Shaft steel for use at -35 deg C

[PeterCharles]

In need of assistance!
Currently we use steel 817M40T, otherwise known as EN24T (sorry about UK steel references) for shafts in our machines. Diameters from 2" to 6".

We have an application where the machines will be used down to -35 deg C.

1) would this steel be OK?
2) if not, any suggestions for a suitable steel?

Thanks.

EN24T
C 0.36/0.44
Si 0.10/0.35
Mn 0.45/0.70
P 0.04 max
S 0.05 max
Cr 1.0/1.4
Ni 1.3/1.7
Mo 0.10/0.20
T = 55/65 T/in2

 

[dbooker630]

What is your heat treat specification?

 

[PeterCharles]

"T" quality is hardened and tempered to 55/65 T/in2.
You can buy it "off the shelf" in this quality in the UK.

 

[metengr]

PeterCharles;
You need to define your impact requirements at -35 deg C (CVN of ? at -35 deg C). Once this is done, you can impact test this material to assure conformance. The Ni content of the above will be beneficial for low temperature service.

 

[PeterCharles]

"You need to define your impact requirements at -35 deg C"

If only I knew :-(
It's a simple rotating shaft subject to torsion and bending from what should be a pretty uniform load. About three changes in diameter and two keyways.

Anyone know any published data on this material at low temperature?

 

[metengr]

Alright, with nothing else to go on, I would use as a minimum

20 ft-lbs or 27 Joules at -35 deg C. Evaluate shaft materials using the above.

 

[TVP]

EN24 can be suitable for this application, but in order to have appropriate fracture toughness at low temperature the P & S need to be limited: I would start with P = 0.015 max and S = 0.020 max. The impact testing recommended by metengr should be sufficient for specifying the toughness requirements.

 

[arunmrao]

TVP, in our country EN 24 is considered a mother of all solutions. Whenever a doubt arises in the minds and we need to suggest the best shaft material available, EN 24 is the choice. Going by that analogy I too shall recommend its use fo the stated application.

Save water Drink Beer

 

[metengr]

http://www.interlloy.com.au/data_sheets/high_tensile_steels/4340.html

 

[RPstress]

If EN24 really is similar to 4340 (and a LOT of websites think it is), then according to the ASMH (Aerospace Structural Metals Handbook) 4340 at Rc 28/130 ksi Ftu the elongation to failure remains above 20% right down to -200 deg F/-130 deg C.

The Charpy V toughness measure at that hardness may either drop fairly sharply between -40 and -100 deg F (-40 to -75 deg C) from 75 ft-lb to 35 ft-lb (fig. 3.0335) or it may drop slowly from 95 ft-lb to 80 ft-lb (fig. 3.0336). Either way it still looks quite healthy at -30 deg C/-22 deg F. NB: it's fairly sensitive to phosphorous content.

The notched tensile stength remains very healthy down to -200 deg F.

For material at 215 ksi Ftu the fracture toughness drops from about 65 ksi.rt" at 0 deg F to about 45 ksi.rt" at -100 deg F. Fracture toughness at room temperature of 125 ksi material should be above 140 ksi.rt".