Heat treatment help please :) (long with pictures)

T

Trick

Joined
Mar 3, 2001
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Hello,Been a long time since I have been here.I have the same question as I did along time ago.First a little background.
I am making diggers to use metal detecting.The only ones you can buy are not near long enough and are made from soft stainless and dull quick(like the short one pictured).The first one I made(pictured) I used 5160 spring steel and stock removal.I never got it too hot and when I was done I could take all my weight(alot of it)and bend it down and it would flex back.I made this for a friend.He posted it on a detecting board and now I have several people wanting me to make them diggers.The first one I left with the curve(helpful to scoop dirt out of the hole)but it was a pain to shape because I couldn't lay it flat on my 6x48,so most of the shaping was done by hand.Well to quicken it up some I straightened some stock in the forge and have them shaped and I just took a piece of railroad track and had a piece of 2inch and a piece of 1 1/2 inch solid rod welded on it so I can shape the digger on them like a garden trowel,cupped,instead of the curve,for dirt removal.Sorry for being so long winded,but I wanted you all to know exactly what I am trying to do and the reason for the question,so now,the question.
When it is all shaped and done,how should I go about heat treating it and tempering?It has to be hard enough that it will not bend and stay bent,but soft enough that it will not snap.Spring seel is how it should be,but my dad says once it has been in the forge,you can not bring the spring back.At least he don't know how,anyway.These will be used with the cutting edge cutting a plug in the ground then the plug will be pried out with the side/front of the digger.Sometimes in concrete hard dirt.The serrations for cutting roots.I am going to be getting way more for making them than you can buy the factory made digger,so I want to make sure I do it right.I want it to be something that will last them for years with proper care.Thanks,Ric
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1. try and do it differentially, you can use clay or clay and ceramic wool mix.
2.Use wax to quench then
3. test blade hardness and if too hard, put in your kitchen oven for an hour or two. Still no good? back to the oven. you can try and get the heating a little up.
4. you can also spring temper it by letting it sit in a food fir for a while

Test it all out once, and find out what works best for you.
For trowers, i made one, I quenched the tip, then tempered it three times at 300 ° C for two hours. I trowed it thousand times, tip bend once, but was easy to straighten. Even the edgeholding was rather good.

greetz, bart.
 
With a pretty woman around like the one in the picture, why would anyone want to spend time heat treating knives?:D :D
 
first, yes you can get the spring temper back, you should do some experimenting first,

in the forge, draw out a piece of the steel down to about 1/8 by 3/8 inch by about 5 or 6 inches long(test piece)

rough grind it, then harden it, then grind it smooth and polish.

the tempering color you are looking for is dark blue.

If I recall correctly(and please check) your tempering color is about 550-600 degrees.

oven thermostats are not to be trusted set your oven at 500, Put it in the oven for 30 min and see what color you get. that's as high as mine goes. If the color isn't right, go up 25 degrees and try it again.continue untill you achive the dark blue or youtop out your oven. tempering can also be done with an open flame or a red hot iron. be careful, if you over heat and get light blue you will have to re harden it and start over. Once you have an even dark blue now give it a quick flex test. If you don't like it, adjust the temp. hotter makes the steel softer. cooler makes it harder (hold an edge better, but also more brittle)

your solution is good, the tempering is doable I'm sure after looking at your blade that It wont pose you a real problem, just play with it you'll get it right.

have fun, EE
 
Thanks all!
I would spend less time heat treating knives R but I don't think my friend would like that,that is his wife! ;)
BART,You lost me bud!I have no idea what you mean by the clay or clay and ceramic wool mix you were talking about.I am new to this! :confused:
Eric,That sounds like the way I can handle!I will give that a try!These are pretty thick,I think a little softer would be better than harder.I am going to go make a test piece today! :D
 
If the knife is thick you might want to leave it in the oven for an hour rather than just 30 min. to make sure that the heat has soaked all the way through.
 
You might consider a different cross section to the blades used for digging. A diamond cross section like a lot of bayonets have would add substantial bending resistance to lateral stress regardless of metals or heat treat.

My thoughts on differential treating is that they add substantial ability to bend without breaking. I'm not sure that is what you are looking for. I'd sugest a diamond cross section, 3/8", or +, thick if you are going to pry with it, with consistant heat treat. I'm no expert on steels for bending resistance, maybe A2, its pretty tough.

Think about small flat crow or pry bars if you are going to pry and bend instead of cut, just a thought!
 
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