The above example shows the advantage of the present invention, When Cr and Mn, the oxides of which have a free energy of formation of -126 and -140 kcal/mole 2 (-528 and -586 kJ/mole 2) at 1000 C respectively, were added as a finely comminuted ferroalloy (powder B) the forged product obtained a considerably lower oxygen content and lower number of large inclusions than in the case of alloying chromium and manganese already into the atomized steel powder (powder A).
, . .~i,`
. ~
~, `i~
. ' , In addition to low content of inclusions it is desired, as mentioned above, that the alloyin~ elements are to a large extent homogeneously distributed in the finished product, For this purpose the component of the mixture containing the oxidation sensitive alloying elements according to the in-vention must be comminuted to a small particle size. This s illustrated in the following 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 mix-tures the components consisted of water atomized prealloyed steel powder comprising 2~ nickel and 0,5~o lolybdenum, and ferro-chromium powder com-prising 45% chromium and 0,3% carbon. In the first case (C) the ferro-chromium powder had an average particle size according to Fischer of 33 um, in the second case (D) 20 /um and in the third case (E) 4 /um. Before compaction 0~5% graphite powder and 0.8~ zinc stearate were mixed into the three powders. They were then compacted to cylinders which were heated to 1120 C in partially combusted propane with a dew point of -3 C and then forged in the manner described in example 1. The cylinders were cut into halves, and the cut surfaces were ground and polished. The chromium con-tent was measured in several points of the cut surfaces by means of a microprobe. The coefficient of variation (CV) for these data were calcula- `
ted as the standard deviation in percent of the average concentration. CV
i9 a measure of the heterogeneity of the material. Material made from powder C had the CV-value 175%. For powder D the CV-value was 135~ and for powder E 45%. At a heterogeneity corresponding to CV 150% the harden-ability enhancing effect of chromium is almost non-existing which means that the addition of chromium in powder C is of no value whereas powder D and particularly powder E resulted in material in which the hardenabili-ty was increased by the addition of chromium.
From the above examples the advantage of adding that component which con-tains oxidation sensitive alloying elements finely in a comminuted state is obvious. The powder particles should have an average size according to Fischer below 20 /um, The example also shows that it is still more advan-tageous that the said average size is less than 5 /um.
. . .
.. . ~ - :.. ~.- .. - . . .
...~ ~ .
... . . .
~ 7 10363~g Of course it is important that the powder described obove does not segre- -- gate after the mixing operation. Possibilities for segregation occur during transportation of the powder from the mixer to the consumer and during feeding to the powder press. One way of diminishing the risk of segregation is to add 50-200 g of a light mineral oil per metric ton powder continuous-ly during the filling of the mixerO Thereby the fine constituents are brought to stick to the coarser steel particles.
A further improvement in this respect is obtained if the mixture is sub-jected to a heat treatment at 650-900 C for a period of 15 minutes to 2 hour~ in reducing atmosphere with subsequent caution~ desinte0ration of the cake formed. By this treatment the finely comminuted alloy powder particles are sintered to the steel powder particles which effectively counteracts segregation. This cautions 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.
, ~
In such cases where the powder mixture has a low content of finely commi-nuted alloy powder, 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 abcve 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, In addition to the components mentioned the mixtures according to the above specification can contain a suitable lubricant, e,g, zinc stearate, The addition of lubricant should not exceed 1%, ~., . .
`:~
, : ' .
.~' .
: : ' - .
. .
::
.,. " ,,
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A powder mixture for manufacturing alloy steel articles having small and few oxide inclusions, comprising a metal powder portion which con-sists of a mixture of two powders, viz. an atomized prealloyed steel powder and a finely comminuted powder containing alloying elements, wherein a first group of alloying elements, the oxides of which have a free energy of formation with an absolute value less than 120 kcal/mole O2 (502 kJ/mole O2) at 1000° C substantially are contained in the atomized prealloyed powder while a second group of alloying elements the oxides of which have a free energy of formation with an absolute value exceeding 120 kcal/mole O2 (502 kJ/mole O2) at 1000° C, are completely contained in the finely comminuted powder.
2. A powder mixture according to claim 1, consisting of 80 to 99% by weight of the atomized prealloyed powder of iron which contains 0.2 to 10%
by weight of said first group of alloying elements, and from 20 to 1% by weight of the finely comminuted powder which comprises a total of at least 25% by weight of said second group of alloying elements, at most 10% carbon, the balance being iron.
by weight of said first group of alloying elements, and from 20 to 1% by weight of the finely comminuted powder which comprises a total of at least 25% by weight of said second group of alloying elements, at most 10% carbon, the balance being iron.
3. A powder mixture according to claim 2, wherein the finely comminuted powder comprises at least 50% by weight of said alloying elements.
4. A powder mixture according to claim 1, 2 or 3, in which the alloy-ing elements contained in the atomized prealloyed powder comprise at least one element from the group consisting of the elements nickel, copper, molybdenum and cobalt.
5. A powder mixture according to claim 1 or 2, in which the alloying elements of the finely comminuted powder are at least one element from the group consisting of the elements chromium and manganese.
6. A powder mixture according to claim 1, in which the finely com-minuted powder consists of a ferroalloy with a total of at least 25% by weight of said second group of alloying elements, at most 10% by weight of carbon and the balance iron.
7. A powder mixture according to claim 6, wherein said finely com-minuted powder comprises at least 50% by weight of said second group of alloying elements.
8. A powder mixture according to claim 1, in which the finely comminuted powder has an average particle size according to Fischer of at most 20 µm.
9. A powder mixture according to claim 8, in which the finely comminuted powder has an average particle size of at most 5 µm.
10. A powder mixture according to claim 1, in which the particle size distribution of the atomized prealloyed powder is such that more than 90%
of the powder passes a sieve with a mesh opening of 175 µm.
of the powder passes a sieve with a mesh opening of 175 µm.
11. A powder mixture according to claim 10, in which more than 97% by weight of the powder passes a sieve with 175 µm mesh openings.
12. A powder mixture according to claim 1, in which the mixture con-tains in addition to the metal powder portion at least one member from the group consisting of graphite and a lubricant up to a maximum of 1% by weight of each.
13. A powder mixture according to claim 12 in which the lubricant is zinc stearate.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7316117A SE378260B (en) | 1973-11-29 | 1973-11-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1036389A true CA1036389A (en) | 1978-08-15 |
Family
ID=20319234
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA214,618A Expired CA1036389A (en) | 1973-11-29 | 1974-11-26 | Powder mixture for the production of alloy steel articles |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US3899319A (en) |
| JP (1) | JPS5429171B2 (en) |
| AT (1) | AT344763B (en) |
| CA (1) | CA1036389A (en) |
| DE (1) | DE2455850C3 (en) |
| FR (1) | FR2253101B1 (en) |
| GB (1) | GB1491726A (en) |
| IT (1) | IT1023230B (en) |
| SE (1) | SE378260B (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE408435B (en) * | 1976-11-03 | 1979-06-11 | Hoeganaes Ab | WAY TO PRODUCE A COPPER-CONTAINING IRON POWDER |
| JPS5950188B2 (en) * | 1979-07-18 | 1984-12-06 | 麒麟麦酒株式会社 | Composition for shielding scratches on glass containers |
| AU539115B2 (en) * | 1979-11-26 | 1984-09-13 | Imperial Clevite Inc. | High density sintered powdered metal alloy |
| US4552719A (en) * | 1980-12-03 | 1985-11-12 | N.D.C. Co., Ltd. | Method of sintering stainless steel powder |
| JPS59232249A (en) * | 1983-06-15 | 1984-12-27 | N D C Kk | Manufacture of porous sintered body of stainless steel powder |
| SE445715B (en) * | 1984-11-30 | 1986-07-14 | Hoeganaes Ab | MANGANESULPHIDIC IRON POWDER MIXTURE |
| EP0222002B1 (en) * | 1985-05-17 | 1992-09-16 | Aluminum Company Of America | Alloy toughening method |
| JPH0745683B2 (en) * | 1987-09-30 | 1995-05-17 | 川崎製鉄株式会社 | Composite steel powder with excellent compressibility and homogeneity |
| AU2569292A (en) * | 1992-09-09 | 1994-03-29 | Stackpole Limited | Powder metal alloy process |
| EP0846782A1 (en) * | 1992-09-09 | 1998-06-10 | STACKPOLE Limited | Powder metal alloy process |
| US5512236A (en) * | 1992-12-21 | 1996-04-30 | Stackpole Limited | Sintered coining process |
| DE4343594C1 (en) * | 1993-12-21 | 1995-02-02 | Starck H C Gmbh Co Kg | Cobalt metal powder and composite sintered body produced therefrom |
| JP4183346B2 (en) * | 1999-09-13 | 2008-11-19 | 株式会社神戸製鋼所 | Mixed powder for powder metallurgy, iron-based sintered body and method for producing the same |
| KR20120137480A (en) * | 2010-02-15 | 2012-12-21 | 페더럴-모걸 코오포레이숀 | A master alloy for producing sinter hardened steel parts and process for the production of sinter hardened parts |
| CN105834435B (en) * | 2015-12-30 | 2020-01-21 | 中国航空工业集团公司北京航空材料研究院 | Wet mixing preparation method of nickel-based high-temperature olefin alloy powder |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3424572A (en) * | 1966-09-13 | 1969-01-28 | Niranjan M Parikh | Alloyed metallic powder process |
| US3716354A (en) * | 1970-11-02 | 1973-02-13 | Allegheny Ludlum Ind Inc | High alloy steel |
| US3725142A (en) * | 1971-08-23 | 1973-04-03 | Smith A Inland Inc | Atomized steel powder having improved hardenability |
-
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/en active
- 1974-11-13 AT AT908974A patent/AT344763B/en not_active IP Right Cessation
- 1974-11-26 DE DE2455850A patent/DE2455850C3/en 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
Also Published As
| Publication number | Publication date |
|---|---|
| IT1023230B (en) | 1978-05-10 |
| FR2253101B1 (en) | 1982-02-19 |
| FR2253101A1 (en) | 1975-06-27 |
| DE2455850B2 (en) | 1979-01-25 |
| SE7316117L (en) | 1975-05-30 |
| DE2455850A1 (en) | 1975-06-05 |
| AT344763B (en) | 1978-08-10 |
| JPS50113402A (en) | 1975-09-05 |
| JPS5429171B2 (en) | 1979-09-21 |
| DE2455850C3 (en) | 1979-09-20 |
| ATA908974A (en) | 1977-12-15 |
| US3899319A (en) | 1975-08-12 |
| SE378260B (en) | 1975-08-25 |
| GB1491726A (en) | 1977-11-16 |
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