[tanshi]

Ok so i have the facts and figures but am not really sure of the actual real world applications and implications of each type.

In peoples real world opinion when it comes to axles which i know need to twist but not break which is the better option. 4130, 4340 or some other that i havent considered?

the facts i have from a friends text book is. the costs i know will not be hugely accurate.

According to my text:
1020 - 1040 or 1050 etc is mildish steel:
4140 should be close to 4130...I hope...lol
4340

Cost
1040: $0.75/kg
4140: $2.95/kg
4340: $3.30/kg

Yield Strength (when they will bend or stretch)
1040: 290 - 375 MPa
4140: 472 - 1570 MPa
4340: 472 - 1620 MPa

Fracture Toughness (shattering fun)
1040: 54 MPa
4140: 55 - 93 MPa
4340: 50 - 88 MPa