Use of Stainless Steel 2205 1

[supstr]

Hello,

I have a part that will be subject to high cyclic loading, cycles of being immersed in salt water to being in the dry, and requires a 50 year design life. The hardness of this part is significant as the part moves and hence its surface must remain relatively undeformed in order to ensure good operation of the overall structure. I have been considering the use of stainless steel CD3MN, the cast equivalent of type 2205(the part has a unique geometry), however, I have not been able to get any information on the hardness of the alloy. From a few conversations with foundries, it seems that this is not something that can be controlled in the fabrication process, but I would like to find further information on this topic. The client who is requesting this part has used type 17-4 for similar parts at other locations that have a similar application and exposure to a marine environment, however, the parts have not been in service long and I would expect them to experience problems with corrosion down the line.

Can anyone recommend any references that discuss the achievable hardness of type 2205 castings? Also, can anyone discuss the use of 17-4 in a marine environment? Regarding the later, some sources seem to imply that higher corrosion resistance can be achieved with 17-4 with a high polish finish, which seems plausible but, perhaps not a long term solution.

Thanks for your time.

 

[EdStainless]

How highly stressed are these? For 17-4PH to work in cyclic immersion you need everything to be just right, and even then they will rust and pit. If there is load and risk of SCC then you need a higher aging temp (lower strength) and this also lowers the corrosion resistance.
First you would want to specify J92205 (the chemistry controls are tighter).
2205 will have much better corrosion resistance. The hardness after casting and annealing (required) will be a factor of the chemistry, so it should be controlled. The alloy will (by spec) have a max hardness of 25 HRC,.
Ask the foundry's for their statistics on the hardness (make sure that it after the anneal cycle).
I would expect hardness to be in range of 20-24 HRC (provided that they keep the N high enough).
If there is surface wear there will be significant surface work hardening.

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P.E. Metallurgy, Plymouth Tube

 

[supstr]

EdStainless,

How highly stressed are these?

This part bears on a surface, the contact pressure is about 76 ksi.

2205 will have much better corrosion resistance. The hardness after casting and annealing (required) will be a factor of the chemistry, so it should be controlled. The alloy will (by spec) have a max hardness of 25 HRC,.

Which spec are you referring to? I was informed that ASTM A890 should be used for type 2205 castings. This spec includes J92205, however, does not state hardness. This is likely because of the reason you mentioned that the hardness is controlled by chemistry.

If there is surface wear there will be significant surface work hardening.

In the case of a part cast from type 2205, is it possible to work harden the surface without adversely affecting the material's properties? My understanding of work hardening is that it is done by bending, shearing, drawing, rolling, or other process to cause a plastic deformation in the metal in order to harden it. One source told me that hardening of the surface of a type 2205 is not possible. Based on what you are saying it seems that it may be possible to harden the surface? Perhaps I am misunderstanding this statement.

I didn't mention this in my original post but in this case, the part would need to have a minimum hardness of 250-280 Brinell (~25 - 30 HRC) at a depth 3/32" below the surface. Could the hardness be controlled this closely?

 

[EdStainless]

You won't get that high of hardness from 2205 without some special tricks.
Are you really sure that you need it that High?
This alloy will work harden, there is no simple heat treatment to harden it.
I referred to the J92205 because it is a better (tighter chemistry control for higher corrosion resistance) than the old CD grade.
There are not many alloys that will survive in seawater and have higher hardness.
What material does this part rub against?

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

You mentioned the part surface is subject to a contact stress of 76ksi, but you also require a subsurface hardness of at least Rc 25 (124ksi TS) at a depth of .094". Is the surface contact stress limited by fretting? What is the reason for controlling just the subsurface hardness rather than the hardness thru the section?

 

[supstr]

EdStainless,

This part will bear against a guide bar/plate made of stainless steel as well. The main stipulation in the client's specification and in the industry standard for this component is that the guide bar/plate surface have a hardness of 20-50 BHN than the part since the guide bar/plate will be very difficult to replace if it wears more quickly than the part. The part is easier to replace than the bar/plate. The part's surface hardness is usually set at 250 BHN. Could peening the surface following a controlled casting of the part (to ensure it reaches high hardness) increase the surface hardness 20-50 BHN? What effects on the material should be expected?


tbuelna,

Fretting is not an issue here as there will not be high vibrations. It seems that the specification is written this way so that the part maintains ductility throughout the section as other materials are typically used, e.g., ductile iron. The hardness is critical at the surface since wear of the surface would significantly impact the part's service and ability to move along the guide bar/plate properly. If the surface hardness were achieved by hardening throughout the section while maintaining the mechanical properties within the allowable stresses, this would work. Is it impractical/more difficult to control one versus the other?

 

[supstr]

To add on to my previous response, I would assume that the hardness of the plate/bar could be controlled more easily since cold working could be performed with more ease than an a relatively more intricate shape.