So Keith explain annealing,
Annealing steel has been defined and explained in the past many times here, but the term is still apparently difficult to comprehend for many people. You could just look it up, but remember that even some sources you'll encounter in a Google search will be incorrect.
A short simple answer is that the steel is brought up a little above the critical temperature, and held at that temperature for a predetermined time... dependant upon the thickness of the steel. This critical temperature is near a point where steel becomes non-magnetic. Then it is VERY SLOWLY cooled at a controlled rate. This process changes the crystalline microstructure of the steel and makes it much softer, more ductile, and more electrically conductive.
In the past, I worked in several different annealing plants where large furnaces were utilized to anneal up to a couple hundred tons at a time. These furnaces had very precise temperature monitoring and control, and atmospheric air was first purged and replaced with an inert gas to prevent scale formation or oxidation. We used catalytic crackers to crack concentrated ammonia to get nitrogen and hydrogen to use for purge gas. Hydrogen is great to keep the steel from discoloring during annealing. It seems counterintuitive to use a highly explosive gas such as hydrogen in a furnace operating at very high temperatures, but it can only burn or explode if oxygen is present in the correct concentration. For such large batches of steel, the heating time often went over 20 hours, followed by a very slow and controlled cooling. The actual times and temps were dependant upon the alloy and thickness of the steel.
Tempering of steel (hardening and then drawing) is another story... also frequently misunderstood.
