My last company bought them for me to file the edges of laser cut holes. They didn't hold up well, so either they weren't HT right or are low carbon, maybe 1070. I needed half rounds for their versatility. I have some big old Nicholsons that are still good after 40 years. I oil my files, like you are supposed to. I found Remington oil is the best as it leaves a thin coating of teflon when it's dry.
Maybe next blacksmithing class I'll take the half rounds down and forge them into a big billet mixed with 15N20, if they do not fall apart. Might make some unusual Damascus. Files, 1080 and 15N20.
And btw if you want to know what a file is made of call Peters HT service and ask them how much to analyze them. They have a laser spectrometer analyzer which hits the metal and vaporizes it and can read the elements in the metal from the vapor. I do not know how much they would charge, but I was talking to them about throwing in 2 file knives in with a batch of O1 and he said they will check the files to see if they can be HT in with the O1. You can call them and ask for Brad, but I don't think it would cost more than $5. At least you would know what you have.
http://www.petersheattreat.com/