I have an ASTM A311-04 1.25" diameter round 1050 steel bar that exhibits a tensile strength reading of 155,227 PSI. Normally, we receive material in the 13-133,000 PSI range. The bar is machined to a 5/8-18 UNF thread.
We have experienced instances where the threads of these machined parts get damaged when installing a prevailing torque nut. The nut is hand tightened and then driven tight with a pneumatic gun. Threads are being cracked off from the shaft during the installation of the prevailing torque nuts. This is a new phenomenon and seems to be centered around threads machined in steel that has this "high" tensile strength (155,227 PSI). The nuts and assembly process have been ruled out as root cause.
Could the material tensile strength create a situation where the threads become susceptible to damage? In tests, it appears as though the threads are being pulled off the shaft and getting embedded in the threads of the nut. The hardness is 33 HRC if that is of interest.