Hougen mag drill with Broken Spindle

[Toolmaker51]

Sent PM with my spin and contact info..........the above suggestions are correct. "A-2" is primarily steel for punches and dies on lesser abrasive materials, "D" is very abrasion resistant, including grinding or resharpening a dieset. They like staying straight, can't picture them suitable for keyed or thread-relieved rotating parts. Chrome Moly Cr would be my choice; good enough for racing axles, so...... and machines nicely. Unsure regarding torque of a mag-drill and bigger annular cutters, some calculations x cross section might allow Stress Proof.
While different companies give the steels various 'names' the SAE-ASTM standards make the products very comparable. Most listings incorporate a conversion.