HR or CR 1144 Stressproof?

[Boiler Room Machine Works]

I am preparing to make a small, one-piece double throw crankshaft and planning to use 1144 Stressproof bar stock. Both HR and CR are available. Is there a significant difference in machining properties between HR 1144 Stressproof and CR 1144 Stressproof?
Tim

[Boucher]

I think it is all HR as the basic process, which is evidenced by the characteristic skin color. It can also bought with a ground finish that removes the color and produces the nominal size. It machines very nicely. I normally buy it with the bark on because it makes it easier to identify if the tag gets lost.

[lazlo]

Stressproof is cold-drawn AISI 1144 that's gone through a proprietary heat treatment to relieve the drawing stresses.
There's no such thing as hot roll stressproof.

http://www.niagaralasalle.com/pdf/stressproof.pdf

Note that 1144 is the AISI spec for cold drawn medium carbon steel. Stressproof is heat treated 1144, but not all 1144 is Stressproof.

[Boiler Room Machine Works]

Boucher and Lazlo,
Two companies offer "HR 1144 Stressproof" on their www. I sent RFQ's to both and followed up today with phone calls. Speaking with representatives from those two stores confirms what you say, regardless of what their site promotes.
Thank you. I sincerely appreciate the good help and clarification.
Tim

[lazlo]

Hi Tim,

That sounds like they're mixing and matching 1144 HR/CF with Stressproof.

If you look at Alro (just a random example), they show 1144 Hot Roll and Cold Rolled, but Stressproof is a seperate line item and is described correctly as heat treated cold-rolled steel:

http://www.alro.com/DIVSteel/MetalsGridCarbon_Bars.aspx

[Boiler Room Machine Works]

Yes. Alro is one of the stores that was contacted and the very helpful salesperson told me that Stressproof is CR, confirming your comments.
I was forgetting that Stressproof is based on ASTM A311 stds and was confusing their CR/HR 1144 catalog lines with Stressproof.
There are a couple of other web sites that have similar catalog lines which led me to think that there might be a HR option.
Thanks again for the help, Lazlo! CR Stressproof stock is scheduled to arrive here by tomorrow afternoon.
Tim

[Jpfalt]

Word of warning

In the past I have worked with stressproof. It isn't equally strong in all directions. The rolling process stretches out the grain along the length of the bar and the end product is very strong in tension along the length of the bar. However, it is also somewhat weak and brittle in tension across the diameter of the bar.

I once made some clamp pads that were parted off of a stressproof bar and when loaded they broke into pie shaped pieces with no distortion of the part surface.

In making a crankshaft, I suspect you will have some weakness at the throws on the crankshaft.

For a crankshaft, I'd use a 41L42 hot roll if it's available, because the stength of the material tends to be more equal in all directions.

The spec for tensile strenght across the grain is called transverse rupture and you usually need to specifically ask for the number to get it.

[Boiler Room Machine Works]

Jpfalt,
Thanks for that. It has been added to my shop notes.
The original crank on this project was turned from keystock and has held up very well. Using the stressproof on the duplicate should be OK but I will take extra caution to avoid machining sharp corners in the throws.
If a larger crank is made in the future, HR41L42 will be requested as you have recommended. I see that LaSalle makes it and it is also meets A311 stds.
Thank you for taking time to share the information.
Tim