I did some research and found this....
"For high performance applications, 1541h steel is an excellent choice. 1541h steel contains a lot more manganese than 1040 or 1050 steels, which adds strength, hardenability, and helps in deep heat-treating. Deeper heat-treating and greater strength are a few of the reasons 1541h is used for high performance and custom axle shafts. It is much stronger than 1050 steel without being a whole lot more costly. The durability of this alloy is very good as long as the heat-treat procedures are completed correctly. 1541h steel is approximately 20 to 25 percent stronger than 1040 steel used in OEM axle shafts.
In extreme high performance use where twisting torque is important but bending stresses are limited, 4140 or 4340 chromemoly alloy steels work well. 4140 chromemoly provides approximately 27 percent more strength than 1040 steel, while 4340 chromemoly provides approximately 39 percent more strength than 1040 steel. This translates into huge gains in twisting strength as long as bending will not be an issue. 4340 is approximately 10 percent stronger than 4140 due to the addition of more nickel, which increases toughness and strength."