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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
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#1
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Normalizing after stock removal?
Should steel be normalized after stock removal? In other words, will steel that comes from the factory, already annealed, and then ground into a blade, suffer some form of grain growth from the grinding, that would benefit from the normalizing cycle(s), before heat treating?
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#2
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There will be induced strain from the coarser grinding belts, and if you have a tendency to turn the steel blue (as we all do some times ) , you just might get some affect during the heating to quench (austenization). Nothing you do below around 1350F or higher (quite a bit higher) will grow grains. Induced strain can affect how the grains will recrystalize when that temp is reached, but if your grinding was even ...
Normalizing, I think, could be overkill after the grinding. If you are really worried about it, a quick stress revlieving operation could be in order. Just heat to around 1000F and let it air cool. This should zap much of that residual strain. If you wanted to play with different grain refining techniques (normalizing) I personally would do it to the raw bar, before the grinding and then spheroidize. But then this could be easier said than done depending upon your alloy. |
#3
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Thanks Kevin, appreciate your input on this!
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#4
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Quote:
Quote:
__________________ ~Andrew W. "NT Cough'n Monkey" Petkus |
#5
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Long complex annealing (like speroidizing) on richer alloys can tie up carbon and necessitate longer soak times, but simple lamellar anneals that can be used on shallow hardening steels don't affect things that much at all. Lamellar pearlite, particularly the fine stuff goes, into solution rather quickly.
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#6
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Is a lamellar anneal the sub-critical one? That's basically just tempered as much as it can be to make it fairly soft, right?
__________________ ~Andrew W. "NT Cough'n Monkey" Petkus |
#7
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The lameller type annealing is the stuff that most bladesmiths do, that is, heat to nonmagnetic and then stuff in wood ashes or vermiculite. The subcritical operations would include spheroidizing. What it comes down to is if you go above critical and form austenite, that austenite will tranform into either coarse or fine pearlite (depending on the rate of cooling) when it cools. If you stay just below critical and do not form austenite the carbides will start to "pool' up. Above 900F, this will form spheroidal cementite, and the previous austenite grains will be untouched if it stays below 1350F, but it will take a longer soak to pull such widely seperated carbon back into solution.
In very general terms: 350F-800F= tempering, 800F-1000F=stress relieving, 900F-1325F= spheroidizing. Last edited by Kevin R. Cashen; 07-04-2004 at 06:09 PM. |
#8
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Ok, I think I got it, thanks.
__________________ ~Andrew W. "NT Cough'n Monkey" Petkus |
#9
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I guess what I need here is a deffination of spheroidizing in laymens terms.
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#10
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Found this, Robert:
Spheroidizing is a process in which most plain carbon steel are heated to 750 to 760 0C for one to four hours and slowly cooled in the furnace. (Higher spheroiding temperature is used for other alloys.) When the materials is subjected to spheroiding treatment, round or globular form of carbide is produced within the microstructure. Carbides are phases in the steel that are very hard. Many tool steels are subjected to spheroidizing treatment in order to improve their machinability. http://www.eng.ku.ac.th/~mat/MatDB/M.../treatment.htm - Jim |
#11
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Robert,
In real simple terms, here's what's going on. Steel in the simplest form is a combination of iron and carbon. In its softened state, the base is a matrix composed of simple iron molecules (ferrite), in which are suspended molecules of iron carbide (cementite) As Kevin stated, if you stay below what we bladesmiths call "critical", and do not form austenite, then the carbides will begin to pool up together into little globules (or spheres), hence the name. What this does is leave larger spaces (or areas) of the softer ferrite. That's why the spheroidized steels are easier to grind, drill, file, sand, etc. |
#12
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Great! Thanks guys! I also re-read Kevins great sword making tutorial real quick and found this:
"What this speroidal anneal does is causes the cementite (carbon) in the steel to gather together into an evenly dispersed collection of spheroidal globs. In this state the carbon is not interacting with the iron to give me any grief from stress or hardness and the metal will be very easy to machine, grind or shape. " So now, between the three of you guys, plus Fitz's PM, I'm up to speed! Many thanks! |
#13
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With the steels that I work with I have found spheroidizing to give the softest condition in the steel of any treament. It is always neccesarry for me to switch indenters and go to the "B" scale to get a rockwell reading from the stuff. Little spheres in a soft ferrite matrix move around a whole lot easier than layers or sheets of cementite and ferrite (as in pearlite). In fact I have become convinced that I do not get the life out of my zirconia belts that I could, because the speroidized material just doesn't fracture the particles as well. I have noticed a difference on harder forms.
You can spheroidize by holding at a temp below 1350F long enough for the carbon to ball up. There is another way that I have used, that is common in industry, in which the steel is heated just a hair above 1350F and held for a short time to let the carbides disolve and then the work is cooled VERY slowly through the transformation range causing the stuff to really ball up. This also does not affect austenite grain in any way and produces the most spheroidal condition, but is also involves more decarburization and requires very good temperature controls. HEY! I have never posted this often to any thread on CKD . It think this forum is going to be a very good thing! |
#14
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Annealing and Normalizing
There are some things about the iron-carbon phase diagram that appear to be misunderstood by a lot of people. First, no molecules in metals. Metals form crystals, not molecules, and the crystals are made of metallic atoms or alloy atoms. Second, austenite forms over a range of temperatures. Only at the eutectoid composition (.78% carbon) does it form at exactly 1333F. At all other carbon levels it forms over a temperature range that is up to 150 degrees hotter than the Curie (non-magnetic) point. Third, ferrite has a very low solublity for carbon. If you do not fully austenitize the steel, the carbides will not totally dissolve. Annealing at a temperature BELOW the fully austenitic temperature relies on DIFFUSION of carbon which is very slow at that temperature. Annealing ABOVE the fully austenitic temperature allows the carbon to dissolve into the austenite and diffuse more rapidly due to the slightly larger inter-atomic distance of face-center cubic austenite. I think there was a few more points I saw in the previous posts but, mercifully, I have forgotten them and will shut my cake hole now...........
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#15
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Quenchcrack,
For goodness sake, DON'T shut your cake hole. Yes, I remember from another discussion that I was not actively a part of, the point being brought up that with steel we are dealing with crystals and not molecules. Shoot man, I have no problem being corrected, and in fact am grateful for it. When I participate in threads, I am not presenting the information as an expert, but rather as a layman who is explaining things as best I understand them. So I am not offended at all when corrected. I believe that you will find about 999 out of 1000 members here will have the same attitude. We're all in this together, with varying degrees of understanding and expertise. By being corrected, we all benefit. Let the discussions resume! |
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blade, forge, forging, knife, knives |
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