As a point of clarification, carbides do not increase ease of sharpening or ultimate obtainable sharpness, in fact they do the opposite and decrease it, hence steels which are intended for very high sharpness (razor blades) have a very low carbide volume, << 5%.
There are main reasons why inexpensive knives are often initially difficult to sharpen (though easy to grind) they are all related to the fact that the edge is likely damaged :
-too much heat in grinding
-steel not protected during the soaking
-less than ideal thermal cycling (will affect the edge most)
In general, for really cheap knives, I have often found it can take up to a mm of metal to be removed before the performance stabilizes. The main reason that people often think so poorly of such steels/knives is that they never see the actual steel in use, just the damaged part.
Most of the inexpensive knives are 5Cr13MoV stainless (a few are 3Cr13), these are actual razor blade steels the same as AEB-L. However the inexpensive ones are usually underhardened so you will lose performance compared to a very nice AEB-L blade, but the edge holding will be 40-50% of that.
As a note for example, I can take an inexpensive kitchen knife :
– 6 to 8 dps primary edge
– 14 to 15 dps micro-bevel (600 DMT)
and cut 250 m of 1/8" ridged cardboard across the ridges and still slices newsprint at the end of the cutting (parallel, with the grain).
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