Abnormal growth after Induction Hardening Process

[Zlatan13]

Experts,
we face abnormal growth in Induction hardened axle bars of Grade SAE1050 ranging around 0.1 to 1.3mm.

Generally we solve this issue by adjsuting concentration of quench medium (if we add water growth will increase and polymer addition will reduce growth).

But now inconsisitenetly the variation hits us ranging from minimum tolerance to maximum tolerance even within one cycle(2 spindle hardening).

I susupect if there could be rootcause from steel maufacturer for this particular heat who produces in BF-BOF-LRF-VD-CCM route.

If there is a correlation between grain size of ferrite pearlite towards growth/shrinkage after induction hardening?

Kindly throw some light on this topic..

 

[3DDave]

Growth by what percent? 1.3 mm in 5000mm or 5 mm?

The change in crystal structure drives the change in dimension; I don't expect that the grain size matters much. I suspect that while grain size is the most observable difference that the volume of material that is converted is the main driver.

https://www.productionmachining.com/articles/craftsmans-cribsheet-distortion-in-heat-treatment

 

[Zlatan13]

@3DDave: Thanks for your insights and response

The height here is 500mm. Generally we anticipate 0.5 to 1mm growth after IH so we cut parts based on this assumption.

We observed that change in heat number doesnt bring this vast variation, hence im looking for variables in each heat which is causing this difference.

 

[TugboatEng]

Is the initial hardness before induction hardening consistent?

 

[dbooker630]

Have you tried changing out your inductor? Also have you checked consistency of your power supply?

 

[Zlatan13]

@Tugboateng: we did check hardness before and didnt found any marked difference. (Apologies for late reply, didnt get notification on time)

@dbooker630: We changed inductor and quench ring also we tried this part number in other machines too using same parameters, still we faced problem and for other part number it doesnot have any such variations. This what puzzling us.

 

[TugboatEng]

I may be way off, in my head induction hardening is a case hardening process. The case would tend to shrink around the core which would make the core elongate. Variations in the hardness of the core may effect how much distortion it seems.

 

[3DDave]

If the case is in tension that would not be a good condition to have for an axle. The ideal is full surface compression by expanding the crystal size either by stuffing some other element in there like nitrogen or transforming the crystal phase to one with a larger size.

That said - the near infinite subtle variations from carbon content and distribution to the presence of other alloying elements means at least sectioning the material for initial grain after it's formed into an axle shape and/or sending out chunks to see what the constituent elements are. It might be some of them have a small variation in those elements that affects the phase change.

 

[mfgenggear]

is the growth after first heat treat or at induction hardening. is any inspecting before heat treat an after heat treat and same for induction harden. did any one conduct test with heat treat which process will minimize distortion and growth. , and these parameters will change from material lot, and heat treaters process. and materials used