hardening steel

[hvw]

My young son has made a knife out of mild steel and wants to harden or temper it as much as possible with our limited resources. Whatever we do probably won't be ideal but he's learning. My plan was to heat it cherry red and quench it in oil. I would appreciate any suggestions before we undertake this project. Thanks

[SND]

Case hardening it would work alright I think. There's a few products sold just for that purpose. If you have an acetylene torch, you could bring the blade to a red color, then turn the torch rich on acetylene for a while, it might soak up a bit of carbon. I'd probably quench it in water for a faster cooling.

[davesisk]

Originally posted by hvw
My plan was to heat it cherry red and quench it in oil.

I know little or nothing about tempering, but I doubt you want to dip a 2500 degree piece of metal into flammable oil, do you?

Dave

[Zrexxer]

Originally posted by davesisk
I know little or nothing about tempering, but I doubt you want to dip a 2500 degree piece of metal into flammable oil, do you?

Dave Oil quench is done all the time - for oil hardening tool steels. As an example, Randall knives are made out of O-1 tool steel, which is an oil hardening variety.

However...It won't make one meaningful iota of difference in a mild steel. Mild steels don't have enough carbon to form the martensite necessary for any real hardness. If your young knifemaker shows promise, buy him a couple of blanks of O-1 or D-2 steel to work with - they're not that expensive and will harden nicely!

[Jerry]

I would get it like you said red then place in water, then reheat to a blueish or so color?

[BillC]

If I were looking for an inexpensive source of steel for knifemaking I would use old leafsprings from the auto junkyard. They are high carbon steel and should harden nicely. Anneal them before you start working on them and then harden them.

After quenching you need to temper the steel or it will be brittle. Do an internet search for metal colors vs temperature so you can estimate the temperature of the steel when you anneal it, when you quench it and when you temper it. You should be able to find recommended tempering temperatures to obtain the appropriate hardness on the internet. If not, ask again and one of us can look it up for you.

Sounds like Fun!

[westval]

The best part about hardening mild steel, is that if you don't like the hardness of the finished product, you can re-heat to red hot, quench, and then feather in your color again. For myself. I like to stop right between purple and blue. Remember that the metal will continue to change even after you take the heat away from it. So have a can of water next to you. I've had fairly good luck using this method on fillet knives made from band saw blades. Good luck. Let us know how it turns out! I'm always looking for new advise!
Clay

[mrimpact]

Originally posted by westval
The best part about hardening mild steel, is that if you don't like the hardness of the finished product, you can re-heat to red hot, quench, and then feather in your color again. For myself. I like to stop right between purple and blue. Remember that the metal will continue to change even after you take the heat away from it. So have a can of water next to you. I've had fairly good luck using this method on fillet knives made from band saw blades. Good luck. Let us know how it turns out! I'm always looking for new advise!
Clay

i never seen purple or blue before :eek: :confused: :(

[westval]

light gold, dark gold, purple, blue - red hot. The lighter the color starting at dark gold, the harder it is. If you temper a punch to blue, it will smash. If you temper it to dark gold, it will chip or shater.

[westval]

HVW,
Try this link. ]Temper color chart (http://www.threeplanes.net/toolsteel.html)

[dsculpin]

Your ability to harden the blade is dependant upon the amout of carbon in the steel. If your blade is made out of anything less then 1018, I don't think you will be able to even case harden it without adding carbon to the surface. Generally, there are two ways to do this. You can pack the blade in carbon (or carbon rich items such as beans or nuts) and and then heat it in a sealed stainless steel or titanium foil pouch for the requisit period of time; or you can use a product called Kasenit that you can buy from online retailers such as Enco or KBC that will allow you to case harden low carbon steel in a much cruder fashion with a torch (follow the manufactures recomendations on temperature, length of heat, and quench). The results you will achive on a knife blade, however, will probably be fairly disiapointing (assuming you intend to use the knife as you would any normal knife). While the blade may have a very thin layer of hardend steal, the blade will still be fairly flexible and will readily bend. Sharpening the blade will probably also wear through the hardened layer. You really need to use a steel that is capable of being harden throughout, above an beyond merely case hardening. Hardening steel, such as D-2, which would make a good knife blade, can get a little bit more complicated. It is best to consult the steel manufactures guidelines as to hardening procedure. This link will put you on the right track. You best bet, however, is to get a good book from the library (or book store) on how to make knives, then buy some good blade steel and have your son make a second knife. You should be able to find a local shop that will properly heat treat your blade for a nominal charge.

Good luck

http://www.timken.com/products/specialtysteel/engineering/tech_info/PDF_Files/air_melt/ColdWorkToolSteels/TLS%20D2.pdf

[mark48310]

what Zrexxer and Dsculpin said...

35 points of carbon (1035) is about the minimum you need to get noticeable hardening with a quench...but it won't make a decent blade...and for steel that low in carbon to harden appreciably, you'll need something faster like water to quench...but water can often crack a thin piece of steel....

if it's mild steel, don't even waste your time...it won't get hard no matter what you do...(other than case-hardening)...you can heat, quench, temper to whatever color you like, quench it in ****** if you want, but it won't get hard... carbon is what makes steel harden...very little carbon, very little, if any hardening. period.