Contact strength of 50Mn chinese steel (AISI 1045 equivalent)

[pharcycle]

Dear all,

We're designing a machine that will implement a slewing gear. NBC who are going to make it for us in china say the material is 50Mn, similar to the AISI 1045 steel commonly used in europe. I'm going through the gear calcs to BS-ISO 6336 and I've managed to get most of the important properties of the steel from the manufacturers (fatigue limit, uts) but i need the maximum allowable contact strength of the material which i can't seem to get from them or online!

The steel would be in its normalised state as they say it would be too large to harden without warpage issues and most ofthe material data for gears assumes that you'll be hardening the teeth.

Does anyone have a ball-park figure of the contact endurance limit for this steel? I get a contact factor of safety of unity assuming 500 N/mm2 as my endurance limit but i'm not sure if this is reasonable.

Regards.
David

 

[TVP]

Allowable contact stress should be > 500 MPa for this grade in the normalized condition. Figure 8 from AGMA C2001 shows a graph of allowable contact stress vs. Brinell hardness for through hardened steel gears, with contact stress ~ 80-90 ksi (550-620 MPa) for 180-200 HB, which is where this grade should be after normalizing.