Knife steel microstructure
The microstructure is a major difference between the Sandvik fine-carbide steels and other knife steels such as ASTM 440, D2 and other coarse-carbide knife steels.
By comparing the pictures on the page about purity it is easy to see the large primary carbides of the 440 type steel and the fact that there are no such carbides in Sandvik 12C27 in the picture right.
These large primary carbides have a diameter of up to 40 microns compared to the maximum carbide size of Sandvik 14C28N / 13C26 / 12C27 / 12C27M / 7C27Mo2 which is 2 microns (average is 0.5 microns). The impact on the edge from these primary carbides is shown in the pictures below.
The knife edge with large carbides (Figure 1 above) will be much more difficult to regrind and it will be more or less impossible to grind this steel to the razor sharpness achievable with Sandvik fine-grain steels (Figure 2 above).