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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 10-02-2017, 09:24 AM
RantNRave RantNRave is offline
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Deciphering Crucible data sheets

So, at the risk of exposing myself for the noob I am, I need ask a question regarding the data sheets on the Crucible web site - specifically, 52100.

It states for hardening:
Preheat: 1200-1250F (650-675C), equalize
High Heat: 1500-1550F (815-845C), soak 10 to 30 minutes. For vacuum or oil hardening, use the high side of the high heat range and soak times. Use the low side of the temperature range for water hardening.

Speaking literally (I do best with literal...), is this saying:
Heat your oven to 1200-1250F, then place your knife in. Let it come back to temperature, then ramp your heat to 1500-1550 and let it sit at this temperature for 10-30 minutes.

Based on the further notes, since I'm using oil, I'm also thinking the high side of both the temp and time ranges.

-Dan


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Old 10-02-2017, 10:40 AM
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Ed Caffrey Ed Caffrey is offline
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Hi Dan!

Based on the information, that is what it's saying.

BUT!!! Remember that this heat treat formula was created for "industry".... which means that in general, the heat treat/formula was intended for maximum hardness, or for a specific end use, which is not necessarily what you want in the knife blade.

I have a great deal of experience with 52100..... if you let it soak that long at the high side temp, the grain size is going to be so large that the blade integrity is seriously weakened. Although I suspect you've seen/read all kinds of things about "soaking" blade steels. The down side of doing so with certain steels far out weighs the up side(s). 52100 is one of those steels.

My method of heat treat for 52100 skips the "preheat"...... because I thermal cycle each blade 3X at no more then 1350F prior to heat treat. I then bring the blade to 1550F, and quench, with NO soak. If you feel like you must soak, I would recommend doing so on the lower side of the "high temp".....that will reduce the problem of grain growth.


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Last edited by Ed Caffrey; 10-02-2017 at 03:36 PM.
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Old 10-02-2017, 10:55 AM
RantNRave RantNRave is offline
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Thanks, Ed, I had kind of thought that these pages were directed more towards "industry."

I do have a follow up, though. Assume (safely) that I am a newbie at making knives. I built my own HT oven, so I have access to that. Could you please describe the Thermal Cycle process? Also, does anything change if we're dealing with a stock removal knife VS a forged knife?

Thanks!
-Dan


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Old 10-02-2017, 11:34 AM
RantNRave RantNRave is offline
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Actually, Ed, never mind as I went to the source: your website!

Thanks, again


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Old 10-02-2017, 11:45 AM
samuraistuart samuraistuart is offline
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Ed, love you do death, my online friend. But soaking is very much an important part of certain alloys. Which alloys? The ones with a good % of alloying in them. Simple carbon steels need not be soaked beyond a good thorough heating to ensure it's even, then quenched.

52100 and O1 have a bit more alloying in them, hence the soak. Some of the most well known metallurgists on the planet who have torn 52100 apart every way you can and looked at it with very expensive scopes, etc etc etc have come to the conclusion that the soak is best for certain alloys. This is very common practice in alloyed steels. Take A2 for example, the next step up above 52100 in many ways. If you were to simple equalize and quench that steel without the recommended soak, your HRC is not going to be very good at all. The chromium has that carbon tied up, and you have to release the carbon to get the hardness somehow. Either TIME, or TEMP. Too high of a temp, as you know, brings it's own problems.

I do recall the test you did with soak vs no soak on a given alloy. I don't recall the alloy but I think it was 1084. I would not soak that one at all, beyond equalizing for a minute or 2. Regardless of the alloy, your test indicated that the knife that DID get the soak was chippy. But you used the same temper temps, IIRC, for both samples when you came to this conclusion.

BINGO. I would totally expect that to happen. 52100 gets no soak, tempered at 350f, maybe not too chippy. 52100 that gets the soak, tempered at 350F, yeah....maybe a little chippy.

The main problem I have with "Industry" 52100 heat treat is the recommended aus temp of 1550F. Good for ball bearings, not so good for knives. 1475F gives the best HRC (assuming we have taken care of any coarse spheroidizing issues), with a short soak to get that carbon in solution. If you used 1475, equalize with no soak at all, then quench, I would expect a sub par HRC. 1475F with 10 minute soak should get 66-67+, and more than likely, a higher temper than you would use otherwise if no soak employed.

I have found the most every alloy I am needing to bump up my temper temps higher than the charts. I use the soak, and usually a fast oil quench, even on 52100.

However, there are more than one ways to skin a cat. I try to think of skinning cats as often as I can. Infernal creatures.
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Old 10-02-2017, 03:23 PM
Kevin R. Cashen Kevin R. Cashen is offline
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Things can get so interesting when you get input from several people, I love it. So I guess I will make it even more interesting and add my input. Fun for us but, yes, confusing for you RantNRave, sorry about that.

It is not that industry is going for maximum hardness, that would be good, but rather that industry is making bearings, which are not knives. If you use their numbers there will be massive amounts of retained austenite, which they will handle in the way that bearings are made, but not the way knives are made. Going above 1500F I would expect to max out at around 63 HRC. And yes, it is better to do some controlled soaking, 52100 is one of those alloys that can almost be soaked for days with no appreciable effect on austenite grain size, if the temperature is controlled, but, once again, the real problem is serious issues with retained austenite if you go much beyond a basic soak time.

Preheat your oven to 1475F, ignore the industrial preheats for something as simple as a knife blade, and then put you blade in for 8 to ten minutes. Quench in any medium speed (11-14 second) quench oil. 52100 isn?t 1095, the chromium in 52100 is for some carbide action but also to make it a deep hardening steel so they don?t have to use fast quenchants, thus a fast oil is just too much. If done correctly any oil could yield 66HRC, without over-stressing the steel and increasing rates of distortion or cracking. Temper accordingly.

If there are issues obtaining maximum hardness, which is what you want for a knife blade that 52100 would be used for, you may have some heavy spheroidization from the mill which can be corrected with a good normalizing heat to 1650F-1700F and air cool and then proceed with the treatment above.

Last edited by Kevin R. Cashen; 10-02-2017 at 06:32 PM.
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Old 10-03-2017, 12:24 PM
jimmontg jimmontg is offline
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I never used 52100 myself as I always thought it was a steel for forging as so many knife forgers use it. I just thought I'd chime in that Data stats are for industry as the guys above have pointed out. I just wanted to add the data sheets are almost universally for much thicker material than knives. The soak for one hour per inch of thickness is a clue. You're making a knife at let's say 1/8" thick, that would mean you would only soak the knife for less than 10 mins and of course as the guys above said that will not be long enough. The 1475 is also the sweet spot for O1 as well. So now you know why experienced makers tell you to experiment as the data sheets have a different target than knives, especially tool steels. It doesn't hurt to ask and I didn't know that the HT for 52100 was pretty much the same as O1 a steel I am familiar with. I learned something as well.
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Old 10-03-2017, 07:54 PM
RantNRave RantNRave is offline
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Yup, truer words were never spoken: "confusing to you"

You say heat the oven to 1475 then put the blade in for 8 to 10 minutes. I know this may sound stupid, but I have to ask. Again, I'm a literal person, so forgive what may be a stupid question. By this, do you mean: heat the over to 1475, put the blade in and let the over heat back to 1475 and THEN time 8 to 10 minutes?

I only ask because the oven drops a good 30 degrees F when I open the door to grab a blade for quenching. I suppose I should just do it and see, but I don't have a hardness tester and I'll have to go somewhere to someone that does, and I would prefer that to not be a wasted effort.

Thanks!
-Dan


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Old 10-04-2017, 10:10 AM
jimmontg jimmontg is offline
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Just put the blade in for 15 mins, at that temp it will not create too much grain growth as the temp ramps back up.


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Old 10-04-2017, 11:21 AM
samuraistuart samuraistuart is offline
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Yes, O1 and 52100 HT about the same. I can't really think of anything that differs between the 2 heat treatments. Normalizing temp is about the same, too. Even the quench oil. Both use medium speed oils. Temper temps are about the same, but as always, verify yourself.

Dan, I know exactly where you're coming from. My kiln is a modified glass kiln, I have a slot cut in the side to insert/retrieve knives. My temp goes down maybe 20 degrees for about 20 seconds after inserting a blade. The higher the aus temp (A2 for example), and the larger the mass of the blade, the more the temp drops and longer it takes to rebound.

I found that a blade, in my kiln, will be AT target temp in just a few minutes. I DO INDEED ADD a couple minutes to my soak time. If I want a 10 minute soak, I set the timer for 12 minutes immediately after inserting the blade. Like Jim said, and Kevin pointed out above, grain growth is a non issue IF you have good temp control.
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Old 10-04-2017, 02:13 PM
Kevin R. Cashen Kevin R. Cashen is offline
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Quote:
Originally Posted by RantNRave View Post
Yup, truer words were never spoken: "confusing to you"

You say heat the oven to 1475 then put the blade in for 8 to 10 minutes. I know this may sound stupid, but I have to ask. Again, I'm a literal person, so forgive what may be a stupid question. By this, do you mean: heat the over to 1475, put the blade in and let the over heat back to 1475 and THEN time 8 to 10 minutes?...
Oven is at 1475F, blade is introduced, oven drops ten to twenty degrees in temperature, when the rebound is done and the blade is at the original set temperature the timing begins.

There may be more time for rebound in an oven, but in my salts, due to the conductivity, as soon as the thermocouple reads the original set temperature, the blade is at temp and the soak begins. I have even programmed it into controllers before that they will read when the set temp is obtained and then the timer is triggered and an alarm goes off when it is time to quench. For steel in average spheroidized condition an 8 to 10 minute soak is enough for maximum hardness. The differences in proper solution can be quite noticeable in as quenched hardness but also in tempering temperatures.

One of the reason I am always very hesitant to give numbers for HRC to tempering temperature is that it is a moving target. Depending on your amount of proper solution the tempering temperatures can varying as much as 50 to 75 degrees for the same HRC number. 1095 with no soak, may reach 59-60 HRC with tempering around 400F-425F, but with proper solution you will be pushing it well beyond 450F for the same hardness.

Last edited by Kevin R. Cashen; 10-04-2017 at 02:16 PM.
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