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Ferritic stainless steel.pptx

  1. Republic of Iraq Ministry of Higher Education And Scientific Research University of Diyala College of Engineering Ferritic stainless steel By : ‫كاظم‬ ‫انيس‬ ‫تايه‬ Supervisor by ‫أ‬ . ‫خليل‬ ‫عادل‬ ‫د‬ 1
  2. Introduction  Ferritic steel is a grade of stainless steel alloy that contains over 12% chromium.  It differs from other forms of stainless steel in two critical regards: its molecular grain structure and its chemical composition.  Ferritic stainless steel is actually defined as a straight chromium non-hardenable class of stainless alloys that have chromium contents ranging from 10.5% to 30% and a carbon content of less than 0.20%.  These steels are non-hardenable by heat treatment, and only marginally hardenable by cold rolling. 2
  3. Ferritic Stainless Steels • Advantages – Relatively Cheap – Low Corrosion rate – pitting & SCC – Low tendency of sensitization • Limitations – High ductile to brittle transition temperature. – 475oC Embrittlement – Formation of undesirable intermetallics such as Sigma, Chi and Laves phases. – Low Weld Ductility with increase in Cr Content – Sensitization – Limitation of Strength at higher temperature 3
  4. Grade C Mn Si Cr Mo P S Comments/Applications 405 0.08 1.0 1.0 11.5-14.5 - 0.04 0.03 0.1-0.3 Al 409 0.08 1.0 1.0 10.5-11.75 - 0.045 0.045 (6xC) Ti min 429 0.12 1.0 1.0 14.0-16.0 - 0.04 0.03 430 0.12 1.0 1.0 16.0-18.0 - 0.04 0.03 446 0.20 1.5 1.0 23.0-27.0 - 0.04 0.03 0.25 N Composition of Important Ferritic Stainless steels 4
  5. Effect of Cr Concentration on the impact properties of Fe-Cr Alloys 5
  6. Fe-Cr equilibrium Diagram 6
  7. Pseudo Binary Phase Diagram of Fe-18Cr Alloy 7
  8. Mechanism of Sensitization 8
  9. Pseudo binary Phase Digram Fe-18Cr-8Ni SS with C C solubility limit in Fe-18Cr-8Ni SS 9
  10. Sensitization Curves for 304 and 347 SS 347 S Effect of Mo on sensitization Effect of N on Sensitization 10
  11. PRE = %Cr + 3.3 x %Mo + 16 x %N Pitting of Stainless Steels 11
  12. Super Ferritic/Austenitic Stainless Steels • To enhance further the Pitting corrosion, Chloride Stress Corrosion cracking, super ferritic, super-austentic Stainless Steels are made : • They have Mo – upto 6% • Nitrogen from 0.1-0.2% • Mostly used in Offshore structure, ships and marine applications • Very costly compared to conventional SS 12
  13. Effect of ferrite content on the pitting rate of duplex SS steel Welds of varying N levels – exposed to 6% FeCl3 + 0.05N HCl solution 13
  14. Cr concentration profile around austenitic-Ferrite interface Containing M23C6 carbide Pseudo binary phase diagram of 65Fe-Cr-NiAlloy 14
  15. IC378 - The darker etching phase is ferrite and the remainder is austenite Microstructures of some Duplex SS IC381 (dark phase is ferrite). IC381 (dark phase is ferrite A219 The austenite is yellow and ferrite is dark brown, with the sigma phase white. 15
  16. Effect of C addition on the gamma loop in Fe-Cr alloys 16
  17. The properties of ferritic stainless steel  Ferritic stainless steels are characterised by their body- centred cubic (BCC) crystal structure, and they contain 11% to 27% chromium and small amounts of ferrite stabilisers, such as niobium and titanium.  Ferritic alloys exhibit ferromagnetic behaviour up to a temperature known as the Curie point (650 °C – 750 °C), beyond which materials lose their permanent magnetic properties.  The BCC grain structure of ferritic alloys, which is the same as that of pure iron at room temperature, is the reason for its magnetic nature.  Ferritic stainless steels, similar to austenitic stainless steels, cannot be strengthened by heat treatment. 17
  18. 18 ferritic stainless steel
  19. The applications of ferritic stainless steel  The magnetic properties of ferritic grades is a major advantage and enabler for many of their applications.  Fastening parts and induction heating, for example, both make use of this property in the production of induction cookers and magnetic fasteners.  Ferritic alloys also have a lower thermal expansion coefficient and higher thermal conductivity than austenitic grades, which makes them particularly suitable for heat transfer applications such as cooking utensils.  The corrosion resistance of some ferritic stainless steels is sufficient to replace austenitic steel 304, and they can be used in the production of dishwashers, kitchen sinks and food processing equipment.  Some specialty grade ferritic stainless steels have additional molybdenum and higher chromium content, which makes them useful in corrosive seawater applications. 19
  20. Uses of Ferritic stainless steels.  Ferritic steels are chosen for their resistance to stress corrosion cracking,  which makes them an attractive alternative to austenitic stainless steels in applications where chloride-induced SCC is prevalent. 20
  21. References 1. Lacombe, P.; Baroux, B.; Beranger, G., eds. (1990). Les Aciers Inoxydables. Les éditions de Physique. pp. Chapters 14 and 15. ISBN 2-86883-142-7. 2. The ferritic solution. 2007. ISBN 978-2-930069-51-7. 3. The International Nickel Company (1974). "Standard Wrought Austenitic Stainless Steels". Nickel Institute. Archived from the original on 2018-01-09.. 4. "304 vs 430 stainless steel". Reliance Foundry Co. Ltd. 5. "Frederick Mark Becket American metallurgist". Encyclopaedia Britannica. 6. Cobb, Harold M. (2012). Dictionary of Metals. ASM International. p. 307. ISBN 9781615039920. 7. Charles, J.; Mithieux, J.D.; Santacreu, P.; Peguet, L. (2009). "The ferritic family: The appropriate answer to nickel volatility?". Revue de Métallurgie. 106: 124–139. doi:10.1051/metal/2009024. 21