Hardening and Tempering of Steel

Factual Questions
1

My question concerns hardening and tempering of steel.
I know just enough to be dangerous.
As I uderstand the process it is as follows:

**1)Forging:**The steel is heated until it is in a plastic state(like wet clay)and beaten with hammer and anvil into the desired shape. This gives the smith the desired shape,but also incorporates many internal stresses which must be relieved.Molecularly it’s a jumble.
**2)Annealing:**In this step the steel is brought to a heat and allowed to cool slowly,thereby releasing the stresses.At this stage the molecules are more ordered,but the steel is now soft.
**3)Hardening:**This next step is accomplished by taking the steel to a heat and quenching it suddenly.This step leaves the steel hard,but fragile,like glass.A magnet is used to determine when the steel is at the correct temperature.(ie.When it is no longer attracted to a magnet,it’s ready to be quenched.)I don’t clearly understand the molecular details of this point in the process.
**4)Tempering:**In this step the steel is brought to a cooler heat,often described as a straw-like yellow color.The hardness is not totally removed by this level of heat,but it is reduced.The metal is then allowed to cool slowly to preserve the level of hardness achieved.Once again,the molecular details are something about which I know little or nothing.
Questions:

**1)**Have I correctly described the process,and the purpose of each step?

**2)**What specifically is occuring at the molecular level in the steel during each step respectively?

**3)**As an alternate to question 2,enlighten me regarding the chrystaline structure of steel,and what role it plays?What transformations does it go through?

EXTRA BONUS POINTS!!!

Please provide a link to a site which illustrates this whole process at the molecular level.
I really want to see how the molecules are lined up at the different stages,and how this affects the steel’s hardness and overall performance.

Thank You,

Forbin

2

I’m afraid that the answers to the questions you’ve raised are too complex for a sufficient response here. For instance, the hardness you get after quenching will depend on the carbon content of the steel, the amount and type of alloying elements present in the material, the peak temperature you reach, the rate a which you cool during quenching, the geometry of the part, and the subsequent thermal processing. It looks to me like you’re on the right track, though. Maybe these will help.
http://www.efunda.com/processes/processes_home/process.cfm

http://howthingswork.virginia.edu/supplements/knives_and_steel.pdf