Difficult to sharpen stainless steel

[MartyGrind]

I have read a very useful thread here on the same subject, but post this in the hope of some more insights...

I am having a terrible argument with a shoarma knife that refuses to get sharp. His younger "brother" (same knife but less worn out) was no problem at all.
The problem knife is worn down to almost half the bevel size. I tried everything I know. Firstly grinding what once was a secondary bevel down to something acceptable since the wearing down made all angles too obtuse (wide). Then the primary bevel still wouldn't get really sharp. Rough stones, fine stones, stropping, machines (Tormek T4 so not a crappy machine) diamond stones… Everything would not get the job done properly.
Any useful help is greatly appreciated!
Now that I found how to upload; this is what I a talking about:

 

[Cementite]

I recently changed my opinion regarding two knives in the house -- including one Gerber Paraframe -- that I thought were impossible to sharpen. (I had recently bought a number of DMT diamond plates and other sharpening stones, and spent several weeks freehand sharpening every knife in the house, and those two knives were the only two in the house that completely resisted my best efforts to sharpen them.)

I got a deal on a HFT 1x30 belt sander and some decent ceramic belts, so just for grins, I tried to raise a burr on those two miserable knives...and I'll be darned if I didn't get them sharp! Followed up with Norton India and Norton Crystolon combo stones, diamond plates and strops, and got surprisingly good edges on both of them.

So I guess the moral of the story is, Don't give up!

 

[Obsessed with Edges]

Two things I've often noticed in inexpensive stainless knives, and cheap kitchen knives in particular:

1. Thick edge grinds - Almost every inexpensive kitchen knife that has given me fits in making it sharp have all eventually benefited greatly by thinning the grind behind the edge. Has usually taken a LOT of work to do this - but eventually, it makes a difference.

2. Likely heat damage from factory edge grinding - Most will have some of this. And one cheap knife of mine in particular needed many edge regrindings over a span of months, before it finally started behaving normally in sharpening. For a long time, the steel near the edge just crumbled to dust if I tried to thin the edge past a certain level of keenness. Wouldn't produce a burr at all during this period. I was frequently tempted to just throw it away. But instead, when I became frustrated with it, I'd just stash it away and forget about it for a period of weeks or even months. Then I'd pick it up and reset the edge again. At some point, many months later, it finally started producing a predictable and ductile burr, which is what low-alloy stainless should do. I was then able to treat it like any other knife in simple stainless and refine and deburr the edge by my usual means. And lo and behold, it suddenly became a decent performer for kitchen use and a knife I liked to use. But it took a very long time to get there and I surmised after fact, the steel near the edge had a lot of heat damage from the original factory grinding and just needed to be ground away until only undamaged steel remains at the edge. I've since read posts from many others who've seen the same sort of thing in cheap stainless blades. So I now realize it's a relatively common occurrance in knives like these, and patience is key in making them better cutters in the kitchen.

For what it's worth, my favorite stone these days for such knives is a simple Norton Fine India, used with oil. For low-alloy stainless that behaves as it's supposed to, the Fine India does a great job.

 

[Blade Lab]

I think the biggest problem sharpening cheap stainless is difficulty removing the burr, or the remnants of the burr once you think you've removed it. Solution is generally to deburr the knife at 1.5-2° higher than the sharpening angle, and then finish stropping at the exact angle.