1. RG1 University of Chemical Technology and Metallurgy Department of Materials Science Microstructure and Mechanical Properties of Austempered Ductile Cast Iron

2. RG2 CHEMICAL COMPOSITION OF CAST IRON: Fe C Si Mn P S Mg val. 3.5 2.5 0.25 0.038 0.015 0.05 Grey cast iron Ductile cast iron Addition of cerium or magnesium to induce nodularisation of graphite No addition of Mg or Ce Tensile strength: 150-400 MPa Tensile strength: 350-800 MPa Elongation: 3-20 % Elongation: 0 %

3. RG3 Microstructure of Ductile irons

4. RG4 1. Austenitising between 850 and 950 o C typically for 60 min. 2. Quenching into a salt or oil bath at a temperature in the range 450 – 250 o C usually between 0.5 and 3 hours 3. Cooling to a room temperature Austempered ductile cast iron (ADI) A further improvement of ductile cast iron is obtained with an isothermal heat treatment named austempering

5. RG5 Mechanical properties STRENGTH : equal to or greater than steel ELONGATION : maintain as cast elongation while double the strength of quenched and tempered ductile iron TOUGHNESS : better than ductile iron and equal to or better than cast or forged steel FATIGUE STRENGTH : equal to or better than forged steel. DAMPING : 5 times greater than steel.

6. RG6 R. Elliott, 1988

7. RG7 ADI has excellent castability, it is possible to obtain near-net shape castings even of high complex parts. ADI is cheaper than steel forgings ADI has a weight saving of 10% Economical advantages and applications Gears Automotive industry

8. RG8 Processing window The bainitic transformation in ductile iron can be described as two stage reaction: Stage I: Austenite decomposition to bainitic ferrite and carbon enriched austenite. Stage II: Further austenite decomposition to ferrite and carbide.

9. RG9 Closed processing window

10. RG10 Microstructure of ADI  Bainite  Retained austenite  Martensite  Carbide  Pearlite

11. RG11 Element Cell boundary Close to graphite Mn1.73 0.40 Si1.752.45 Mo0.600.07 Element Cell boundary Close to graphite Mn0.81 0.57 Si2.312.49 Mo0.16 0.12 Fe-3.5C-2.5Si-0.55Mn-0.15Mo

12. RG12 Homogenised at 1000 o C for 3 days Austempered at 350 o C for 64 min o

13. RG13 Volume fraction of retained austenite and hardness

14. RG14 Austempering temperature and carbon content in retained austenite

15. RG15 = a + b (%C) + c (%Mn) = a + b (%C) + c(%Mn) + d (%C x %Mn) VV = sin (%C) + tanh (%Mn) Variables for modelling include: C, Mn, Si, Mo, Ni, Cu V  sum C x W c Mn x W Mn TATA MnC VV VV INPUT HIDDEN OUTPUT

16. RG16 Volume fraction of retained austenite to different temperatures

17. RG17 Hardness /Vickers, HV/ to time of austempering, min Other mechanical properties:

18. RG18

19. RG19

20. RG20

21. RG21 Physical Model for Retained Austenite

22. RG22

23. RG23

24. RG24 Babu etal. 1993

25. RG25 Volume fraction of cementite I part

26. RG26 Volume fraction of cementite II part

27. RG27

28. RG28 Treatment, temperature and time

29. RG29 SEM vision

30. RG30