Eskabar D2 carbides

[Chris "Anagarika"]

Martin,

Thank you!

Does the last statement negates usual recommendation to burnish on paper over WB?
Good discussion & glad Bluncut joins in. I learn more & more.

 

[HeavyHanded]

400x pic - lumps/bumps we are seeing, I don't think they are carbide. Carbide density can't be that high, since D2 has only 2% carbide volume. Google a few D2 carbide images, clearly carbide distribution is more sparse.

You may be 100% correct, I need to figure out another way to narrow this down if possible. By inferrence, the after image does show that micopitting over a pretty high percentage of area. Also, I did scan the edge looking for strong visual representation...

Are there other carbides or differences in the steel grain density that would etch at different rates?

 

[HeavyHanded]

Martin,

Thank you!

Does the last statement negates usual recommendation to burnish on paper over WB?
Good discussion & glad Bluncut joins in. I learn more & more.

On D2, 154cm, even 440c to some extent and certainly the high Vanadium carbide steels it has noticeably less effect, especially when stopping at a medium finish. Still get good results using a low pressure clean up on plain paper, but the higher pressure burnishing mechanism doesn't do a whole lot for some steels. Better off stopping after hitting it with compound on paper, though it doesn't seem to hurt either. In theory the PM steels should take it better than non-PM with the larger carbides.

 

[Obsessed with Edges]

400x pic - lumps/bumps we are seeing, I don't think they are carbide. Carbide density can't be that high, since D2 has only 2% carbide volume. Google a few D2 carbide images, clearly carbide distribution is more sparse.

I'm pretty sure the chromium in D2 is mostly tied up in chromium carbides, with a small fraction of it contributing to corrosion resistance (in chromium oxide). By volume, the chromium accounts for ~11-12% in D2, and the carbide volume will be influenced by that, as well as by the carbon content. The vanadium content will contribute to the carbides as well. See the chart below; as seen at the right, carbide volume in D2 apparently can range between 10-14%, depending on austenitizing temperature:

(chart is from the book 'Tool Steels, 5th Edition', by George Adam Roberts, Richard Kennedy, G. Krauss)



David

 

[BluntCut MetalWorks]

David - you are right, my calculation #s didn't translate from carbide mass % to volume % .

Where Carbon is 4+x lighter than Fe/V/Cr, and 1/8 of Mo. So 2 % mass translate to about 10% volume. edit: yeah, I tried to simplify presenation, inadvertently criss-crossed between count and mass %, so my #s are somewhat off.

btw -
Here is my carbide mass % calculation:
D2 has 1.55%C and ~ 0.7% taken/locked-up by martensite matrix, hence ~0.85%C balance

VC + MoC consume about 0.33%C
0.52%C balance for Cr

VC&MoC ~(.26% + 0.26%)
Cr7C3 ~ (1.02% + .53%)

OK, this works out about 2.07% carbide mass %.

For comparison M390/20CV has 1.9%C, ~1.2%C balance
VC+WC+MoC taken ~0.92%
Cr7C3 ~ (0.42%+ 0.18%)

= ~ 1.52% carbide mass %.

** Although M390 has lower carbide mass %, it has higher carbide molecular count because VC,WC,MoC formula form.

I'm pretty sure the chromium in D2 is mostly tied up in chromium carbides, with a small fraction of it contributing to corrosion resistance (in chromium oxide). By volume, the chromium accounts for ~11-12% in D2, and the carbide volume will be influenced by that, as well as by the carbon content. The vanadium content will contribute to the carbides as well. See the chart below; as seen at the right, carbide volume in D2 apparently can range between 10-14%, depending on austenitizing temperature:

(chart is from the book 'Tool Steels, 5th Edition', by George Adam Roberts, Richard Kennedy, G. Krauss)

David