About ETD-150|Elevated Temperature Drawn 150. LaSalle Steel's (now Niagara LaSalle) proprietary process applied to
4140-type chemistry. The '150' refers to 150 KSI minimum tensile strength. Pre-hardened to HRC 32+ with very low residual stress, so it holds size during machining and doesn't go goofy when you cut a keyway. Machinists love it. It cuts as easily as
1144 Stressproof but it's about 30% stronger. Selenium and sulfur are added to enhance machinability. The low stress means you can skip the stress-relieving step you'd normally do with 4140 pre-hard before nitriding or finish machining. Expensive (roughly 2x the cost of regular 4140) and only available in round bar. Not weldable. Compare to 4140 pre-hard (cheaper, might move during machining, needs stress relief),
1144 A311 CL-B (similar concept but lower strength), and Fatigue-Proof (even stronger ETD product at 175 KSI).
