Case hardness variation

[smurali1]

We are doing carbursing case hardening on a SAE 8620 material in an Integral/Sealed Quench Furnace using LPG+N2+Methanol atmosphere. The case depth : 1.5-2.4mm, Surface hardness: 58-62HRc.

We are currently facing a problem:
1. Case depth below specs but surface hardness OK
2. Surface hardness varies between 24-59 HRc in same part.

Currently we found one pc each of above problem in one furnace load (1500 pcs)

Following are questions:
1. We have initiated a containment action of eddy current sorting for low case depth. Is this the best method?
2. We are yet to have a containment action for within part variation in HRc. Is there a right method?
3. What could be root causes for this?

Thanks

SPM

 

[mcguire]

Why not start by looking at the microstructure of the soft area to see if it has low carbon or retained austenite which would indicate irregularities in carburization? Until you know the root cause you can't do # 1 and 2.

 

[baskargk]

If ur facing a surface hardness variation, eddy current method can't detect this problem correctly.
tell me the configuration where ur finding this problem. whts is the capacity of the furnace? temperature of oil bath? if u can provide all the details, i can provide sme help.


baskar

 

[smurali1]

Hi Baskargk,

What do you mean by configuration - if it is part geometry, then the part is like a spider. The furnace capacity is 600 kgs. The oil bath temp. is 120 deg.C

 

[EdStainless]

How are you measuring the hardness?
What are the case hardnesses?
You need to do this carefully on prepared samples with low load testing. You may be confusing multiple issues here.

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