probelms in carburizing 3

[limct]

Hello,
What should I tackle in the heat treating process when I find the core hardness is OK but the case hardness and EHT are out?
Are this concerned with the carbon potential and Ammonia gas supply, or maybe the layer arrangement of the parts is too thick... or is there any other thing that I should look into as well?
Thank you.

Best regards,
ct

 

[Carburize]

More information please -
1)What is the material
2)Outline of current process
3) What case depth - surface hardness is required
4) What case depth - surface hardness are you getting????

 

[limct]

Hi Carburize,
1) The parts are made of C1018
2) It's a vacuum furnace with automatic conveyor system.
3) specs 450~550 HV surface, 270~390 HV core
4) actual 390~420 HV surface, 300~340 HV core
Thanks.

Best regards,
ct

 

[Carburize]

The quench rate may not be sufficient to harden the case.
The carburizers "bible" Parrish's book "The Influence of Microstructure on the Properties of Case-Carburized Components" and his more recent "Carburizing- Microstructure and Properties" indicate that these lean alloys do not possess very good case hardnenability even when using liquid quench.

 

[TVP]

What is the carburizing temperature? What is the exact quenchant? As Carburize already mentioned, 1018 is not going to develop a very hard case. What is the target for case depth?

 

[unclesyd]

My data shows that 1018 CS is capable of a very hard case (62 HRc; 761 Hv) using 8 Hrs @ 1675°F using a carburizing pot and pot cooling.
The metal was then reheated to 1425°F and quenched in water then a 350°F temper. Case depth 0.047" Core hardness is 147 Hv. This is for a 1" bar.
It looks like you need to get the carbon potential up and increase the quench rate if you can.
You also might need to look at gas circulation and composition over time.

By using NH3 in your atmosphere are you by chance trying to Carbo-Nitride?

 

[Carburize]

One of my concerns was that if the vacuum carburize operation uses a gas quench the alloy would not have sufficient case hardenability.

 

[limct]

Hi all,
Thanks for all the valuable advise.
To answer TVP's question, the carburizing temperature is 880°C, the type of quenchant is oil. Besides all those possibilities as you all highlighted, I do believe the temperature of the oil could be the possible culprit in this case. In fact I'm gonna have a process audit done on this supplier. Things should be sorted out very soon.
Again, many thanks to you all.

Best regards,
ct