Topic: Extremely hard steel - CPM REX 121

[Sharpco]

Do you know what is the most difficult steel for sharpening? Maybe this is it.

http://zknives.com/knives/steels/cpm_rex_121.shtml

My customer said it's even much harder than ZDP-189 and asked me if I could sharpen this steel. I think my CBN wheels can grind it. But I don't think my leather honing wheel & PA-70 can hone it.

Has anyone sharpened this steel with Tormek? Do you think plenty of PA-70 can be solution?

[kwakster]

Haven't sharpened CPM REX121 steel yet, but your CBN will certainly grind it as it is much harder than both the steel matrix as well as all it's alloying elements.
For deburring however i would definitely also use fine CBN (or diamond) compounds to cut through the large amount of vanadium carbides, which will provide for the best possible edge that will also last the longest.
PA-70 being aluminium oxide is literally unable to cut through vanadium carbides.

[Ken S]

Good reply, Kwakster.

We should mention that PA-70 was not designed for steel this hard.

Ken

[Jan]

Good reply, Kwakster and Ken. 

The attached graph shows, that aluminium oxide is harder than tungsten carbide but less hard than vanadium carbides.

Jan

[Sharpco]

Thank you everyone.

[Fernando]

Good reply, Kwakster and Ken. 

The attached graph shows, that aluminium oxide is harder than tungsten carbide but less hard than vanadium carbides.

Jan

remain with the doubt of where the carborundum is, I know that it is above the aluminum oxide but I do not know if it is harder than the vanadium carbide

[kwakster]

Carborundum = Silicon Carbide

[Fernando]

Carborundum = Silicon Carbide

Good information, thanks for sharing

[Sharpco]

https://youtu.be/o2FHwnTH_sE

He honed the REX 121 steel with the PA-70.