1095 questions

Everything I forge gets 3 thermal cycles right before annealing, and 3 more just prior to hardening. It significantly reduces warpage for me.
 
Will stress reliving or normalizing reduce the chances of warpage on 1095 steel?

Thanks

Aaron

Aaron, proper stress relieving and normalizing are perhaps the only ways to reduce or eliminate warpage and distortion in the heat treatment. What causes warpage is sometimes anybody’s guess, from something done at the mill to the phases of the moon, and it can be frustrating. But at the heart of it is uneven strain energy within the steel. This can be from inhomogeneity from when the steel was made, uneven forging techniques, uneven heating or cooling, strain built up during machining or grinding etc…

The way to deal with this is to either annihilate that strain energy or at least equally distribute it and that is what normalizing and stress relieving is all about. Proper normalizing is done at temperatures that reset the internal structures in the steel in a more even a homogenous state. Carbon and alloying products are dissolved and redistributed in a fashion that will foster uniformity and more even response to subsequent heat treatments.

Stress relieving is another tool that allows you to leave the structures as they are but deal almost exclusively with the problematic strain energy. Let’s say you did all your normalizing and have your microstructures, carbides and grain size just how you want them, but then really got on the steel with hogging at the grinder or heavy machining. The concentrations of strain energy could still give you distortion grief during heat treatment. This is why it is a bad idea to turn steel blue on a grinder even if it is before the final heat treatment, strain energy is invisible to anything but crystallographic equipment (such as X-ray diffraction) but its effects are very in your face. Stress relieving will work below the recrystallization temperature and simply annihilate the strain energy by correcting defects in the crystalline lattice via s process known as recovery.

Put together, these two treatments are your most powerful weapons in fighting distortion in later heat treating.
 
I'd like to expand on the original question if I may since I'm fairly certain I'd don't know enough about the steel I work with to probably even be working with it, lol. I hear a lot about normalizing steel before working/hardening and such but do I need to do that with a piece of let's say 154CM if I am just a stock removal guy or is that for steels that are forged and hammered? I've often wondered about this but never asked the question. I will say that I've had no problems with any warping when I harden the blades I grind, which are usually 440C, 154CM, S30V, 52100,and such, but most of my work is under 12" in length. Just curious about this. Thanks for the good question and getting my mind thinking.

Wayne
 
I'd like to expand on the original question if I may since I'm fairly certain I'd don't know enough about the steel I work with to probably even be working with it, lol. I hear a lot about normalizing steel before working/hardening and such but do I need to do that with a piece of let's say 154CM if I am just a stock removal guy or is that for steels that are forged and hammered? I've often wondered about this but never asked the question. I will say that I've had no problems with any warping when I harden the blades I grind, which are usually 440C, 154CM, S30V, 52100,and such, but most of my work is under 12" in length. Just curious about this. Thanks for the good question and getting my mind thinking.

Wayne

Well… normalizing air hardening steels would not be possible because it would technically no longer be normalizing but instead would be hardening. Steel (except perhaps 1080) has two “critical temperatures”. One is a lower critical that all iron-carbon systems have where the process of putting things into solution will begin. The other is an upper critical temperature where everything will be in solution, this upper temperature is rarely exceeded in hardening of high carbon steels because it will create problems by overdoing the solution. Normalizing is different because it is normally to be followed by other treatments and its goal is homogeneity, so, with total solution being the goal, normalizing, almost by definition, must exceed the upper critical temperature. Because of this it can be tricky with air hardening alloys because of the common pitfalls of quenching after overheating.

On your list, the two steels that could definitely benefit from some level of normalizing would be 1095 and 52100. In recent years industry has really stepped up the level at which they spheroidize steel, making machining a dream but putting those huge spheroidal carbides back into solution a real pain, normalizing can fix that. Older 1095 was some of the cleanest and reliable steel I ever worked with but about 10 years ago there were at least a couple of batches that circulated with some heavy segregation, enough to be a real problem, heavy normalizing was the only way to correct the issue before proceeding to the other heat treatments, this would have been true for the stock remover even more-so than the forging guys, since forging can be seen as a whole series of heavy normalization type heats. 52100 is coming heavily spheroidized these days and if you are not forging it (once again, essentially repeated normalization heats) it may be well worth it to normalize at some point before the final heat treatment, I have had some folks who followed this advice see the difference of 3 points Rockwell in the hardened product.
 
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