309, 310, 314...for high t 1

[macmet]

Hello everyone,

I have been searching this site looking for tips on the most effective form of stainless steel to use as a cover plate in a furnace system. I've seen bits in a few threads that have helped but then other threads that seem to contradict previous ones.

Ny problem is that we have a plain carbon steel and it is warping badly. The plate is exposed to some abrasion in the system with cyclic conditions probably reaching 2300F. This temperature is only reached with operation error and under normal conditions the temperature would be quite low.

So I have been asked to find a way to minimize this warping if possible. I have been looking at 309 or 310 but I have a few sources that say 314 would have better performance. I'm worried that with the combination of such a high temp and cyclic conditions that no stainless would be effective. I'm wondering now if I should essentially use a sacrifical plate and just replace it every X months.

Are there any stainless (or economically practical alloys) that may be effective at this temperature? Would either 309, 310 or 314 be effective? What about just using 304, or 304H?

It is just a cover plate, but any warping causes drafts which we need to minimize.

 

[NickE]

Maybe try cast iron? (Grey cast iron)

 

[MikeHalloran]

How about wrapping a carbon steel plate in 321 sheet?

E.g. just on the hot side, and folded around the edges to secure it.



Mike Halloran
Pembroke Pines, FL, USA

 

[macmet]

NickE,

Do you mean use cast iron with the intention of replacing it or a regular basis?

Mike,

What would be the advantage of wrapping a 321 sheet? Would it add oxidation resistance reducing the likelihood of the plate warping?

To give a little bit more information, the plates we have in there now might be about 10'L x 1-2'H x 1"W. We join two or three of these and they're welded to supports. We've noticed that where they're joined to the supports the shape retains its original shape better. Possibly b/c of heat transfer to the supports?

 

[NickE]

GCI (Iron) wont work, cause it dont like to weld...

And a piece 1"x1-2'x10' would be really really heavy, though steel wouldnt be much lighter.

I do know that cast iron is often used when warping due to temperature cant be tolerated. The flake graphite tends to absorb dimensional changes caused by heat. Also one surface could be chilled to form white iron, if your temps only occasionally go very high then that would provide some wear resistance also.

If 2300F is your peak error temp, what is normal max, min, and nominal?

Maybe limit the temp excursion through another method than operator, IE put High limit on the heater...

 

[MikeHalloran]

A poor bond between the 321 sheet and the steel plate will moderate the steel's temperature and allow it to retain some strength.

I might try a layer of 316 screen between the 321 and the steel to make sure the heat transfer is poor, though that might be overdoing it.







Mike Halloran
Pembroke Pines, FL, USA

 

[21121956]

Hello everybody:

I think that a possible solution to this problem is performing on the carbon steel plate a metalizing (welding powder applied in layers with an oxi torch) with 309 stainless steel and leave it as it is.

Mike, I think that you are rigth with your idea, but for experience in some works I have been involved with, when your base material is mild steel or low alloy steel, it is necessary to apply a layer of 309 before any other type of inox is welded, especially 316; this in order to obtain a good bonding between these disimilar materials and to act (the 309 layer) as a buffer to stresses developed during operation.

Ricardo

 

[MikeHalloran]

My point is that in this case you don't _want_ a good bond.

You want a bond that's just good enough to keep the 321 from melting, but not so good that the structural plate will warp.



Mike Halloran
Pembroke Pines, FL, USA

 

[lewtam]

Hope it works Ricardo, I was thinking of another avenue.

Take the plates to a forge house, get a full anneal with very slow cool. Might need a straighten/flattening at the recryst. temp but the forge will be able to handle it.

I suppose it depends on how that hot temp is encountered - slow temp rise to max temp, not there for long and slow cool is how I'm looking at it. If only a thin ss coat, the mild steel base might still get to a temp where it wants to turn back into a coil if you haven't addressed those residual stresses.

 

[macmet]

To answer the questions asked by NickE...

It is difficult to actually know the max/min/nominal temperatures. Our furnace design does not allow for any thermocouples to be placed in the area.(this is something we are looking to correct for future projects)

Generally the plate should be covered by our fuel, meaning these plates should avoid any exposure to direct heat. What happens though is that if fuel is not fed in properly the plate is left uncovered, and exposed to the chamber where temp. reach 2300F.

 

[rolledalloy]

Using a stainless will add strength and scaling resistance to the situation but a couple of things you should consider.

Stainless steels and nickel based heat resistant alloys expand significantly more than carbon steel and they have low thermal conductivity compared to steel. As a result of the low conductivity, they are more susceptible to uneven heat up and cool down. These hot spots coupled with the high expansion commonly lead to distortion.

304 and 321 are only suggested for use to 1600F max due to scaling concerns. Do you seen much scaling of the carbon steel when it gets overheated? It wouldn't take long at 2300F for it to oxidize away. 309 is good to abotut 1900F and 310 to 2000F. Also what type of fuel is involved?

314 is not readily available in North America in plate products. Its more prevalent in Europe. If the temperature gets above 2000F, then RA330 would be typically be our suggestion as a step up in performance from 310 stainless.

 

[macmet]

The expansion of the stainless steels is our major concern if we switch from cs. We are looking to change the design slightly that would be more accomodating to expansion, although we are having some difficulty. We're also looking at covering the plate with a refractory, etc.

There does appear to be a lot of scaling on the carbon steel.

This application uses wood fuel.

Everything I have looked suggests either 309 or 310. Beyond that though I'm having difficulty picking the better choice. Of course price is a big consideration, and 309 I expect to be cheaper than 310 b/c of the lower Ni. 310 has a higher intermittent service T...but lower thermal conductivity, possibly leading to more hot spots and distortion?

Can anyone tell me one 309S is?