Bonding stellite 6 to alloy steel

[river1]

Our wps states a preheat of 500 F we have maintained that. With a maximum 650 F interpass temp. we have maintained that. minimum 2 layers of overlay. why are we getting cracks in the second layer? not the first. tig process,1/8" filler.

 

[metengr]

Because of weld shrinkage stresses and the inability of the Stellite 6 layer to absorb these stresses. Have you used an Inconel butter layer prior to depositing Stellite 6? Another option is to use Stellite 21 on the steel substrate followed by Stellite 6.

 

[river1]

In reading about stellite 6 i have noticed that the "buttering" step is usually involved. However, my wps shows only RCoCr-A as the deposited material.

 

[metengr]

Try using the Inconel butter and deposit the Stellite 6 on top of this layer - keep the preheat and interpass temp requirements as is and use stringer bead placement, no weaving.

 

[river1]

metengr, thanks for your input, I appreciate it. Anymore ideas, I'll be open to them. thanks

 

[weldtek]

A few years ago, I had to develop a procedure for multi layer crack free Stellite 6, applied to a multi faceted c.s. part. In other words, the overlaid surfaces met at 90 degree angles, inside and outside corners. The overlay had to be ground smooth and pass a penetrant test, i.e. no indications. From experience, the only way to achieve crack free # 6 is to preheat to 1000 F minimum, maintain that temperature throughout the overlay process and slow cool by wrapping the part in ceramic fiber insulation or equal.
We built an insulated box with a piece of grating to place the parts on for welding. There were heaters inside the box and we applied heat from the top also. As you know, at 1000 F, the c.s. parts are red. The welders wore insulated suits with forced air cooling. GTAW process.
A preheat of 500 F is a minimum preheat, but, it won't garantee crack free deposits.
I have heard an outfit in France is achieving crack free Stellite 1, but, to date I haven't been able to do so.

 

[metengr]

weldtek;
We had a local machine shop that did HP steam turbine part repair work for us and they were able to deposit Stellite 6 on Grade 22 substrate using a 600 deg F preheat with Inconel butter. These were GE, HP steam turbine startup, by-pass valve discs. There were no problems, the trick was bead placement and avoiding interruption of GTAW welding.

 

[weldtek]

Metengr,
In our case no butter layer was allowed. The harface was deposited directly on the substrate.

 

[river1]

We were successful applying the Stellite 6 to the carbon steel substrate without indications. After a 24hr. slow cool we performed a dye penetrant test and passed. We sent it off to PWHT and then to the machinist, after they machined the piece it passed another dye penetrant test. For some reason they then performed a magnetic particle test. It shows indications in the form of a line around the entire welding area where the two materials are joined. Is this from the difference in magnetic properties of both materials? I have been unable to find anything on the magnetic properties of stellite 6.

 

[metengr]

It shows indications in the form of a line around the entire welding area where the two materials are joined. Is this from the difference in magnetic properties of both materials?

YES. Make sure they use Liquid penetrant inspection and not a magnetic particle examination. What you are viewing is the break in the applied magnetic field causing the particles to line up.