The reason for the different types is because thats what the different customers want. Yes,each receipe will have some variation but must fall within set limits. examples of what I mean are shown below. 52100 Carbon .95-1.10 Manganse.25-.45 Silicon .15-.35 Chrome 1.30-1.60 Moly trace 52100 modified type 2 C .85-1.00 Mn 1.40-1.70 Si .50-.80 Cr 1.40-1.80 Mo trace 52100 modified type 4 C .95-1.10 Mn 1.05-1.35 Si .15-.35 Cr 1.10-1.50 Mo .45-.60 Sorry, its hard to read in in a nontable form. Note- each type has its own receipe with a range that the elements can fall within. However each type has different ranges. Notice some have no molybdenum{Mo} other types {type 4 here} have quite a lot. Carbon can range from .85-1.10 Equally important is how the steel was made, the melt shop practices that each mill usues. These are trade secrets within each company but must follow certain guidelines. These are only a couple of the different types of 52100 that have been made. I have info on several others as well. To make things evan more confusing a steel type called 51100 is /was used for bearings and races. My point is that unless you get an analysis of what you are using its mystery metal.Good results can be had with any of this material but some ,no doubt, will be better than others. I hope this helps. I can send some info if anyone is interested,let me know. I can't type very well and its impossible to post it all. Thanks Rex
