Rebuild of a 17-4 PH fatigue broken shaft 5

[0707]

Is it correct to rebuild a 5meter 17-4 PH material, fatigue broken shaft thought a SS 410 welded sleeve ring? What would be the filler material for joining 17-4 PH with SS TP 410? What kind of PWHT would be required? What would be the alternatives to such repairing?

Thank you

Luis Marques

 

[Metalguy]

If you proceed with this repair, you need to know if 17-4 in the H1150 cond. is OK, because you will need to PWHT the 410 at least to 1150 deg F. If you can PWHT at 1175 the 410 will be less likely to crack.

I suspect the weld metal will be less a concern than the HAZ in the 410.

 

[Carburize]

More details please - what is is the diameter,loads, shape etc.
First reaction is that it is not a good idea.
The PH steels develop mechanical properties by ageing and the precipitation of fine particles - the effect of the heat from the welding process is effectively to over-age the material in the weld heat affected zone producing a soft region next to the weld. If the same loads exist which caused the fatigue crack you are trying to repair then these soft zones are likely to be the initiation site for the next crack.
But as I noted at the start of this response - more details.

 

[unclesyd]

I would not attempt to repair a broken 17/4 shaft in the manner you describe.
First you will create 4 metallurgical notches where evidently you had just one before if this is a bending fatigue failure.
You will also have the mechanical notches at the heel of each weld.
And so on.

Can you comeback with more information on the shaft and failure?
What was the geometry of the shaft at the failure?
What was the heat treatment of the shaft?
What is the dia of the shaft?
What is the service?

I would think seriously about a replacement.

 

[0707]

Thank you all for the emphaty.

The shaft is 50 mm. dia and failed at 3/4th length just adjacent to bearing
seating surface. It was also noticed one subsurface cavity like
defect which probably acted like stress raiser.

Regards

Luis Marques

 

[unclesyd]

I would look at a replacement made from 17/4 PH that has been treated for use as boat shafting. This type shafting will get you the optimum in mechanical properties for a shaft. The two US names are Aqualoy17 or Aquamet 17.

Armco recommends that 17/4 shaft be heat treated at H1125 or 1150 for use a shaft material.

You didn't mention the service enviroment, could you comeback with this information.

http://www.aquamet.com/index/aqua17.cfm

http://www.aqualoy.com/index.asp

 

[boo1]

We have welded repaired 100+ of 17-4 PH shafts using TIG and laser methods. But if your material is fatigued, titmay be at the end of its service life.

 

[Metalguy]

Boo1,

If he only had one fatigue crack the rest of the metal could be fine. But such a repair is questionable at best.

 

[stanweld]

0707
The fillet weld repair that you contemplate will have much, much less resistance to fatigue failure than the original shaft; furthermore, fatigue life cannot be quantified. Welding residual stress is additive to the imposed design loads and the fillet weld design presents a mechanical notch. Any such repair should be considered highly temporary at best. The shaft must be rebalanced as well.

A mechanically connected sleeve repair or other mechanical connection could be designed with calculations providing some basis for remaining fatigue life. Again, I would consider such a repair to be temporary but at least predictable. Note, the problems with rebalancing the shaft.

Repairing the shaft with a full penetration weld repair, machining to size and fully heat treating to the original temper will provide a better solution, but again, full restoration of fatigue life will not occur. The weld repair will still be the weak link.

Replacement is your best bet for a long term fix.

 

[boo1]

I agree with Stanweld if the metal is fatigued the the assembly is suspect. If economics can afford it replace.... You dont need a 5 meter shaft flying around.

 

[Metalguy]

Just want to clarify something here for the forum. The presence of a fatigue crack should not imply that the rest of the part/metal near the crack *is* "fatigued". While there may be other fatigue cracks nearby, esp. if corrosion is involved, in non-corrosive environments a cyclic-stress-driven fatigue crack frequently is one single crack.

Another thing to remember is that the crack initiation time is usually far longer than the time to propagate the crack from *tiny* to large-esp. where the stress cycles are fairly constant.

 

[0707]

Dear Sirs
You have to consider that this procedure is just provisional (it is only to give time) because definitively in the short term the shaft must be replaced. With the TP410 sleeve or by welding rebuilding is it correct to use AWS E/ER630 welding consumables? Considering that the shaft is in the overage condition is it correct to PWHT it above 620 ºC?
Regards and thank you for your inputs
Luis Marques

 

[Maui]

I recommend that you send the shaft to a company that specializes in failure analysis to determine how and why this component failed. Without this knowledge, you may suffer the same failure again. For this reason I would not attempt to repair the broken shaft, but would preserve the broken pieces for evaluation by a failure analysis expert. Also give them as much information about the application that you can, as well as pertinent information regarding methods of producing the component, heat treatment, etc. The more information that you provide to them, the more they will likely be able to help you.

Maui