Porosity in CA6NM castings
Porosity in CA6NM castings
(OP)
thread330-257321: Porosity in CA6NM Castings
I am having a similar problem with porosity in CA6NM on impellers and casings. Porosity appears on sections less than 0.5" and naturally in the risers.
Melt process is air induction furnace with Ar plug. Charge includes revert, 1010, ferrochrome (0.05% N according to the vendor) and electrolytic nickel. I've maxed out Ni, minimized Cr. Using Mn and FeSi for initial deoxidation in furnace and Al and Graphidox (54%Si, 10% Ti, 6% Ca) in final procedure before pouring to laddle.
Last two times we poured CA6NM were rainy overcast days with high humidity, both times castings were scrapped. We've had issues in the past but I would have to look up weather on those days to say anything definitive about moisture. However, the porosity observed did appear on the drag side possibly indicating off gassing from the no bake phenolic mold. I've sent samples out to confirm N content, should get them back in a week.
Can anyone recommend laddle deoxidation procedure? I'm curious about using either more Al, or trying FeTi, or Zirconium (read that 0.1% should be enough). If Al, can anyone specify max to avoid AlN embrittlement? Any experience would be helpful.
lkrzyzan
I am having a similar problem with porosity in CA6NM on impellers and casings. Porosity appears on sections less than 0.5" and naturally in the risers.
Melt process is air induction furnace with Ar plug. Charge includes revert, 1010, ferrochrome (0.05% N according to the vendor) and electrolytic nickel. I've maxed out Ni, minimized Cr. Using Mn and FeSi for initial deoxidation in furnace and Al and Graphidox (54%Si, 10% Ti, 6% Ca) in final procedure before pouring to laddle.
Last two times we poured CA6NM were rainy overcast days with high humidity, both times castings were scrapped. We've had issues in the past but I would have to look up weather on those days to say anything definitive about moisture. However, the porosity observed did appear on the drag side possibly indicating off gassing from the no bake phenolic mold. I've sent samples out to confirm N content, should get them back in a week.
Can anyone recommend laddle deoxidation procedure? I'm curious about using either more Al, or trying FeTi, or Zirconium (read that 0.1% should be enough). If Al, can anyone specify max to avoid AlN embrittlement? Any experience would be helpful.
lkrzyzan





RE: Porosity in CA6NM castings
Now to the gas porosity problem. I hope you are not super heating the metal . Please control the pouring temperature. Your observation of wet days is correct,and either I would avoid melting those days or take extra precautions,of drying the molds,ladles,charge materials,alloys etc.
You can add FeSiZr,in the melt before pouring along with CaSi. It should help. As you mention about impellers,are these the open type or closed ones (shroud). Please check the core ,and ensure proper escape of core gases. Perhaps,you might pour one in another alloy,to eliminate the possibility of porosity due to mold/core materials.
Hope it helps.
_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: Porosity in CA6NM castings
RE: Porosity in CA6NM castings
C is kept below the max of 0.06. Impellers are closed. Prior heat is usually a stainless 18-8 or variant of it like CF8C. I instruct the melter to keep material below pouring temp until its ready to pour. Last tapping temps were below 2940 F. Laddle is heated, molds are not but the wash is dried before closing. I'll have to talk with the chief foundry engineer regarding any gating mod to reduce turbulence.
I'm curious is anyone can shed light on why CA6NM seems to have a worse problem with porosity than other stainlesses. Solidification to a martensitic structure? Does the alloying change the interfacial energy appreciably enough to foster bubbles or is it the an issue with changing solubility on solidification?
Thanks.
RE: Porosity in CA6NM castings
Try pouring one similar casting in carbon steel and look for porosity?
_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: Porosity in CA6NM castings
RE: Porosity in CA6NM castings
_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: Porosity in CA6NM castings
Add vents for gases from mold and cores.
And we used to change the melt schedule based on the weather.
It is a pain but it works.
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Plymouth Tube
RE: Porosity in CA6NM castings
_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: Porosity in CA6NM castings
Talked to the foundry engineer but he said in the past Zr and Ti additions haven't made much of a difference. Pinholes do not worm so I don't think its a hydrogen issue. Vanes are under half inch.
We'll try some vent rope, have the mold heated prior to closing and pour it on a sunny non-humid day. I took some of the modl and will do an LOI to see if there is a significant difference from norm. I'll look for the Zr and add it in the laddle after deoxidation procedure to lock up nitrogen on austenite to martensite tranformation and look into slowing down solidification to allow gas time to diffuse.
Thanks.
RE: Porosity in CA6NM castings
It's the same reason E410NiMo is easier to weld, but if you really want to improve weldability for the end user, keep the C (and N) as low as technically possible.
RE: Porosity in CA6NM castings
What is the shape of the porosity. Is gas (round) or pipe (irregular)? Is there any slag connected to or inside the porosity? Calcium Boride is another deoxidizer you could try, but I would think the Mo in the alloy would be an effective deoxidizer. However, this statement is very telling:
"Porosity appears on sections less than 0.5" and naturally in the risers."
To me, it sounds like a feeding issue.
brimstoner,
You are correct. Too narrow a freezing range can lead to fusion problems and folds, however in this case I think I believe it's a feeding issue.
Metalhead
RE: Porosity in CA6NM castings
RE: Porosity in CA6NM castings
What you said is true, but the fact is that the porosity is only seen in sections of thicknesses less-than 0.5" thick. If it were a micro-porosity issue you would see it throughout the casting- especially in large grain areas. I'm just going on the info that has been provided by lkrzyzan. We still need more info about the shape and size of the porosity.
Metalhead
RE: Porosity in CA6NM castings
We poured another casing and impeller. Molds were reheated for longer time prior to closing. It wasn't raining but the day was muggy. Extra vents were added. On surface inspection I have not seen any porosity. I'm waiting for the cleaning room to process the castings further to see if any other issues are found.
RE: Porosity in CA6NM castings
If you are confident that the porosity is round then it sounds like a gas problem. The extra vents will help you release any trapped air, which can cause gas porosity in sections that freeze too fast. I hope that solves your problem for your welders sake!
MH
RE: Porosity in CA6NM castings
LK
RE: Porosity in CA6NM castings
Fortunately you have not encountered core breakages! .
_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: Porosity in CA6NM castings
Is the porosity still in the thin-walled locations?
MH
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