Heat treating and Normalizing confusion

[scott.livesey]

Only if forged. Why would being heavily spheroidized require normalizing before hardening? PG 01 comes ready to harden and temper. After grinding, it should be stress relieved, but mainly to help prevent warp. Spheroidizing has nothing to do with grain size, so why would you cycle it? All the PG 01 I have ever checked had a grain size as good as one could want, HTed as is. Spheroidized carbon is slower to go into solution than is lamellar carbon, but 01 needs a good soak before quenching anyway.

just a little confused on the whole subject. i also have been sorta accursed of cutting corners by not doing multiple pre-hardening heat cycles. thought this would be the place to get straight answers and move on with production. my main thought was adding any heat cycles would increase chances of decarburization and grain enlargement. thanks for the replies.

 

[Kevin R. Cashen]

Machinability and hardenability are somewhat at odds with each other in that a mainly ferritic matrix with fewer coarse spheroidal carbide will machine very nicely, however you now have all of your available carbon locked up in these huge spheres. It is like dissolving the little sugar granules in your mouth compared to the time it takes to dissolve a huge jawbreaker. Both are just sugar but one will dissolve much more quickly than the other. I have seen alloys that were going to see heavy machining spheroidized so well that at the normal austenitizing temperatures you were talking about hours instead of minutes in soak time, so the best option was to bump up the temperatures and risk retained austenite. I have also created this condition myself with being too zealous with the spheroidizing. If this is the case a normalization before the final hardening will remake the carbide condition so that it is more receptive to your austenitizing heats, thus it is sometimes advisable depending upon how the steel was prepared at the mill. As has been mentioned, Aldo had some 52100 that was very nice but spheroidized for machinability, it would not get above 63HRC regardless of the soak, so I worked out a heat treating regimen that involved a quick normalization at 1650F to dissolve the 95%+ spheroidal condition and allowed you to get 65 HRC with a simple heat and soak. I also have two spheroidal anneals that I use in my shop, one for quick austenization and maximum hardness and one for steel that will see a lot of machining.

 

[gnique]

As has been mentioned, Aldo had some 52100 that was very nice but spheroidized for machinability, it would not get above 63HRC regardless of the soak, so I worked out a heat treating regimen that involved a quick normalization at 1650F to dissolve the 95%+ spheroidal condition and allowed you to get 65 HRC with a simple heat and soak.

I realize that this thread is over a month old but I've been riding motorcycles while the sun shone. Now that it is nice and miserable here in the Beaver State, I begin the indoor part of my year - knifemaking. The statement above was, to me, the most interesting part of this thread. This "quick normalization" that you worked out seems to be nothing more than taking the steel to 1650F, holding it for X minutes and cooling it in still air. Now if 1650F is the Ac3 point for 52100, the instruction set may be further generalized to: Take the steel to the Ac3 point, hold for X minutes and cool in still air.

I am an unrepentant engineer so I have a very linear and literal mind and in areas of study where my grasp of the literature is tenuous, I tend to semplify and generalize sometimes, maybe, too much. Is once enough? If more than one cycle is needed what is the second temprature?

Is normalization required for eutectoid and hypoeutectoid steel?

Kevin, I know that you DETEST recipes and you convolute your words to avoid giving explicit instruction sets BUT, how does my outline above square with the generally accepted definition of normalization? Thanks - as always.

 

[samuraistuart]

Once is not enough if we are making a knife. 1650F, if we didn't do anything after that, would cause large grains to be formed, however they will be uniform in size throughout the blade. However, large grains are not conducive to a good edge stability, so we need to reduce the grain size. (I think it is understood that large grains if uniformly distributed are preferable to mixed grain size not uniform). To reduce grain size, we do further normalzing, but with descending heats. Usually it is 1650F, equalize, cool in air. 1550F, same thing. 1450F same thing. Now the blade is normalized, our grains our evenly sized and small, and evenly dispersed. Our first higher heat evened out the internal structure, but made the grain large. Our successive heats helped to reduce the grain size (carbide refinement) for a good edge. Normalization is not usually needed, as steels eutectoids and hypereutectoids generally are received in the spheroidized condition....ready to machine...ready to harden. However, Aldo's particular 52100 batch had seen what is called "coarse spheroidization". While super soft and a joy to work....it must be normalized to get max hardness. Most other eutectoids and hypereutectoids are received in "fine spheroidized" condition....no need to normalize. This was for a particular batch of Aldo's 52100. While not necessary most of the time, I like to do it anyway...that way I KNOW exactly what condition my steel is in going in to hardening. Hitachi steels and the O-7 from Germany I do not normalize, as there are fine spheroidized and only require a 10-15 minute soak during austenitizing. Hope that helps explain why Kevin used this procedure for that 52100. He can certainly expound WAY beyond what I have written!

Kevin just gave you a "teaser" I guess you could say! That first heat of 1650F is critical to get the coarse spheroidized 52100 to behave correctly, the most important part of that normalizing process.

 

[Kevin R. Cashen]

52100 has a full 1% carbon, since the Fe/Fe3C phase diagram does not account for any alloying other than iron and carbon the temperature designation for the upper critical would be AcCm (Acm if not dealing specifically with heating or cooling). Although this is why we can't use the Fe/Fe3c phase diagram like a CCC or I-T diagram, because due to the alloying we are actually dealing with a steel that starts out behaving like a hypoeutectoid and ends up being a hypereutectoid; this blows the concept of equilibrium out of the water and makes the Fe/Fe3c all but useless. You would need a more complicated diagram to account for Cr carbide as well as cementite.