Large Chunks of Extremely Strong Steel

1. Large Chunks of Extremely Strong Steel 52nd Hatfield Memorial Lecture

2. an apple weighs 1 Newton = 1 Pa 1 m

3. Brenner, 1956

4. Scifer, 5.5 GPa and ductile Kobe Steel

7. 1 Denier: weight in grams, of 9 km of fibre 50-10 Denier Scifer is 9 Denier

8. Morinobu Endo, 2004

9. Claimed strength of carbon nanotube is 130 GPa Edwards, Acta Astronautica, 2000 Claimed modulus is 1.2 TPa Terrones et al., Phil. Trans. Roy. Soc., 2004

10. 36000 km tethered space elevator Arthur C. Clark (1979)

11. geosynchronous orbit

12. strength 130 GPa modulus 1.2 TPa

13. data from Pan et al. 1991, Yu et al. 2000

14. An equilibrium number of defects. Strength of a nanotube rope 2 mm long is less than 2000 MPa

15. Summary • Strength produced by deformation limits shape: wires, sheets... • Strength in small particles relies on perfection. Doomed as size increases.

16. Smallest size that can be achieved in a polycrystalline substance?

18. Yokota & Bhadeshia, 2004

19. Summary Thermomechanical processing limited by recalescence Need to store the heat Reduce rate Transform at low temperature

20. DISPLACIVE RECONSTRUCTIVE

21. Swallow and Bhadeshia, 1996

22. Fe-2Si-3Mn-C wt% 800 B S 600 Temperature / K 400 M S 200 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Carbon / wt%

23. Fe-2Si-3Mn-C wt% 1.E+08 1 year 1 month Time / s 1.E+04 1.E+00 0 0.5 1 1.5 Carbon / wt%

24. Low transformation temperature Bainitic hardenability Reasonable transformation time Elimination of cementite Austenite grain size control Avoidance of temper embrittlement wt%

25. Homogenisation Austenitisation Isothermal transformation 1200 C o 2 days 1000 o C 15 min Temperature Air 125 C - 325 C o o slow cooling hours - months cooling Quench Time

26. 700 600 500 Vickers Hardness 400 T = 200°C 300 1.E+04 1.E+05 1.E+06 1.E+07 Time/ s

27. 700 600 500 400 o B ~ 350 C Temperature/ oC S 300 200 o M = 120 C S 100 0 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 Time / s

29. Cooking temperature? 180 to 220 °C

30. 100 retained austenite 80 X-ray diffraction results 60 Percentage of phase 40 bainitic ferrite 20 0 200 250 300 325 o Temperature/ C

32. a g a g g 50 nm

33. g g a a a 20 nm

34. Conclusions Low temperature transformation: 0.25 T/Tm Fine microstructure: 20-40 nm thick plates Carbide-free Designed using theory alone Typical mechanical properties:

37. Faster Transformation Cobalt (1.5 wt%) and aluminium (1 wt%) increase the stability of ferrite relative to austenite Refine austenite grain size

38. 200oC 250oC 300oC

39. 700 650 600 550 H V 500 450 30 min 400 60 min 24 h 300 350 400 450 500 550 600 650 o Temperature / C

40. Fe-0.34C-5.08Cr-1.43Mo-0.92V-0.4Mn-1.07Si wt%

41. excess carbon in solid solution in ferrite !

43. Peet, Babu, Miller, Bhadeshia, 2004

44. Peet, Bhadeshia, 2004

45. Stress / GPa Velocity km s-1 Hammond and Cross, 2004

46. GRP mild steel “superbainite” vehicle steel GRP Peter Brown (DSTL) Dave Crowther (QinetiQ)

47. “more serious battlefield threats”

49. 650 HV 590 HV

50. ballistic mass efficiency consider unit area of armour