Found this on pirate.
I think that for $200 more I can have chromoly ones from ECGS. I'll just bite that bullet.
"Most OEM shafts are 1040-1050 but some may also be 1541. Most aftermarket stock replacement shaft are 1541 and most of the custom rear flanged axles like all the Currie, Dynatrac, Dutchman, and Moser rear shafts are 1541. 1541 is a plain high carbon steel similar to 1040 but with added manganese for better hardenability, but there is not enough alloying elements in it to be classified as an "alloy" steel. 1040 & 1541 are used because it is cheap and good enough for what is required by stock axles, they heat treat 1040 & 1541 by induction hardening which is a production form of case hardening, it is fast, cheap and works very well, 1541 is able be be hardened to a greater depth (better hardenability) than 1040/1050 and therefore stronger. 1541 is not much more expensive than 1040/1050, it probably equates to only a dollar or two more per axle, when your dealing with the scale of OEM axle production numbers that is a lot of money, but with aftermarket axle production numbers that is not that big of a deal and the consumers would pay that extra amount without question for the increased strength.
4140, 4340 and 300M are true alloy steels. 4140 is alloyed with chromium, molydenum and 4340 with chromiun, molydenum and nickel. 300M is also called 4340 modified because it basically 4340 with silicon added. The strength of steel is generally directly related to the hardness, the harder you can get the steel, the stronger it is (tensile strength) but you generally loose toughness. These alloys give the steel increased hardenability and good toughness at higher hardness/strength levels, they can be induction hardened but their purpose and advantage is that they can be thru hardened because of their better hardenability. 4340 has better hardenability than 4140 so is can be heat treated harder and thus stronger than 4140. 300M has a similar hardenability to 4340 but the added silicon gives it more toughness at higher hardness levels. The 4140 and 4340 raw material is available in commercial and aircraft quality and 300M is generally only available in aircraft quality. Aircraft quality means it is vacuum melted to minimize the impurities but costs more. Most 4140 and 4340 axles are made of commercial quality steel. The material cost differrences between 1541 and commercial 4140/4340 is not that great, again it probably only equates to only a few dollars more per axle, the big cost difference is from the increased heat treating costs and the smaller production runs of 4340 axles. 4140 and 4340 axles have to be thru hardened in an oven which costs more than induction hardening of a 1541 or 1040 axle. 300M should be heat treated in a vacuum furnace and other expensive process to make it correctly plus the added material costs for aircraft quality materal make the end product more expensive. 300M axles are usually custom made, a few sets at a time which adds to the production costs."
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