"Knife Steel Talk" with Metallurgist: Microstructures?

PhD Larrin Thomas
(Knife Steel Nerds)
We have a conversation about what went into to the micrograph process for his epic 42 micrographs. We than talk at length about the differences between these steels such as carbides, sizes and toughness, etc
Here is the article we are discussing
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[@jeremiahshine]

I was taking a tour of Newcore Steel's first mini-mill. Every laborer there worked 3 on 4 off 12 hour shifts for a base $50k paycheck. I was at school so didn't apply... I should have! We were on the catwalk above a huge crucible cooking a batch of some type of stainless due to be cold rolled. A guy was dumping bags of additive powders in when he accidentally dropped an open bag of something (bag and all) into the huge pot. Flames and sparks belched out of the orange liguid and horns and sirens began to wail a few seconds later. Everyone in sight started running. The plant manager who was giving the tour calmly but quickly led us away off the catwalk. About 20 seconds of calm speed walking he began to run as the wail continued. We ran as far as we could to an exterior factory wall to a set of stairs. About half-way down the first flight the noise stopped. He stopped and caught his breath. Red faced and sweating he explainex "break-outs". At the end of the tour he took my buddy and I into his office and we sat drinking a soda pop talking. He nonchalantly explained that if the stainless had broken out we'd probably be dead as by time the alarm goes we wouldn't have been able to get to safety. To this day I don't know if it was a ruze or if we got lucky.

[@FearNoSteel]

Crazy! Thanks for sharing!

[@danielbottner7700]

Looking to buy steel to make thin (0.060 - 0.065") Santoku style (1.5" to 1.75" tall) x (5.5" to 5.5" long) blades with good to excellent corrosion resistance. I like 1.3º to 1.4º flat grinds with 0.005" to 0.006" behind the cutting edges. Any suggestions for 3 or 4 of your top picks & who to get them hardened by would be much appreciated.

[@greekveteran2715]

My personal favorites (Fixed blade guy), are Vanadis 4 Extra and handforged Ballbearng steel. Please, let me explain why: Either general use knives (Full flat grind or Saber grind knives), or specialized knives ( Scandi grind, Hollow grind, Convex) all are used in the outdoors as hard use knives. Words "Outdoors" and "hard", means you need ease of sharpeing, to be able to fix easily, any edge issues and in the same time toughness and edge stability. Marketing in the USA, pushed the CPM 3V, as the most premium steel for such knives. When there is smoke, there is fire says an old sayng, means that CPM 3V, is indeed a very good steel! However, I've seen better performance from both steels I've mentioned, and that puts CPM 3V, at a lower spot, on the "proper" steel list for those kind of knives. I get better edge retention, a bit better edge stability and in the same time easier sharpening, from both steels I mentioned.

[@Zayaraq]

so much information that I'm gonna explode lol. Awesome video 🤤

[@elonquemattheson6151]

1:07:15 on Larrin's newest set of graphs (knifesteelnerds.com/2021/03/25/cpm-magnacut/), the CPM154 has about half of the toughness (9.5 ft-lb) it had in this older version (18 ft-lb, which would have been on-par with MagnaCut) and appears to be the only steel which has changed. The weirdly high toughness discussed here could just be an error which was later fixed. Great interview btw

[@monkpato]

BBB, you do an excellent job with these discussions in bringing out questions and issues that illuminate the subject. It seems that sometimes Larrin ignores or doesn't mention a factor because it's obvious to him but not the majority of us dabblers. When you push a little more it is very helpful.

[@TheDuckofDoom.]

I'm only disappointed that traditional 154cm wasn't tested next to cpm 154. Still 42 samples is quite a range.

[@hantusmostert]

What material will you recommend for special forces, corrosion resistance very important. I don't trust the marketing knife folks

[@JimiJamesIII]

Really good stuff here. Thank you Shawn and Larrin for the great amount of time and effort that went into producing this data.

[@southerncross100]

I like your desire for everyone to understand the information that is publicly available.

[@notcatfish]

wow that picture of maxamet is impressive.

[@frozenturtlefarts1025]

.) Odin likes this

[@oldschoolprepper2273]

Very interesting thank you for your hard work It benefits so many in the knife making community

[@shadow6pt533]

Do u have a website where u sell the knives u make?

[@JDStone20]

Awesome!

[@rustytygart405]

I don’t know how I have never managed to find this video in two years time but whatever I’m late … funny how from midway through I kept coming back to thinking about super blue and thinking how surprised I am that even after the two years since this video that we’re not seeing more clad steels it really is a genius way of getting better toughness from a blade with an ultra hard wear resistant blade… I’m really excited about the FACT that the knife industry has become so advanced in metallurgy at the same time programs like fusion 360 are pushing design popularity that we are inevitably going to continue to see progression in fantastic carbides … I don’t want to offend larren but when magnacut is looking like 440c imagine what will be in our pockets ….. love it

[@justinmcslappy]

I need to know why you have a "Hair" bookmark folder. Otherwise, you and larrin taught me alot today.

[@brad6689]

Thank you for taking the time to do these vids. Supper helpful and learned a lot. It brings the article to life.

[@eachday9538]

Yep, that was awesome

[@JDStone20]

Nice to see what I was thinking about M2 steel verifiied!

[@FearNoSteel]

Oh nice, I was very surprised by that.

[@JDStone20]

@@FearNoSteel Me too, I was thinknig that the powder steel version of M2 was what I was thinking would work better but it turns out that the ingot version of M2 will work fine

[@FearNoSteel]

@@JDStone20 yea man .80 Carbon and the carbide types formed really help keep the size down

[@kevinmc1111]

Definitely an underrated steel

[@stevegreiner7653]

That was great, thanks to both you and Larrin for doing this! I read his articles, but hearing the discussion adds a LOT.

[@cwsmith17]

Such a great vid. Great information thank you!

[@biscuitkitchentreviews]

Does anyone else feel smarter just by having watched this?

[@tacticalcenter8658]

id like to see some micro-graphs in the same steels but at different HRC's and or heat treatment techniques. like say m390 at 55-58hrc and one at 62hrc. id also like to see the difference between the same steels using cryo vs not at the same hrc.

[@FearNoSteel]

That doesn't change what you see at this magnification as significant as you would think so that would be a waste of time since its not adding any value. if we look at the mechanics, The more tempered 55rc m390 would have more fine (difficult to see) temper carbides from the martensite shrinking from being allowed to diffuse the trapped carbon with time and heat. With the carbon diffused, the martensite is less needle like and softer and that diffused carbon now makes precipitated carbides which aren't as badass as the primary carbides not in solution nor does it shrink the primary carbides. The cryo would have less patches of retained austenite which look like very fine gaps between the "needles" of martensite but it is too difficult to see and measure with 1000x and would need xray diffraction to calculate RA % per sample or Thermal dynamic software to predict. So basically M390 will still look like M390. HT will not drastically change the appearance unless the HT is complete crap. There are great articles about the mechanics I just talked about on knife steel nerds. search "tempering" and "cryo" both are 3 part articles, dig in.

[@danmichell7516]

the best information , for me to wrap my head around this complicated topic the banter is great .

[@steeltoez8345]

Doesn't look like my original comment posted up but thanks to Larrin for sharing your findings.

[@FearNoSteel]

Haha thanks Matt but these are Larrin's findings. I contributed some steels for these micrographs though

[@steeltoez8345]

@@FearNoSteel my mistake should have said these findings. Original post was dope tho so I just wanted to show some love towards Larrin and the work he's doing. Distracted me all day from picking up some k390 I found at a good price but finding material as rich as this stuff is awesome. I'm gonna watch this quite a few times cuz it's loaded with many nuggets of info.

[@FearNoSteel]

@@steeltoez8345 haha Thanks Matt

[@glockgaston2922]

Really great video brother!! Thanks for sharing all of this awesome knowledge!!!

[@mikeobrien6984]

I'll venture a guess as to why the M2 had weirdly fine carbide structure; looked up the composition on Zknives and it has about 6% tungsten, maybe that's preventing the carbon from coming out of solution to grow carbides? I'm in way over my head with this stuff, ymmv.

[@FearNoSteel]

It's the .80% C which isn't enough to make the larger Carbides in D2 which is rocking 1.50% Carbon and large amounts of Chromium. We have to remember Carbides are a mix of the carbon and the Metallic elements bonded together. So the carbon not put in solution to make the steel hard stays locked up as carbides. We also say the trend that with enough Chromium Carbides were larger clusters especially with volume. Hence another factor why the M2 was finer is the Moly/Tungsten rich M6C Carbides are finer clusters than the high volume chromium rich Cr23c6 Carbides. I'm sure if we had more carbon in M2 it would chunk it up more with the Carbides having more building blocks to cluster more.

[@mikeobrien6984]

Thanks for the reply, really appreciate the educating work you're doing

[@mikeobrien6984]

Thanks man, really enjoying your output lately, great stuff.

[@jonugalde1275]

Guys, I'm enjoying this video a LOT. Thank you for sharing your knowledge. 👍👍 I have found a confusing point, at some moment Thomas comments there is not any carbide at all at forging tenperatures. That's incorrect, what you don't have at those tenperatures is the cristaline structures steels forms around carbides, but the carbides continue there. For example Vanadium carbides need almost triple of forging tenperature to reach the melting point. Go on my friends!

[@FearNoSteel]

Kaixo Jon, ikusgarria. Entzun zati hau

[@FearNoSteel]

1:00:00

[@jonugalde1275]

Kaixo berriz ere Shawn! I'm refering to what you are talking about at minutes 29 and 30. You talk about carbides in general, mention chromium carbides and then Larrin says carbides disappear at forging temperatures. He may be talking about cementite, it's impossible to dissolv other carbides in the steel as chromium carbides at forging temperatures, their melting point is too high, chromium carbide melting point is at 1895°C. What I think is other carbides work as seeds for the structures which form and dissolve in the steel at the temperatures we are talking about. What it seems is they behave the same way as tiny diamonds are used to grow bigger industrial diamonds or how the powder in the atmosphere works for the formation of different water structures. You can make the structures steel forms to be smaller controlling the heat treatment. That's the easiest way and the one the industry needs. But there is another way to make them smaller, a more Orkish and the same way sophisticate one, smashing them. Take any of the steels we are talking about here as wootz steel. With very big care you could forge it just below eutectoid temperature breaking those structures and making them smaller. Depending in the steel and if you don't want pearlites you have a marging of some minutes to forge it. Then you could take your time and produce a lower bainite steel, producing an end product I'm dreaming with for long time ago. Have a good day! 💪💪

[@jonugalde1275]

I have listened it again with subtitles and I was wrong, he says carbides will be there even at forging temperatures. That's right. But then he says those carbides will be bigger and will keep growing. That' what confuses me, cementite forms, dissolves and forms structures at the temperatures we are talking here, but not the other carbides. Those stay stable

[@CJ-hw4zc]

Top notch video man 👌

[@andrelarocque5967]

Excellent exchange.

[@dandildarious4849]

Much appreciated!

[@stevenlachance8576]

Shawn do you know if the carbides in the samples prepped for microscope are present or absent, eg does the acid etch remove the carbides or the matrix.

[@FearNoSteel]

It's a special acid designed to eat the matrix and make the Carbides "POP" more. I believe Larrin talks about it in the beginning of the video. The bright white dots and globs are the carbides.

[@stevenlachance8576]

BBB so what would happen if one sharpened a knife with say a weak acid (forget etching issues for this discussion). Probably want to use ceramic stones, but could one expose more carbides and would that be a good thing? I’m thinking vinegar.

[@felurianmasters4369]

​@@stevenlachance8576 thinking out loud here, wouldn't you effectively just wear down the exposed carbides, making the batch at the edge smaller. That would just decrease the wear resistance at the edge. You might also increase the risk of tearing out the carbides as they wouldn't be held in by the surrounding material. Interesting thought, I'm no expert.

[@macro820]

I really understood this better than I do reading his articles I hope you do another one some time

[@Airel17]

Great discussion and educational information. Hopefully more videos like this to come.