I have been offered studs in 17-4PH

[FennLane]

I have been offered studs in 17-4PH Double Aged but at H900 +H900.

Will this steel be resistsnt to SCC in this condition? or should I use H1150 + H1150

Thanks

 

[EdStainless]

The 900 material will be less resistant to SCC than material aged at 1050 and higher.
If it is important then keep looking.
These could be re-aged.

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[FennLane]

That's what I thought, there is some chance of chlorides being present but strength is not such a big deal as we have plenty in hand.

 

[CoryPad]

You can review NASA MSFC-STD-3029 or ECSS-Q-70-36C for information regarding materials selection for SCC resistance. Stainless steel 17-4PH in all conditions is listed as having moderate resistance. Better alternatives are:

Custom 450 stainless steel H1000 and above
Custom 455 stainless steel H1000 and above
15-5 PH stainless steel H1000 and above
PH 14-8 Mo stainless steel CH900 and SRH950 and above
PH 15-7 Mo stainless steel CH900
17-7 PH stainless steel CH900

 

[FennLane]

I would have chosen 15-5PH but it is almost unobtainable in the UK other than to special order as it seems only 17-4 is imported in any quantity.

Stockholders over here charge like a bunch of wild horses for any 'specials' and this tends to dominate choice.

One company has benn using 17-4PH for smoe years without any reported problems but I will try again to find the 15-5PH.

Thanks

 

[metengr]

Perhaps my age has been getting the best of me lately, if you are going to use 17-4PH and your company has used this stud material for many years with no issues, what is the problem? Unless the service environment has changed, use the same condition of 17-4 PH stud material as before where you had demonstrated no problems.

 

[FennLane]

I have never used 17-4PH for any studs - another Comapny uses this material and hasn't reported any problems but this isn't an absolute guarantee as I don't suppose anyone would promote failures.

I think I did say 'one' Company.

My problem is that the environment that the studs will be used in differs greatly and it would be difficult to simulate actual operating conditions.

Having said that and AALCO publication states that 17-4PH Corrosion resistance is similar to that found in grade 304 stainless steel.

In warm chloride environments, 17-4 PH is susceptible to pitting and crevice corrosion. When aged at 550°C or higher, 17-4 PH is highly resistant to stress corrosion cracking. Better stress corrosion cracking resistance comes with higher ageing temperatures.

Corrosion resistance is low in the solution treated (annealed) condition and it should not be used before heat treatment.

http://www.aalco.co.uk/datasheets/Stainless-Steel_1.4542-17~4-PH_100.ashx

Other data sheets give a little more information:


Corrosion Resistance
Alloy 17-4 PH withstands corrosive attacks better than any of the standard hardenable stainless steels and is comparable to type 304 in most media.

If there are potential risks of stress corrosion cracking, the higher aging temperatures then must be selected over 550°C (1022°F), preferably 590°C (1094°F). 550°C-1022°F is the optimum tempering temperature in chloride media.

590°C-1094°F is the optimum tempering temperature in H2S media.

The alloy is subject to crevice or pitting attack if exposed to stagnant seawater for any length of time.

It is corrosion resistant in some chemical, petroleum, paper, dairy and food processing industries (equivalent to 304L grade).

 

[EdStainless]

Martensitic PH grades; 17-4, 15-5 is modified for lower residua ferrite and better toughness (large sections or low temps), 13-8 contains Mo for slightly increased pitting resistance. (13-8 is also commonly available as VIM/VAR material with special higher fatigue resistance)
semi-austenitic PH grades (austenitic when annealed); 17-7, 15-7 is the Mo bearing version.

If you are not welding or using thick sections (>2") then 15-5 has no real advantage over 17-4.

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