4140-4142 Annealed or Heat Treated?

[bry1]

I am designing a short shaft that will see high torque loading. I need the YS to be around 90ksi. My steel supplier has these 2 options in 4140:
4140-4142 Annealed
4140-4142 Heat treated
(Vague at best, I realize)
I would prefer to just buy, machine, and install if possible. What is my best choice if limited to these 2?

 

[metengr]

What is the shaft diameter for this application?

 

[swall]

4140 or 4142 annealed won't cut it. The heat treated version will. Presumably, this is something like LaSalle/Niagra etd 150, which has around 130,000 psi yield strength. Verify this with your supplier and you should be good to go.

 

[bry1]

Thanks for the reply. The shaft is .750" dia. I am looking at STRESSPROOF® - ASTM A-311 Class B - Grade C1144 for this app.

 

[rorschach]

I would not use a resulphurized steel (1144) in a application where it could see cyclic loading. Free machining steels of this sort have terrible fatigue properties.

 

[NickE]

How much machining do you have to do?

Pre-Hardened 4140-4142 is going to be a bit of a bear to cut with normal cutting tools, (even carbide). But it can be ground with ease, and should be straighter. Teh annealed material will be relatively soft and can be cut easily. You will need to be carefull during heat treat to assure straightness. Or you could start with much thicker stock and grind the OD to size after hardening, and provide straightness.