20CrMnTi versus 20CrNiMo 1

[ATVextreme]

Working on an application for a CV axle. Material called out for the cage in the supplier print in the CV joint is 20CrMnTi. This material was said to be equal to SAE 8620. I believe SAE 8620 is equal to 20CrNiMo. The part is to be carburized to HRC 58-62. This is an aftermarket application where increased strength and toughness over OEM is the goal. I believe 8620 would have a higher core toughness than the specified 20CrMnTi because of the Ni and would handle impact loads better. I understand that 20CrMnTi is frequently used for OEM CV Joint race and cages. My question is would 20CrNiMo be stronger or tougher than 20CrMnTi with the same heat treat. I do not have access to spec sheets on either material. Thanks for any feedback in advance.

 

[dbooker630]

I think this material is more like 4120, it is not equivalent to 8620. At my company we restrict use of 4120 from severe driveline applications, sticking with 8620 instead. We converted some apps to the non-nickel grade back when nickel was over $20/lb, but the price until recently was below $10.

 

[TVP]

The answer to your question is a qualified yes. 20CrMnTi does not have a lot of alloying, and therefore will not produce a deep case or great core toughness. Alloys with Cr & Ni, like 8620 and 4120, and Cr-Ni-Mo alloys like 4320 will definitely have better core toughness, and better hardenability as well. Properties of case hardened parts depend a great deal upon the details, including carburizing temperature, austenitizing temperature (if different from carb T), presence of defects like IGO, NMTP, etc. 20CrMnTi processed in a vacuum furnace with high pressure gas quenching may have a hard, shallow case with essentially no defects, while a 4120 part processed using an atmosphere furnace and oil quenching may produce a deeper case, higher core toughness, but lots of surface IGO. Which one is better? It depends...