This document summarizes research on the alloy design of high-manganese maraging steels with precipitation hardening and transformation-induced plasticity (TRIP) or twinning-induced plasticity (TWIP) effects. The steels contain low carbon levels for ductility and manganese plus minor additions of nickel, aluminum, and titanium to increase strength through nanoscale precipitates during aging at 450°C while maintaining ductility from retained and newly formed austenite. Characterization showed the formation of coherent precipitates around 5 nm in size that increase hardness over aging time up to 192 hours. The steels exhibit ultrahigh strength from precipitation hardening combined with excellent ductility from TRIP/TWIP effects during

1. Alloy design of nanoprecipitate-hardened high-Mn maraging-TRIP and -TWIP steels D. Ponge, O. Dmitrieva, J. Millán, S. Sandlöbes, P. Choi, A. Kostka,G. Inden, D. Raabe Düsseldorf, Germany WWW.MPIE.DE d.raabe@mpie.de Dierk Raabe

3. Compositions and processing

4. Mechanical properties and microstructures

5. Characterization of precipitations

6. Formation of new austenite during aging

8. Small amountofaustenite (TRIP, TWIP)

10. Compositions and processing

11. Mechanical properties and microstructures

12. Characterization of precipitations

13. Formation of new austenite during aging

15. Low carbon: ductile martensite Compositions in mass%: newlean maraging steels PH PH PH Precipitation Hardenable Mn (+Ni): austenite (TRIP) Raabe, Ponge, Dmitrieva, Sander: Adv. Eng. Mat. 11 (2009) 547

16. Processing Vacuuminductionmelting Annealing Hot deformation Solution heat treatment + retained austenite Quenching Martensite “Maraging“ retained + new austenite Aging (450°C) Dmitrieva et al. ActaMater 59 (2011)

18. Compositions and processing

19. Mechanical properties and microstructures

20. Characterization of precipitations

21. Formation of new austenite during aging

23. 12MnPH after aging (48h 450°C) precipitates in a` no precipitates in Dmitrieva et al. ActaMater 59 (2011)

24. Tensile tests Ni-Maraging aged (450°C/48h) (X3NiCoMoTi18-12-4) quenched 12MnPH aged (450°C/48h) quenched D. Raabe et al. ScriptaMaterialia 60 (2009) 1141

26. Compositions and processing

27. Mechanical properties and microstructures

28. Characterization of precipitations

29. Formation of new austenite during aging

31. 09MnPH aging at 450°C, Proxigrams Fe Fe 09MnPH 450°C/48h 09MnPH 450°C/192h matrix particle matrix particle Ni Ni Mn Mn Al Al Ti Ti Dmitrieva et al. ActaMater 59 (2011)

32. Chemical compositions (09MnPH; 450°C/48h) 47.11 Ni50(Mn,Al,Ti)50 possible: Dmitrieva et al. ActaMater 59 (2011)

33. 09MnPH aging at 450°C 48 hours 192 hours Iso-conc. surfaces: 14 at.% Ni only Feand Nishown 10 nm Dmitrieva et al. ActaMater 59 (2011)

36. Compositions and processing

37. Mechanical properties and microstructures

38. Characterization of precipitations

39. Formation of new austenite during aging

41. Effectofaging on ductility aged 450°C/48h Precipitation hardening 2 as-quenched increase of austenite fraction during aging -Fe (Martensite) -Fe (Austenite), vol. fraction 15-20%

42. Effectofaging on ductility aged 450°C/48h Precipitation hardening 2 as-quenched increase of austenite fraction during aging ? strain 0% strain 15% 2 1 1 -Fe (Martensite) -Fe (Austenite), vol. fraction 15-20%

43. APT results: Atomic map (12MnPH aged 450°C/48h) Martensite decorated by precipitations Austenite ? ? 70 millionions Laser mode (0.4nJ, 54K) Mn atoms, Ni atoms Mn iso-conc: 18 at.%

45. Compositions and processing

46. Mechanical properties and microstructures

47. Characterization of precipitations

48. Formation of new austenite during aging

50. + controlled amounts of Ni (2 wt%), Al (0.15 wt%), … increase strength during aging by formation of nanosized precipitations without significant reduction of ductility

51. By controlling the austenite stability (here by Mn) martensite can be refined and ductility can be further increased by retained and reverted austenite (TRIP)