[Ed Clarke]

Hello all!
I am currently normalizing a full tang hunter and I recall reading somewhere that when normalizing more than once (3 times) it is acceptable to simply allow the blade to drop below critical before heating again for the next cycle. I am using 1084. Is this true? I did it three times and I believe I could actually see the dark areas as the blade cooled become more "organized" each time. Also, if I worked the steel too hot (I'm still learning)in the beginning, does the normalizing process reduce the grain size sufficiently if performed properly? Thanks for any help / info.
Ed C.

[Kevin R. Cashen]

Ed Clarke, on 27 February 2011 - 09:29 PM, said:

Hello all!
I am currently normalizing a full tang hunter and I recall reading somewhere that when normalizing more than once (3 times) it is acceptable to simply allow the blade to drop below critical before heating again for the next cycle. I am using 1084. Is this true? I did it three times and I believe I could actually see the dark areas as the blade cooled become more "organized" each time. Also, if I worked the steel too hot (I'm still learning)in the beginning, does the normalizing process reduce the grain size sufficiently if performed properly? Thanks for any help / info.
Ed C.

Ed, grain size is one of the easiest and controllable factors in our arsenal, once you understand how it works. I just demonstrated to my intro class yesterday how easy it is with one heat to bring burnt 1084 grain size back to a nice and fine ASTM size 8 or 9, with simple temperature control, and without a hammer touching the steel. Some were not even aware that every time you bring the steel through what we commonly call "critical temperature" you hit the reset switch as a whole new set of austenite grains are formed. In fact on every heating and cooling cycle no less than three different sets of grains are involved, the initial grain structure, the new austenite grains that begin to form as soon as we pass Ac1 (the first critical temperature just below non-magnetic) and then the new crystalline phase that is created when the steel cools. This all offers us plenty of opportunity to affect and control grain size. As for seeing recalescence or decalescence (the light and shadows) becoming more organized, well I doubt that was the case since this stuff occurs in a much different scale than that.

The magnet can actually be even more useful here than in hardening. You see in order to make new grains you need to recrystallize to austenite by heating, but if you reheat the same austenite you will only grow it and not make new and finer grains, so you need to cool it enough to create a new phase to work from. For 1084 this will be pearlite when you cool to around 1000F, check the steel with your magnet, as soon as the magnet sticks again you have made enough body centered stacked crystals for the atomic electron spin to restore ferro-magnetism, in short you have made pearlite from which can can brand new little austenite grains when you reheat. Some steels like L6 and O-1 to some extent do not like to make pearlite, that is why they harden so easily, so you will need to cool them about 300 degrees cooler to make yet another phase and stick the magnet before reheating.

[Rick Baum]

"you have made enough body centered stacked crystals for the atomic electron spin to restore ferro-magnetism"

Wow! Now that's a mouth full... That and a glass of milk and I'd be full for the day!

Seriously though, Good stuff Kevin. I always seem to glean something new from your posts. Thank you!

In your experience, is there a benefit in hitting the reset switch more than once or is it a case of diminishing returns?

Thanks for continually sharing your knowledge.

Rick

[Ed Clarke]

Thanks Kevin! Very interesting and informative. I did take it from megnetic to just inside of non-magnetic, and back again down to fully magnetic. As for the recalescence and decalescence, am I right to think that those are the "shimmer" we see throughout the steel? If so, that did not change each time I took the steel through the heat cycle. What I saw was the areas that cooled to black first appeared to be "splotchy" throughout the work-piece (even though the thickness is fairly uniform, ie- no hammer marks, etc.), and each time I reheated and allowed the piece to cool it seemed to cool to black in a more even pattern. I know that each time I reheated I became more carefull to do so as evenly as possible, so maybe that is what I saw. Either way, it was fascinating (and alot of fun). I second Rick's question..."is there a benefit in hitting the reset switch more than once or is it a case of diminishing returns?
Thanks for the help

[Rick Baum]

So now, after Ed's last post, I have a second question and maybe it can't even be answered, but, Ed mentions the splotchy appearance of the blade as it cooled and it got me to wondering something. Could the splotchiness be caused by grain differences in the steel as a result of hammer blows during the forging process, even though there was a lack of hammer marks? Then Ed goes on to say that the splotchiness gradually disappears through multiple normalizing cycles. Could this visual phenomenon be due to the grain size evening out over the length of the blade? If true, this may be an answer to my own question regarding diminishing returns for multiple normalizing cycles. Also, if true, we would have a great visual reference to know that we have completely and effectively done a good job of normalizing/relieving the stresses within the forged steel. Hmm...

Rick

[Ed Clarke]

Rick,
That is what I thought was possibly happening, or something along those lines. First normalizing cycle, very splotchy as it cooled . Second normalizing cycle, less splotchy and it looked like the dull red areas were getting more organized and slightly arched . During the third normalizing cycle as the steel cooled the darkening area moved across the blade and appeared to "push" the dull red hotter area in the shape of a perfect arch which corresponded with the thicker / thinner areas and edges of the steel (this is a hunter with a dropped handle) . Keep in mind the shop was very dark so I could watch what happened and learn to judge colors. Now I'm starting to think I was seeing things so I want to hammer out another blade to try it again. What do you think, Master Smith's?

[Rick Baum]

Bump...

Hopefully Kevin will see this and contribute with some of his experiences, if any, that pertain to what Ed noticed during his multiple normalizing cycles.

I wish I had a laboratory like Kevin's. Without a controlled environment, it's difficult to say what exactly Ed is seeing in regards to the splotchiness evening out over multiple cycles. I'm guessing that to empirically know what is happening it would take controlled heat, samples and photomicrographs.

Sorry to put it all on you Kevin, but I don't know of any other HT gurus that frequent the forum.

Rick

[Mike Krall]

There is advantage in more than one normalizing cycle. In industry practice, it is common to normalize one time. The temperature used for 1084 and like-steels is 1600F. But industry does everything at controlled temperatures, so the grain size of a piece has not gotten either very large or greatly uneven. Hand forging blades tends to do both... temperatures go above grain growth low-end temp. (1695F to 1795F... steel dependent) so the grains get very large, and hammering is inevitably uneven, which causes localized strain that causes more grains to nucleate where the strain is higher. By the time a blade is done, there is a lot of large grains and grain-size unevenness. One high temperature normalizing cycle will equalize grain size (what industry is after in a piece that has had little to no grain growth). For a hand forged knife blade, more cycles will refine grain size. Over a long time of looking at this, it has been found that three cycles is as many as a person needs... two can be fine... more than three is unnecessary and/or self defeating. A likely problem with more than three normalizing cycles is decreased hardenibility. With 10xx steels, W1/W2... steels with low hardenibility under best conditions... further reducing hardenibility will cause the steel to not fully harden (thicker sections cannot lose heat fast enough to form martensite).

My personal response to feeling I was seeing more even color loss, less splotchy color, in air cooling blades was to think I was maybe getting them heated more evenly to begin with. The color change is always uneven based on area thickness. A ground blade will lose color more evenly than a hammer pocked blade due to more evenness in thickness, though I don't know if a person can see that.

Mike

[Ed Clarke]

Thanks Mike,
Although I thought I heated the piece evenly each time, it very well may have been "maker error" as far as even-ness of the heat, and, although the blade was hammered to a very smooth finish, the thickness, I am sure, is not perfectly even. On my next few blades I will see what happens. If this re-occurs and I still have no explaination, I will repost with pictures.

[Rick Baum]

I look forward to hearing what you come up with Ed. I'm going to do something similar to what you are doing. Maybe we can compare notes when we're done.

My plan is to manipulate(hammer)a piece of steel in just one identifiable spot. Then I'm going to take the hammered steel and grind it all to the same thickness/dimensions. After it's all uniform in dimension I'm going to normalize it to see if the hammered area cools at a different rate, ie, looks splotchy. If it does look different from the surrounding steel, I'm going to normalize it again, and, if necessary, again to see if the splotchiness goes away with multiple cycles. My problem is that I'm using a propane forge for my heat source, not exactly a controlled environment, but it might tell us something. This is the part that makes me wish I had access to equipment like Kevin's.

I look forward to hearing what you come up with.

Rick

[Ed Clarke]

Rick,
Just in case any of the following helps with your experiment: I have both a propane forge and a coal forge. I used the propane forge for the initial shaping of the blade, then finished shaping the handle in the coal forge so I could control the heated area better. Normalizing was performed in the coal forge because I feel I can control the heat and where is it applied better (ie.-edge up, thickest part in hottest area of fire, etc.) and I was able to get a pretty even heat on the blade each time. This blade has a tapered full tang (hammered in taper) and the blade has a very similar distal taper to it, so the thickest section is the ricasso. I have just come in from the shop and have hammered out a new blade, but still need to work on the handle. It will be a similar style drop point hunter, so I'll let you know what I find as well. Thanks for your interest.
Ed

[Mike Krall]

Ed Clarke, on 06 March 2011 - 11:42 AM, said:

Thanks Mike,
Although I thought I heated the piece evenly each time, it very well may have been "maker error" as far as even-ness of the heat, and, although the blade was hammered to a very smooth finish, the thickness, I am sure, is not perfectly even. On my next few blades I will see what happens. If this re-occurs and I still have no explaination, I will repost with pictures.

You are certainly welcome, Ed.

The one thing catching my eye and causing me to respond was your initial mention of evenness of heat for normalizing... then I never mentioned it in my post. I can't explain the negatives of uneven normalizing temps. (can't ever remember what I've learned from Kevin C. and many others), but it is more important than the actual normalizing temperature (as long as that temp is in the austenitizing range).

In case it will help... I normalize three times. At the high end of 1600F - 1650F, they stepping down for the next two. If a steel is going to be quenched from 1475F, and the initial normalizing was from 1600F, I'll step down about equally... 1600/1560/1520/quench 1475. A hard thing to do in a forge but not at all impossible. Before we bought an EvenHeat kiln, all we had were a couple of propane forges (big one and a "two-brick") and we got stepping down figured out.

Mike

[Ed Clarke]

Thanks again Mike
I think I actually stepped down each normalizing cycle, although not intentionally. The first time I got it a little hotter than I wanted, each time I got closer down to critical (not very exact but I've only done this a few times).
Ed

[Mike Krall]

Ed Clarke, on 07 March 2011 - 07:30 PM, said:

Thanks again Mike
I think I actually stepped down each normalizing cycle, although not intentionally. The first time I got it a little hotter than I wanted, each time I got closer down to critical (not very exact but I've only done this a few times).
Ed

That's the way it was when we were doing all HT processes except tempering with forges... temps were relative to magnetism and viewable phase change via noticeable color change... both up and down. "Too hot" on the first normalizing cycle may have a person in the grain-growth range but the grains will still equalize. Even if they are equally very big, stepping down will refine them. If getting too hot was a byproduct of getting the entire blade the same color, it was OK with me... an awful lot of this is really evenness dependent.

Mike

PS -- Maybe you have already, but if you get a chance to see blades come out of a kiln or a salt pot, take it... that first quick view is the definition of evenly heated.

[Ed Clarke]

Mike,
I've seen pictures of blades coming out of both a kiln and a salt pot. My last normalizing cycle was probably as close as one could get to that using the equipment I have, but it was challenging to do. Thanks again

[Karl B. Andersen]

Mike Krall, on 06 March 2011 - 09:10 PM, said:

I normalize three times. At the high end of 1600F - 1650F, they stepping down for the next two. If a steel is going to be quenched from 1475F, and the initial normalizing was from 1600F, I'll step down about equally... 1600/1560/1520/quench 1475.
Mike

Mike, in reference to the above quote, and this one,

"...A likely problem with more than three normalizing cycles is decreased hardenibility. With 10xx steels, W1/W2... steels with low hardenibility under best conditions... further reducing hardenibility will cause the steel to not fully harden (thicker sections cannot lose heat fast enough to form martensite)."

Do you do the triple normalize and quench even on your 10XX and W1/2 steels?
I will often do a post-forging high heat normalize followed by two reducing heat cycles, quench at around non-mag + 50 degrees or so and then an oven controlled spherodize for shaping, grinding, drilling, tapping, etc.

Do you feel I am losing hardenability in my W2 and such?

[Kevin R. Cashen]

The lowered hardenability is due to finer grain size producing pearlite much more readily. Pearlite initiates at the grain boundaries, particularly at corners where three grains meet. With larger grains there is more inside grain area and less grain boundaries, and there are certainly less grain boundary corners because there are fewer grains. With decreasing grain size all of these points of nucleation increase, and can take the 3/4 second to avoid pearlite in hardening and push it to 1/2 second or less. Anybody can easily observe this by doing a simple exercise with a blade made from 1084. Just quench it normally in oil and clean it up to a 220X finish, you will probably have formed a natural hamon, hardening line where the blade thickness exceeded the speed of the oil. Without any other treatments and without overheating just re-quench the same blade and clean it up again. With each subsequent quench you can move that hardening line closer to the edge as the hardenability lowers.

[Karl B. Andersen]

Kevin R. Cashen, on 09 March 2011 - 07:58 AM, said:

......formed a natural hamon, hardening line where the blade thickness exceeded the speed of the oil. Without any other treatments and without overheating just re-quench the same blade and clean it up again. With each subsequent quench you can move that hardening line closer to the edge as the hardenability lowers.

Thanks, Kevin.
Can I make a semi-accurate assumption that if I am having no appreciable difficulty in keeping observable hardening lines/zones above the working portion of the blade that I have not reduced my hardenability to the point of creating minimal martensite?
I don't feel that I am reducing my hardenability by over-doing the thermal cycle steps and my performance testing indicates a rather effective blade.

[Ed Clarke]

Very interesting Kevin. Are you indicating that the current blade I'm working on (1084) may not harden properly because I normalized three times and the grain size may have reduced too much, hence too much pearlite==> ie.-the steel can't cool quick enough to properly form martensite, or enough martensite? If this does occur, could I perform a second quench or even a third to increase hardness/martensite?

[Kevin R. Cashen]

Not at all, careful normalizing is essential, the only time you may encounter issues is if your quenchant is already borderline in its cooling capabilities. However, should the goals shift from making a knife to making the finest possible grain size there will be these limiting factors with shallow hardening steels. Carbide size and distribution is of much more importance than grain size finer than the ASTM 8-10 it takes to make an excellent knife. As with all things in knifemaking it is all about the perfect balance and compromise to achieve our goals.