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Posted by Dave K. Royal [75.81.249.81] on Friday, January 06, 2012 at 13:18:25 :
In Reply to: Dave Royal re 8620 posted by clueless [201.202.29.210] on Friday, January 06, 2012 at 10:49:58 :
There was 8620,8622,8630, all of these are carbon changes, the other alloys will change, but always within the perimiters of the spec's. there is a low and high for each alloy in a given grade of steel. I have seen all of the aforementioned grades of steel with a military spec go out the door. if, by some chance your friend just happened to get a set of gears that were at the top of the specs for that grade, then yes, that particular batch of steel would be slightly better than another given batch even within the the same grade. now having said that, sometime the gear companys discovered that carbon could be sprayed on hot steel and would produce a harder surface (wear factor) I don't know when this started, so it could be a factor in the date your friend adhered to. if you have ever picked up a piece of tempered steel that was black in color then you know what carborizeing looks like. also sometimes the spec will change in mid stream, that could account for a certain date being better. we made steel in batches of 65 tons per heat, and would make hundreds of tons per week(5hrs per, 24-7). 8620 is also used as armor plate,wear plate, and many other things depending on heat treat. as far as whether or not it was always stamped into the gear I do not know for sure. some of the racing companys started using 3310 steel for drag cars, able to handle at least double the HP. over 5% nickel and over 5%chrome w/less than one tenth of one percent carbon! bad,bad stuff. we made steel that you could shave the teeth off of a file with. the ringgears that dana made were dated, I'm not sure about NP. But your friend could very well be right, if at some point the spec changed. Dave.
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