M2 tool steel carbide pullout or nonmetallic inclusions? 2

[swall]

As the dark spots are co-mingled with the carbides and follow the same distribution pattern, I think they are pull-out. You could probably verify this if you can put the mount on an SEM.

 

[coreman73]

I forgot to clarify that I can actually focus inside the dark spots so that would mean they're small voids. So maybe it most likely is really carbide pullout?

 

[coreman73]

Thanks swall. The dark spots are oriented as you describe so for now I will go with pullout as I don't have access to an SEM.

I don't mean to cross post but what might be an adverse effect (if any) of high manganese level in an M2 tool steel? From my photos, I can clearly see inhomogeneous microstructure/segregation and wonder if maybe the excessive manganese could be a contributor to this.

 

[salmon2]

It looks like carbide to me as well as you can see stringer inclusion in your first pic as well, lower portion, faint line.

High Mn is absolutely a contributor to segregation. Slightly higher austenitzing temperature may help you to reduce segregation. But you don't want huge grain either.

 

[coreman73]

I very much appreciate it salmon2.

 

[salmon2]

I am glad if I help any. Thank you for the star

 

[coreman73]

Salmon2 or anyone else,

Is there any online literature available that would further explain exactly how an increase in the amount of Mn (in this case M2 tool steel) would contribute to segregation? I would appreciate any references to help with my own education.

 

[salmon2]

All alloying elements will tend to segregate if their solubility in austenite is limited. It is not specifically related to manganese, but it is common for Mn because it is the most cost effective element to get hardenability, toughness, etc.

I did an search by "manganese and segregation" and found a bunch of scholarly articles. Don't know any classic books covering this.

 

[Maui]

I discuss the effects of alloying with manganese on the properties of high speed steels and tool steels in my book, as well as the effects of a variety of other alloying elements including silicon, chromium, tungsten, molybdenum, and vanadium, among others. The micro that you provided appears to have remnant polishing defects. I have seen these myself on several occasions. They appear to be pulled out carbides, individual grains, and possibly non-metallics. I assume that these samples were polished on an automated polishing stand where you are able to dial in the applied pressure that is used to polish the specimens. As the applied pressure is increased, the polishing process can be accelerated, but only to the point where surface defects are not created. I suggest that you ask the individual who set up the parameters in the polishing process to back off on the applied pressure to a certain extent. This will increase the amount of time required to polish your specimens, but they should be free of these types of defects.

Maui

 

[coreman73]

Thanks Maui. I was the one that polished this particular sample and was under a bit of a time crunch so used more pressure than normal. I will look for your book.

 

[Maui]

Coreman73, you can find my book here:

http://www.asminternational.org/portal/site/

http://www/menuitem.2b9d1953d012ee1...b76d47ff2f210VgnVCM100000621e010aRCRD&itemId=

If you scroll down after clicking on this link, you'll be able to look at the contents of the book.

Maui

 

[Maui]

Apparently that link didn't work. Let's see if this one works:

http://www.asminternational.org/portal/site/www/

Maui