Post Weld Heat Treat Procedure to Reduce HAZ Hardness on Part with Chrome Plate in Adjacent Area

[EngineerTex]

Part: Hydraulic cylinder barrel - 18" OD ASTM A106 w/ 2.5" thick wall - 33 inches long
Weld: 0.25" thick Inconel 625 overlay for about 5" wide band around entire circumference of the OD.

I have a customer that needs us to weld an Inconel 625 overlay onto the OD of the part. Since the overlay will be applied with laser, the overall temperature of the part will not get much over 400F (There will be a 400F preheat).

Here's the monkey wrench in the works: the HAZ has to be kept below 22HRC and the ID of the part has chrome plate that has already been ground and polished.

My gut tells me that throwing this in a furnace will ruin the chrome plating and will likely distort the part. Heat blankets seem to be a reasonable idea, but I don't know how this will affect the chrome plate. I've been told that the OD could possibly be torch annealed while keeping the majority of the part in a water bath to keep the ID from getting too hot, but that doesn't sit well with me either.

Is there a coating that I can put on the chrome plating that will prevent damage to it? Does anyone know what preheat I should reach if I want to avoid post-weld heat treat altogether? I would develop a new WPS if I'm sure that I can reliably get low hardness in the HAZ after welding and if the preheat and interpass temperatures won't be so high that they damage the chrome plating.

Is there any literature on this particular subject that I can point to which would put my customer's mind at ease?

All input is appreciated.

Engineering is not the science behind building. It is the science behind not building.

 

[metengr]

Having been around welding and seeing all types of unique projects, I'll be honest, you need to remove the current plating to have this done correctly. Preheat, perform the weld overlay and re-chrome plate as required. Otherwise, the risk of delamination or spalling is significant.

 

[EdStainless]

So the barrel is only 22RC now?
That seems soft for a cylinder.
You should run a trial and see if you need PWHT.
With this being laser weld you may not need it.
It will depend on the hardenability of the steel and the heat input.
If you need PWHT you will need to strip the Cr, weld, PWHT, re-plate, and re-grind.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Agree with Ed. Run a trial; you may well be able to meet the HAZ hardness without PWHT or by reheating with the laser to only heat the overlay and penetrate to the HAZ. You might also preheat using the laser to only affect 1/4" below the surface. You have a great heat sink in the 2.5" thick cylinder wall and I believe that the ID Surface temp can be kept below 200F.



f.

 

[metengr]

I don't agree, the thermal gradient from preheat applied and some heat input from welding can easily crack a hard chrome plating. A temper bead technique may keep the hardness below, but I would not trust a brittle, hard chrome plating on this type of application. Going though all of this, one can strip chrome plating and re-plate.

 

[EngineerTex]

Well, this is disappointing. Thanks so much for the valuable information, though.

EdStainless - Yes - the MTR shows 15HRC and 49.7ksi YS/73.7ksi UTS. The carbon equivalent is 0.427%.

Our current thought is to weld and perform a heat treat afterwards with thermal blankets and if doing so damages the chrome, we will strip and re-chrome. However, in the hopes that the PWHT doesn't damage it, we will close (not seal) the ends during the heat treat and employ a slow argon purge. I recognize that this may be a waste of time, but I have found at least one company on the internet that shows their chrome plating to be suitable for use at temperatures up to 600C/1112F. I have also asked the customer to contact the chrome plating company to ask for the normal service temperature, but I do not have an answer yet.

If, after we heat treat, it has obvious cracking and/or spalling, then it's time to re-chrome. My question is now this: If, after rattling some chicken bones and hoping that the stars align, the chrome appears to be ok visually, what type of examination would I use to prove to the customer that it has to be re-chromed? My understanding is that all chrome plating has normal microscopic cracks throughout that would not work for a dye penetrant or mag particle inspection. Or should a visual inspection determine to a high confidence level that it is good/bad? Any other thoughts about inspecting suspect chrome? The decision will not be in my hands as to whether or not to use it -- it will be up to the customer and I don't want this part to go to the field if I have any documentable suspicion about its suitability.

Thanks.

Engineering is not the science behind building. It is the science behind not building.

 

[tbuelna]

EngineerTex-

You did not specify the type of chrome plating used on the cylinder bore, but both hard chrome and thin dense chrome should easily handle exposure to around 350degF. This is the level of temperature used in post plating bake out for embrittlement relief. It would not take much effort to instrument the bore surface to record temperatures during the rework.

To be honest, I'd be more concerned about taper/out-of-round distortions in the bore near the section being welded. Hydraulic cylinders require fairly precise bore surfaces. If the weld overlay process distorts the bore beyond acceptable size/shape limits you would need to bore/grind/hone the ID oversize, build the surface back up with chrome plating, and then grind/hone the plated surface to the size/shape/roughness required.
I'd suggest you document the size/shape of the cylinder bore prior to any reworking. This will help resolve questions in the event there is distortion of the bore after welding.

 

[EdStainless]

If you get done and it is still in tolerance and still looks OK I would have the most sensitive florescent LPT possible done on it.
With all of this work rechrome and grind does not sound like that much work. And you would know that it is good.

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P.E. Metallurgy, Plymouth Tube