Heat treating ?

[razorback]

Well I tried to heat treat my first knife today and it warped.

It is a piece of #4 planer iron (steel), I annealed it and then ground the shape. I heated it to red and let cool, twice, to normalize it. Today I heated it to above non-magnetic, left it there for about 15 minutes and then quenched it in old motor oil. When I removed it it was warped. I put it in tip first and held it steady. Any ideas as to why it did this.

I have heated it again and let cool slowly to soften it again so I can straighten it out. Any advise on straightening it would be appreciated as well.

Thanks, Tony

[Wampus]

For a thin material like a knife, I don't think there's any need to heat it above critical that long.  Before I got my kiln, I would heat to just above magnetic for about a minute and then quench.  Without good temp control, you risk overheating the steel.  If you're letting it get too much above critical temp then you grow the grain size and make it more prone to warping or cracking in the quench.

A lot of heat treating manuals call for heating 15 minutes or more, but they assume larger parts than a thin knife blade.

[razorback]

Thanks Wampus.

Any suggestions for reducing the grain and straightening the blade.

[Ragnarok Forge]

You have already started over so, heat the blade to a low red and use a good hammer on a hard flat surface ( metal ) preferably and anvil and flatten that sucker.  Another good trick is to put a really heavy flat edged chunk of steel on top of the steel while at a high red and it will flatten it nicely.

You definately do not want to hold a knife blank at nonmagnetic for 15 minutes. The grain in that sucker was very large when you quenched it.  

It sounds like you had everything right except for the holding time at nonmagnetic.  Just repeat your process and this time make sure your temperature is steady and barely above nonmagnetic and then hold it for about a minute and quench.