Effect of heating to straighten a 316 stainless steel rudder shaft

[IANW530]

I have a 7 ft long x 3 inch s/s shaft in a yacht rudder that was bent at its tapered lower end by the boat being towed onto a sandbank. It had approc 1 inch bend over the lower 18 inches. A local machine shop tried straightening using various machines and presses, no effect. They then applied heat to the area and pressed it to within 2mm of straight.
Can anyone advise What structural / strength effect will this have had on the shaft? Is it weakened significantly? Gather this may make the s/s crystalline/ more brittle?

Thanks

 

[EdStainless]

What strength is this material?
If this was cold worked to provide high strength then it is highly likely that the heated areas are significantly softer.

And if there is any surface discoloration (heat tine) the corrosion resistance will be significantly lower.
If the heat tint was removed by wire brush or light sanding it will still have corrosion issues.

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P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

"within 2mm of straight"

I'm thinking that is not straight enough.

Does the manufacturer have a "service limit" type specification ?

 

It will never be returned to a 'straight' condition; within 2mm is not very close.
It could possibly be made serviceable, depending on the arrangement and operating conditions.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MagBen]

It is unlikely 3'' shaft experienced much of cold work. Depending on the temperature you straightened, the strength level could remain the same, if temperature was lower than 1000C.
Corrosion resistance was likely degraded because you could get carbides and other precipitates especially if the material is not 316L, low carbon.

 

[kingnero]

lol at a 7 ft shaft "within 2 mm of straight".
Wouldn't want to be around when they get it running again. Bearings and end couplings must appreciate it, even for such a non-high rpm application...

 

[Tmoose]

I read the OP again. "Yacht rudder" shaft, not prop shaft.

Having the lower ( lowest?) 18 inches bend suggests the shaft was held quite securely at the 18" mark.
I'm picturing more of a kink than a bend.

 

Thanks Tmoose.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."