4000 Series Steel vs 1144 Fatigue Proof
4000 Series Steel vs 1144 Fatigue Proof
(OP)
We are currently designing a rather large stationary axle, that has a large moment on the ends of it. The axle is stationary but will see large forces, repeatedly applied, fluctuating from small nominal (almost 0) to a large value. Because of this loading the design is ok in normal loading but fatigue added to a stress concentration at one of the many step downs, fatigue is our limiting factor. We are trying to keep weight and size down for this axle. Currently we are considering using 1144 Fatigue proof or, maybe using a 4000 steel that is heat treated, we are looking for the best cost option betweeen some sort of heat treating and buying the stronger material so that we have 120ksi Yield, and 145ksi tensile, (or similar) anyone have experience making a similar decision? There is a lot of machining that has to happen to this axle which starts around 3.5" diameter down to about 1.5" at the ends, and it is almost 4 ft long, so machine-ability is important.





RE: 4000 Series Steel vs 1144 Fatigue Proof
RE: 4000 Series Steel vs 1144 Fatigue Proof
Higher strength will improve fatigue life, but if the structure isn't clean you may not gain much. The are Ca treated steels (for inclusion shape control) that are used for high toughness applications. These would be appropriate for this application.
I would look at 4335 (maybe V mod, or Impact 7) or 4340, and look for some with high transverse toughness. I would go to higher strength also, 140-160ksi yield is easy in these alloys and delivers a good balance of strength, toughness, and fatigue resistance.
If you could find some Timken Impact 7 that would be a great option.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: 4000 Series Steel vs 1144 Fatigue Proof