Iron powder compositions

Details Iron powder compositions Iron powder compositions

2001-01-24

2003-09-16

King, Roy (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Loose particulate mixture containing metal particles

C075S246000

Reexamination Certificate

active

06620218

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns iron based powder compositions for the preparation of compacted and sintered products having improved properties. More specifically the invention concerns the influence of the largest particles of the lubricant and the iron based powder used in the composition on the dynamic properties of the final products.
BACKGROUND OF THE INVENTION
Fatigue performance of sintered steels are influenced by several factors which are interacting. The density was early established as one of the most influential factors together with the microstructure and alloy element content but also homogeneity, pore size and pore shape are known to influence the dynamic properties. This makes fatigue performance one of the most complex properties of PM materials.
OBJECTS OF THE INVENTION
An object of the present invention is to improve the dynamic properties of sintered steels, specifically sintered steels having a density between 6.8 and 7.6 g/cm
3
.
Another object of the invention is to eliminate the influence of the particle size of the lubricant on the dynamic properties, especially the fatigue strength of the sintered parts.
A third object is to provide a method of improving the fatigue strength by selecting the particle size of the lubricant in view of the particle size of the iron powder.
SUMMARY OF THE INVENTION
According to the invention it has now been found that, even if the amount of the very largest particles of a lubricant constitutes a negligible or almost negligible fraction of the lubricant particle size distribution as well as of the amount of the lubricant, this fraction has an unexpectedly large detrimental effect on the pore size and accordingly on the dynamic properties.
Similarly it has been found that the very largest particles of the iron powder, i.e. the maximum size of the iron powder has an unexpectedly large detrimental effect on the dynamic properties. Thus in order to get improved dynamic properties the maximum size of the lubricant particles as well as the maximum size of the iron powder should be reduced. For presently commercially used ferrous based press powders this means that the maximum particle size of the lubricant should be less than about 60 &mgr;m as measured by laser diffraction measurement.
In order to achieve the best dynamic properties for a given iron based powder (at a given density) a relationship between the maximum size of the particles of the lubricant and the maximum size of the particles of the iron based powder has also been established. The term “maximum size” as used in this context is defined in the formula below.
In accordance with the invention it has been found that the particle size of the lubricant in a composition including the lubricant and an iron based powder for powder metallurgical preparation of compacted and sintered products should be selected so that the largest pores of the compacted and sintered product prepared from this composition should be equal to or less than the largest pores obtained in a compacted and sintered product prepared from the same composition without the lubricant, which in practice means that the compaction is performed in a lubricated die.
Empirically we have found the following relationship between the largest lubricant particles and the largest iron powder particles in order to avoid the influence of the lubricant on the size of the largest pores.
Lub
max
≦0.31×Fe
max
−26, wherein
Lub
max
is the lubricant particle size in &mgr;m whereas 99.99% of the lubricant is finer.
Fe
max
is the iron particle size in &mgr;m whereas 99.99% of the iron powder is finer
(this could also be expressed as Lub
max
is the size of the largest one hundredth of a percent fraction of lubricant particles in &mgr;m,
Fe
max
is the size of the largest one hundredth of a percent fraction of the particles of the iron based composition in &mgr;m). This means that the maximum particle size of the lubricant as defined above should be less than about 0.3 of the maximum size of the iron or iron-based particles.
DETAILED DESCRIPTION OF THE INVENTION
The iron based powder according to the invention may be an alloyed iron based powder, such as a prealloyed iron powder or an iron powder having the alloying elements diffusion-bonded to the iron particles. The iron based powder may also be a mixture of an essentially pure iron powder and the alloying elements.
The alloying elements which can be used in the compositions according to the present invention may be one or more elements selected from the group consisting of Ni, Cu, Cr, Mo, Mn, P, Si, V and W. The particle sizes including the maximum particle sizes of the alloying elements are smaller than those of the iron or iron-based powder. The various amounts of the different alloying elements are between 0 and 10, preferably between 1 and 6% by weight of Ni, between 0 and 8, preferably between 1 and 5% by weight of Cu, between 0 and 25, preferably between 0 and 12% by weight of Cr, between 0 and 5, preferably between 0 and 4% by weight of Mo, between 0 and 1, preferably between 0 and 0.6% by weight of P, between 0 and 5, preferably between 0 and 2% by weight of Si, between 0 and 3, preferably between 0 and 1% by weight of V and between 0 and 10, preferably between 0 and 4% by weight of W.
The iron based powder may be an atomised powder, such as a wateratomised powder, or a sponge iron powder.
The particle size of the iron based powder is selected depending on the final use of the sintered product and, according to the present invention is has been found that also the maximum particle size of the iron based powder has an unexpectedly large detrimental effect on the dynamic properties of the sintered product.
The type of lubricant is not critical and the lubricant may be selected from a wide variety of solid lubricants. Specific examples of suitable lubricants are conventionally used lubricant such as Kenolube®, Metalub, (both available from Höganäs AB Sweden) H-Wachs® (available from Clariant), and zinc stearate (available from Megret). The amount of the lubricant may vary between 0.1 and 2, preferably between 0.2 and 1.2. Furthermore the vaporising temperature of the lubricant should be below the sintering temperature of the compacted part. Presently used lubricant which may be used according to the present invention have vaporising temperatures less than about 800° C.
The amount of graphite varies between 0 and 1.5, preferably between 0.2 and 1% by weight of the composition. Also, the maximum particle size of the graphite powder should be equal to or smaller than the maximum particle size of the lubricant.
In addition to the iron based powder, optional alloying elements, graphite and lubricant(s) the compositions according to the invention may also include optional conventionally additives, such as MnS, Mnx™.
The improved dynamic properties which can be obtained according to the present invention are especially interesting in sintered products having densities between 6.8 and 7.6 g/cm
3
, especially between 7.0 and 7.4/cm
3
.
Examples of preferred iron based powders plus preferred amounts of graphite follows below:
Iron+4% Ni+1.5% Cu+0.5% Mo where the alloying elements are diffusion bonded to the iron particle mixed with 0.4 to 1% graphite.
Iron+1.75% Ni+1.5% Cu+0.5% Mo where the alloying elements are diffusion bonded to the iron particle mixed with 0.4 to 1% graphite.
Iron+5% Ni+2% Cu+1% Mo where the alloying elements are diffusion bonded to the iron particle mixed with 0.4 to 1% graphite.
Iron prealloyed with 1.5% Mo and 2% Ni diffusion bonded to the iron/Mo particle which are mixed with 0.4 to 1% graphite.
Iron prealloyed with 1.5% Mo and 2% Cu diffusion bonded to the iron/Mo particle which are mixed with 0.4 to 1% graphite.
Iron prealloyed with 1.5% Mo and 2% Cu and 4% Ni diffusion bonded to the iron/Mo particle which are mixed with 0.4 to 1% graphite.
Iron prealloyed with 1.5 or 0.85% Mo and mixed with 0.4 to 1% graphite.
Iron prealloyed with 3% Cr and 0.5% Mo and mixed with 0.

Affiliated with

Also associated with

Rating

Iron powder compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Iron powder compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Iron powder compositions will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3013365