Axles Total Chaos (4130) vs Currie (4340)

I'm not buying either of these but I'm curious on the comparison of the two.

TC is made of 4130

• Tensile 97k psi
• Yield 63k psi
• Elongation 25.5%

Currie (All Pro uses them) made of 4340

• Tensile 185k psi
• Yield 125k psi
• Elongation 12.2%

The obvious think not listed here is the diameter. My main question is with the longevity of each. My hypothesis is that the 4340 axles fail sooner than the 4130. I also think the extra elongation would help reduce strain on the rest of the drive train.

Please try to support responses with evidence if possible.

 

Finding perfect apples to apples isn't easy, but the short answer is that assuming identical geometries, the higher Ftu 4340 will have longer fatigue life for same applied load, (or for same number of cycles 4340, can carry higher stress). Data here is not for identical forms, and not exactly for your stress, so it isnt perfect. I used Mil-Hdbk-5H for data source.

Comparison below is for stress concentration (Kt) of 1 (no shoulders, holes, fillets, etc) and Stress Ratio of -1 (meaning every cycle on the test machine is from full positive load to full negative on every cycle).

4340 with heat treat to Ftu=150 ksi, Runout (essentially stress for infinite cycles 10^7 ) is 70 ksi
4130 with heat treat to Ftu=117 ksi, Runout (essentially stress for infinite cycles 10^7 ) is 45 ksi

However, surface finish, fillets radius, etc are equally as important for long fatigue life as material choice. (these things are less important for ultimate strength and low cycle fatigue)

4340



4130

 

Not what I expected at all. Very good post!