Shaft Hardening 1

[khalil1]

Hi There,
I recently joint the group and I came up with following issue which very much related to material selection and applying the right heat treatment. we are using A.I.S.I 1144 steel for our starter armature shaft (.8225/.8240')and carburising the full length of spline to R/C 48/55 (depth of .02/.05) but we are getting 30% more twisting issue in comparison to OEM product after applying the same torque during the application. please advise if can it be the result of hardening depth or the strength of material? Or there is any alternative material/Process for this application?
Thank you

 

[CoryPad]

Is the twisting issue plastic deformation during static loading? If so, then the core strength may not be sufficient, which would require a different alloy/heat treatment process. If the twisting is spline distortion, then you may have insufficient case depth or surface hardness. Your listed hardness makes no sense for a case hardened part, by the way.

 

[khalil1]

Yes, Exactly it is a plastic deformation and it is hapening after dynamic application.So if it is the case if there is any substitude material with higher TS and suitable for machinning?

 

[CoryPad]

Why are you carburizing 1144?

You can get improved core strength through higher alloying (e.g 5120, 4120, 4320) of the steel and keep the carburizing treatment, or you could use a different alloy (e.g. 1040, 4140, 4340) and quench and temper it for core strength then induction harden the local areas that need high surface hardness.

 

[khalil1]

Just I am wondering if we go for Q&T process with recomended alloy(1040,4140,...), doesn'it affect our machining process?( which needs to be done after Q&T application).

 

[khalil1]

will it be any issue for machinning process after we do our quench & tempering process or not? please advise.
Thank you

 

[CoryPad]

Critical dimension will need to be created after heat treating, same as for carburizing. You are quenching the parts from ~ 900 [°]C to ~ 100 [°]C with either process.

 

[khalil1]

Thank you CoryPad,
Your advice was realy helpful.