# Case hardening Oxy/ Acetelene



## bigrigbri (Aug 20, 2011)

If this has been mentioned before please excuse me.
If you heat up the workpiece to be hardened with oxy/acetelene to the req`d temp 680c say then still with the flame on the job turn the oxy off.
This will then give a sooty flame in which the metal will absorb into the skin.(a few seconds is all it takes)
Just quench and the jobs done.

Brian.


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## compspecial (Aug 20, 2011)

That's a great idea Brian! sounds much easier and safer than rolling parts around in toxic powders and the like.
             cheers Stew


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## rkepler (Aug 20, 2011)

Sorry, but the migration of carbon into the steel will take a lot longer than "a few seconds", and in your situation I don't think that you'll see any migration as the carbon likely doesn't have much if any mobility. Adding a case to most steels involves fairly significant time at elevated temperatures in an environment with a lot of free carbon. 

That being said a lot of steels will show appreciable hardening without adding a case, even low carbon alloys. If you can get it to quench really, really fast you can get 1018 to show some nice harness (look up "Rob's Superquench").

If you section the rod and polish the end and etch with nitric you should be able to see if you've added a case. There's a nice shot showing the end results here: http://www.citysteelht.com/surface_treatments.html Be aware that other processes can show something like that - cold rolling will leave a hard skin that can show on etch, etc. Even an interrupted quench can show that by leaving a slightly hard skin over a soft core.


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## bigrigbri (Aug 20, 2011)

Im not sayin that this method wil produce >70 rockwell on mild steel but I have found that it works well even on en3 en8 mild steel bar stock .
Its only probably .001" deep but its enough to give a slower wear rate say on model engines IC and steam.
Using resorces to solve difficult and often costly upgrades is all that this hobby is about
when given increasing financial restraints.
Try it on a piece of stock and offer up a file to see the difference.

Brian.


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## rkepler (Aug 21, 2011)

bigrigbri  said:
			
		

> Im not sayin that this method wil produce >70 rockwell on mild steel but I have found that it works well even on en3 en8 mild steel bar stock .



EN3 has .25% carbon, EN8 has .40% carbon and both will harden appreciably in a fast quench. I make bullet forming (swaging) dies from 4140 which is quite similar to EN8 in terms of carbon, it'll harden to about 50RC quite reliably.



> Its only probably .001" deep but its enough to give a slower wear rate say on model engines IC and steam.
> Using resorces to solve difficult and often costly upgrades is all that this hobby is about
> when given increasing financial restraints.



A lot of folks have been under financial constraints in a lot of places, they haven't found the direct application of soot to steel to do anything useful. I would suggest that if they had it would have a use in industry.

Here's a reference to time and case thickness: 

http://info.lu.farmingdale.edu/depts/met/met205/casehardening.html

Note that it's talking hours in an optimum environment for carbon migration and hours of soak and ending up with a case of .050".  



> Try it on a piece of stock and offer up a file to see the difference.



Alternatively I'd suggest that you have a friend process a few pieces of steel half using your process and half simply quenched without and see if you can distinguish them after cleaning (maybe painting as well?). If you can identify them consistently then you have a process, until then I'd suggest that you're simply seeing the normal hardening of a low carbon steel in a quench. (With a really fast quench you can even take 1018 to a pretty good hardness - check out "Super quench", a really fast quench that some claim will take a mild steel to chisel hardness {well, into the 40's anyway}).

I'm not trying to rain on your parade or say you're not seeing something, just suggesting that what you're seeing isn't caused by what you're attributing it to. I regularly harden steels similar to your EN8 "file skittering" levels with nothing but a brine quench.


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## Jasonb (Aug 21, 2011)

> Note that it's talking hours in an optimum environment for carbon migration and hours of soak and ending up with a case of .050".



For model use we are hardly likely to want anywhere near that depth of hardness, as brian says a thou or two is plenty to stop two surfaces picking up when rubbing together. If I went for that depth of case on some of the parts I've done they would be hard right through and far too britle to be any use. Same again with quenching small parts the core will become hard and brittle when all thats needed is a slightly harder surface.

Without some good magnification there is little point in us sectioning a rod to see 0.001" thickness of case.

I can't see much difference between coating the hot part in carbon from a flame to placeing a hot part in case hardening powder that model engineers have been doing for years.

J


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## Tin Falcon (Aug 21, 2011)

Guys: there are many ways and methods of doing almost any procedure used in model building. Many perspectives many experiences. Lets remember to be open to all Ideas unless there is a safety issue even then remember tact and respect wen correcting folks. . 
I know there are lots of home-brew favorite heat treating methods. from old time smithy techniques to modern controlled industrial methods .It is all good if done safely and meets your hobby needs. 
Tin


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## bob ward (Oct 2, 2011)

FWIW I've been getting quite good results with Cherry Red case hardening powder.

http://www.rosemill.com/v/html/cherryreddemo.wmv

In reference to the 'poisonous' powders, that is probably a reference to Kasenit which is not entirely accurate. The active ingredient of Kasenit is (possibly was, it seems to have disappeared from the market) sodium ferrocyanide, which itself is not poisonous and is used widely as an anti-caking additive in foods.

When sodium ferrocyanide is burnt one of its decomposition products is hydrogen cyanide, which IS nasty, but not a problem with small quantities when used in a well ventilated area etc etc.


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## Blogwitch (Oct 2, 2011)

Bob,

I posted on here a while back about Kasenit.

I will just reiterate.

If you have some that you inherited or bought, even from say 10 years ago, get rid of it quickly, purely for the reasons Bob quoted. It just isn't worth taking the risk with.

The latest version going under the same name has a different chemical build up, and is safe to use, just follow the instructions that come with it.


With regards to turning the oxygen down using oxy/acet.

That is just another use that a carburising flame can be used for (that is what the flame type is called). Also, when bronze welding (and brazing, using brass as a filler rod), we were always taught to use a slight carburising flame. You can also use a pure acetylene flame for soot blacking the parts you don't want the braze to stick to.

There are many different flames when using oxy/acet, not just the neutral that people normally use.

http://en.wikipedia.org/wiki/Carburizing


John


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