I tried to find out what they were made from and the best I could ever come with was they may be 1095, W2, or W1 with or without a proprietary mix to ensure the best product for our cusomers.
That being said I have made some good knives from nicholson files and like Robert use one in my shop all the time. It holds a tough sharp edge that has cut many sheath patterns.
I back my work 100% for the useful remainder of my life, that's the best I can do.
check me out on Instagram at J.HOOVERKNIVES