On Thu, Apr 23, 2020 at 05:28 PM, Bill in OKC too wrote:
4140 is an ordinance (sic) steel
"...4140, also known as
ordnance steel, was one of the early high-alloy steels, used in 1920s' aircraft frames and automotive axles in addition to rifle barrels."
Ref:
Can be purchased annealed or pre-hardened (Heat Treated - 4140HT)? This common alloy is machinable in the Heat Treated condition. I use it often.
Raymond
