Forging is fun. Steel needs to be hot forged but iron can be cold forged, needing only to be annealed when hammering has hardened it.three small knives
Common nails are made of iron. Sometimes common nails can be of mild steel, in which case you must anneal them (bringing the steel to red-heath and letting it air-cool) when you notice they are hardening. Any nail, around 3 inches long, can be turned into a small knife, old bent nails cost nothing so you can try and explore different shapes at no cost and in no time.
Or you can make small traditional shapes such as scimitar, kukri, kriss (haven’t tried yet).
To make a simple blade
1) The blade has to be thinner on the cutting edge and thicker on the back, but the edge that gets thinner becomes longer because the squeezed metal must find space anyway: your blade would bend upwards.
So you first slightly bend the blade then hammer the inside of the curve.