No one really knows for sure, but it is theorized to be a Sandvik variety. As seen on the SOSAKOnline FAQ section:
For both blades we use chrome molydenum stainless steel with 0.52% carbon, 15% chromium, 0.5% molydenum, 0.45% manganese and 0.6% silicium. After a sophisticated hardening process at 1040°C and an annealing temperature of 160°C the blades achieve a hardness of RC 56. * The woodsaw, scissors and nail files have a hardness of RC 53, the screwdriver, tin opener and awl a hardness of RC 52, and the corkscrew and springs RC 49. * The metal saw and file, in addition to the special case hardening, are also subjected to a hard chromium plating process so that iron and steel can also be filed und cut. * The separators have been made from aluminium alloy since 1951. This makes the knife lighter and easier to carry in one\'s pocket. Formerly these separating layers were made of nickel-silver.
That blurb is straight from Victorinox.
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