I just want to clarify a few things that may have gotten confusing today when we were talking about annealing and normalising.
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Both screenshots come from the same website: Metal Supermarkets | Steel, Aluminum, Stainless, Hot-Rolled, Cold-Rolled, Alloy, Carbon, Galvanized, Brass, Bronze, Copper. They both say the same things to describe two slightly different processes. If metal is being annealed the cooling rate is slower and more controlled, whereas normalising is done in the open air whereby the metal is cooled slowly but not as slowly and controlled as annealing.
If getting the metal as soft and workable is the aim you would anneal. If maximum workability is not important but relieving stresses in the material is, then you would normalise because it is quicker, cheaper. and requires simpler equipment.
There are many ways that this can affect a manufacturing process but I will stick to the blade making application here as I believe that was what most of us were interested in. I will go through a series of steps involved in making a blade with annealing and normalising emphasized to show how they work together.
Once you have designed your blade(knife, plane blade, chisel,whatever) you select the type of metal you want to use.
If you are using brand new metal purchased for the purpose it will come as annealed bar stock. There is no need to anneal it. You would go straight to either forging or grinding depending on how you wish to make the blade. If you are using recycled metal, such as a leaf or coil spring you may choose to anneal it first.
If you are forging, you may, depending on the metal and the design of your blade, go straight to forging as once the metal is heated up to straighten and/or shape it the metal becomes soft while it is hot and it will cool slowly because you won't be quenching it at this stage. It won't be as soft as it would be from a proper annealing but that may not be critical to the build.
So, lets start out with a piece of leaf spring that we want to make a plane blade out of. We are aiming for optimum results so we will anneal and normalise at the appropriate points.
1. Anneal the spring. Heat it to the appropriate temperature. While it is hot you may as well straighten it. Then cool it slowly over several hours to anneal it as fully as possible (maybe up to 24 hours cooling)
2. Shape the blade form the annealed stock by forging, rolling, grinding, filing, milling, drilling etc to get the blade shape you want. Leave the cutting edge about 0.8 to 1 mm thick at this stage to minimise problems with burning the thin metal of the edge and warping.
3. Normalise the blade to refine the grain structure and minimise stresses in the metal. The general consensus among the top knife makers is to do three normalising cycles. Heat the blade to cherry red then remove from the forge and wave it in the open air until it no longer glows. Repeat three times. After the third normalising cycle let it cool for an hour or two. We often bury the blade in vermiculite for that time to slow down the cooling a bit. It is also better than putting the blade down on a flat surface which can result in warping as the blade cools faster on one side than the other.
4. Heat treat. Heat in the forge till non-magnetic then quench in the oil. Put the blade back in the vermiculite to cool to room temperature prior to tempering.
5. Polish and sharpen
So basically, from a blade making perspective, you anneal at the start of the process to get the metal ready to work and you normalise at the end of the shaping of the metal to remove internal stresses and refine grain structure prior to heat treating.
There may well be other manufacturing processes where the order of work is quite different and the lines between the two processes can become blurred but the way I have described it would be understood by the blade makers.
I hope that clears up any murky areas.
