Tormek Community Forum

In the Shop => Knife Sharpening => Topic started by: Sharpco on November 11, 2018, 11:15:05 AM

Title: Extremely hard steel - CPM REX 121
Post by: Sharpco on November 11, 2018, 11:15:05 AM
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?
Title: Re: Extremely hard steel - CPM REX 121
Post by: kwakster on November 11, 2018, 04:19:51 PM
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.
Title: Re: Extremely hard steel - CPM REX 121
Post by: Ken S on November 11, 2018, 04:48:51 PM
Good reply, Kwakster.

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

Ken
Title: Re: Extremely hard steel - CPM REX 121
Post by: Jan on November 11, 2018, 05:17:33 PM
Good reply, Kwakster and Ken.  :)

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

Jan
Title: Re: Extremely hard steel - CPM REX 121
Post by: Sharpco on November 12, 2018, 08:29:33 AM
Thank you everyone.
Title: Re: Extremely hard steel - CPM REX 121
Post by: Fernando on November 16, 2018, 10:09:02 PM
Quote from: Jan on November 11, 2018, 05:17:33 PM
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
Title: Re: Extremely hard steel - CPM REX 121
Post by: kwakster on November 17, 2018, 11:24:38 AM
Carborundum = Silicon Carbide

(https://s18.postimg.cc/s3hf5r6xh/Carbide_hardness.jpg) (https://postimg.cc/image/s3hf5r6xh/)
Title: Re: Extremely hard steel - CPM REX 121
Post by: Fernando on November 19, 2018, 05:51:11 PM
Quote from: kwakster on November 17, 2018, 11:24:38 AM
Carborundum = Silicon Carbide

(https://s18.postimg.cc/s3hf5r6xh/Carbide_hardness.jpg) (https://postimg.cc/image/s3hf5r6xh/)

Good information, thanks for sharing
Title: Re: Extremely hard steel - CPM REX 121
Post by: Sharpco on December 16, 2018, 12:47:04 AM
https://youtu.be/o2FHwnTH_sE

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