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I am preheating a WC6 casting to 850F and then overlaying one side.

First and foremost, what is the overlay material you are applying?

Also, what is the heat treat condition of the part prior to overlay/stress relief? Normalized and Tempered? Quenched and Tempered?

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My question is, is there a limit on the number of times I can stress relief this part?

Typically a low-alloy part like this can take multiple cycles of 3 to 4 times depending on your hold time at temperature, usually one cycle is 2 hrs minimum. For best practice, you should qualify the total time at temperature and at the bare minimum check tensile and hardness of the material.

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Some procedures state the part must stay hot after welding and go straight to PWHT and others say the part can cool prior to stress relief.

No problem letting the part cool, not considering your overlay material, as long as you slow cool in still air.

The devil is in the details; she also wears prada.

All the welding works shall be as per WPS (Welding Procedure Specification) and the WPS shall be supported by PQT (Prequalification test)

If the specific number of times of PWHT is covered by PQT, the application of the number will be within acceptable range.

Generally, during PQT, several mechanical tests (ex., tensile, yield, impact) are carried out after 3 cycle's simulated heating for weldment. The meaning of 3 cycles is "simulated" condition of 1 time of initial welding and 2 times of repair welding in future. As it were, with the PQT once it passes the tests, total 3 times of welding are allowed at site (1 time initial welding, 2 times repair welding.)

In a same way, check if the number of times for PWHT you would apply can be covered by PQT and WPS. If not, additional testing for the simulation might be required.

Note that welding has various factors to affect weldment quality. They would be heat input, travel speed, PWHT, Preheat, material, welding electrode, heat treatment, etc., Again, all the welding works shall be within qualified WPS and PQT. Maybe it would be good idea for you to discuss with welding engineer who handles with WPS & PQT.



Lee SiHyoung,
Engineer - Material & Corrosion Specialist
WorleyParsons Oman Engineering,
cap1a79@gmail.com

DVWE- The part is overlaid with Stellite 6 and it comes Normalized and Tempered at 1100F. In this case, we had a four piece order. The first two parts went through with no issues, the second two have been overlaid twice and the Stellite has cracked both times.

stoverdr,

Here is a thread discussing this matter. I agree with an inconel butter layer, and I also believe your preheat is way too high.

https://www.eng-tips.com/viewthread.cfm?qid=224562

The devil is in the details; she also wears prada.