You have received some excellent advise on what to do to modify and make new chisels. I am now an old man who spent much of the last 60 years metal smithing and gunmaking. Old guys like me will tell you to heat your steel up to a red color, or maybe a cherry red color then quench the steel in water or oil. Following our instructions you may or may not get the steel hot enough at a red color or maybe too hot.
However, I give you this tip. Heat the steel up to a red color where a magnet will no longer stick to the surface of the red hot steel, then it is at just the right temperature to quench.
O-1 silver steel (or drill rod as it is known in USA) is an excellent steel for chisels and gun parts, however quench it in oil, not water. You can have your quenching oil to hot or too cold--I like for mine to have a temp of about 80 degrees F.
