52100 Ultra low hardening/aust temperature

I normalize 52100 coupons using 1850F (high=fast) to check my oven TC's for +/-1 around Curie point. As update above, my oven TC is +/- 5F around 1414F. Done this calibration in one batch.

Following batch - prepared(1650F normalized+cycles+*** steps) 9 coupons ready for hardening. Aust 1440F;1430F;1420F. 3x3 Quench in Parks50; Brine; Super Quench. Hardness results (P50; Br; SQ): High 50's; ~61rc; 65+. Microscope view look like mix pearlite with P50 & Brine. Finally I fuzzy-view this with microscope, before that I've been hand-waving/conjecture. Don't mean, it's confirm but sub second PN seem makes most sense. I think many KM encountered similar situation of failure to harden W2 with too many thermal cycles. Yes, Stuart, 1850F + hardly thermal cycles + harden most likely end up with grain size < 9 (i.e. 20+um).

Last weekend batch - mostly coupons + 1 paring w/ attach coupon. Corrected the carbides size and reduced grain some more. Aust at 1425F, SQ. 65+rc AQ.

Next 2 or 3 batches - probably flailing/trying to get 1um grain and make carbides go sub 250nm. Success when hardness > 63 and can't hardly see carbides with my microscope. I think, I am within my target of 0.2-0.5um carbide size and 15+ grain, so going beyond is a longer term research. However I not am convinced sub-micron grain is applicable/beneficial for edge-tools, maybe more useful in armor/structure/etc...

Micrograph is very helpful to confirm/reject and fine-tune theories/conjectures. Open mind is a most powerful tool/equipment.

samuraistuart said:
Mr La, may I ask how you get the pearlite nose of 52100 to be sub second, requiring that faster quench medium? I think I know but was hoping to get more info from you. Something that caught my eye....your sequence of 1850F, 1520F, then austenitizing....1850F seems awfully high, and with only one thermal cycle (1520f) between that 1850F and austenitizing temp (1430F or what have you), the grains would be larger than wanted?

Really curious about the 0.6 second PN and how you achieve this! This is VERY interesting for sure. I wish we all had access to the equipment needed to do these cool experiments! Keep it coming!
Click to expand...
 
I still would like to know how you are achieving a PN of less than a second on 52100 steel. I would like to see your entire working sequence for once. As in a simple formula:

1650F for 5 minute soak, air cool
1550F for 10 minute soak, air cool
1450F for 10 minute soak, quench
1425F for 10 minute soak, quench
(any sub critical steps would go here)
1475F for 10 minute soak, quench (or whatever temp you choose)

If super fine grain is what you are after, I can understand trying to do that using the lower austenitizing temps. But I would think it would require the thermal cycling as mentioned as well for the ultimate in grain refinement. I must admit I am having a hard time understanding the premise, theory, hypothesis, and even the experimentation. I'm not saying that it's wrong, or a waste of time, or anything like that. It's just that I, and others, aren't quite "getting it". I think the biggest thing is the thermal cycling. I think you HAVE to be doing them in order to get the PN that low (sub second), but they are not quite mentioned, the quench that you perform on them (air vs oil). It seems that you are doing a number of sub critical steps as well.

Very captivating anyway!
 
Stuart,

Respectfully, I am sorry for not disclosing a 'how' method/procedure to achieve sub-micron carbide and grain size 15+. Along my journey, I've shared online 'what' can be done and hand-waving physics 'why' it can be done. It cost me into 5 digits$ to obtain a 'how', hopefully I come across as fair with my share of contribution. At this point in time, my ht knowledge probably consider as competent, so I am willing to provide sound guidance/opinion to specific ht question within the context of the person seeking idea/help.

*For 3/32 or 1/8" thick*
Steps listed below (minus sub critical) will give you grain size 10. Increase 1650F soak to 25-30 minutes give you grain 11+. Reduce soak times for other steps probably will yield (max-out) grain at astm 12. Hardening temp & soak will determine the tempering conversion & precipitation curve. 5 minutes help lower grain boundary precipitation & cementite coarsening.

Due to diverging of grain vs carbide size, in which prevalent ht technique (non mechanical/inductance/fancy-atomic) high unlikely to break astm grain 13 and carbide smaller than 1.5um. Those willing to play with super quench with crack/ping/tink/fancy-vocabs consequences, astm 15+ and sub-micron carbide await on the other side.

Benefits of fine grain - http://en.wikipedia.org/wiki/Grain_boundary_strengthening

samuraistuart said:
I still would like to know how you are achieving a PN of less than a second on 52100 steel. I would like to see your entire working sequence for once. As in a simple formula:

1650F for 5 minute soak, air cool
1550F for 10 minute soak, air cool
1450F for 10 minute soak, quench
1425F for 10 minute soak, quench
(any sub critical steps would go here)
1475F for 10 minute soak, quench (or whatever temp you choose)

If super fine grain is what you are after, I can understand trying to do that using the lower austenitizing temps. But I would think it would require the thermal cycling as mentioned as well for the ultimate in grain refinement. I must admit I am having a hard time understanding the premise, theory, hypothesis, and even the experimentation. I'm not saying that it's wrong, or a waste of time, or anything like that. It's just that I, and others, aren't quite "getting it". I think the biggest thing is the thermal cycling. I think you HAVE to be doing them in order to get the PN that low (sub second), but they are not quite mentioned, the quench that you perform on them (air vs oil). It seems that you are doing a number of sub critical steps as well.

Very captivating anyway!
Click to expand...

Here is coupon#0 of SQ52100 from the same batch. Aust 1420F, 65+rc, fresh martensite, 1000x magnification. ooohhh there is a skull in there - gotta be evil :p
20150314_SQ52100_c0_02.jpg
 
It's all good, Bluntcut. All is fair in love and ......... heat treating!!! I figured you wouldn't want to just turn loose of some info that you've spent $$$ and time on. I'm still dubious as to the actual performance benefits of trying for grain size 15. Pretty cool that you can get it.....if you can get it.

I find it interesting that increasing the soak time at that normalizing temperature helps to reduce grain size in subsequent cycling.

The secret of your theory lies within the subcritical steps you perform then?
 
Cautiously optimistic I believe my result grain is at astm 15 size. I went over my experiment data - 3 coupons failed to harden the first time low 40 rc, 2nd time 65+rc. There is a possibility that carbides in those coupon were sub 0.25um and grain 17+ but transfer time & quenchant were not fast enough. I will do a new 3 coupons experiment with speed up transfer time & ice chill super quenchant, then micrograph result regardless of hrc.

As for performance benefit of super fine grain. Nothing super duper perf shows up for my 63rc test paring knife YET. It just seem a bit sharper - easy to push cut newsprint cross grain. And a bit tougher than my other 52100 blades (astm 13 grain) when wood working with 0.008" behind 10dps edge. Shave about the same.

Very good guess on my non-disclosed steps however keep in mind, experimentation comes after conceptual/theory.

samuraistuart said:
... I'm still dubious as to the actual performance benefits of trying for grain size 15. Pretty cool that you can get it.....if you can get it.

I find it interesting that increasing the soak time at that normalizing temperature helps to reduce grain size in subsequent cycling.

The secret of your theory lies within the subcritical steps you perform then?
Click to expand...
 
Caution - speculating & extrapolating ahead

This afternoon I experimented with 6 paring blades with coupon attached. Hardened 3 (~44rc; 56rc; 58rc). Captured micrographs of coupon has 58rc. Quite stoked to see expanding martensite into mix microstructure region. Aus grain in mix-microstructure is about 19-20 astm(0.5 - 0.35u), no carbides were visible. Martensite region shown carbide coarsen to about 0.25-0.3um and unclear grain boundary. Extrapolated grain size around 16-17 astm (1.4 - 0.99u).

Maybe tomorrow, I will harden the other 3 blades with longer soak time to avoid mix-microstructure... then take a look.
 
Finally I managed to captured a pic of grain network using 1000x color negative. The faint grey web of boundaries, where I estimate the average diameter around ~0.9 micron. Map to ASTM grain size between 17 (0.99um) and 18(0.70um).

Fresh martensite (i.e. AQ state). I will grind & test this 4" paring blade.
m1_07_neg.jpg


:sleeping:
 
Just a thought that actually Stacy had typed out some time back, so I don't take credit for this, all goes to Stacy.....

Have you ever tried taking two kilns, programming one of them to hold your austentizing temperature of, let's say your low 1430F, soaking for a short while, then transferring that blade to a second kiln that is held right at 1350F, soaking for a bit, then quench?

Just curious as to what that might do for you. I'd do it if I had two kilns just to play around with!
 
i bet you'll get carbide precipitates in the austenite grain boundaries during the 1350F soak
 
Bluntcut, you may want to explain how do you see/measure aus-grain size from that pictures, unless you are talking about carbide sizes
 
Stezann....I think you may be on to something there. Probably dead on right! I can't tell how you can measure aus grain size in that picture at all.
 
I got to thinking a bit more about the transfer from austentizing temp to a 1350F oven, and what that might do, and how credit goes to Stacy for the idea. I think I need to sort that out for Stacy's sake. I believe the steel in question when he made the suggestion was 1084.....so the carbide precip to grain boundary wouldn't be too much of an issue. With 52100...yeah it would be. With 1084...no, hence the suggestion. I got your back Stacy.
 
Sorry for my slow response, I am very busy dealing with a hypervisor server died.

You guys are spot-on with 1350F soak - grain boundary precipitation, sure don't want that. Nevertheless, you can do that with just one oven. Just create another segment for 1350F, ramp 9999, open oven door for 2-5 seconds.

Carbides are spheroid & oblong spheroid shapes, while grain boundaries resemblance variable/distorted honeycomb. Pearlite has finger like look; martensite fern like; bainite plate like; aust padding near grain boundary. Yeah, my grain read could be all wrong - maybe a wishful thinking eh. While sharpening using a 240grit waterstone, I notice (maybe no significant at all or desperately looking for lame anecdotal evidence), swarf float and aggregated into distinct floating clumps on ceiling of clear water layer on top of the stone via water tension. Once touch with finger tip, it uniformly disperse into dark grey water. SEM I am.

Of course here, scrutiny is a must, since claim grain size 17 = extraordinary can't just back-up with a fuzzy pics :cool:

Back to server hell I go...
 
FWIW - ** no pics - maybe it didn't happened! **

took total 45 SEM & EBSD(Electron BackScatter Diffraction) images for 3 coupons, magnification range from 0.75K to 100K. Images taken & interpreted by a Steel Scientist (not sure how Steel Scientist diff than Metallurgist).

* Max carbide diameter less than 500nm, well distributed carbide nominal size around 200nm. excludes sub 100nm carbides population.

* Unable to identified grain boundary. I sure can see martensite quite clearly at 100K (500nm scale) image. Well, could be my polishing was far from good(220, 500, 1K, 4K, 8K, 1um diamond, 0.5um diamond).

edit: after a lot of stared & compared, I think avg grain dia around 500nm. And high likely there are fine RA dispersed could be on grain boundary.
 
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If I may ask a few questions...

1. You are using an Evenheat kiln for your experimentation. Which model? Any modifications or add-ons?
2. How are you assuring consistency with your superquench?
3. How are you grinding your coupons prior to hardness testing?
4. I am still unclear on how you are determining average grain size. Can you please elaborate?(perhaps I missed it. I'll check through your posts again)

Forgive my bluntness but as it stands, it seems you are merely playing metallurgist here. I see minimal control in your methods. You come across as though you are "pushing the boundaries" of conventional metallurgy and are already playing the "proprietary/secret squirrel" card(as apparent in your response to Stu). There is something in all of us that wants to believe the "breakthroughs" only come from people who "challenge the norm". Sometimes this is the case, but those individuals/teams are usually tackling the problems with NEW approaches/technology. You rarely(if at all) see people dig through old data and rehash standard practices to advance knowledge. Everything you are doing has been done by people with better equipment and working knowledge in the field of metallurgy. I suspect anything that you deem as unexpected or beyond convention is actually a misinterpretation of the data.
 
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Rick,

I am very much a metal tinkerer/hack than anywhere in the realm where metallurgist roam. This blind-noseless-squirrel "secret nut found" could very much be a piece of dry dog t*rd. My recent interaction with a steel scientist, perhaps reflected my willingness to accept reality - either I've something or delusional. I started out with a vision/theory and have been chasing it for almost 2 years. And 100% sure, I am rehashing old physics; however it would be super cool rehashing if I smart enough to invent a microstructure sequencer :p

Let's treat rhetorical 1-4 questions as statements of skepticism.

My apology.

Rick Marchand said:
If I may ask a few questions...

1. You are using an Evenheat kiln for your experimentation. Which model? Any modifications or add-ons?
2. How are you assuring consistency with your superquench?
3. How are you grinding your coupons prior to hardness testing?
4. I am still unclear on how you are determining average grain size. Can you please elaborate?(perhaps I missed it. I'll check through your posts again)

Forgive my bluntness but as it stands, it seems you are merely playing metallurgist here. I see minimal control in your methods. You come across as though you are "pushing the boundaries" of conventional metallurgy and are already playing the "proprietary/secret squirrel" card(as apparent in your response to Stu). There is something in all of us that wants to believe the "breakthroughs" only come from people who "challenge the norm". Sometimes this is the case, but those individuals/teams are usually tackling the problems with NEW approaches/technology. You rarely(if at all) see people dig through old data and rehash standard practices to advance knowledge. Everything you are doing has been done by people with better equipment and working knowledge in the field of metallurgy. I suspect anything that you deem as unexpected or beyond convention is actually a misinterpretation of the data.
Click to expand...
 
Sorry, bud. I didn't intend to be offensive but my post sure turned out that way. I do applaud and respect the investment you've made toward expanding your knowledge.

My questions are valid and sincere. They mostly address the "control" aspect of your procedures... which I think is the foundation of effective experimentation.

I am not trying to set you up. I just think these are potential problem areas.
 
Nada then... perhaps I was too groggy this morning and misconstrued your words.

Rick Marchand said:
Sorry, bud. I didn't intend to be offensive but my post sure turned out that way. I do applaud and respect the investment you've made toward expanding your knowledge.

My questions are valid and sincere. They mostly address the "control" aspect of your procedures... which I think is the foundation of effective experimentation.

I am not trying to set you up. I just think these are potential problem areas.
Click to expand...

Repeatability is essential for doing some sort of control experimentation. Practicality must paves the way there. I try not to end up in the realm of novelty physics - e.g. super conductor.

1. KO 18 - as shipped. Thinking about argon injection but didn't see a real need yet, since decarb or ssfoil or clay doesn't impede or terribly inconvenient my thermal steps - YET. There certainly want: salt pot, induction, vertical vacuum ht chamber, etc...

2. Room temp, coupon/blade: 80 sanded surface, equal thickness (sometime just rectangular piece, not profile cut out). Dip & slice back/forth. For 1/8" thickness, touchable 3 seconds after the sound-shock. Not a single crack for the last 40+ blades. My SQ is getting dirty, I keep add surfactant which seem to keep vapor jacket to minimum.

3. My coupon nowaday is just an extended tang with notch to break off. As-quenched (fresh martensite). Use fresh belts to grind decarb (hardness test), progress up to 400 grits while never let sample more than lukewarm - hardness test. Polish for micrograph: Waterstones 220, 500, 1K, 5K, 8K, leather rub abrasive (diamond/cbn/Cr0) down to 0.5um.

4. 1. Count grains inside 100um^2. or 2. use XY axis fit within about 50 random grains, where X is the longest diameter across, dia = (X+Y)/1.8 or 3. eyeballs grain against scale hand-wave an avg grain dia.

Rick Marchand said:
If I may ask a few questions...
1. You are using an Evenheat kiln for your experimentation. Which model? Any modifications or add-ons?
2. How are you assuring consistency with your superquench?
3. How are you grinding your coupons prior to hardness testing?
4. I am still unclear on how you are determining average grain size. Can you please elaborate?(perhaps I missed it. I'll check through your posts again)
Click to expand...

Get to this point, it took me a while. I will employ more instruments and formal research IF/WHEN warranted. Combination of life; mental ceiling; mis-guided theory; etc... could easily doom/end what I want/seek/hope with metal research.

I understand and appreciate this community keeps mis-information from spreading. For myself, I share what I am doing with SQ, Ultra low aust, etc... At the same time, I repeatedly state these are not for non-tinkerers and not for non-over-lapping area of metal tinkering/finetuning. Just as I agree, even if these stuff possible, don't mean they are useful in the context of knife making.

Just learned in the last 24hrs: BackScatter Electron Diffraction is way better than SEM for study/examine crystal micro-structure. It provides more 3D (depth) and higher image clarity.
 
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