Hardness reduction of stellite 6 on Incoloy 800

[mforoutanfar]

Hi everyone,

We're having a problem with an incoloy 800 part overlaid with stellite 6.

The part is a thermowell shaped roughly like a drilled partial cone with large diameter of 28mm, small diameter of 20mm, height of 90mm and drill diameter of 10 mm. The overlay thickness is 2mm and has been carried out by manual welding. (The original thickness was more than 2mm, the extra thickness has been machined)

After carrying out a hardness test on the finished part, it turned out that the surface hardness decreases drastically (from 436 HB to 182 HB) as you get closer to the small diameter. The required hardness is between 300 and 400 HB.

Now here are the questions:

- Why does the hardness differ in different points? Where did we go wrong?
- Can the hardness be restored in any way without machining and overlaying the part all over again? (e.g. some kind of heat treatment, etc.)

Thanks!

 

[metengr]

Based on what you have stated, you may have reached the dilution zone of the Stellite 6 weld deposit on the Incoloy 800 substrate. The only way to verify this is to cross section the thermowell in the small diameter section and evaluate the weld region.

No, there is no way to increase the hardness. You need a thicker layer of Stellite 6 after final machining.

 

[mforoutanfar]

Thank you so much for your answer. We too came to the conclusion that it must be a dilution problem. What we can't figure out is why the hardness hasn't been reduced uniformly throughout the part. The only possibility I can think of is that the welders grew careless for some reason as they neared the cone's tip and, say, exposed the part to too much heat.

Actually, this part has been manufactured before by some other company and we're making our part according to their drawings. Funny thing is their overlay thickness is even thinner than ours (1 mm!), and yet their part seems to have been acceptable.

 

[metengr]

mforoutanfar;
Agreed. You need to cross-section the piece to confirm the as-found weld deposit thickness, and make necessary adjustments to your process. This is the only way to determine if the welder added enough weld metal.

Stellite 6 is hardfacing material so it is important to have enough material deposited – heat during welding will not affect this material.

 

[tomwalz]

Louw De Jong
Stoody Deloro Stellite
604 463-2140
ldejong@stellite.com

I have found him to be a great resource on Stellite. Nice guy, dead honest, bright, been with Stellite for Decades. If he doesn't know the answer ha can find someone who does.

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[mforoutanfar]

Thanks everyone.