Re: fractured rods

[bearbvd@domain.elided (Greg Hermann)]

>
>BTW, don't conrods see both tension and compression loads?  If so,
>wouldn't maraging steels be a bad idea?  Tney have great static properties
>but fail amazingly fast under reversed loading.

Not really, Bob. The right ones have rather high endurance limits--if I am
not mistaken, they are used in applications like main rotor shafts for
Hueys! Not exactly a low fatigue, non-reversing load, or non-critical to
life safety application there!!

I have personally applied a 250 KSI maraging steel in an extreme, full
alternating stress (full tension to full compression) situation (in a wear
test machine), and it put the fatigue performance of 4340 e to shame!

The 350 psi tensile (and higher) maraging alloys are indeed better applied
in things like molds, but they still have pretty  good fatigue properties.
They just do not have quite such astounding impact strength as the "lower"
strength alloys!

Cost is the problem with these alloys, not performance. Their high cost
(been a while, but maybe 3 to 5 times the cost per pound of 4340e??) is
somewhat offset by ease of machining and heat treatment, though. The ease
with which maraging alloys accept nitriding is another positive factor,
both for fatigue and wear resistance where such are design considerations.

The most amazing property they have is an extremely high impact strength at
very high hardness. This is due to their very low carbon content. A
properly selected and age hardened sample of maraging steel will all but
laugh at a Charpy impact test!

Regards, Greg

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