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Hard surfacing for abrasive wear resistance

2000

We are looking for a process that will economically improve the wear resistance of mower blades. The process needs to be economic for production quantities. Material Science, heat treating and coatings are not my specialty. Therefore I seek your advice.

The blades are currently 5150 or 10B38 steel heat treated (austempered) to RC 40-45. The processes I have investigated so far are: Boriding, ZrN, Tungsten Carbide brazing, and Hard chrome.

We want to end up with a blade that has the same structural properties as the current blade (provided by the substrate), improved abrasive wear resistance, and the ability to accept localize damage due to a strike without failure a larger area of the coating.

I am concerned about adhesion of the hardened layers with ZrN, Tungsten Carbide braze, and Hard chrome. I almost want to rule out Hard chrome due to hydrogen embrittlement. I have yet to see a plated part that can consistently avoid this issue on a production basis, and the results of a fatigue fracture on this type of part could be "very bad"

Boridizing sounds appealing, especially Borochromizing. Do you know any drawbacks to this outside of the processing issues? Do you have any contacts for Borochromizing?

Any suggestions for processes that I have not mentioned, issues with pre or post process heat treating that I need to be aware of, etc.?

Thanks for any input or suggestions you may have.

Mark

Mark Atterbury
- Beatrice Nebraska

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We've been having great success increasing the life of metal cutting tools and threading dies by metal ion implantation. Basically, rather than coat the surface we use a beam of nickel and titanium ions to micro-peen it. The result is a very significant increase in the surface toughness that results in much greater wear resistance. Most of the treated parts last two to three times longer. The process is conducted at very low temperatures -- under 200 F -- and takes around thirty minutes, so there is no thermal distortion. As it is not a coating process, there is no adhesion problem and no change in tolerances. Sharp edges remain sharp. Hydrogen embrittlement is also not possible. Jim Treglio - scwineryreview.com PVD Consultant & Wine Lover San Diego, California 2000 My research into the use of coatings indicates that they are not a good candidate for your application. They are usually quite thin, and the mode of failure is that the metal under the coating deforms or cracks out. Try cryogenically processing the blades. This should increase the abrasion resistance of the blade considerably, an will increase the fatigue life as well. It will make the blade more tolerant to damage due to accidental strikes. F. J. Diekman - Streamwood, Illinois 2000

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