It all depends on the type of steel, mainly the Carbon content of it. For example 'mild steel ' such as vehicle bodywork cannot be hardened easily but a chisel, scriber, punch etc could be hardened (makes it brittle) and then tempered to give it strength without being too brittle.
Yes it's for chisels and screwdrivers I was wanting to do this. Please would you tell me the right way to do it?
Depends on what you are cutting with the chisel (wood/steel etc) . In all cases first harden by heating the cutting end/ blade end of the screwdriver to a cherry red heat and then quench into clean cold water. The tool is then fully hard and brittle. It then needs to be tempered to the correct hardness depending upon use and then quenched again to fix the temper. The working part of the tool needs to be cleaned after hardening with emery paper to get it bright and shiny prior to tempering. The tool is then gently heated and the polished part will start turning colour. You must then immediately quenched the tool into water when the correct colour is reached for the tools purpose. Google for the colour you require. Remember the harder the tool the more brittle it is. If you get it wrong just start again from the beginning and harden again.
Some carbon rich stuff requires different liquids I believe. Older tools tend to be richer in carbon than newer this is especially true of carpentry tools
Quenching in oil has it's uses and as @nell#2 says very high carbon steels can use it. Quenching in oil produces a slower quench, the oil doesn't move the heat away as quickly as water, so is beneficial in certain cases such as very thick section materials and very high Carbon steels. In thick sections the outside could be quenched quite cool and the centre still very hot which could lead to cracking if quenched in water, hence oil or sometimes liquid salts. I've never had a problem with things like screwdrivers and chisels using water. Be aware...cheap tools are often made of cheap materials and may not always harden and temper correctly.
This is mostly incorrect .. You would need to know what grade of steel your hardening and the correct temperature / time to heat it too . It would then depend if air or oil quenched and what tempering is required to get to your required hardness .. The only use of water is for case hardening or bedway induction hardening .. molten salt is used to heat the item . Usually knife If annealing copper it only needs to be a dull red and just leave to air cool .. but as it’s soft it usually deforms or becomes damaged .
I'll be honest my limited knowledge is down to Rockwell files and a spark test on how much carbon is in tooling. Most of the stuff I heat up is already burnt so needs taking back a bit. It's not critical if it's stressing or going to explode under tension.
