My last blog post was followed by further discussion that might be helpful to other
readers.
My last blog was followed by further discussion that might be helpful to other
readers.
Comment:
Thanks so much for taking the time to reply. I understand
that it was not your intent to discuss ferritic nitrocarburizing.
Unfortunately, the one specimen that was identified in the article as being
salt-bath nitrided was actually nitrocarburized … and poorly at that. The
composition of nitrocarburized surfaces are different as well as much shallower
than nitrided materials, and they require a different approach when defining
terms and taking measurements. I completely understand that you only knew what
you were told by someone else, which, I’m sure, was their understanding as well.
This is a common problem in our experience.
The primary business of our company is salt-bath nitriding
(nitrocarburizing). And, despite all facts to the contrary, this technology has
already been negatively portrayed by some over the years. This negative
perception is often difficult to overcome. We must, therefore, try to correct anything
that might feed the perception whenever possible. I realize that this is a
minor point in the article, and I apologize for making it an issue. But, for obvious reasons, it is a major point
for us.
Regarding your suggestion to evaluate salt bath “nitrided”
(nitrocarburized) specimens, we would be more than happy to provide some
samples and have further discussion.
Response:
You do understand, I hope, that I never used the term
"ferritic nitrocarburizing" at all in my article. I did not
claim that this process was good, bad or indifferent. In the 1215
specimen, there is absolutely no evidence of carbon diffusion into the specimen.
I can only see some Fe4N needles in the ferritic matrix. As there
was absolutely no increase in carbon in this specimen, I would never have
assumed that it was carbonitrided or ferritic nitrocarburized. The point
that I made was that you need to have alloying elements in the steel that can
form very fine hard nitrides to obtain a high case hardness when
"nitriding." You can see that very clearly in the hardness profiles
of the three specimens shown.
I am sorry to learn that ferritic nitrocarburizing has
received bad press. That is something that I would be totally unaware of. I was
certainly not criticizing anything other than poor
metallographic/microstructural work done in the past – such as identifying the
so-called "white-etching" grain boundaries as iron nitride when they
are cementite.
If you wish to supply me with properly made ferritic
nitrocarburized specimens for future metallographic studies, that is fine. I'd
love to have them. But my comments focus on the specimen preparation, etching and
microstructure and hardness of specimens, not about the value of such a
process. I am not promoting any surface-treatment process over another, and I do
not discuss which process is best for a particular application. That is not my area
of expertise.
