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+--- Thread: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven (/showthread.php?tid=70)
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - me2 - 01-17-2018
Mr Jan, I'm not sure what you mean by the last paragraph?
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - Jan - 01-17-2018
Me2, thanks for your explanatory comment.
Prof. Verhoven was aware of the problem with the volume fraction, because on the same page where he defines volume fracture he writes a footnote comment "Strictly speaking this formula gives weight fraction ferrite." (In my copy page 22). For me it means, that strictly speaking all estimates based on the Fe-C diagrams are expressed in weight % C.
It is not difficult to calculate that pure cementite contains some 6.7 weight % C*, but it is difficult to calculate volume % C. I am not quite sure how to do it.
Jan
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* Cementite has a formula Fe3C, atomic weight of Fe is 56 while atomic weight of C is 12.
Hence the Weight % C = 12 / (3*56 + 12) = 0.067 i.e. 6.7%.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - Mark Reich - 01-17-2018
(01-16-2018, 11:04 AM)me2 Wrote: Carbide volume fraction is a way to measure how much carbide is in a steel. So if you have 100 cubic inches of steel and a volume fraction of 5%, then 5 cubic inches is carbide all mixed up in little tiny bits.
These carbides are the same as those in hardened steel. This is where the phase diagrams come in handy. In a simple steel like 1095, the carbide is Fe3C, iron carbide, or cementite, all are the same. It is present at room temperature in annealed 1095 steel, at about 15% volume fraction. When heated for hardening, it will typically have 2% to 5% volume fraction. These are the same carbides as at room temperature, and when quenched they are still the same. The phase diagram can be used to calculate volume fraction. Carbides can be bigger or smaller, it depends on temperatures used.
From the little I think I may know, I assume the reason for the drop in carbide percentage between annealed 1095 and hardened 1095 is because at austenitizing temp the carbon atoms leave the big clumps of carbides, and are free to roam about and create hardened steel upon quenching... right?
I presented this before reading the posts that came after this post by Mr. Me2.
I really don't have much comprehension of such studious posts as your's, Mr Jan. I'm sorry, you're just way beyond what bladesmiths need to understand.
I only know that martensite has a larger volume than the unhardened version, which may be pearlite and/or cementite with retained austenite...
My simplified explanation to that statement would be that at room temp, unhardened phase, the Fe atoms and C atoms mainly separate, with most of the C atoms clumping together in carbides.
After full austenization and Quenching, the C atoms have been free to move around amidst the Fe atoms, then, when quenched, the C atoms are "frozen" in place, and lock the Fe atoms in place, with the resulting phase becoming martensite.
If that's basically accurate, it might be understandable that atoms mixed and... (I don't know a term for) "frozen" or "locked" in place, upon quenching, would create more volume than when in a natural relaxed phase.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - Mark Reich - 01-17-2018
If I have explained this more than less accurately, with simplified jargon and comprehension, it is because I have read Dr. Verhoeven's work pertaining to bladesmithing.
I still need to have it simplified to such a degree that I could present this to a non-bladesmith level, and be more or less understood.
In this case, "carbide volume fraction" might have some meaning to me. I would take it to represent how much carbon has been released from the carbides, and is now in martensitic form, with C atoms dispersed between Fe atoms, locking them in place.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - me2 - 01-17-2018
Mark, yes exactly. If you have a look at the iron-carbon diagram on page 20, you can see on the left side near room temperature that ferrite, or alpha, can only dissolve a tiny amount of carbon, 0.02% maximum at higher temperatures. So, that carbon has to go somewhere, and it combines chemically with iron to form cementite, Fe3C, iron carbide, different names for the same thing.
Once you start to heat the steel to harden it and cross into the austenizing temperatures, the Fe3C can dissolve into the austenite and the carbon is free to move around. Now, with steels with more than about 0.8% carbon, not all the cementite dissolves at once, and you can choose, within limits, how much you want based on the temperature you heat to before quenching. It is this "undissolved" carbide that has such a large influence on wear resistance and toughness in steels. The difference in wear resistance between 1095 and 1075 at the same hardness is due to the presence of these undissolved carbides in the 1095 and not present in 1075.
Mr. Jan, you are correct. However, the difference between the density of alpha iron (ferrite) and cementite is only about 3%, so volume percent carbide and weight percent carbide are close enough for most purposes. This was a source of confusion for me when I started looking into steels, as the two were used without that explanation. It's so common that it took some real digging to find an acceptable reason to look at a weight percent graph and get volume percent carbide.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - Mark Reich - 01-17-2018
Well, great Thanks to you, Mr. Me2. You have had quite an influence on my relative understanding of phase diagrams and composition of steel in different phases, over the years.
Yes, I have been listening for years.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - me2 - 01-17-2018
Mr. Mark, that is a great compliment and I thank you. My other occupation has taken on some teaching, and at least I know my ham fisted attempts at teaching can get through to people who want to learn. I have a long way to go in that endeavor.
It is important that the scholarly work explain and match up with the observed behavior, otherwise, what's the point? It's also handy to have as much understanding of the theory as possible, as it minimizes dead ends and trial and error work, and we only have so much time to pursue improvement.
"My simplified explanation to that statement would be that at room temp, unhardened phase, the Fe atoms and C atoms mainly separate, with most of the C atoms clumping together in carbides."
That's a handy way to look at it. In steel, carbon is what is known as an interstitial element. That means it fits between the iron atoms. Carbon has only two places to go in steel. It fits between the iron atoms, which is to say it dissolves in the iron. Or, it combines with the iron to form a chemical bond and makes carbides. The arrangement of atoms in ferrite, or alpha iron, doesn't have much space between the atoms to put carbon, so it can't all go there. The only other place it can go is to chemically combine with iron to form cementite.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - me2 - 01-17-2018
(01-17-2018, 12:13 PM)Mark Reich Wrote: If I have explained this more than less accurately, with simplified jargon and comprehension, it is because I have read Dr. Verhoeven's work pertaining to bladesmithing.
I still need to have it simplified to such a degree that I could present this to a non-bladesmith level, and be more or less understood.
In this case, "carbide volume fraction" might have some meaning to me. I would take it to represent how much carbon has been released from the carbides, and is now in martensitic form, with C atoms dispersed between Fe atoms, locking them in place.
A good analogy I have found for carbides in steel is one for fruit in Jello. The fruit bits are the iron carbide and the Jello is the steel. Here we can have a whole grape in the jello, or we can have that grape chopped into little cubes. Either way the fruit volume fraction in Jello is the same.
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - Mark Reich - 01-17-2018
Yes, Mr. Me2, the Jello-fuit salad analogy is one I remember, and have found helpful. Perhaps I've finally moved on to a slightly more advanced understanding, which I'm just now realizing.
Not ready to take the training wheels off or anything, but with kind and thoughtful guidance from conscientious teaching, it's beginning to take on meaning I can use to ask better questions. This is encouraging, and I am beholding to you for not giving up on me! I recognize it has taken steady effort on your part, which induces me to try harder, with more patience, instead of dismissing it as overwhelming.
Perhaps in time, I will have greater comprehension of Mr. Jan's mathematical analysis. At least I'm hopeful, as I very much appreciate the perfection of mathematical diagnosis.
Thank you, Gentlemen!
RE: Metallurgy of Steel for Bladesmiths- Dr. Verhoeven - me2 - 01-17-2018
You seem a bit like one of my childhood friends. He is convinced calculus is beyond him. However, I've had him do calculus. I just didn't tell him that's what he's doing.
Tomorrow I'll beable to dog into this some more, but I have a project due first.