Casted Replacement for 4340 Nitrided Component

[metalman8357]

Hi All,

Currently we have a part that is 4340 hardened to 36HRC and gas nitrided. A needle bearing rides on the surface of the component and requires high hardness and great surface finish. We are thinking of switching this component to a casted part to save a lot of time and cost on machining. Can anyone recommend a suitable alloy that is ideal for high strength and is compatible with nitriding? It is likely to expect that the toughness and fracture toughness of the casted component will be lower?

Thanks,
M

 

[TVP]

Ductile iron, including austempered ductile iron (ADI) may be a good choice. Very high strength, reasonable toughness. Capable of being nitrided.

 

[swall]

Metalman8357--my first comment is that your application with a needle bearing running on a nitrided surface is somewhat unusual. A carburized surface would be more common in this application. As to ductile iron as a replacement--I'm not comfortable with a needle bearing running on a ductile iron surface (I am assuming it would be ground) because of the mechanical notches created by the nodules.

 

[metalman8357]

The section thickness of the part is very small and carburizing produced too much distortion in the shape. Nitriding has been working great for us; we're just looking for a suitable replacement.

 

[arunmrao]

You could consider casting in 4340 alloy itself.Any issue? Else you may consider 52100 steel.

 

[redpicker]

Without knowing the size and geometry of the part, we are really just guessing at an appropriate choice. What may be suitable for a 5 pound part may not be for a 75 pound one.

It is likely to expect that the toughness and fracture toughness of the casted component will be lower?

This is likely, how much lower depends on material choice and processing options.

rp

 

[jwhit]

Take a look at ASTM A958-Steel Castings, Carbon and Low Alloy With Tensile Properties Similar to Standard Wrought Grades. SC4340 Cl. 160/145 would be very similar to what you have now. Also, it sounds like this part may lend itself to investment casting.

 

[tbuelna]

metalman8357,

It is unlikely you will obtain the same cleanliness and grain microstructure quality in any casting that you are getting in the wrought 4340 material. With regards to fatigue life of a rolling element bearing race surface, these characteristics are of significant importance. I would recommend taking a careful look at the reduction in calculated adjusted life you will see with your bearing by switching from a wrought material to a cast material for the race. The difference in material reliability factor between a cast and a wrought material could make a difference of anywhere from 2X to 4X (or more) in the calculated adjusted life of the bearing system.

Hope that helps.
Terry