4140 is excellent stuff (modern bbl steel), as Taylor says, heat red/oil quench and then polish it bright so you can follow the color changes, heat to the color the axe men tell you and allow to cool-that's your drawing temper-which reduces the brittleness brought on by the quench which is what gives you the hardness you seek. A working edge will chip/crack out if you leave it full hard/brittle, plus would be awful to sharpen.
I've yet to do it, but an oven can be used for tempering too. Others can tell you temps and durations.
Propane will work, might be easier to not overshoot draw temps with the ~3,600F Propane/air mixture vs. ~6,300F Oxy-acetylene yo. You can get ~4,500 with oxy-propane also FTR.
Also, the great thing is that if you overshoot your temper color, you can just start over-red hot, quench, polish, draw...it's just fuel and time in the shop.