The Tamahagane SAN Chef knife features 3-ply stainless steel construction. The middle layer is VG No. 5. This layer is very hard and acts as the cutting edge. The two outside layers are made of SUS410 stainless steel. The outside layers are softer and more stain resistant than the cutting edge and actually protect the cutting edge.
The 3-ply stainless steel has an original thickness of 20 mm and is thinned by repeated rolling to a thickness of 2 mm. You might want to look at this rolling process as a modern forging technique. Also, this rolling process removes all the impurities in the steel leaving you with a very hard, very pure stainless steel. After the rolling processes, the V-G No. 5 cutting edge reaches a hardness of 61 degrees on the Rockwell scale and a final thickness of .65 mm. The outside layers each reach a thickness of .675 mm.
The edge on the SAN knives is a minute, beveled edge. The angle of the edge is between 14 and 15 degrees. To appreciate the quality of the edge, you must first look at its incredible mirror polish and then try cutting with it. Kataoka has achieved the perfect balance between sharpness and strength with the SAN and SAN TSUBAME edges.