1141 stress proof
What exactly does 'stress proof' mean ?
Stressproof is a trademark of LaSalle Steel Co.
It's basically their 1144 product with some cold working thrown in, if I recall correctly, or if I ever even knew.
As far as I know, it's just a fancy name for normalized. They run it through the appropriate processes to anneal/heat treat/normalize to eliminate the internal stresses in the material. It mainly used where you are turning sections that you don't want to warp or tweak over time. At the metallurgical level I'm sure there is a manufacturing process to ensure the grain is parallel to the direction of the shaft. I think Hardinge makes their machinable collets out of "stress proof".
All of LaSalle's stuff in that line, StressProof, FatigueProof, and ETD 150, are run with LaSalle's proprietary elevated temperature drawing process. They're not actually cold-drawn per se, so you don't tend to have the large hardness gradient near the surface like you have with normal CD stock. That hardness gradient and the resultant residual stress in CD stock is the primary cause of warping when you cut something like a flat along the length of a piece of round stock. With CD stock, your cutting doesn't cause stress, but rather relieves it by cutting away the most highly stressed material at the surface. This imbalance the allows the residual stress that was present in the bar all along to now push or pull the remainder into a warped or bowed condition.
Clean ETD stock will typically run closer to nominal size than run of the mill CD stock, and it will have a dark brown surface color instead of the lighter gray we normally associate with CD.
The cost difference between Stress Proof and normal CD 1144 can be noticable, depending on quantity. Definitely worth the difference on parts with assymetric features, but less so on concentric parts unless it happens to just be the customer spec'd material. Strength wise, both are right around 100ksi ultimate spec, but I've always found the ETD stock to have much less variation in hardness as compared to the average from-who-knows-where CD 1144.
Just as I suspected......
It mainly used where you are turning sections that you don't want to warp or tweak over time.
In case you're wondering, it's super nice stuff to work with.
Yeah it is nice stuff. Even ETD 150, which is a variation of 4140 with a hardness in the upper mid 30's will take a single pointed thread whose appearance will make you wonder if you're cutting 1212 screw stock.
Yes.....used it many times.
Have 6) 17" long shafts to make.....1" stock, various diameters down to 3/4 and 3 keyways along the length.
I 'reverse engineered' a worn out sample, and spec'd 12L14 on my drawing.
Then I got to thinking.....1144 is a better choice...
Needed to clarify the definition of 'stress proof'.....wondered if -possibly- it meant "more crack resistant" rather than the suspected meaning....
The only trouble I ever had with Stress Proof was highly loaded washers that retained something by means of a countersunk flat head screw. They would crack and pull off right over the screw.
Machines very nicely, but I'll give it low marks for toughness. We replaced all those washers with 4340 heat treated to about 35 Rc - none cracked.