L3 steel heat treat

S

Spela

Joined
Mar 16, 2014
Messages
44
Hello everyone,

I'm thinking about making 3 general purpose knives from L3 steel and one big slicer.
Steel specs:
AISI: L1/L3
DIN: 100Cr6
Chemical comp. by weight:
C:1,02%
Si:0,25%
Mn:0,33%
Cr:1,50%

I plan to cut it, forge it, grind it. Therefore, some serious normalization process will have to be done.
This is my plan for normalizing this steel:
1) Heat up to 1580f (hot enough to redissolve chromium), soak for 5 min., air cool to black, water quench.
After this, the grain should still be pretty coarse, but the elements should be equally dispersed and distributed again.

2) Heat up to 1400f, soak for 5 min, air cool to ''black heat'', water quench.
Grain getting smaller this time...

3) Heat up to 1250f, soak for 5 min, air cool to ''black heat'', water quench.
By this point, the grain should be very fine, elements equally distributed and the steel in a relaxed state, ready for full austenitising.


When quenching: Heat from 1100f to 1545f, soak for 5 min. quench in aggitated oil, till oil stops bubbling and fuming, after that; cool in still air till cool to touch.

Temper immediately 3x25min, with water stops in between.



What do you think? Seems good?

Best, Vito
 
One error in your plan is the 1250 soak. No grain refinement will be done on a sub-critical cycle. For grain refinement, try 1580/1480/1380 steps, the spheroidize at 1250. I would also soak at 1250 for 10 minutes.

I would suggest the normalization cycles be done after forging and before grinding/drilling.

Your analysis looks more like 52100 than L1/L3
http://www.zknives.com/knives/steels/steelgraph.php?nm= L3, 52100, L1&hrn=1&gm=0

Your austenitization temp may be a bit high for a knife blade, especially with no W or V in the steel. I would try a blade or test piece at 1500F and see what the result is first.

Perhaps some of the 52100 folks will chime in with their suggestions.
 
replied with advice on BB forums. Posted here for convenience.....Stacy did mention something I left out....the sub-critical 1250F.

the numbers look really good. That formulation is extremely close to 52100. The only thing I might would change would be the normalizing temperature and then the hardening temperature. I would go with normalizing at 1650F (~900C) for 5 minutes....air cool to black then quench in water if you like. Then do the cycling down, however you want to do that. Since the normalizing and cycling have taken care of carbides AND aus grain....the final hardening temp should by kept below 1500F (815C)....preferably at 1475F (~800C), with a 10 or 15 minute soak.

The way I currently understand tool steel heat treating is that you can go one of two ways.....
1. As mentioned above. Use the lower temp of 800C to harden once the normalizing/cycling has been done. This puts just enough carbon in solution for to obtain max hardness, and leaves the rest of the carbon bonded as carbide. Plus...the RA (retained austenite) will be very very minimal.

2. Use the higher end of aust temps, as in 840C-850C. This will put more carbon in solution, but at the expense of carbides AND more retained austenite, which then you might want to employ a sub zero to take care of the RA issue.

Just now noticing your tempering times. I like the fact that you are going against traditional thinking of two hour tempers times 3! But 25 minutes may not be long enough. I would shoot for one hour times two, or three. Water quench during temper....yes!

Looks as though 100Cr6 is indeed 52100 with a slight touch of V. Not enough for primary carbide formation, but enough to help pin grain boundaries.
 
I missed the temper info, too. Two tempers at one hour is enough for most blade steels. Three is OK if you are worried about high RA, but with lower austenitization, that should not be an issue in carbon steels.
 
Stacy, thank you for answering.
Yes, I also think that I will raise the normalizing temperatures a little bit but I thought that the last temp. should be held at below critical for a while (5-10min), shouldn't it? Not just because of the grain size but also because stress relieve (more like annealing than stress relieve, but still), or does stress relieve step gets covered in previous, hotter steps?
Also the need for spheroidizing? Solely for increased ease of machinability correct? Why before grinding and machining? I intent to do it after that to relieve the steel and re-disperse and re-distribute elements evenly. In this case, I won't be using air hardening steel, so why should I worry if the steel is soft enough before I go on and machine it? Just some dilemas that I have hehe
And again, thank you for help and answer.

Best, Vito

Stacy E. Apelt - Bladesmith said:
One error in your plan is the 1250 soak. No grain refinement will be done on a sub-critical cycle. For grain refinement, try 1580/1480/1380 steps, the spheroidize at 1250. I would also soak at 1250 for 10 minutes.

I would suggest the normalization cycles be done after forging and before grinding/drilling.

Your analysis looks more like 52100 than L1/L3
http://www.zknives.com/knives/steels/steelgraph.php?nm= L3, 52100, L1&hrn=1&gm=0

Your austenitization temp may be a bit high for a knife blade, especially with no W or V in the steel. I would try a blade or test piece at 1500F and see what the result is first.

Perhaps some of the 52100 folks will chime in with their suggestions.
Click to expand...
 
haha samurai, I saw that yes :) Thanks for replying on both forums ;)
Anyway, here's my answer to you, again:
Samurai, yes, I have also noticed the simmilarity between the two. Aha, I understand, you would go even higher for the first normalization temperature. If your method is applied, I presume that the next cycle should be kept well below 900celsius (about 780celsius), correct? And the next one about 100C lower and that's it for the normalization part? May I ask why going higher with that 1st normalization temperature?
I picked that high quench temperature in faith that that will redissolve more carbon, but later, when reading my own posts, I thought of retained austenite.
After a good look, I do think that I will go with your quench number, I just don't know about the 1st norm. temperature yet hehe
About the tempering time...I think that shorter periods with progressively increasing temperatures, would result in somewhat cleaner, ''more thorough'' tempering and therefore a tougher blade. What do you think?
Thanks for replying and all the help.
Best, Vito


I can see that both of you mentioned the problem with retained austenite after quench with high temp. (1550-1575). But don't you think that higher heats should contribute to re-dissolvement process of also other alloying elements, other than just carbon?
All the best, Vito
 
Forgot to add this: for example chromium needs decent high temp and a soak to properly dissolve (much like vanadium?).
Or should I consider ''alloy distribution process'' done after the normalization process...?

Thank you for helping with solving my dillemas hehe

best, Vito
 
Vito,
Normalization and grain refinement are similar, but have different desired end results. They overlap a good bit, though.

In grain refinement, the grain size is being reduced. This is usually done as part of the final HT process. The resulting structure or internal condition is not a concern, as the final quench will harden it into martensite. A sub-critical step before the final hardening is often done but actually isn't needed. It is just an extra assurance against warp.

In normalization, the internal structure is being reset to a less stressed and softer condition. Alloy ingredients are put into a solution that is suitable for working the steel with tools and abrasives. The normal desired structure is coarse perlite, and the best form of that is spheroidite. Normalizing is similar to annealing in many aspects. Normalizing is done after all thermal events ( forging and bending) are complete, but before grinding and machining are performed. If the steel has been normalized before machining, there is no need to repeat any grain refinement steps before final HT.

The reason for the high first cycle temperature in grain refinement is that spheroidite takes a while and high temperature to fully dissolve and put the carbide formers back into solution. The subsequent steps are usually about 100°F down each. Thus 1650/1550/1450°F are usual. If doing normalization, the last step is a hold at below the critical point, usually 1250°F. This allows the carbides to become balls and rods that are bunched together. This is spheroidite, and is the most machinable/workable form of steel. Since no structure change occurs, there is no grain refinement, just a shift in how the structure is arranged.

With 52100 and similar hyper-eutectoid steel, a higher first step temperature is a good practice, as many are so highly spheroidized from the mill that it is very difficult to HT them with good results. Some are 98% spheroidite. 1650°F is a minimum, and a good long soak is required, 10-20 minutes.
 
Stacy and samurai, once again, thank you for a great explanation of the process.
I hope that you don't mind me quoting your replies, I only do that to ease the reading and comprehension of this discussion, as otherwise, I normaly don't like to quote people if you know what I mean hehe :)
But anyway, here it goes.
Ok, now I actually do understand the reason behind the higher first cycle temperature. Do you think that the method of higher 1st cycle norm. temperatures could be applied to all tool steels (or maybe just ''cold work'' tool steels?)?
Now, that you've explained why go higher and after I have read some more literature, it makes perfect sense. What about holding times? I intended to leave holding times as they are (about 7min for each cycle). Or maybe I should apply ''the 15 minute rule of soak'', that you mentioned for every tool steel, just to make sure, or can harm be done (''burning'') to certain steels if going that high for first cycle of normalization?

You also mentioned that after machining and grinding, another grain refinement is not necessary. How come? For example: when doing stock removal, there can be A LOT of heat generated by cutting, grinding, drilling, etc. Wouldn't another cycle of grain refinement be advisable? Or is just ''dunking the metal in the water pot during the grind up'' enough to remain the grain ''small''?


Well, loads of questions, I know. But my grandfather said to me once: One who asks is a fool for a day, one who does not, is a fool for life :)

Thank you!
 
Vito< i would agree with the other guys. That 1545F austenzing temp would probably be fine if you were making bearings and wanted big carbides for extra abrasion resistance, but most of the guys who use that steel now for kitchen knives and such, are going with a temp of 1475F so as to not put all of the carbon in solution. That makes for very low RA, very fine grain and tiny carbides apparently. Just the ticket for a knife that can take a very fine stable edge. I supposedly also makes for a pretty tough blade too. As for the stress relief cycle, I have been doing one after grinding for a few years and it has pretty much eliminated most warping issues.
 
jdm, thanks for the ''confirmation-oriented'' response. I have already realised that it's better to leave aus. temperatures low, after that first high temp. normalization and after those temp. cycles. Pretty much, samurai artist and stacy explained me that by doing cycles of 1675/1560/1450/1350, I can pretty much equally distribute carbides, redissolve alloy elements, ''shrink'' the grain AND relax the steel prior to final aus temp. And if I would be going higher with aus temp than 1475-1500 for quench, basically I would ''de-value'' all those previous cycling steps and actually go back to beginning again.

Thank you all for great, quality answers. Truly appreciate it.

Best, Vito
 
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