Got a potter to heat my wishbones to 800 degrees C for 3 hours in his electric kiln. It seems to have relieved the stresses nicely but a lot of black
scale crap fell off them. He gave me about half of it in a bag and it has some weight to it, maybe 200g.
With hindsight, getting them very hot in an oxidising atmosphere wasn't the best idea.
Anyone have any expert opinion on whether I've shagged the bones or done something else bad to them (hydrogen embrittlement I've heard of
too..)
I was planning to clean them up and micrometer the flat bits, see if I've lost any significant amount of steel.
500 degree C is enough to stress relieve
Hydrogen embrittlement is what you get when you use electrolysis to remove rust, so I doubt you will have suffered from that.
I think you'll be fine to be honest, but I'll let the experts confirm.
Jesus Blueshift,
You ain't half making this wishbone building lark hard on yourself arn't you!
Mark Allanson did his in his kitchen's oven... how hot do they get?
And I didn't bother at all and have managed 2000miles ok so far.
Cheers,
James
mountains out of molehills, that's my motto
If you realy need to warm up parts to that temperature, there are special "metal bags" for in the oven to prevent the parts from goiing
black.
I buy them here in Holland at a specialist shop. But I agree, 500 C is more then enough!
I'm not an expert but:-
I think 800 C will have had them glowing red and unless your oven was purged with an inert gas, oxidisation would take place like TIG or MIG welding
without the shielding gas then I'm sure the wishbones will have oxidised.
I would seek expert advise before using them, usually stress relief is done in the jigs aswell - no?
They were done in the jigs, that was the point.. so they wouldn't spring out of the jigs into the wrong shape.
I'm hopeful that with a cleanup the bones will be ok, I just hoped someone with expert knowlege would come along and say for sure that no other
unpleasant effects could have occurred.
To fully anneal low carbon steel (I am presuming this is what the parts are made of)
900-950 Deg C for 20 mins per inch cross section with slow cooling. Considerable scale will be formed.
Sub critical annealing can be done at 650-700 Deg C. this would be suitable for most applications.
Any Longer or higher may result in some hardening of the material.
HTH
Daz
800 C is too warm! Only for hardening steel products it should be above 700 C. Then you would cool it off in oil. (cool it off in water will create
more stress!)
Depending on what material you use and how your wishbones are cooled down the wishbones should go back into a oven some ware between 200 and 300
degree C for several hours. (depending on thickness off the material and the type of material).
Alway's better to get information before you start.... ;-)
They were cooled off in the kiln over a long period of time, min 8 hours, so I don't think they should have hardened.
I was led to believe they should be cherry red for stress relief, oh well..
Just trying to determine if they are in any way not fit to go on a car now.
If they are fully annealled then they may be a little soft, Stress relieved should be fine. An inspection & "test" with a small hammer in an inconspicious area should confirm.
Do you have any tube left?
If so, heat treat a piece the same as your bones and compare it with a non heated piece.
A simple bend test would give you peace of mind.
Maybe use a torque wrench to give you some figures.
Just an idea.
Paul G
Hmm, I would but:
- the guy wants 20 quid a shot to fire stuff in his kiln
- he doesn't want to do it again after it filled his kiln with scale not until he's built a gas kiln in a month or so.
hum.
quote:
Originally posted by blueshift
Hmm, I would but:
- the guy wants 20 quid a shot to fire stuff in his kiln
- he doesn't want to do it again after it filled his kiln with scale
hum.
If they were kiln cooled they will be annealed.
You will have basically slightly overtemp isothermally annealed them.
They will be very soft now.
My opinion is that you've now made some scrap.
You've annealed the steel so now its good and soft, the process to temper it back to a useful state could be done but if their trip to 800C
didn't modify the dimensions of the parts then tempering them will.
Refer to this article for background information.
In the car parts factory I once worked in as a heat treatment inspector the furnace operators would take great delight in picking up parts fresh out
of the stress ovens by hand and throwing them at people to catch, of course you'd yell and drop the part but they'd laugh their tits off.
Thanks Doug, NS Dev.
Bugger.
Oh well, back to the drawing board.
Best way to learn , by mistakes, etc.
The man who never made a mistake never made anything!
quote:
Originally posted by NS Dev
Best way to learn , by mistakes, etc.
The man who never made a mistake never made anything!
Yeah, I'm feeling quite philosophical about it. Fortunately I enjoy the process of building and learning.
Now to see if I can find someone who can cut me some shapes out of plate.. why did my mate quit his job at the sheet metal workers? doh!