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gmm22
05-25-2008, 10:08 PM
I would like to make some small fastener like components from tool steel. Even after reading a bit, I am still confused about air hardening tool steel. The things I want to make and harden are round, 5/32" diameter or smaller, and 5/8" long.

I would be grateful for advice on whether to go with O1 or A2. Both will be overspec., but I want to go the steel that is more forgiving in hardening and tempering. A few simple steps to harden and temper such small pieces would be greatly appreciated.

Evan
05-25-2008, 10:25 PM
Use 1040 carbon steel instead. It machines well and hardens up nicely by heating to red and quenching in water. It can be drawn back in the kitchen oven or a toaster oven or by just playing a propane torch on it.

wierdscience
05-26-2008, 09:44 PM
A-2 much easier,heat until a magnet won't stick,then soak at that temp for a few minutes,remove from heat and blast it with dry compressed air,Finishes out at 65-67rc,draw down to whatever hardness you need in the kitchen oven.

x39
05-26-2008, 09:57 PM
I'm with wierd, A-2 is really a very nice steel to work with in every respect.

juergenwt
05-27-2008, 01:13 AM
Use O-1. A-2 is a good steel but you have to heat it to 1750 deg F. and draw at 450 to about 60RC. It does not go to 67 RC.

O-1 is much more forgiving. Since you have small parts, heat to a cherry red (1450 deg.) and quench in oil. Clean up with emery and draw to light brown using a propane torch. Result - about 59-61 RC. You can easy get to cherry red with a propane torch. With O-1 you can draw to any desired hardness down to blue - near spring temper. You can also draw some areas to any hardness you desire, like having the end drawn blue and the tip light brown. Experiment!!!

gmm22
05-27-2008, 10:02 AM
Thanks for the interesting and very beneficial replies.

Evan
05-27-2008, 10:56 AM
A basic rule of thumb re hardening steel:

Straight carbon steels may be hardened by water quenching if they contain sufficient carbon. The amount of carbon is indicated by the last two numbers in the type designation. 1018 steel contains 0.18 percent carbon which isn't enough to produce significant hardening. Any carbon steel that contains more than about .20 % will harden to a degree that depends on the amount of carbon. 1040 steel contains .4% carbon and hardens well. 1090 steel hardens to the extreme and is used for spring steel.

Alloy steels are usually designated by the first two numbers being something other than 10. They are usually air or oil hardening as a water quench is too abrupt and will produce cracking and/or serious distortion.

The most easily machined and one of the toughest of the tool steels is O6 tool steel. It has a machinability rating of 120% compared to O1. It is ideal for making small parts and gives a beautiful finish with ordinary HSS tooling.

bhjones
05-29-2008, 03:45 PM
Evan, could you elaborate on what the machinability ratings mean. I've noticed this rating in various places and I'm like to better understand it.

Thanks.



The most easily machined and one of the toughest of the tool steels is O6 tool steel. It has a machinability rating of 120% compared to O1. It is ideal for making small parts and gives a beautiful finish with ordinary HSS tooling.

Evan
05-29-2008, 04:10 PM
Machinability ratings are only useful for comparing like to like, as in tool steel to tool steel. I don't actually know what criteria are used to derive the ratings and they must differ depending on the class of material. Aluminum alloys have very different properties than steel alloys and so machinability ratings in the aluminum alloy ranges will be based on different criteria than for tool steel.

The rating is referred to what is considered the "standard" of machinability within the group. Again, I don't know who makes that choice. Machinability ratings cannot be compared between different metals. The ratings for bronze cannot be compared to the ratings for aluminum or steel. They are only an indicator within a particular group of similar materials. I do find them to be fairly accurate for most materials.

juergenwt
05-30-2008, 12:40 AM
Evan - you are absolutely right about O-6 being easy to machine and to harden. One question: gmm2 is making small parts - can you get O-6 in drill rod size?
We us O-6 for draw dies and wear plates. It has that "slick" feeling. Also good for plug gages etc. . O-1 is readily available and cheap in all sizes and keeps a sharp edge when hardened and drawn to light brown (approx. 59-61 Rc.) For gen. purpose tooling I prefer O-1.

Evan
05-30-2008, 12:54 AM
I bought a 1/2" x three foot stick of O6 some time ago. I ordered it from our local supplier and they had no trouble obtaining some.

The reason it's so nice to machine is that it has free graphite at the crystal boundaries. It acts as a lubricant much like lead does in free machining steel but of course doesn't have the negative implications.

bhjones
05-30-2008, 01:39 AM
Using the O6 at 120% compared to O1 example, is the O1 the material at 0% (baseline)?


Machinability ratings are only useful for comparing like to like, as in tool steel to tool steel. I don't actually know what criteria are used to derive the ratings and they must differ depending on the class of material. Aluminum alloys have very different properties than steel alloys and so machinability ratings in the aluminum alloy ranges will be based on different criteria than for tool steel.

The rating is referred to what is considered the "standard" of machinability within the group. Again, I don't know who makes that choice. Machinability ratings cannot be compared between different metals. The ratings for bronze cannot be compared to the ratings for aluminum or steel. They are only an indicator within a particular group of similar materials. I do find them to be fairly accurate for most materials.

Philip Bayer
05-30-2008, 05:37 AM
I make components for pocket watches, which are obviously quite small. I use O-1 drill rod, and have fairly good success with it. It machines nicely and is fairly easy to polish, harden and temper.

I am a novice hobbyist, so I would defer to the pros, but I especially like the O-1 rod since it is available in metric diameters and the set of collets to my watchmakers lathe are metric, so it makes things a bit easier in that respect.

Philip

Evan
05-30-2008, 06:30 AM
Using the O6 at 120% compared to O1 example, is the O1 the material at 0% (baseline)?

No, the O1 is 100% machinability. Harder to machine is less than that and easier is greater. It seems to be that they use the most common/popular material as the reference material. I also think that the scale is pretty subjective and depends a lot on your equipment and experience.

For instance, I don't hesitate to do hard machining of something like a bearing seat, even with an interrupted cut. It isn't going to hurt the spindle bearings on the SB9 since they are plane journal bearings and if it trashes the tool I just regrind it since I use a solid carbide stick and have a handy 10" diamond wheel.

(BTW, bicycle hub bearing seats are hard)

wierdscience
05-30-2008, 08:05 AM
Use O-1. A-2 is a good steel but you have to heat it to 1750 deg F. and draw at 450 to about 60RC. It does not go to 67 RC.



Hardness as hardened is 65-67 before drawing,WORKING HARDNESS is 62 on down depending on draw temp.But that's according to which mfg you ask.One says draw at 400f to 62 and another says draw at 300f to 62.Which one is right,probably both:D

Mcruff
05-30-2008, 09:25 AM
If I remember right W-1 tool steel is the baseline for machining in my Carpenter tool steel book. All other steels are graded for comparison from it.

Evan
05-30-2008, 09:33 AM
Could well be. I haven't looked up any of this and am operating strictly from memory. Whichever it is I don't think there is any particular "scientific" reason for the choice. In my opinion, I would pick the most machinable and set that as 100% with all the others grades being equal or lower. It's a bit of an oxymoron to have a machinability that is greater than 100%. What does it do, machine itself?

JCHannum
05-30-2008, 10:03 AM
From information in several steel and alloy catalogs, it appears that machinability for steel is based on 1212 or 1112 as 100%, while tool steels are based on 1% carbon steel as 100%, which is about 60% machinable compared to 1212.

Brass is based on 360 free machining brass rod as 100% and aluminum on 2011-T3 as 100%.

Swarf&Sparks
05-30-2008, 03:12 PM
Pardon my ignorance.
First I've heard of this "machinability" quotient.

Where do alloy steels (incolloy, hastelloy, 316 SS etc) fall in this scale?

How about Ti, Cu?
:confused:

Evan
05-30-2008, 07:40 PM
You won't find a machinability index for all alloys. The index can't be used even across all steels with any meaning. Superalloys such as hastelloy don't have much in common with other alloys so there isn't much to compare with that has any meaning.

Here is the mechanical properties entry on Matweb for O6 tool steel. Note the the yellow highlighted line:

http://vts.bc.ca/pics4/o6.jpg