S143 is precipitation hardening stainless bar and forging (composition 14%Cr-5.5%Ni-1.5%Cu-1.5%Mo-0.25%Nb). As such it's pretty similar to 15-5PH which is in the MMPDS (15%Cr-4.5%Ni-3.5%Cu-0.3%Cb according to ASMH).

S143 is a version of the old Vickers spec FV520B. It has a duplex precipitation heat treatment, the first bit of which is 750°C (1380°F) and the last bit of which is 550°C (1025°F). This gives Ftu 130 ksi, Fty 115 ksi and KIc about 75 ksi√in with extension to failure e of 15%.

That's more-or-less like 15-5PH in the H1100 condition (Ftu 140 ksi, Fty 115 ksi, KIc about 85 ksi√in and e 14%).

S143 says the tendency for SCC is "Resistant" and for SCC MMPDS warns about 15-5PH being vulnerable if precipitated at temperatures below H1025 so the H1100 might well be ok. This may need checking in more detail depending on your usage.

The S143 aerospace spec controls the properties so they should always be those listed above (from the ESDU MMDH (Metallic Materials Data Handbook)) but if the material is given different heat treatment its properties will be different (and of course it won't conform to S143).

As always, make sure your usage isn't relying on some property that is either not listed or not comparable (e.g., manufacture; in this instance, 15-5's weldability should be about like S143's which is rated "Good" by MMPDS except for flame welding, and formability should be similar (comparable e and Fty) but again, details of the forming process might need investigating in more detail, especially if aspects of manufacture and heat treatment are being combined).

Heat treatment of 15-5PH should be slightly cheaper than S143, but there's got to be a reason why S143 needs duplex precipitation.

15-5 has good availability of crack growth data and KIc is similar but da/dN data needs checking if damage tolerance is an issue.

I don't have any Charpy or Izod data for S143 or any type of FV520. If something like reduced temperature toughness is an issue in the end-use that will need checking (the similarity of KIc gives hope for that sort of thing).

Thanks for detail reply RPStress. Much appreciated. Usage is for fastener

If you are looking for either higher corrosion resistance or better toughness/fatigue properties then look at 13-8PH. It is a double melted product, very tough and similar properties.

The S143 looks to be more like 17-7PH in terms of metallurgy. Fully austenitic when annealed. These alloys require an austenite conditioning step prior to age, just how they work.

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P.E. Metallurgy, Plymouth Tube

Thanks the suggestion EDStainless. Currently we are not looking at a specific "requirement". S143/S145D is on my list of preferred material ie the (only )one I can use but I have no strength vs. temperature data. I am therefore trying to see if there is something "equivalent" in MMPDS-05 to get ,at least, an idea of the knock-down factor.