Tough Environment.... 2

[NickE]

I have a tough one here....

currently a modified 420ss (+1%Mo) (HRc~54) is failing relatively fast, we prototyped 302 Rolled to Spring temper; at 160F they lasted longer than the teh 420, at 212F they dont last long at all.

Environment: 212F, saturated steam, some fine particulates, tap water, condensate.

Application: Reed Valving. Compressor head, both intake and discharge.

Failure analysis results: 420mod is failing either through general corrosion or IGC, both have been observed on different failures. EDS shows a small Cl peak, along with other Ionics. Teh 302 is not failing through obvious corrosion, there is some red rust appearing on the surfaces, no IGC or general corrosion damage at the intiation location.

At this point I dont want to go to inconels or elgiloy, but I need a high strength spring material, current gague is 0.003" thick.

Any recommendations?

Nick
I love materials science!

 

[israelkk]

Is the rust from the 302 or it may come from the tap water due to rusted pipes? Did the 302 was passivated? How about 301, 321, 347?

 

[TVP]

I would talk to Sandvik about one of the following:

a. Grade 11R51, which is a spring temper Type 301 that has some Mo added to it. My guts say that this will not be enough of an improvement, but my guts aren't that smart.

b. Grade SAF2205, which is a duplex (ferritic-austenitic) alloy that can be cold-rolled to a spring temper. It is not as strong as either 11R51 or the 420 grade you started with, but the tensile strength can be ~ 1500 MPa.

c. Grade SAF2507, which is another duplex grade with even better corrosion resistance than SAF2205. I think 2205 would be sufficient for corrosion resistance, but the "Spring" section of the Sandvik Strip website only shows 2507, which makes me think 2205 may not be available in sub 1-2 mm thickness range.

 

[NickE]

I'm pretty sure the red rust present on the 302 is a result of other components of the system. This is a sealed system so the water is added once. I dont think rusty pipes are a cause of the problem.

israelkk- we dont passivate any of our SS product, either 420 (Hitachi or Sandvik Matl.) or the 302.

TVP - yeah, 11R51 was thought of, however I didn't think it was going to be substaintially better than 302, though the Mo might help. Thanks for the info on the duplex steel, I was unsure if the duplex steels were available in a spring temper.

 

[sreid]

Stainless Steel Rouging might interest you.

http://www.corrosion-doctors.org/MatSelect/rouging.htm

 

[sreid]

Do you have any speculation about the failure mechanism? Do you think it's a fatigue failure?

 

[NickE]

I'm pretty sure the 302 is just not strong enough, with the addition of the environment along with the mechanical abuse a reed valve sees.

IE: Mechanical fatigue accelerated as a result of the environment.

We visted the customer yesterday, at this point I think only exotics are going to solve the problem.

Thanks for the help.
nick