Look closely at the base of the seat tube. From one angle you can make out a "41..." and from the other angle you can read "...30". So, at the risk of going even farther out on the fool-limb, I am pretty sure it is 4130 Cromoly.
jim
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Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
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SB forever