Kevin R. Cashen
Super Moderator
Both nickel and chrome are big tubby atoms but nickel is the winner at distorting the iron atomic lattice. The iron latticework is a nice repeating crystalline pattern of stacked atoms in straight lines, this allows those atoms to slide past each other and deform when needed (like when austenite transforms), but a big fat nickel atom in the middle of the mix skews all those straight lines around it, creating a log jam in the sliding action. Carbon does the same thing when trapped between the iron atoms when we super cool the steel to harden, like little wheel chocks keeping things from moving. put the two together and you can get the effect of trying to push an austenite truck up a chromium-nickel hill that is littered with wheel chocks so that you can get to the martensite on the other side. You then need a push from some extra cooling (sub zero) to get it over the hump. Chromium does this as well but it only takes a little nickle become problematic. I work with L6 all the time, but if L6 only had around .15% more carbon I would probably be freezing it due to its nickel content. At .75-.80% C the nickel by itself in L6 is not problematic. It is also worth noting that another Simple alloy containing nickle, 15n20, also limits its carbon content to .75%. Those eggheads making the steel kind of know what they are doing after all.:3: