The spheroidal graphite (SG) is ductile iron and this is exactly what should be specified other than a fabricated or cast steel wheel. The SG iron actually exhibits as good as or even better mechanical properties in comparison to malleable iron.
A valve hand wheel is not exactly challenging the limits of design or materials.
There is generally no need to make it supper light, or supper stiff or supper strong or supper low rotating inertia or supper anything.
It is one of those things that just has to be "good enough".
You can get there by changing the strength of the material used or the amount of material used. That is to say more weak material is just a good enough as less strong material.
Real malleable iron requires lengthy heat treating after pouring as white iron .. Ductile or nodular iron just requires adding a pinch of magnesium into the recipe for cast iron.
Thank you, ASTM A47Gr3250 has tensile 50ksi & yield 32.5ksi & SG400/15 has tensile 58ksi & yield 36ksi, can we conclude SG is superior than Malleable iron please
It's a handwheel! Stress is on the order of hundreds of pounds - and that only if a lengthy prybar is used as a lever. Your point of highest stress is the broached (square ?) hole where the handwheel fits on the valve stem.
Unless it's a rising stem valve, where the center hub is threaded.
In that case you might want to design so that thread failure happens in the cheap and easy to replace part, not the expensive and hard to replace part when that prybar is used to try to turn the wheel too far.
It just might be that the OP's client want's to ensure this happens by asking for an "inferior" material.
The OP needs to engage brain, not seek answers on the internet to poorly defined questions.
Better yet, have an actual discussion with the client, rather than trying to blindly convince the client that "our standard material is better, which is where the OP seems to want to go.
I never believed that a low technical product, would have so much attention. Malleable iron is history and Ductile Iron has replaced it for over 20 years. Even in its hey days, these wheels were produced by foundries, with very low technology or infrastructure, but these parts did not need any certifications. Several times these wheels would break.
"Even,if you are a minority of one, truth is the truth."
