best steel to learn heat treating?

bladsmth said:
With 1095, you can pull your hair until you look like Aldo, and still may not get it right for a while.
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Not a pretty sight, folks...:D




bladsmth said:
With 1084, the eutectiod, it is a simple process of reaching the austenitization point, then cooling it down to the martensitic conversion point fast enough to avoid pearlite. As Kevin said - you either did or you didn't. Now that will teach you proper HT procedures.
Stacy
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Stacy, isn't 1084 hypereutectic? I thought just about anything above .65 or .7 was hypereutectic...:confused:
 
Well technically the 1084 we use is slightly hypereutectic since it has a fair amount of manganese. The iron carbon diagram shows .85 as the eutectoid point but that is for a simple iron carbon alloy with less than .3% manganese I believe. Increasing alloying elements decreases the percentage of carbon needed to reach the eutectoid point so in a steel with .5% manganese or more and a tad of silicon the eutectoid point is closer to .75% carbon. For all practical purposes the steel we know as 1084 acts like a eutectoid steel (though for some of the batches that have closer to .90% carbon I have to wonder). In any case, a soak time at temperature never hurts even a eutectoid steel and I get better results with 1084 with extended soak times at lower austenitizing temperatures to be sure all the carbon I want is in solution.
 
.83% carbon is the eutectoid. For an empirical study, 99.17% iron and .83% carbon is the true eutectoid steel. For practical forging steels, 1084 is the eutectoid.

What all this means in HT is the lowest point on the curve for HT. At .83% carbon, steel reaches solution at 1333F.If you heat it above this point and cool it down gradually,it will convert from the austenite formed above the solution point,into alternating layers of ferrite and cementite, as it crosses 1333F on the downswing. This structure is called pearlite.

Now,Heat 1084 to about 1500F and hold for enough time to make sure it is fully at that temp. Quench in a fast rate quenchant and (if all goes right) it will miss the pearlite nose, and convert into martensite, staring at around 450F. Because there is no shortage of carbon (hypo-eutectoid), the steel converts fully...prety much all at once....with no retained austenite.
Because there is no excess of carbon ( hyper-eutectoid), there is no problem with carbides needing enough time to get into solution and reform on cooling.

I posted a dance analogy a while back, I'll try and find it.
Found it:
The eutectoid point in steel is .83% carbon, so 1084 is eutectic steel.The critical point for eutectoid steel is the lowest on the curve. If you raise the carbon content ,or lower it ,the transformation point goes up. For most situations in HT of a blade, about 50-100F above this critical point is a good temperature to austenitize the steel. Most blade steels have a soak temperature from 1475F to 1525F.

Now, to complicate things, the carbon has a real square dance party when it is above the critical point. In the case of hypo-eutectoid steel it has to run from one partner to the next , because of all the available iron. In hyper-eutectoid steels, it has to play musical chairs, and if it can't find a chair ( too much carbon -too little iron) it just hangs out with the other carbon atoms over at the punch bowl. At the end of the dance, as the austenite cools below the transformation point the carbon gets to go home with the iron atoms it was dancing with. These lucky foursomes become Fe3C ( iron carbides) called cementite. The wallflower iron in the hypo eutectoid steel becomes ferrite, which can only be truly happy in Massachusetts and California. The carbon in hyper- eutectoid steel are all a bunch of swingers.The dancers go home in groups, and depending on how fast they leave (cool down at quench) the ones who mosey out to their cars become pearlite, the ones that stay and smoking cigarettes and chatting for hours become bainite, and the really hard core folks rush out and jump in their cars to beat the traffic and become martensite. So the steel usually becomes a mix of structures.

Back to real metallurgy:
To allow the carbon to completely diffuse in hypo-eutectoid steel, and for the carbides to dissolve in hyper-eutectoid steel, you have to hold (soak) the steel at the austenitizing temperature for a little while. About 5-10 minutes for simple carbon steel is enough. The temperature is lowered a bit as you move away from 1084, not because the transformation point is lower (it is higher), but because you will be giving it a little more time to get the carbon situated. Since grain growth occurs as a result of time and temperature, making the time longer necessitates lowering the temperature. So 1050 and 1095 are held for 5 minutes at 1475F and 1084 is held for one minute at 1525F.
Stacy



Stacy
 
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Thanks Guy and Stacy!

I knew all of this - I just couldn't remember the exact numbers... which of course calls into question everything I thought I knew!:D Guess it's time to got back and read Verhoeven - again.

Not sure where my wires got crossed, but I'm pretty sure I should have made that right turn back at Albuquerque!;)
 
Ok this is a lot to try to understand at once and i've spent a long time reading about all the different crystalline structures and such... phew, it makes a lot more sense now. I also came across this page which give a rough guide to identifying unknown types of steel, so in case anyone else is interested...
http://www.anvilfire.com/index.php?...thing and metalworking FAQ from anvilfire.com
Can someone who has done successful heat treats with 1084 give me a quick write-up of the steps you follow? i only need detail where it counts... mainly i would like to know
How you determine it is time to quench (time/color?), do you soak at all? what quenching medium you use, rough volume, and what temp it is at (room/warm/hot?), do you agitate it in the quenching medium? how long do you quench for? also do you let it cool to room temp before you temper or put it in the oven right when it comes out of the quench? how long and at what temp do you temper at?
 
Luke,
You still need to read and study some more, but here is a basic HT for a blade in 1084:

After the blade is finished forging/grinding/sanding, all holes are drilled, the blade is sanded to 400 grit, with a .030" edge -
NORMALIZE: Heat to 1600F and air cool. Repeat again if the blade was forged.
AUSTENITIZE: Heat to 1500F and hold for about one minute.1084 does not need to soak. This temperature can be estimated by using a magnet to determine the Currie point (about 1350F), and allowing the blade to heat up a bit more before the quench. Using a color to go by is useless unless you have established the color in your own location ( my red-orange may not be your red-orange). Avoid overheating. Far more blades are ruined by too high a temperature than those underhardened by too low a temperature.
QUENCH: Quench in fast oil ( parks #50 or similar), moving the blade back and forth from edge to spine ( in a cutting motion) to speed cooling. Leave in the tank until all sound and smoke have stopped ( about one minute).
TEMPER: Remove the blade, wipe it off with a rag, and check the edge with a file. If the file skates off like you were filing glass, it hardened right. Wash the blade with dish soap,dry it well, and place in an oven (kitchen oven is fine) at 450F for two hours. Take out, cool to room temperature, and put back in for another two hour bake. The blade is now fully hardened and tempered. Soak the blade in vinegar overnight to soften the scale.
Sand/grind the blade, dipping it in water often to keep it coo (if grinding), to finish the knife.
Stacy
 
bladsmth said:
... Using a color to go by is useless unless you have established the color in your own location ( my red-orange may not be your red-orange). Avoid overheating...
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While obviously I agree with Stacy, I would add that one can train their eye to their particular conditions in order to read temperature. I believe one smith telling another smith on the other side of the country how to read color is indeed an exercise in futility. However if you use the magnet in conjunction with watching the color under the same lighting conditions every time, you can use decalesence to recognise the shades of light in the blade to be more accurate in heating. The transformation we are looking for requires energy so when it begins it will use up energy at a greater rate than what you are putting into the steel jus to heat it, so there will be a lowering of incandescense coming from the steel to you. When you see a shadow or darker area in the steel the transformation has began there, the brighter area beyond this area is when it is complete. Continually checking with the magnet will confirm this.
 
Aldo Bruno said:
Hey, I resemble that remark!!
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You're beautiful, bro!

:barf::barf:


:D



In reference to Kevin's observation about color temperature, I'll add that I witnessed a group of smiths estimate the temperature in a forge (by eye) at a hammer-in I attended... none of them were within 150 degrees, and most (including myself) were off by 400!!!! I believe that one can train oneself to judge temperature by eye, but I have neither the time or the patience... I'm buying an oven, and hopefully soon!
 
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