Low alloy steel powder for plasma deposition having solid lubricant properties
Reference Number: N 01-02
Inventors: Rao, V. Durga Nageswar; Rose, Robert Alan; Yeager, David Alan; Fucinari, Carlo Alberto
In a first aspect, it is an object of this invention to provide an iron-based low
cost metal powder useful for plasma deposition of a coating that (i) will possess
an ultra-low dry coefficient of friction (i.e. about 0.2) and (ii) will readily conduct
heat through the coating. To this end, the invention is an iron or copper based powder
composition for thermal spraying, composing H.sub.2 O atomized Fe or copper based
particles having at least 90% of the Fe or copper metal, that is combined with oxygen,
is combined in the lowest atomic oxygen form for an oxide of such metal o. The invention
is also more particularly a low alloy steel powder composition comprising (a) H.sub.2
O atomized and annealed iron alloy particles consisting essentially of (by weight)
carbon 0.15-0.85%, oxygen 0.1-0.45%, an air hardening agent selected from manganese
and nickel of 0.1-6.5%, and the remainder iron, with at least 90% of the particles
in Fe or iron alloy form and nearly all the oxygen combined in the FeO form.
In a second aspect, it is an object of this invention to provide a method of making anti-friction iron powder that (i) is highly economical, (ii) selectively produces FeO and (iii) promotes fine flowable particles. To this end, the invention is a method of making low alloy steel powder suitable for plasma deposition, comprising the steps of (a) H.sub.2 O (steam) atomization of a molten stream of steel containing carbon up to 0.9% by weight to produce a collection of comminuted particles; the steam atomization is carried out to exclude the presence of other oxygen, restricting reaction of iron to the oxygen in the water-based steam thereby encouraging the creation of FeO, and (b) annealing the particles in an air atmosphere for a period of time of 0.25-10.0 hours in a temperature range of 800.degree.-1600.degree. F. to reduce carbon in the particles to about 0.15% to 0.45% Another form of the powder is produced as sponge through the reduction of magnetite or hematite (Fe.sub.3 O.sub.4 or Fe.sub.2 O.sub.3) with H.sub.2 O and CO to reduce to Fe and FeO. It is extremely important that the final composition be completely free from Fe.sub.3 O.sub.4 and Fe.sub.2 O.sub.3 and the amount of carbon present be in the range of about 0.15% to 0.4%.