Casting within a casting

[DAVIDSTECKER]

I am looking for reference materials and/or pointers for a casting a steel part that incorporates a precast stainless steel component.
I have seen bronze gears cast around a steel hub.
The stainless steel would be shaped like a shell of the inside of a toroidal field (dough nut hole)
The steel would be cast around the stainless and become the structural support to be welded in place.
Stainless would most likely be ASTM A743 Gr. CF-8 and the steel A27 GR 70-36.
The stainless would weight maybe 300# and the steel 500-700#
In general most of the wall thickness' will be between 1-2" thick.
Thank you in advance for your input.
Best regards, David

 

[arunmrao]

Interesting application. Can you please provide a sketch and also tell us more about its end application. I hope we are discussing sand casting.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Dalinus]

Would not there be a problem with different heat treatment for these materials?
880°C + cooling on still air versus 1040°C + water or rapid air cooling?

 

[SwinnyGG]

Also keep in mind that on a part this large, you will need the core to be heated (before the second casting operation) to avoid very high forces developing in both parts.

If it were me, Id be investigating how to cast these parts separately and then weld them together.

 

[WKTaylor]

Davidstecker...in addition to other's comments...

Parts-within-parts are usually throw-away items never intended for repair or overhaul.

This Assy... in the a sense of scale you describe... does NOT seem like a low-cost throw-away item. IF some element ever needs 'fixing' this could get challenging, fast.

Also... After NDI of the outer casting [which might be challenging in-and-of-itself], I suspect that You may have-to ensure [re-validate] that the item buried within the outer casting is 100% unaffected by the process: IF SO... HOW?

Regards, Wil Taylor

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[DAVIDSTECKER]

arunmrao, yes it will be sand cast even though the cores are going to be real tricky.
Dalinus, very good point regarding heat treatment, I'll have to be sure to check that out.
jgKRI, I had planed on pre heating the core, just not sure just how high we should raise the temp. My first thought is in the 2,000F range but it needs to be explored.
I have attached a photo of the basic design, what we are working on is much larger with so casting completely in SSTL maybe too costly.
We are working a split liner design were we would weld the flanges and a center seam.
Thanks again for your input.

 

[EdStainless]

How much of the inside needs to be stainless? Just the surface or all of it?
I can picture formed liners being explosively welded inside.
Do you need special properties in the stainless?
Why not all stainless? (there are higher strength grades)

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P.E. Metallurgy, Plymouth Tube

 

[DAVIDSTECKER]

EdStainless, Then min wall for one version is 1/2" and the other we are about 1".
Given the size and shape of the liner, 1" is most likely going to be close to having flow issues in the mold.
The rest of the casting will be at least 2" thick with reinforcing ribs.
Why not all stainless, are we looking at 4,000-5,000# parts and the quantities involved warrant looking at different options.
We do make some 300# versions of this in cast SSTL because it is more economical that trying to fit and weld plate into the opening.
Also the end product is going to be welded to the support structure by run of the mill welders.
The SWL of these are in the 200 ton range.
The reason for stainless is for corrosion resistance only as paint and the like will not hold up to the pressure of the high tech rope these are for.
We need to keep rust and other abrasives from getting into the rope fibers.
OH I would so love to try explosive forming. To quote Myth Busters; David want BIG boom.

 

[ornerynorsk]

Eutectic coating?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[btrueblood]

Flame sprayed coating?

 

[ornerynorsk]

Btrueblood, yes. I used to do a bit of both cold and hot flame spraying back in the '80's. Just a thought. It's a nice way to add hardness and abrasion resistance on a cheap substrate. An amazing variety of materials is available.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[DAVIDSTECKER]

We hard surface some other castings here to about 1/4" but it is extremely labor intensive, we'll spend almost 2 weeks on one part, not to mention the cost to preheat a 3,000# part.
Most flame spray from what I've been told has limits on the pressures it can handle, it's prone to peel off under high loads.
Propeller shafts are routinely built up by flame spray and with great results due to the fact that the plain bushings they run in have an even lower pressure rating in most cases.
Also I think it's limited to a 1/16" to 1/8" when it comes to building up a surface.
These type of rope has tensile strength almost equal to the steel cables it is replacing.
I recently did some parts laser weld clad with a 17-4PH stainless powder that were to take the pressures of steel cables and so far it doing well.
But it to is limited on how much it can build up a surface.
The 17-4PH parts are small enough that they can be removed and redone if required, the new products are going to be welded in place for the 30-50 year life span of the ship.
Thanks again for everyone's input, a lot of good thoughts.

 

[EdStainless]

It looks like a job for a welding robot and heavy weld overlay work.
A few passes to build up enough material.
Personally I would look at Nitronic 50 for the wear surface.

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P.E. Metallurgy, Plymouth Tube

 

[DAVIDSTECKER]

EdStainless,
That is on the table too, we have our primary wire supplier putting us in touch with shops that have robots.
The salt water corrosion rating of the Nitronic 50 appears to be comparable to 316, that's great.
Nitronic 50 appears to be a Wrought class specification.
I found cast references in ASTM A743 and A351, what grade would be comparable to the Nitronic 50?
Again cost is a big player, just shooting from the hip I'd estimate we have about 25 Sq-Ft of surface and a 1/2" min (Currently)required by the customer, that would calculate to about 500# of wire each.
You know I've been in the marine industry for about 20 years now and the scale of some of this stuff still amazes me.
On the ship the anchor in the photo is for, it's hardly noticeable.

 

[EdStainless]

The weld wire is UNS S20980, ER209.
I believe that the cast grade is CG6MMN in both ASTM specs.

The other option would be a duplex stainless such as 2205, also strong and corrosion resistant.
The weld filler is called 2209.

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P.E. Metallurgy, Plymouth Tube

 

[bobjustbob]

The heat treatment for CF8 is a solution anneal at 1950°F followed by a rapid cool, usually a water quench. The heat treatment is required to dissolve all the carbides that form during the slow cooling after casting. When you slow cool stainless you risk sensitizing the material. The carbon and Cr form carbides at the grain boundaries that tie up the Chromium. That reduces the stainless nature of the part at the grain boundaries.

The heat treatment for A27 is usually a normalize at 1650°F followed by an air cool. You could water quench the A27 but it would need a temper at about 1200°F to get the properties you need in A27.

If you did heat the combination up to 1950°F and water quenched it and tempered at 1200°F you should get the correct mechanical properties out of each. Now, I question weather they will stay together after the quench due to differences in thermal expansion.

You will have a problem with corrosion resistance in the CF8 due to slow cooling on the temper. To avoid this you should specify CF3 to limit the amount of carbon thus limiting the ability to form carbides. Even better hedge against sensitization would be to specify CF8C with a carbon max at .03%. I don't remember if A351 has a CF3C or not. From the foundries perspective I always tried to melt CF8C with as low of a carbon set point as I can to avoid cracking, especially on large parts.

 

[DAVIDSTECKER]

EdStainless and bobjustbob,
Thank you to both of you.
A lot of great information and a lot to consider and research.
Best regards, David

 

[DAVIDSTECKER]

Where are my manors.
Thank you to everyone that took the time to contribute.
Best regards, David