I'm doing a fatigue analysis for our rear sprocket for which I have considered 4130, 4140 and 4340 steel grades. The steel suppliers do not have any fatigue data and since this is our first year we too don't have any testing data. I need a reliable source for the SN curves of the above grades although I'm aware they'll just give me a rough idea of fatigue life.
I found a military handbook online:
http://www.knovel.com/web/port...L_DISPLAY_bookid=754