Steam treatment 1

[Tuptus]

Hi.
Does anyone have info on corrosion resistance of steam treated P/M part (salt spray exposure)
Thanks
Tuptus

 

[kenvlach]

From your description, I can say that it's in the range of 0 to infinity.

 

[Tuptus]

ye
I am afraid so.
I was hoping that somebody could have salt spray data on steam treated metals
Thanks anyway
Tuptus

 

[kenvlach]

OK,
Honestly, there are probably studies somewhere for ~fully dense P/M materials, impregnated P/M, for plated, chromated (depending on base metal) & painted parts.

I have chromated porous Al castings that had first been vacuum impregnated (w. polymethylmethacrylate), & passed salt spray req. of MIL-C-5541, Chromate on Al.

But, since your parts were steam treated, I presume this means a blueing or blackening on some steel, yes?
In this case, not much corrosion protection, even on wrought material. Add the variables of alloy, porosity, steam treatment T & P, and I don't think you can find test data for equivalent parts.

 

[Tuptus]

Thanks.
yes this is blackening-blueing process, based on exposing metals to overheated steam at very specific temperature range - for steel alloys around 950F, so adherent layer of magnetite is being form on surface. In P/M parts it also helps to close open porosity. Plastiv impregnated parts can not be used becouse of processing temperature. We have found that parts steam treated have much longer shelf life, but no specific studies have been performed by us to quantify it or for salt spray.
Regards
Tuptus

 

[kenvlach]

Hi Tuptus,
I found a one page article on your process. Its source was ASM Handbook, Volume 4, Heat Treating, pp. 229-236, "Heat Treating of Powder Metallurgy Steels" (1991) published by ASM Int.

http://www.asminternational.org/

It also said, additional information can be found in a paper, "Mechanical Properties of Steam Blackened P/M Materials" by L. F. Pease III, in Modern Developments in Powder Metallurgy: Proceedings of the International Powder Metallurgy Conference, [published or sponsored by?} Metal Powder Industries Federation (1988). I found the website

http://www.mpif.org/

which claims "This website is the world's most comprehensive resource for information about Powder Metallurgy (P/M)"

Re steam blackened parts, as you have said, the steam causes magnetite to fill the surface porosity, which improves wear resistance, corrosion resistance and sealing capacity. The article cautions that the treated parts are very brittle (can fracture if dropped on the floor), and it gave a limit (max.) for carbon content of 0.5 wt% to minimize this brittleness.

I would expect that, based on my knowledge of carbon steels where the heterogeneous microstructure (e.g., ferrite + carbide) causes ready--made galvanic corrosion sites and limits the formation of a continuous protective iron oxide surface, that the same situation applies for your parts: Better corrosion resistance at lower C content due to a better magnetite coverage.
I also did an Internet search for 'Steam Treatment of Powder Metal.' Lots of vendors. One mentions that the Fe3O4 layer is about 0.004 mm thick, another refers to a book: Powder Metallurgy Design Solutions, 1999, Metal Powder Industries Federation 105 College Road, East Princeton, NJ USA, 2001.

The following site says "Steam oxidation ... is also used before painting, plating and coatings to increase salt spray test hours, up to 1,000 hrs. Steam Treating is replacing resign impregnation due to the fact that oxide will not bleed out from high temperature and friction in the use of this type of product that is used for these purposes. Other characteristics of Steam Treating oxides are: increased hardness, corrosion resistance, increased density, wear resistance, fitness to galvanic, plus porosity sealing and the control of sizes and oxide thickness for the automotive industry, lawnmowers, furniture, electrical fixtures, toys, combustion-furnace, water heaters, and many other types of burner parts, etc."

http://www.elkcountyheattreaters.com/Process.htm

I hope this is useful to you. I have learned about a process application that previously I only knew for treating gun barrels.
Ken

 

[Tuptus]

Thank you kenvlach
You have been very helpful
Regards
Tuptus