I have no experience with cryogenic "tempering" but have been offered access to the process and would like to see if it will have any beneficial effects in the following application:
The part in question is a pin 0.55" diameter x 4.5" long. It is part of a roller bearing cage assy in a large (about 40" diameter) thrust bearing with 40 radially arranged tapered rollers. The pins serve as "axles" that pass through axial holes in each roller and hold them in their assigned position within the cage/roller assy.
The pins are made of 4140Q&T material (120ksi yield) that has been induction hardened to yield a surface hardness of about 53-55RC or 8620 case carburized material hardened to about 57-60RC. Both methods have proven acceptable. The rollers spin at about 2000rpm and there is circulating ISO150 gear lube present.
Pin wear and fatigue strength are the primary factors of concern. On paper, the load should be constant, but the bearing is in a rock crusher and everything is subject to high vibratory and impact loading. Fatige failures of pins have been a problem in the past. The current pins have good fatigue life that I attribute at least in part to the ductile core and hardened surface. Through-hardened pins have not performed as well.
Is Cryogenic tempering likely to be an improved substitute for surface hardening treatments in this type of application and will the part be any more brittle than other through-hardened methods?
The part in question is a pin 0.55" diameter x 4.5" long. It is part of a roller bearing cage assy in a large (about 40" diameter) thrust bearing with 40 radially arranged tapered rollers. The pins serve as "axles" that pass through axial holes in each roller and hold them in their assigned position within the cage/roller assy.
The pins are made of 4140Q&T material (120ksi yield) that has been induction hardened to yield a surface hardness of about 53-55RC or 8620 case carburized material hardened to about 57-60RC. Both methods have proven acceptable. The rollers spin at about 2000rpm and there is circulating ISO150 gear lube present.
Pin wear and fatigue strength are the primary factors of concern. On paper, the load should be constant, but the bearing is in a rock crusher and everything is subject to high vibratory and impact loading. Fatige failures of pins have been a problem in the past. The current pins have good fatigue life that I attribute at least in part to the ductile core and hardened surface. Through-hardened pins have not performed as well.
Is Cryogenic tempering likely to be an improved substitute for surface hardening treatments in this type of application and will the part be any more brittle than other through-hardened methods?