Heat treating 17-7PH stainless in a mini melting furnace?

[antknee]

I have some stainless steel 17-7 PH that is currently in condition C. So now I need to heat it to condition CH. I'm wondering if I could use one of the mini melting furnaces noted below. The part will fit in there, the furnace is cheap and I only need a few parts. The 17-7 needs 900 degrees F for 1 hour so I think in theory this will work. My concern is that flatness will be compromised or it'll age unevenly. Is this a good idea or bad idea? I've not tried to heat PH stainless before and I'm not sure what would be cheap and effective. Regards. Ant.

http://www.ebay.co.uk/itm/Mini-Meta...760?pt=LH_DefaultDomain_0&hash=item4cffa51e40

 

[EdStainless]

Nope, not that one.
You need a small box furnace.

http://www.ebay.co.uk/itm/Assay-and...646?pt=LH_DefaultDomain_0&hash=item4149182a16

Though you could use a lower temp rated one.
A Blue M or Thermcraft would be just right.

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Plymouth Tube

 

[redpicker]

You will find the temperature uniformity in that little pot is unsuitable for your application. You could fill it with liquid lead, but you could expose the 17-7 to liquid metal embrittlement (LME) and cause a lot more problems for yourself.

You should be able to find a commercial heat treater that has small furnaces that could very well be cheaper than that little furnace. That's what I would do.

rp

 

[antknee]

I've found a purpose made steel hardening furnace on ebay. I'll bid on it and cross my fingers. It's an 8 hour round trip to go and pick it up, but that'd be better than several hundred pounds / dollars.

http://www.ebay.co.uk/itm/CARBOLITE..._Metalworking_Supplies_ET&hash=item416405e3f2

 

[btrueblood]

Does he need to worry about atmosphere control for ht of 17-4? Or just wrap the piece in 321 stainless foil and hope for the best?

 

[redpicker]

Does he need to worry about atmosphere control for ht of 17-4? Or just wrap the piece in 321 stainless foil and hope for the best?

I guess that depends on antknee's application. A H900 treatment will produce a very light brown oxide on the surface, but for most applications it is not an issue. The usual practice to prevent this would to be maching/grind/poslish after heat treatment, if necessary. This is another reason these materials are often heat treated before machining.

rp

 

[MiketheEngineer]

Just send it out to be heat treated. If they screw it up - you get your money back. Eight hours round trip?? and what do they pay you??

Now, if you are going to do this every week - that changes the equation a bit!!

Don't forget the cost of running this "little" oven or any mistakes you might make!!

 

[antknee]

I'll be heating the 17-7PH to 900 degrees F for 1 hour to get maximum hardness in the CH conditon. The surface finish isn't that important, I won't machine or polish. Will I need any atmosphere control? And what is the purpose of wrapping the 17-7 in foil? Regards. Ant.

 

[btrueblood]

Foil wrap cuts down on how much air can reach the part, and how heavy an oxide layer will develop, or decarburization of e.g. tool steels. Go with redpicker's advice, you probably don't need it, esp. if the heat tint/surface finish is not important.

 

[antknee]

I might get outbid. It is hard to estimate a fair price for a second hand furnace. Any idea on what the one I mentioned above is actually worth? It is currently up to £40/$60

Would it make any difference using a mini kiln? I've seen one that is small and could be sent by courier.

 

[EdStainless]

It is rare to find a new one for less than $1,000.
These are popular with knife makers and other hobbyists.

A small kiln might work, but you need to run a few trials to get the temp settings worked out.


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Plymouth Tube

 

[MiketheEngineer]

40-60 lbs - that's chump change. Go for it!!

 

[btrueblood]

But we are talking about the 2nd one, not the first one you posted, antknee, right?

 

[antknee]

Yes we're talking about the second one I posted. I wouldn't get it at £40/$60. I can get a brand new budget mini kiln shipped for £350/$500. So the price range I'd bid up to would be somewhere between £50 and £350. I don't want to overbid so what would be a fair value, it looks 10+ years old but probably cost 1000+ originally. The bid ends tomorrow, so this convo will come to an end soon regardless.

If you're really bored pick a final price. Closest gets awarded a smug grin!