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11-03-2009, 11:51 AM #1
decarb free surface (what it it?)
I am buying some steel to make some parts and it is advertised as "decarb free." what does this mean, and what kind of surface can I expect from it?
"mill finish" or "polished and ground" is pretty clear to me, this term is not.
11-03-2009, 11:59 AM #2
Genearally apples to tool steel that was finished in a metal removal operation after thermal processing. I.E., a product that would not result in a soft skin during thermal processing at your plant.
"It had the bad stuff removed before they sold it to you"
11-03-2009, 12:04 PM #3
so the surface would be smooth and shiny, but not as uniform in diameter and overall straightness per foot as precision ground?
I suppose the metal removal processes of which you speak would make it machine more uniformly, too?
11-03-2009, 12:11 PM #4
You can get a piece of tool steel beautifully ground that will have a soft skin when heat treated because it was NOT decarb free.
I.E., you are missing the point.
Tool steel is for making things from that require heat treat. What it "looks like" when you buy it is not what you are paying for.
Many tool steels depend upon relatively high carbon content in order to perform (in heat treat) as expected. De Carb Free is an assurance of that performance right out to the as bought surface.
11-03-2009, 12:22 PM #5
The round stock I have bought as decarb free has not got a smooth ground surface. It has a surface that apparently has had a very coarse feed lathe tool turn it. The cuts are about 1/4" or so wide,like you took a cut over the surface with the fastest feed you could get.
They have just eliminated the outer,decaurberized surface with a very coarse cut. It is not suitable for use as a finished surface. There is extra diameter left so you can turn it down to a smooth finish of the nominal diameter.
I buy it to make punches and dies from.
11-03-2009, 12:24 PM #6
gotcha. I do need one of the parts hardened (at least the skin) so that is good. I am making a little offset cam to hold material against a die for a Di-Acro Bender that we have on our shop. It looks as though W1 would do the job, since this bender doesn't get major abuse and will only be bending something as hard as cold rolled mild steel at the most.
this is my first foray into using real tool steel for making parts instead of random things from the scrap bin, and I wanted to make sure I knew what I was ordering first.
11-03-2009, 12:48 PM #7
11-03-2009, 01:26 PM #8
I have access to some heat treat furnaces though a friend here at work. worst case, I could probably fake it in the small gas forge we have as long as I wrap it in stainless tool wrap with some CI chips. I guess I could also probably make a small "oven" with insulating fire brick and use the oxy/ace torch with a slightly carburizing flame to heat.
if I am lucky, it will be hard enough without hardening and I can save that step. If not, I have time to learn a little on the job. part is kind of non-critical (just a simple cam locking clamp), and hopefully won't warp too much when I heat treat/harden it.
11-03-2009, 06:27 PM #9
When I was an apprentice I had to learn how to run the decarburization machine.It was called a shaper.
11-03-2009, 08:04 PM #10
In "Ye Old Days", (long before I started), I understand that tool steel had a "Bark" that had been decarburized during processing. So if you wanted to make a punch that was to finish at 1 " diameter, you might use a bar of 1 1/2 inch stock, to make sure you got below the decarb layer, and into all clean steel. Old toolmakers told me that leaving any of the decarb layer was a sure recipe for a part that cracked after heat treating. Timken tool steel books from the 70's made quite a mention of the decarb free issue. Bottom line is... Present day decarb free tool steel will safely clean up at the listed dimension, with no decarb.
11-03-2009, 09:01 PM #11
decarb free means what it says, you havent lost the carbon out of the skin of the steel so when hardened it wont leave you with a soft layer [softer]
11-04-2009, 04:02 AM #12
W1 is the most treacherous steel there is to warp and crack during quenching. If you decide to use it,take fine steel wool and a flat nosed punch and a hammer. Stomp the holes in the part as tightly as you can with steel wool. this will keep the hole from cracking. They used to fill holes with clay,but with clay the walls of the hole don't harden,which isn't good if you need a hardened hole.
11-04-2009, 06:01 AM #13
im a total hack myself, but I do make some hardened parts. I think o-1 is pretty easy. very forgiving of my crapy "process control"
o-1 comes fairly cheap in ground flat stock or rounds. I heat it in a propane forge untill it glowing red-orange. (& not magnetic), then I swish part in bucket of oil. after that it should not be fileable. it it is, you didnt heat it hot enough. then i buff a section shiny and heat again untill it turns yellow-brown.
I think that o-1 operates fairly with much foregivness. it machines fair as-supplied. I think it's pretty much the easiest of choice to work with for the occasional user like me. but then, I have not tried the others. I dont keep a brine bath around. My oil-bucket is typically my used motor oil. I dont have tool wrap foil or a nice furnace. I have a propane weed buner and a dozen firebricks i stack into a box on my welding table. I do occasionally temper in my toaster oven, some will not quite get hot enough, some will.
11-05-2009, 02:03 PM #14
decarb free means the mill scale has been removed and taken to a nominal size.
for example if you buy .250" thick decarb free material it is ground to +.020"-.040" oversize.
this gives you stock to heat treat and then finish grind or whatever.
some steel suppliers can offer decarb free or plate with the decarb on it at a lower cost.
For example when I decarb plate for tool steel warehouses if i am going to ..250" thick the plate is starting out at approx 1/2" thick. This is about as thin as they can hot roll it.
Unless you have the means to hog a lot of material off you are best to buy decarb free.