Hardfacing overlay on cast iron glassmould 2

[saanu]

Hi Experts,

I am welding a PTA overlay of - Colmonoy 42-P2 Powder on a Cast iron glass mould. We are facing a problem of porosity. We have taken care of cleanliness, quality and quantity of shielding gas etc. Will be glad to read suggestions on eliminating the porosity.

Parameters are
Current 63 amps
Volts 24 V
Pre Heat Temp 450 C

Chemical composition of Cast Iron
C 3.55 ± 0.10
Mn 0.6 ± 0.10
Si 2 ± 0.20
P < 0.10 ± 0.20
S < 0.10 ± 0.20
Cr < 0.10 ± 0.20
Ni < 0.10 ± 0.20
Mo 0.45 ± 0.05
V 0.13 ± 0.03
Ti < 0.10 ± 0.03
Ceq. 4.15 ± 0.10

Chemical composition of Powder
Boron 1.64
Carbon 0.37
Cobalt 0.10
Chromium 10.00
Iron 2.48
Nickel Balance
Silicon 3.07

Suggestions most welcome. Thanks in advance.

S. Vignesh

 

[metengr]

What shielding gas are you using? Have you checked hoses for leaks? Is the shielding gas welding grade?

 

[EdStainless]

IF your gas does not have low dew point at the torch (not just in the cylinder) then you have no chance.
You also need to bake out the castings so that they are dry and outgassed, your preheat should work, but with a long hold time.

I have seen molds coated by applying powder that is porous, and then fusing it in a vacuum furnace.
That said I am leery that a Ni based coating will hold up on plain cast iron molds. The CTE is very different and thermal shock will be a real issue. This is why molds are often high Ni cast iron or in the ultimate case cast BeNi.

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P.E. Metallurgy, Plymouth Tube

 

[saanu]

Hi Metengr,

We use welding grade argon for shielding as well as the transport gas for the powder.

thanks,

SVignesh

 

[saanu]

Hi Ed,

I will work on your suggestion of baking out the casting. Can you suggest the time and temperature for the procedure. The casting weighs 8.4 Kgs. Do let me know the hold time for the preheat.

Thanks and Regards,

S Vignesh

 

[EdStainless]

So these molds are 450C while you are hardfacing them, correct?
I would like to see them sit at 450C for a couple of hours before coating, but this creates an issue with surface condition.
Aren't they going to start discoloring and scaling at this temp? If so then you will not get good adhesion and you will need to use a lower temp.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Place the molds in a vacuum for 30 minutes to remove any moisture.

 

[saanu]

Thank you for the suggestions. Will work on them and come back to you once the issue is resolved.

Best Regards,

S Vignesh