annealing or normalizing

David Stifle

David Stifle

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Nov 20, 2008
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How can I determine if I have properly normalized my blade? I use a coal forge, go above magnetic for a short soak, and let it air cool. But to anneal a blade, you pretty much do the same thing, only (as I understand) the blade does not reach critical. I'm confused here, can someone shed some light on this? And, if a blade is fully annealed, but not normalized, have I lost whatever protection normalization might offer to prevent warpage.breakage?

Thanks

Dave
 
Dave

Annealing is the process used to soften a metal, there are many different ways to soften a metal through thermal cycling depending on the end result you want. Normalizing is usually performed around a 100°F above critical temperature. It is used to refine grain structure and redistribute the constituent elements the steel is made up of. In the case of the 10xx series steels, which are made up of iron and carbon (remainder impurities) this would be carbon. Heat the blade to about 100°F above critical and let cool. Here is where the controversy comes in. Historically you let it cool until it is cool enough to touch with the bare hands (or if you don't want to burn you fingers, room temp). After the steel has cooled below the critical temp, there isn't a whole lot of movement of the carbon so taking it completely to room temperature isn't necessary. Take a scrap of the bar stock type you plan on working with, heat it up into the orange/yellow range and let it soak. Don't heat it until the sparks fly, this will ruin the steel. After say 10 minutes, let the steel cool to just above critical and quench in the appropriate medium. Do not temper! While wearing safety glasses and other safety equipment, hang about a quarter inch of the corner of the bar over the edge of the anvil and snap it off with a hammer. You might want to forge this corner down thinner before the quench so it will be easier to snap off. Look at the grain on the end of the bar. The overheating and soaking should have promoted grain growth. Now reheat the steel to 100° above critical, remove from the heat and let cool until black. Wait one minute and quench in water. Repeat again twice more, but on the last cycle let it cool to room temp. Reheat until critical and quench again. Snap off another chunk on the same end as last time and examine the grain size. You should find a significant improvement. If this doesn't work the try letting it cool to room temp each time. Multiple quenching also refines grain without redistributing the carbon as much, but can cause warping!

Hope this helps. What works well for one steel, doesn't necessarily work best for the next.

Jim Arbuckle ABS JS
 
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Thanks Jim and Stacy,

Jim, I was going along reading your post, nodding my head, yeah, yeah, got that-then when I got to the point about quenching, well, that I didn't get. I thought an annealed or normalized steel was, as you said, brought up to a certain temp and then air cooled. Is a quenched steel still an annealed, or normalized steel? I may have missed your point here.

Stacy, I'll look the charts you provided over.

Dave
 
Industry, for the most part, has one set of definitions for “normalizing” while there can be as many definitions among bladesmiths as there are bladesmiths. The idea behind normalizing, as has been stated is to evenly redistribute carbon and structures and resulting stresses in the steel. Grain refinement is often more a reference to homogenous grain size, whatever that size may be, and for good reason since uniformity can often be more important than actual size. True normalizing requires heats high enough to put the material in full solution and thus is often in the 1600F – 1700F range. Air cooling is important for actual normalizing in order to keep things into solution evenly on cooling, and to be certain things cool uniformly. So to actually normalize blades the first heat should be well above critical, but as mentioned never “yellow” or “white” hot.

Bladesmiths then follow this heat which equalized things with a heats to refine that condition further. These heats are almost universally referred to as “normalizing” by bladesmiths but should actually be called thermal cycles to be more accurate. The next heat will be to make smaller grains from the evenly sized ones and is done just to critical and then air cooled. Some will quench at this point instead, I often do, to increase the grain refinement, a quench will replace around two air coolings with careful heating.

For any of these refinements, you really only need to air cool to Ar1 (when the magnet sticks again) before reheating, but if you quench you will need to go to room temperature in order to see gains, otherwise you will only be reheating the same internal condition (austenite) again.

Often smiths finish up on a dull read final heat. This can create subgrains, like grain seeds that will sprout into new, finer grains on the next heating. But if one is careful not to allow the blade to go nonmagnetic this dull red heating can also substitute for an anneal, and is preferable for steel with more than .8% carbon.

Annealing is for the expressed purpose of softening the steel and can be a full (lamellar) anneal, where you heat to critical and then slow cool (wood ash, vermiculite oven etc…). Or you can got with a sub-critical anneal which takes us back to keeping the heat below nonmagnetic and softening the steel that way, this is called spheroidizing. Spheroidizing is highly recommended for anything over .8% carbon and also helps keep everything you did in the normalizing, while full annealing tends to undo some of it.
 
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