Which is the most appropriate magnetic stainless steel alloy which possesses good creep resistance, excellent corrosion, and thermal fatigue resistance? The alloy must also be able to take moderate dynamic loads while in operation for a temperature range of 300-800 deg C. Please advice.
Dear Dr. Ashish Jose M.,
I suggest that you take a look at the following notes that I think may be useful for your question:
-Materials and Applications Series, Volume 18 - Stainless Steels at High Temperatures
By Euroinox (2012)
Available at: https://www.bssa.org.uk/cms/File/StainlessSteels_at_HighTemperatures_EN.pdf
-How to Select the Right Stainless Steel or High Temperature Alloy for Heading
By Douglas G. Frick - Carpenter Technology (2019)
Available at: https://www.carpentertechnology.com/en/alloy-techzone/technical-information/alloy-selection/how-to-select-the-right-stainless-steel-or-high-temperature-alloy-for-heading
-DESIGN GUIDELINES FOR THE SELECTION AND USE OF STAINLESS STEEL
A DESIGNERS' HANDBOOK SERIES No 9014
By NiDI
Available at: https://www.nickelinstitute.org/media/1667/designguidelinesfortheselectionanduseofstainlesssteels_9014_.pdf
Best regards, Pierluigi Traverso
Pierluigi Traverso Thanks for your notice and the information shared. I will definitely take a look at the notes. Appreciate it.
Magnetic stainless steels will have either ferrite or martensite matrix. These magnetic stainless steels may not have high creep resistance at temperatures greater than 600 C. Austenitic stainless steels such as 309, 310H etc., will have high temperature stability but are non-magnetic. Still, the long-term creep resistant service temperature for any stainless steels is below 650 C.
You need to go for nickel base super alloys if you are looking for creep and corrosion resistance at 800 C. At this temperature any material will be paramagnetic!
Krishnan Raja Thank you for providing me this valuable information.
Krishnan Raja and Pierluigi Traverso Allow me to break it down even further. The stainless steel that has to be considered must be heated by means of induction heating up to a range of 600-800 deg C for its operation and maintained at a specific temperature in mentioned range continuously. Where 800 deg C is the worst-case scenario considered. To improve the heating efficiency it is recommended to consider the magnetic SS(ferritic or martensitic). Please advise which grade of material will be able to suffice the induction heating requirement and also sustain such high temperatures by maintaining the micro structural integrity during it's continuous operation.
There are many factors that determine the suitability. The following points may help select a suitable alloy:
Higher the chromium concentration, higher is the high temperature oxidation resistance up to say 800 - 850 C. If the temperature is higher than 900 C or for continuous operation at > 800 C, 5wt% aluminum addition is required for oxidation resistance. I think, Al is not required in your case. Creep strength can be achieved by precipitation hardening mechanism by secondary phase precipitates such as gamma prime (Ni3Al, Ni3Ti), and carbides (MC and M6C type). Since grain boundary sliding may NOT be the predominant creep deformation mechanism at
Another option is PH 15-7 Mo precipitation hardening stainless steel. This has 15% Cr, 7% Ni and 2 % Mo. This is a semi-austenitic stainless steel that can be converted to fully martensitic by a 760 C conditioning treatment and cryogenic soaking. The recommended max service temperature is only 540 C. The creep strength of PH 15-7 Mo will be higher than that of 17-4 PH SS because of 2% Mo addition but the oxidation resistance will be lower due to 15% Cr as against 17% Cr.
Krishnan Raja Thank you so much for providing such a detailed insight and this profound explanation has helped me understand the material aspect to a greater extent. The recommendations provided will work exceptionally well for operating at temperatures between 540 and 600 deg C. Thank you again for taking your valuable time.
May I please request you to also recommend a material If I were to consider a service temperature of 700 deg C for continuous operation with similar requirements such as creep strength, fatigue strength, resistance to dynamic loads, corrosion resistance, etc. Is there any option of considering a magnetic stainless steel/semi austenitic stainless steel as stated which can be converted to martensitic by treatments for 700 deg C service temperature? If not, is my only alternative nickel-based superalloys for this reference temp?
Also once the induction heating is seized for the materials 17-4 PH SS and PH 15-7 Mo and the material returns back to normal room temperature and further heated for its operation. Will this form of intermittent heating affect it's strength and will it be detrimental? How can I anticipate it's longevity in the service condition?
You may want to look at the materials used in super critical coal fired power plants which operate at ~700 C. I could not see any ferritic/martensitic materials at this temperature range. Most of the alloys are nickel based superalloys.
PH stainless steels will have the required thermal shock and thermal fatigue resistance at
For 700 C service, you may also consider super austenitic stainless steels such as super 304H, NF 709 etc, but these alloys will be inferior to nickel base alloys.
Dear, Krishnan Raja you have provided me such vital information and cleared many doubts on many grounds. I'm sure all these details will assist me in determining the best material for the application. I will also look into collecting more details and literature for thermal cycling and nickel based super alloys. Thank you for your valuable time.
Wishing you all success in your endeavors! If possible, please share your experience with these materials in 'real' life extreme environments!!
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