Stainless 17-4?

[Kent Johnson]

A survey of my boat indicated that it needed a new shaft. The shaft was suppose to be 316 stainless, but it was very magnetic. When I asked about its composition, they told me it was made of stainless 17-4, supposedly superior to stainless 316. My research indicated that stainless 17-4 is as corrosive as stainless 302. Who is right? Any suggestions?In the meantime, I had two machinist look at my old bronze shaft. Both said it just needed cleaning and there was nothing wrong with it. Both also said it would probably last 4 times longer than the magnetic shaft. Neither were familiar with 17-4.

 

[GARRY @ S/V TASHTEGO]

Stainless

17-4 is a specification of the nickel and chromium content of the metal. The 400 and 600 series of stainless steels are ferromagnetic. The 300 series (304 and 316) are not. The alloy number should be specified when you buy stainless. 316 is somewhat more corrosion resistant than 304 and is a little stronger too. 304 is easier to form. If your bronze shaft is OK use that and save the money.Cheers,Garry

 

[Kevin L. Woody]

Shaft material

Hello Kent: I have never heard of that particular material being used for shafting. Current thoughts for shafting is material called Aquamet 19, 22, 25 and 28. Aquamet is a trade name and often infers hybrid material like Timet 28 and others. These materials will eliminate the use of 304, 316 and other types of stainless probably in the same manner 316 eliminated the use of bronze. Of coarse materials like 316 stainless and bronze are still found in the market place but they have less of a following. I'm in agreement with Gary that the bronze shaft, if in good condition, could be used with good results. Sorry I can't help with the 17-4. Sincerely, Kevin L. Woody