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Multiphase Bainitic Steels at the Max Planck Institut in Düsseldorf

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Steel, Bainite, microstructure, properties, processing

Steel, Bainite, microstructure, properties, processing

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  • 1. Max-Planck-Institut für Eisenforschung GmbH
  • 2. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 3. Aims of High Strength Long Products - Projecttensile strength of 900 to 1400 MPagood ductility and toughness(K1C≈150MNm-3/2, CharpyV-notch energy ≥ 30 J at -60°C)develop refined multi-phasemicrostructures (carbide-freebainite/acicular ferrite with filmsof retained austenite trappedbetween the platelets
  • 4. Aims of High Strength Long Products - ProjectDefine medium carbon steel compositions(addition of Si, Mn, Cr, Mo, Ni, V, B)
  • 5. Aims of High Strength Long Products - Projectindustrial cooling conditionsfor Long Products(wire rods from 16 to 22mmdiameter with cooling ratesof 1–4 K/s)guidelines for the processingparameters (thermomechanicaltreatment (TMT), austeniteconditioning (hot rolling parameters)and cooling strategies (continuousor more-step-cooling)
  • 6. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Nanoindentation
  • 7. Upper and Lower BainiteUpper and Lower Bainite:•tend to form as aggregates(sheaves) of small platelets orlaths (sub-units) of ferrite•difference:carbide precipitationUPPER BAINITE(High TransformationTemperature)LOWER BAINITE(Low TransformationTemperature)Carbon supersaturated plateCarbon diffusion intoausteniteCarbon diffusion intoaustenite and carbideprecipitation in ferritefromausteniteCarbide precipitation fromausteniteCarbide precipitation10µm0.2µm
  • 8. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 9. Incomplete Reaction PhenomenonAe3Tox Carbon in austeniteTemperature
  • 10. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 11. Overview on Proceedings9 different steelcompositionsDilatometer tests WUMSI testsIsothermalMulti-step cooling:temperatures: 400°C, 425°C, 450°Ctime: 1h, 15minContinuousMulti-step cooling:breaking points:600°C and 700°Cno deformationdeformation at 800°C110  sTransformationparameters:AC3, MS, BSAustenite graincharacteristics:Grain sizeElongated or equiaxedMicrostructurecharacteristicsMaterial testing:Tensile testsCharpy-V-notch testsMicrostructure:Light opticalmicroscopySEMEBSDAusteniteStability:X-rayNano-IndentationTTT and CCTdiagrams
  • 12. Chemical analysis of steel compositions• Base composition: 0.3 wt% C - increasing the strength of the steel,stabilizing the austenite 2.0 wt% Si - retarding the carbide precipitation 1.5 wt% Mn - stabilizing the austenite• Additional alloying elements: Cr, Mo, Ni, V, B and P – influence the trans-formation (inhibitdiffusional, promotebainitic transformation)
  • 13. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 14. BF + PInfluence of alloying elements on transformationMn, Ni, Mo, Cr, BCr,Mo,V, SiMn,NitimetemperatureMsCr,Mo,V,Mn,NiC, Cr, Mo, Mn, Ni, V
  • 15. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 16. Austenizing, tempering and etching testsVariation of:Tausten.= 950°C-1200°CTtemper= 300°C-600°CEtchant: aqueous oralcoholic picric acid + Cu2Cl atroom temperature or heated at80°C; alcoholic nitric acid;mixture of nitric acid and picricacid + Cu2ClMP_MnSi: Tausten.= 950°C; Ttemper= 450°C, aqueous picric acid; G = 11-12
  • 17. Thermal etchingMP_CrMoNi:Tausten.= 1200°CThermal etchingG = 2-3
  • 18. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 19. Determination of CCT-diagrams without deformation0,1 1 10 100 1000 1000002004006008001000HV5241260274351404487temperature(°C)time (s)SteelBase of chemical composition (wt%) Additional alloying elements (wt%)C Mn Si S P Al N Cr Mo Ni V BMP_MnSi 0.3 1.5 2.0 0.0135 0.0110 0.04 0.005 - - - - -
  • 20. MP_MnSi, 32K/s to 1K/s32K/s 16K/s 8K/s4K/s 2K/s 1K/s
  • 21. Determination of CCT-diagrams without deformation0,1 1 10 100 1000 1000002004006008001000HV5288335410498545557590temperature(°C)time (s)SteelBase of chemical composition (wt%) Additional alloying elements (wt%)C Mn Si S P Al N Cr Mo Ni V BMP_B 0.3 1.5 2.0 0.0135 0.0110 0.04 0.005 - - - - < 20ppm
  • 22. MP_B, 32K/s to 3K/s32K/s 16K/s 8K/s6K/s 4K/s 3K/s
  • 23. Determination of CCT-diagrams without deformation0,1 1 10 100 100002004006008001000504HV5410467508551582593temperature(°C)time (s)SteelBase of chemical composition (wt%) Additional alloying elements (wt%)C Mn Si S P Al N Cr Mo Ni V BMP_Mo 0.3 1.5 2.0 0.0135 0.0110 0.04 0.005 - 0.6 - - -
  • 24. MP_Mo, 32K/s to 2K/s32K/s 16K/s 8K/s4K/s 3K/s 2K/s
  • 25. Hardness (HV5) of continuous cooled samples0 5 10 15 20 25 30 35250300350400450500550600MP_CrMoPMP_CrMoVMP_CrMoNiMP_CrMoBMP_MoMP_CrMoMP_CrMP_MnSiMP_BHV5cooling rate (K/s)
  • 26. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 27. Determination of CCT-diagrams with deformation1 10 100 100002004006008001000temperature(°C)time (s)SteelBase of chemical composition (wt%)Additional alloying elements(wt%)C Mn Si S P Al N Cr Mo Ni V BMP_B 0.3 1.5 2.0 0.0135 0.0110 0.04 0.005 - - - - <20ppm
  • 28. MP_B, 32K/s to 2K/s16K/s 4K/s8K/s
  • 29. Determination of CCT-diagrams with deformation1 10 100 1000010020030040050060070080090010001100temperature(°C)time (s)SteelBase of chemical composition (wt%) Additional alloying elements (wt%)C Mn Si S P Al N Cr Mo Ni V BMP_Mo 0.3 1.5 2.0 0.0135 0.0110 0.04 0.005 - 0.6 - - -
  • 30. MP_Mo, 16 K/s to 4 K/s16K/s 4K/s8K/s
  • 31. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 32. WUMSI (isothermal tests, without deformation)T5min@1050°CSalt bath1h@450°C1h@425°C1h@400°Ctair800°C1min@1100°Cairt8/5 =37ssKT 8Cs 1050@10,3.0 1
  • 33. WUMSI (isothermal holding 1h, without deformation)Without deformationSteel Tiso=400°C Tiso=425°C Tiso=450°CMP_BMP_MoB265B340B351fine B501B381B+M458HV5= HV5= HV5=HV5= HV5= HV5=
  • 34. WUMSI (isothermal tests, with deformation)T5min@1050°CSalt bath1h@450°C1h@425°C1h@400°CtairairCs 800@10,3.0 1
  • 35. WUMSI (isothermal holding 1h, with deformation)With Deformation (0.3; 10s-1@800°C)Steel Tiso=400°C Tiso=425°C Tiso=450°CMP_BMP_MoB311B+M+P325B+M+PB+M368B+M411M+B553HV5= HV5=HV5= HV5= HV5=
  • 36. WUMSI (Continuous cooling)T5min@1050°C-8K/sair (-1K/s)600°C / 700°C1min@1100°CTtwith deformationT5min@1050°Ctair (-1K/s)600°C / 700°C-8K/sCs 800@10,3.0 1Cs 1050@10,3.0 1
  • 37. WUMSI (Continuous cooling)F+P+M+B240B+F+P+M310B+M334P+F250B+M378M+B (50%)379M+B(?)391M+B(50%)439MP_CrMoBMP_B700°Cwithout def.700°Cwithout def.600°Cwithout def.600°Cwithout def.700°Cwith def.700°Cwith def.600°Cwith def.600°Cwith def.
  • 38. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 39. WUMSI (LePera-etching, EBSD map)MP_Mo:•without deformation•Isothermal holding (1h@400°C)•HV5: 501
  • 40. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSD / SEMd. Tensile Testse. Nanoindentation
  • 41. WUMSI (EBSD maps, Mo_iso_400_oU)
  • 42. WUMSI (SEM-graph, Mo_iso_400_oU)
  • 43. WUMSI (EBSD maps, Mo_iso_450_oU)
  • 44. WUMSI (EBSD maps, Mo_iso_400_mitU)
  • 45. WUMSI (EBSD maps, Mo_iso_450_mitU)
  • 46. WUMSI (SEM-graph, Mo_iso_450_mitU)
  • 47. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSDd. Tensile Testse. Nanoindentation
  • 48. 400 410 420 430 440 45012001250130013501400145015001550160016501700no deformation, 1hno deformation, 15minwith deformation, 1hwith deformation, 15minUTS(N/mm2)Isothermal temperature (°C)Tensile Tests for MP_Mo steel10 20 30 40 50 6012001250130013501400145015001550160016501700no deformation, 400°Cno deformation, 450°Cwith deformation, 400°Cwith deformation, 450°CUTS(N/mm2)isothermal holding time (min)
  • 49. Transformation Behavior of MP_MoNo deformation With deformationTiso=400°C Tiso=450°C Tiso=400°C Tiso=450°Ctiso=60mintiso=15min
  • 50. Content1. Aims of project2. Upper and Lower Bainite3. Incomplete Reaction Phenomenon4. Overview on Experiments5. Influence of Alloying Elements on Transformation6. Dilatometrya. CCT without deformationb. CCT with deformation7. WUMSIa. Experimentsb. LePerac. EBSDd. Tensile Testse. Nanoindentation
  • 51. Nano-Indentation, (Mo_iso_400_oU)3.785.686.368.134.775.906.56.543.997.096.85.928.323.86.395.61 6.265.784.686.726.29.938.7911.519.9210.374.895.287.164.824.825.955.246.866.075.29.219.910.169.628.226.196.47109.29.157.65.94.64 4.82H in GPaPmax=1000mN
  • 52. Conclusion• Using EBSD microstructural characteristics can be revealed. This methodcan be supported by LePera etching or nano-indentation.• Additional alloying elements have a strong influence on the bainitictransformation and after all trials the most promising steels can be fixed: for isothermal treatment: MP_B and MP_Mo for continuous cooling treatment: MP_B and MP_CrMoB• The influence of deformation on the bainitic transformation is less than thatof the additional alloying elements and the variation of the processparameters (e.g. isothermal holding temperature)
  • 53. Future work• Tensile tests for all steels with promising microstructures• Charpy-V-notch tests to investigate the toughness properties• Nanoindentation tests not only to identify the single constituents but alsoto determine the their mechanical properties and compare these results withthe mechanical properties of the whole sample• X-ray measurement to define volume fraction of retained austenite andits C content → stability of retained austenite

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