Experience from 20CrMnTi 4

[DesignerH]

I have been proposed to use Chinese 20CrMnTi for a gear application. We have been using European material 34CrNiMo6 for a long time with good experience. The gears run only short times, but can be heavily overloaded due to the rough application. By changing material we expose ourselves to the danger that the new material is not durable enough. What is your experience with this material in your applications?

 

[CoryPad]

Do you induction harden or case carburize the existing gears? The proposed material would need to be case carburized. Case carburizing can produce essentially the same effective case depth for either alloy, which means similar wear resistance. The core hardness of the proposed material will be much lower than your current gears, which makes them less fatigue resistant and lower in overload strength.

 

[DesignerH]

I got some more on this material. What I am surprised of is that the properties are fairly good.
20CrMnTi China material
Rel 850 MPa
Rm 1100 MPa
HB 217
Elongation A[%] 10
Reduction of area R[%] 45
As I understand this is the base property without any Q and T after machining. If so this ought to be a good material. I have a memory that Rm and HB has a linear relation. Is this correct?

 

[TVP]

First, yes, there is a relation between R[sub]m[/sub] and hardness. Perform a google search of "equivalent hardness" or similar to find more information. Next, the properties that you list are achieved by quenching and tempering 20CrMnTi. These properties would be applicable for the core. This steel would need to be case hardened if it is used in a highly loaded gear. Hardness will be much higher just below the surface (0.8-1.8 mm typical), with a surface hardness of ~ 58-62 HRC (650-750 HV). HB is not appropriate for extremely hard sufaces because the ball can deform.

 

[Hamermm]

We have been having gear failure with gear and pinions of our small gear reducers (2083 ftlbs torque)using this 20CrMnTi but the larger gear boxs have not failed (38,000 ftlbs torque)

The design did not change only the steel and we have gearbox's still in service after 27 years of service with no wear to gears or bearings.


In my 23 years of design exp. I have always ordered my gear boxs for what ever application I needed but now I have to debug this one.

In my research I have found that ideally we would want a Casehardened Pinion running with an oil-treated Gear treated to a Brinell hardness in which the teeth may be cut after being treated negating the distortion and the pinion should be Casehardened after cutting and should be double quenched to refine and toughen the core, being relatively small, the distortion is minimal.

Pinion 57-61 Rc I think these are right.
Gear 30-40 Rc

With this combination it has been found that the harder pinion teeth correct the errors in the gear teeth to some extent by the initial wear and then seem to burnish or polish the teeth of the gear and increase its ability to withstand the wear by the greater hardness due to the cold working of the surface.

Are these statements true

 

[Hamermm]

After further analisys we beleive they have had the Brinell hardness combination wrong..........Something to watch for

 

[edendebrock]

We are starting to use gears made from 20CrMnTi,in the past all gears have been made from 8620 or 4320. These gears are case hardened our spec is for the hardness to be 60-64Rc after grind with a case depth of .04 to .05 deep.
We also spec less than 15% retained austenite.

The gears teeth seem to wear well but the bearing journals are starting to fail. The aplication for the gears is hydraulic gear pumps.

Does anyone have experience with the use of 20CrMnTi as a substitute for 8620?