In my understanding steel crystalline structure below deep scratches, caused by using very rough grit, is disrupted to a depth which may be larger than the depth of the surface scratch itself. The existence of such a deep scratches near the cutting edge is limiting its strength.
The principle is following: when the scratch is parallel with a slip band of a surface grain it can cause a tiny step in the metal surface which may serve as a stress riser where fatigue crack can initiate.
It is a riddle for me how it is possible that a toothy blade with reduced strength near the edge performs in some aspects better than nicely polished smooth edge. I would expect that many teeth will be broken off during cutting and initiate nicks on the edge. May be, that even the reduced strength of the edge, is still sufficient for everyday cutting applications.
The principle is following: when the scratch is parallel with a slip band of a surface grain it can cause a tiny step in the metal surface which may serve as a stress riser where fatigue crack can initiate.
It is a riddle for me how it is possible that a toothy blade with reduced strength near the edge performs in some aspects better than nicely polished smooth edge. I would expect that many teeth will be broken off during cutting and initiate nicks on the edge. May be, that even the reduced strength of the edge, is still sufficient for everyday cutting applications.