I have a rasp that no longer works and I found out it's made of 1090 steel, and want to use it to make a tomahawk, but I can't find the proper temperature for quenching.
In case that's important: I use a gas forge.
A challenge depending on how hard you want it to be. Assuming it is carbon steel. No alloy means low hardenability so it need a severe quench to make high hardness. The high carbon means it is more susceptible to cracking during a severe quench. For a hatchet, a combination of adequate toughness with limited hardness should be possible. A hardness of HRC 30 to 40 appears very possible according to Jominy bar hardness and that should be very satisfactory. The TTT curves( time, temperature, transformation) for 1080 steel ( 0.8 Carbon) indicates it needs to cool to below 250 F in about one minute. So an oil quench from about 1550F may be good depending on thickness of the part. Sounds like a good senior project for metallurgy students. It may be more hit or miss as a "do it yourself" project. A big advantage would be a hardness tester. There are a fair number of variables such as loosing carbon during hot forging.