20CRMnNi Steel for Gears

[winchengr]

Have been told this is equal or better than 8620 for gears which have hardness of RC 58-62.

Can anyone comment on this? Chemicals are quite different. The 20CR material shows no Moly and the Ni and Cr are a lot lower than 8620.

 

[TVP]

Are you sure that the designation is correct? None of my references show a grade 20CrMnNi.

 

[winchengr]

Sorry, I should have indicated that this material has been quoted as an alternate by a China manufacturer.

They are saying it is equal or better than 8620 for gears. My concerns are the differences in chemicals and whether or not it can be carburized to RC58-62, depth of .020 to .030 as specified on current gears.

Here is the chemical certification for 20CrMnNi:
.19 C, .27 Si, .89 Mn, .017 P, .004 S, .02 Ni, 1.017 Cr, .029 Cu, and no Mo.

Thanks for the reply.

 

[lgearhart]

Winchengr, the 58-62 Rc surface hardness, along with the 20 to 30 mil case depth to HRC 50 is dependent on the carburizing practice. Any decent carburizing house will be able to do that. The main reason to use different steels comes from what properties you want in the core. Your heat treater should be able to comment on that.

More than composition comes into play when you talk about steels that are "equal or better". Amount of wrought processing, grain size, surface condition, etc all are things that figure into whether one LOT of steel might be as good as, or better, than another LOT of steel.

Another comment I have is that your composition doesn't SEEM right. You'd think that a designation of "20CrMnNi" would have some nickel content. Your 0.02 % is a residual amount- i.e., the amount I would expect to find in a steel that does not have any nickel specified.

 

[Flesh]

The steel chemistry you provided is bascially a AISI 5120H chromium carburizing steel. This is a medium strength (core), and wear resistant steel (when carburized). The AISI 8620 material is a high strength (core), and wear resistant steel (carburized). Carburizing to a hardness of >58 is not a problem. The main difference between the two is core strength, and so, I would not say they are equivalent. However, if a hard wear resistant layer is your primary concern, then the alternate material should be fine since carbon is the potent hardening element.

 

[TVP]

winchengr,

The chemical composition that you provided equates to grade 20CrMn according to the Chinese standard GB 3077. There is no 20CrMnNi designation. As lgearhart and Flesh have pointed out, there are other factors to consider when determining the proper steel grade, such as core hardness/strength, toughness, etc. The equivalent Chinese grade to SAE 8620 is 20CrNiMo according to GB 3077.

 

[winchengr]

Have received another matl composition of material and it say the material is 20CrMnTi with following chemicals:
.21 C, .26 Si, .93 Mn, .04 S, .11P, 12.2 Cr, .5 Ni, .15 Cu, .7 Ti. The 12.2 Cr must have a displaced decimal point?

They are saying that 20CrNiMo is available only in large qtys and want to substitute the 20CrMnTi or whaterever it is??

Since 8620 contains Moly and this material does not, wouldn't this affect the gear life if not other characteristics vs. 8620?

 

[Carburize]

Provided the heat treat facility can get the required case depth, case hardness and core hardness along and the base material meets the other metallurgical quality criterial listed in documents such as AGMA 923 or ISO 6336-5 - the rating numbers will still be valid.