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I've noticed that most guys thermal cycle after they forge and before rough grinding. I normally forge, rough grind, thermal cycle 3 times and then edge quench. I've always been under the impression that grinding also induced stress into the blade. So if thermal cycles reduce the grain and reduce stress why wouldn't I want to do it after rough grinding? All my blades are usually between 57-59 and seem to perform pretty good, but if there is a better way please educate me. Oh yea, I mostly use Aldo's 1084 and parks 50. Don't know if that helps any or not. Thanks in advance for your comments and wisdom. Danny

Hello Danny, I hope I can shed some light on the topic by exploring some of my reasons for how I do things.

Thermal cycling is a term used to differentiate the operation from strictly normalizing, and does not necessarily involve any stress relief. Thermal cycling can involve a wide range of temperatures and cooling methods ranging from air cool to quenching, while normalizing technically occurs in a set range of heat (approx 1600F to 1700F) followed by a slow air cooling to homogenize the internal structure. If this is done on a simple steel like 1084 or 1095 it can indeed relieve stress, but if done on an alloy steel it can even add the stress.

Most like to do an anneal on the steel to prepare it for grinding and machining this necessitates that all the grain and carbide refinement be done before hand, and the best time is immediately following the forging so that things behave themselves a little better during grinding.

Machining and grinding can indeed induce stress issues and this is most effectively dealt with using a “stress relieving” operation. A stress relieve is yet another entirely different heat treatment that involves heating to below critical (around 1200F) in order to allow the steel to recover from any strain induced problems but doe not effect carbide distribution or grain condition as it is performed entirely below recrystallization. This is particularly good for not messing with any of the things you carefully set up in the normalizing and annealing operations.

Another reason some may choose to do all of the heavy heating before grinding and only leave stress relieving for afterwards is decarburization, and scaling. If you have your blade ground fairly close to shape heavy thermal cycles will produce decarb and scale that will require even more grinding to remove, but if the heavy heats were done when the piece was still covered in forging scale nothing is lost.

Of course if one uses a heavy lamellar annealing method (slow cool in forge or vermiculite) then thermal cycles later on may not be a bad idea either.

Alright Kevin, I think I'm pickin up what you're puttin down buddy. Thanks for taking the time to share some wisdom with me. I definitly appreciate you investing in guys like me with what you know. Talk to ya soon. Danny

Hi,

I know your question was concerning stress build up, but since you included the info, I

have a couple ??

Is your 57-59 hardness as quenched? I have found parks 50 to work great on my w-2, but to be too fast for my 1084, causing an occasional crack. For my 1084, canola oil gives me more consistent results. As quenched >62 hardness.

My opinion on stress relieving: Nothing wrong with relieving right before hardening, but if you don't do any thermal cycling, or normalize before you grind, and then do heavy grinding, adding more stress, you have much more of a chance of the blade warping in heat treat. Forge close to shape= less grinding. Thermo cycles= small grain. Normalize= easy grinding. Sharp belts= less heat/stress. Dan

|quoted:

Hi,

I know your question was concerning stress build up, but since you included the info, I

have a couple ??

Is your 57-59 hardness as quenched? I have found parks 50 to work great on my w-2, but to be too fast for my 1084, causing an occasional crack. For my 1084, canola oil gives me more consistent results. As quenched >62 hardness.

My opinion on stress relieving: Nothing wrong with relieving right before hardening, but if you don't do any thermal cycling, or normalize before you grind, and then do heavy grinding, adding more stress, you have much more of a chance of the blade warping in heat treat. Forge close to shape= less grinding. Thermo cycles= small grain. Normalize= easy grinding. Sharp belts= less heat/stress. Dan

Thanks for the feed back Dan. Yes the numbers are as quenched and yes I do get an occasional crack. Since I started leaving a little more on the edge I rarely get a crack. I try and follow the Jim Batson school of thought, start forging close to critical and as my blade is getting closer to being finished the last couple of cycles into the forge are just enough to put some color into the steel and I do short light taps along the spine and so forth to make sure everything is straight and this normalizes the blade. Then I let the blade air cool and start grinding.