Kevin & all - as one of what I suspect are many "lurkers" reading this thread I just want to thank you for sharing your knowledge & experience. I'm still trying to wrap my brain around phases, temps, and timings. THANKS! now I'll just take 2 aspirin and go back to lurking...

Thanks Kevin! Very interesting to say the least. Would the Pearlite that is forming too late be forming in the spine section, the edge or the transition area? My guess would be the transition area... but my guesses are usually wrong. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

Thanks again for your contributions!

Rick

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Kevin,

I remember coming across various discussions between you and others on this, but quite a while back. Do you happen to have a link to one that fills out what you mention in your last paragraph here? I'm mostly trying to make simple process connections between "blade shape and cross section", but I'd like to have a better understanding of the whole.

Mike

The blade shape most susceptible is one that is not as wide and is a simple flat grind from edge to spine (think of a Scottish Dirk) the easiest way I have found to avoid it is to spine down quench such blades. But be aware that clay will change everything and that I most often do not take clay into consideration when discussing this issue.

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Thanks Kevin! Very interesting to say the least. Would the Pearlite that is forming too late be forming in the spine section, the edge or the transition area? My guess would be the transition area... but my guesses are usually wrong. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

Thanks again for your contributions!

Rick

That gets very complicated and if you were here I would show you several of my micrographs from Japanese swords so that you could see the kind of controlled chaos that happens, particularly in the habuchi area where things are really going on. But for the most part if you want an upward curve you need bcc stuff (pearlite in the spine) when the edge starts expanding, you never want pearlite in the edge and if you can get things balanced in the middle you may manage to keep things straight.

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Kevin & all - as one of what I suspect are many "lurkers" reading this thread I just want to thank you for sharing your knowledge & experience. I'm still trying to wrap my brain around phases, temps, and timings. THANKS! now I'll just take 2 aspirin and go back to lurking...

Michael,

I've read your post a lot... every time I get called back by a newer response.

Headaches... oh yes... and tail chasing where a person catches it, and wishes otherwise. Everybody is different, but I struggled seriously and still do. I've no idea where you are on the metallurgy learning curve, nor where you want to be. If you think there may be a possibility I can help you some and want to find out... holler, and I'll try... this thread... new one... private... I don't care.

I am not going to be able to take anyone to where Kevin is with this stuff... not by quite a bit. I roughly understand what real metallurgy is... that's a long ways short of the real thing.

Mike

Mike - Thanks! I'll respond here - if you or others would rather not see this thread cluttered we can "take it outside" <grin> I'm basically an old dog trying to learn new tricks.

I can see how the presence of pearlite while martensite is forming and the blade is under stress would cause warping... my headache comes from trying to keep all the factors (blade geometry, phases, temps, timings, grain sizes, repetitions, quenchants, clays, angle of quench...) in my head as they apply to my crude propane forge/magnet-test/quench bath setup.

I've done the intro course in Old Washington (that course took at least a year of learning curve and put it into 2 weeks - THANKS!!!). Also re-re-reading heat treat advice from Goddard, Fogg, Hrisoulas, etc. Plus my limited experience making/testing knives - a few for myself and friends - half a dozen blades in 5160 to the J.S. performance test specs - about half of them passed, half broke on the bend test, and a couple of them have had curious spots along the edge that did not harden - or maybe I heated that spot doing final edge on the belt grinder???

I'll summarize my Steel metallurgy knowledge and /PLEASE/ correct me where I've misunderstood.

The basics:

* Ferrite: A body centered iron crystal structure that can hold a little carbon (hence - can become steel).

* Cementite: Iron carbide - a ferrite and carbon mix.

* Carbides: Cementite is one carbide, others are based on silicon, vanadium, etc.

* Austenite: A face centered structure that holds more carbon than ferrite. Forms at high temp (above 1350f-1450f depending on % carbon and whether you are talking about full transformation). Non-magnetic. Ductile.

* Transformation Temp (A1/A2/A3 - noted as Ac1/Ac2/Ac3 when heating, Ar1/Ar2/Ar3 when cooling): Heat up ferrite and here's where it transforms into austenite. You can tell you've hit Ac2 when it goes non-magnetic. When somebody says "Critical Temp" I assume they mean A2.

* Decalescence: When heating steel, around Ac2 the steel is absorbing heat w/out raising its temp while the transformation from ferrite to austenite happens (causes a shadow on the blade).

* Recalescence: When cooling steel, around Ar2 the steel radiates more heat/light as austenite transforms back to ferrite in the cementite/pearlite mix (causes a light on the blade).

* Pearlite: A matrix of cementite and plain ferrite in microscopic platelets - more ductile than cementite alone. Created by allowing austenite to cool over minutes or hours (depending on the steel composition).

* Bainite: Created by cooling austenite a little faster than for making pearlite - but still going through the "nose" of a phase transformation diagram. I imagine bainite as a matrix of martensitic crystals and pearlite.

* Martensite: Created by cooling quickly in front of the "nose" on a phase transformation diagram - a second or two or less depending on the steel composition. With air hardening steels like D2 this apparently can be many seconds. Martensite is composed of oriented needle-like crystal structures that have captured excess carbon atoms from the austenite into room temperature crystals. Brittle but very hard.

* Grain: All of the above form crystal grains - if the grains are allowed to grow large (course) the resulting steel will break more easily - one thing I've gleaned from this thread is that if the grains are refined to a /very/ fine size it impedes hardenability due to pearlite forming readily along grain boundaries.

Processes:

* Normalizing: Used for quick stress relief and grain size control. Heat comfortably above Ac3 (you mentioned 1600 as the high end) - let austenite form - then (for steels like 1084 or 5160) air-cool past A1. Repeat a 2nd or 3rd time to ensure even grain reduction - each time at a lower austenite temp. This produces pearlite, right?

* Annealing: Used to fully soften steel for machinability and also reduces grain size. Heat to /barely/ above Ac3 and cool very slowly. Also produces pearlite, correct?

* Spheroidized annealing: I have not looked into this...

* Hardening: Produce as much martensite as you can.

* Tempering: Heat to 400f + or - depending on the steel - leave it there for hour(s) and pearlite forms on the martensite grain boundaries - which reduces brittleness while retaining the hardness of the martensite.

... that's my state of knowledge - probably what I need most is more practice/experience... any corrections &/or suggestions are much appreciated!

Michael Kemp

p.s. And here I spent hours organizing these thoughts when I was *supposed* to be cutting code - or maybe sneaking down to the knife shop - but it's helped coalesce my state of knowledge.

Michael, you put a lot of time into your post, showing how deidcated you are to understanding this stuff, allow me to "adjust" your definitions for greater accuracy. Please note that my going point by point is not nitpicking but just keeping it all straight in hopes of helping:

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...

* Ferrite: A body centered iron crystal structure that can hold a little carbon (hence - can become steel). Actually it is all steel, ferrite is called ferrite because it is not pure iron but has limited solubility of carbon. It is all an iron crystalline matrix inside of what we call "steel", just the arrangement of iron atoms allows for different levels of solubility. Ferrite, austenite, martensite etc... are all mixtures of iron and carbon and not true compounds, thus folks get in trouble for saying "molecules" when discussing steel. Except for...

* Cementite: Iron carbide - a ferrite and carbon mix. This is an actual compound and not a mixture. Carbides are Little areas within the matrix where carbon actually chemically bonded to form a compound, in this case instead of sitting between iron atoms the carbon atoms decided to bond with them to form a very hard compound.

* Carbides: Cementite is one carbide, others are based on silicon, vanadium, etc. See above. In steel certain metallic elements will bond to form very small particles of compound with the crystalline makeup, some form VERY tight bonds and can be VERY hard (titanium, columbiun, vanadium...) while others not so much like iron or chrome, and some elements reject carbon when present in steel, like silicon and nickel, and leave it for the iron to have.

* Austenite: A face centered structure that holds more carbon than ferrite. Forms at high temp (above 1350f-1450f depending on % carbon and whether you are talking about full transformation). Non-magnetic. Ductile. Yep

* Transformation Temp (A1/A2/A3 - noted as Ac1/Ac2/Ac3 when heating, Ar1/Ar2/Ar3 when cooling): Heat up ferrite and here's where it transforms into austenite. You can tell you've hit Ac2 when it goes non-magnetic. When somebody says "Critical Temp" I assume they mean A2. You nailed it! Not many get the subtle differences between A, Ac, and Ar but you did, so you are well on your way!

* Decalescence: When heating steel, around Ac2 the steel is absorbing heat w/out raising its temp while the transformation from ferrite to austenite happens (causes a shadow on the blade). It begins at Ac1 and ends at Ac3 or Accm (in pure iron-carbon systems) Ac2 is just the Currie point within it at 1414F. This is why some steels work well with the magnet and others don't for determining temp.

* Recalescence: When cooling steel, around Ar2 the steel radiates more heat/light as austenite transforms back to ferrite in the cementite/pearlite mix (causes a light on the blade). Once again, good we just need to separate the Currie point from the equation. It begins at Ar3, or Accm and ends with Ar1, in the case of pearlite formation. It is also worth noting that Ar temps will be lower than Ac temps and that is why the need for separate designations.

* Pearlite: A matrix of cementite and plain ferrite in microscopic platelets - more ductile than cementite alone. Created by allowing austenite to cool over minutes or hours (depending on the steel composition). Yep. But there are degrees of spacing of the platelets (lamellae)based upon the rate of cooling, seconds- fine pearlite, minutes coarse pearlite.

* Bainite: Created by cooling austenite a little faster than for making pearlite - but still going through the "nose" of a phase transformation diagram. I imagine bainite as a matrix of martensitic crystals and pearlite. Bainite is actually a phase all to itself with characteristics of both martensite and pearlite, there are two types- upper or feathery bainite, and lower or lath bainite. This is only relevant due to the time and temp needed for each. Upper takes little time at high temps, while lower takes much time at lower temps.

* Martensite: Created by cooling quickly in front of the "nose" on a phase transformation diagram - a second or two or less depending on the steel composition. With air hardening steels like D2 this apparently can be many seconds. Martensite is composed of oriented needle-like crystal structures that have captured excess carbon atoms from the austenite into room temperature crystals. Brittle but very hard. That is basically it.

* Grain: All of the above form crystal grains - if the grains are allowed to grow large (course) the resulting steel will break more easily - one thing I've gleaned from this thread is that if the grains are refined to a /very/ fine size it impedes hardenability due to pearlite forming readily along grain boundaries. Yep

Processes:

* Normalizing: Used for quick stress relief and grain size control. Heat comfortably above Ac3 (you mentioned 1600 as the high end) - let austenite form - then (for steels like 1084 or 5160) air-cool past A1. Repeat a 2nd or 3rd time to ensure even grain reduction - each time at a lower austenite temp. This produces pearlite, right? Not always pearlite but the idea is uniform structures and strains so good enough.

* Annealing: Used to fully soften steel for machinability and also reduces grain size. Heat to /barely/ above Ac3 and cool very slowly. Also produces pearlite, correct? Correct, except it is best done with steels below .8% carbon, for higher carbon contents the pearlitic condition can be problematic and that is where you do...

* Spheroidized annealing: I have not looked into this... In alloys above .8% it is best to keep the anneal subcritical and ball the carbide into little spheres instead of lamellae, this will keep it from tearing up tooling and keep it out of the grain boundaries.

* Hardening: Produce as much martensite as you can.

* Tempering: Heat to 400f + or - depending on the steel - leave it there for hour(s) and pearlite forms on the martensite grain boundaries - which reduces brittleness while retaining the hardness of the martensite. A little rough on this one, but tempering is the least understood by most folks... Pearlite forms at around 1000F and you don't ever want it in the steel you want martensitic. It starts at around 250F but doesn't have any effect noticeable to us until 350F, when enough carbon has slipped out of solution to form incredibly small (need an electron microscope) tempering carbides withing the martensite. We work withing the range of 350F to 500F for most bladesmithing steels.

... that's my state of knowledge - probably what I need most is more practice/experience... any corrections &/or suggestions are much appreciated! Well you did ask for it <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />. I applaud you for what you have already picked up but more importantly for your desire to know more. It is much more productive than the common approach of declaring in-depth knowledge of our medium unnecessary egghead gibberish and then proceeding to make things up as we go based on assumption and wishful thinking. Steel doesn't give a rip about our wishes or even the name of the smith working it, it will do what the laws of physics and chemistry dictates regardless of our ideas.

Michael Kemp

p.s. And here I spent hours organizing these thoughts when I was *supposed* to be cutting code - or maybe sneaking down to the knife shop - but it's helped coalesce my state of knowledge.

Kevin:

Thank you for your expert guidance and the time that you devote to helping all of us.

Kevin - MUCH obliged... those corrections/clarifications are very clear. Thank you thank you thank you!

and to coin a phrase - the proof's in the pudding. Practice practice practice. Test test test.

Michael Kemp

Kevin, thank you. You are the man. Great reply's and clarifications. I am glad we have someone with your expertise to help us sort all this out.

Brion

Wow....I will have to read this thread a few times to absorb all the content and knowledge! A HUGE thank you to all involved for sharing the vast amount of knowledge contained within this thread! Makes me realize how "green" i really am....

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Wow....I will have to read this thread a few times to absorb all the content and knowledge! A HUGE thank you to all involved for sharing the vast amount of knowledge contained within this thread! Makes me realize how "green" i really am....

Glad to see you made it here! In my opinion the "green" phase for makers has traditionally been a little longer than necessarry due to adherence to recipes, which I believe could be an artifact left from the old guild apprentice systems. The master would tell the apprentice "you do this exactly this way with no deviation or it won't work",

"But why do we do it that way?"...

WHACK!, "You don't need to know that (meaning- I myself don't know), now do it 100 times to be certain you do it exactly as I showed you".

I believe the craft is overdue for a paradigm shift, since we can't actually have apprentices living with us to sweep the shop floor for years anymore, and this is why I always try to give the why's of it. I may sound like a broken record but instead of recipes I prefer to supply people with tools, in the form of information, that will allow them to write their own recipes and not be limited to rigidly following the ones given to them.