Neda,
We have low pressure vacuum carburized 4140 at 950°C. Because of the high carbon content in the base alloy, the amount of carbon supplied to the alloy (boost time) during the carburizing process was substantially less compared to conventional low carbon steels in order to satisfy the case hardness and case depth requirements without forming carbides or excess retained austenite. Additionally, because the base alloy already has high carbon content, the rate of diffusion is also slower and required more diffusion time. Essentially there is less driving force for the carbon diffusion due to the low differential of carbon from the case, core, and carburizing atmosphere.
We have gas nitrided 4140 and 4150 and found the 4140 had higher surface hardness however shallower nitrided case depth compared to 4150. I do not have experience if this trend would continue as the carbon continues to increase to the levels seen in carburized steels nor the risks associated with white layer composition as a function of carbon content.
Regards,
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Trevor Jones
Solar Manufacturing Incorporated
Sellersville PA
(215) 721-1502 x 1220
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Original Message:
Sent: 11-23-2020 22:12
From: Neda Mandkarian
Subject: Carburizing of 4140 steel
Hi metallurgist friends,
For a specific design, we need to carburize a 4140 shaft and to do a liquid nitriding after. What are your thoughts on below:
1- Is there a risk of getting carbides network on the surface due to saturation of carbon? Does shorter carburizing cycle time help with that? Any recommendations for carburizing time?
2- Are there any risks in liquid nitriding of carburized 4140 steel? E.g flaky surface etc,..
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Neda Mandkarian
Metallurgist
McLAren Engineering
Livonia
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