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3rd CAMS 2014_TWIP-TRIP Steels_FINAL_2014

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Bruno Charles De Cooman
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MATERIALS DESIGN LABORATORY Alloy Design UHS Intercritically Annealed 6%-12%Mn TWIP+TRIP Steel B. C. De Cooman Materials Design Laboratory, Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang, South Korea CAMS 2014 MATERIALS AUSTRALIA November 26th-28th, 2014 Sydney, NSW, AUSTRALIA
MATERIALS DESIGN LABORATORY Pohang University of Science and Technology Graduate Institute of Ferrous Technology Pohang
MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
MATERIALS DESIGN LABORATORY Global Trends Automotive Steel Grades The increasing use of AHSS/UHSS use is driven by… • The need for high volume vehicles at competitive prices. • Stringent regulations and corporate goals for: Passenger safety Fuel economy Lower greenhouse gas emissions • Sustained efforts by the steel industry to innovate and create advanced steels, and original, steel-based solutions and methods, which underline the large potential of steel. Car makers test, utilize multi-materials designs, but steel remains dominant… • Steel, the material of choice for BIW: 99% passenger cars have a steel BIW. • 60-70% of the car weight consisting of steel or steel-based parts. • Globalization requires world-wide availability and global procurement of standard materials. • The automotive industry makes excursions in light materials applications but there is only a slight actual increase in the use of Al, Mg and plastics…. but this may change!
MATERIALS DESIGN LABORATORY Lightweighting: Mass “Containment”, Mass “Reduction” • Low gas mileage: 0.3l-0.6l/100km fuel use reduction for a 100kg weight reduction • Less greenhouse gas emissions: 2020 target ~100gr/km • NHTSA CAFE Standards for 2017 New mpg target: DOUBLE the average mpg for new cars, trucks 54.5 mpg will cut of gas emissions by HALF Current situation Best US highway mileage 2012: 42 mpg (Chevrolet CRUZE) Other example: 32 mpg (VW Passat ) General situation: 25mpg in US, 45 mpg in EU, better in Japan Passenger Safety: • Low peak deceleration, long crush length, long time duration of crash pulse • High energy dissipation with minimum intrusion • Higher impact strength for A and B Pillars • Anti-Intrusion applications: front and rear crash, side intrusion • Tougher collision and rollover safety test for the 5-star rating Closure Applications: • Dent resistance Coated Products: • Perforation and cosmetic corrosion resistance • Surface quality, visual Other Issues: • Noise and Vibrations • Vehicle Handling, Stiffness and Torsional Rigidity Global Trends Automotive Steel Grades
MATERIALS DESIGN LABORATORY Weight spiral: Safety Space Performance Reliability Quality Comfort 1500 1400 1300 1200 1100 1000 900 800 700 600 500 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 Curbweight,kg 88% increase in weight EU mid size vehicles Year CAFE Fuel Economy 40 45 50 55 60 Wheelbase . track Gasmileage,mpg 40 45 50 35 30 Year 2012 2014 2016 2018 2020 2022 Prius Doubling mileage Regulations Influence on Materials Selection
MATERIALS DESIGN LABORATORY Weight spiral: Safety Space Performance Reliability Quality Comfort 1500 1400 1300 1200 1100 1000 900 800 700 600 500 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 Curbweight,kg 88% increase in weight EU mid size vehicles Year Regulations Influence on Materials Selection Passive Passenger safety
MATERIALS DESIGN LABORATORY Mechanical Properties Yield Strength Tensile Strength Uniform elongation Total Elongation Automotive Sheet Steel Products
MATERIALS DESIGN LABORATORY RoughingReheating Finishing Cooling Coiling Conventional HSM, CSM and CA/HDG Processing Cold rolling Continuous Annealing Hot Dip Galvanizing
MATERIALS DESIGN LABORATORY Mechanical Properties Yield Strength Tensile Strength Uniform elongation Total Elongation Bake-hardening Springback Normal Anisotropy Planar Anisotropy Deep Drawability Stretch Formability Crashworthiness Geometrical Properties Dimensional Width Thickness Shape Edge Drop Crown Flatness Technical Properties Weldability Phosphatabilty Roughness Waviness Friction Corrosion resistance Phosphatability Paint adhesion Visual appearance Automotive Sheet Steel Products
MATERIALS DESIGN LABORATORY Press-forming Spring-back Hole expansion Bending RSW
MATERIALS DESIGN LABORATORY 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 IF CMn HSLA Conventional Automotive Steels 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% 10.000MPa.% IF LC CMn HSLA
MATERIALS DESIGN LABORATORY MA 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA First Generation Advanced High Strength Steels DP TRIP MACP
MATERIALS DESIGN LABORATORY Automotive Body Materials Selection 6% HPF + 5% MA 23% HSS 30% DP / Multi Phase GM AVEO 34% IF +LC +BH Cadillac CTS PHS VW: 6% (GOLF 6) → 28% (GOLF 7)
MATERIALS DESIGN LABORATORY Al alloys Polymers Mg alloys Automotive Steel grades CFR-Composites Ti alloys Automotive Body Materials Selection
MATERIALS DESIGN LABORATORY Al alloys Polymers CFR-Composites Automotive Body Materials Selection Monocoque: 5754 (Structural) 6111 (External parts) Space frame: Multiple Al products integration High strength die casting Al-extrusion Hydroform extrusion Issues: Strain hardening: low Strain rate sensitivity: negative Cost: 4-6$/kg (1.3$/kg Steel)
MATERIALS DESIGN LABORATORY MA 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA Second Generation Advanced High Strength Steels TWIP Fe22Mn0.6C Fe18Mn1.5Al0.6C
MATERIALS DESIGN LABORATORY MA 300 400 500 600 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA Third Generation Advanced High Strength Steels 3rd Generation 0.2µm UFG TRIP Low Mn TWIP SBIP MBIP + 700 800
MATERIALS DESIGN LABORATORY Strain Hardening Engineering True strain 0 0 Truestress,strainhardeningrate,MPa )( u   d d
MATERIALS DESIGN LABORATORY Strain Hardening Engineering True strain 0 0 Truestress,strainhardeningrate,MPa )( u   d d
MATERIALS DESIGN LABORATORY Strain Hardening Engineering 0 0 True strain Truestress,strainhardeningrate,MPa Gain in strength and ductility ! u )(   d d
MATERIALS DESIGN LABORATORY 0 0 True strain Truestress,strainhardeningrate,MPa Gain in strength and ductility ! Strain Hardening Engineering u )(   d d Dislocation Accumulation or Storage (Stage II) Dislocation Annihilation or Dynamic recovery (Stage III) ρkρk dε dρ dε dρ dε dρ   21
MATERIALS DESIGN LABORATORY  d/d 0 0 0.1 0.2 0.3 0.4 1000 2000 3000 4000 5000 True strain Truestress,strainhardeningrate,MPa TRIP TWIP HS IF TRIP Strain Hardening Engineering
MATERIALS DESIGN LABORATORY What is Strain Hardening Engineering? 1. Strengthening mechanisms: • Solid solution strengthening (Alloying) • Grain size refining (Alloying and Processing) • Precipitation strengthening (Alloying) • Bake-hardening (Processing) 2. Plasticity-enhancing mechanisms: • Multi-phase steels: austenite required • TRIP effect: Strain-induced Transformation • TWIP effect: Deformation Twinning g strain g →a’ TRIP-effect a’ g g →gT TWIP-effect g
MATERIALS DESIGN LABORATORY High Mn TWIP Steel TWIP: TWinning-Induced Plasticity 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Eng.Stress(MPa) Eng. Strain (%) 20 22 24 26 28 30 700 750 800 850 900 10-4s-1 Fe18Mn0.6C1.5Al g →gT TWIP-effect g 10-3s-1
MATERIALS DESIGN LABORATORY Rolling directionTWIP 1000 High Mn TWIP Steel
MATERIALS DESIGN LABORATORY HER Diffuse necking No diffuse necking IF steelTWIP LMIE HDF Fe22Mn0.6C Fe15Mn2Al0.7C Zn Zn
MATERIALS DESIGN LABORATORY 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C2Al Engineering strain, % YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 SFE** mJ/m2 Fe15Mn0.6C 509 1124 51 12 13 Fe15Mn0.6C1.5Al 480 976 58 26 21 Fe15Mn0.6C2.0Al 488 939 58 30 24 * Saeed-Akbari et al., Metall. Mater. Trans. A 2009 ** Dumay et al., Mater. Sci. Eng. A 2008 YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe15Mn0.6C2.0Al 10% 20% 30% 40% 50% 60% 712 989 1071 1122 1261 2394 991 1167 1319 1407 1590 1737 43 23 15 10 9 7 30 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Engineering strain, % 10% 20% 30% 40% 50% 60%
MATERIALS DESIGN LABORATORY YS (MPa) UTS (MPa) Total Elongation (%) SFE* mJ/m2 SFE** mJ/m2 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2.0Al 486 492 478 838 900 915 16 30 41 12 26 30 10 18 21 Fe12Mn0.9C1Si-0.0V Fe12Mn0.9C1Si-0.2V Fe12Mn0.9C1Si-0.5V Fe12Mn0.9C1Si-0.7V 434 614 722 741 1166 1324 1276 1260 45 38 25 22 26 - 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2Al Engineeringstress,MPa Engineering strain, % 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 0.2%V0.7%V 0.5%V Engineeringstress,MPa Engineering strain, % V-free V-additions: increased YS and increased strain hardening
MATERIALS DESIGN LABORATORY YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe15Mn0.6C2.0Al 10% 20% 30% 40% 50% 60% 712 989 1071 1122 1261 2394 991 1167 1319 1407 1590 1737 43 23 15 10 9 7 30 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Engineering strain, % 10% 20% 30% 40% 50% 60% 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 0.2%V0.7%V 0.5%V Engineeringstress,MPa Engineering strain, % V-free YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe12Mn0.9C1Si-0.0V Fe12Mn0.9C1Si-0.2V Fe12Mn0.9C1Si-0.5V Fe12Mn0.9C1Si-0.7V 434 614 722 741 1166 1324 1276 1260 45 38 25 22 26
MATERIALS DESIGN LABORATORY Classification of the Mn UHSS Steels High Mn Medium Mn %Mn >25 22 - 15 12 - 6 7 - 4 Processing Conventional annealing Intercritical annealing Q & P Cold rolled Shear bands Deformed g Deformed a’ After annealing g UFG g  a Plasticity SBIP TWIP TWIP+TRIP TRIP g-ISFE (mJ/m2) >75 >20 >20 <10 g-stability g-composition g-composition and size Role of Mn g-stability / SFE g-stability / SFE / Hardenability
MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 DP980 Truestress,MPa Workhardeningrate,MPa True strain TiIF Ti-IF: standard highly formable steel DP 980: standard 1st generation AHSS Mechanical properties at reduced Mn alloying
MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 TWIP1000 DP980 TiIF Truestress,MPa Workhardeningrate,MPa True strain Ti-IF: standard highly formable steel DP 980: standard 1st generation AHSS Mechanical properties at reduced Mn alloying DSA )(   d d
MATERIALS DESIGN LABORATORY TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 12Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain Mechanical properties at reduced Mn alloying
MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 10Mn Truestress,MPa Workhardeningrate,MPa True strain TWIP1000 TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Mechanical properties at reduced Mn
MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 6Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Medium Mn 3: 8%Mn0.4%C3.0%Al2.0%Si Medium Mn 4: 6%Mn0.3%C3.0%Al1.5%Si Mechanical properties at reduced Mn DSA
MATERIALS DESIGN LABORATORY Original concept: TWIP Steel Deformation g g Fully Austenitic Low SFE Dislocation plasticity Twinning-induced plasticity Low YS / High Strain Hardening g g High Mn TWIP Steel Design Concept Austenite: e.g. 18% Mn 0.6% C +Al
MATERIALS DESIGN LABORATORY YS (MPa) UTS (MPa) Total Elongation (%) SFE* mJ/m2 SFE** mJ/m2 Fe18Mn0.6C Fe18Mn0.6C1.5Al Fe18Mn0.6C3.0Al 484 498 499 1106 960 849 60 59 50 14 28 40 17 25 32 Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C3.0Al 509 480 488 1124 977 939 51 58 58 12 26 30 13 21 24 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2.0Al 486 492 478 838 900 915 16 30 41 12 26 30 10 18 21 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe18Mn0.6C Fe18Mn0.6C1.5Al Fe18Mn0.6C3Al Engineeringstress,MPa 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C2Al Engineering strain, % 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2Al
MATERIALS DESIGN LABORATORY )(Gb)( o gag  Kocks-Mecking Model [1] P. S. Follansbee, Metall. Mater. Trans. A, 41A (2010), pp. 3080-3090. [2] T. Gladman, Mater. Sci. Tech-Lond, 15 (1999), pp. 30-36. [3] J. G. Speer, B. C. De Cooman, Fundamentals of Steel Product Physical Metallurgy, AIST, 2011. [4] S. Takaki, K. Takeda, N Nakada, T Tsuchiyama,, IAS 2008, Pohang, Korea, p. 107 [5] Y. Estrin, H. Mecking, Acta Metall., 32 (1984), pp. 57-70. [6] O. Bouaziz, Y. Estrin, Y. Brechet, J.D. Embury, Scripta Mater., 63 (2010), pp. 477-479. o )T,(p g  [1] )d,f( preprepre [2] )X( is [3] D ky [4] )(k)( b k b P d d 2 1 gg g  - Ferrite Austenite [5] 0D  gg 111 a D ' ' 0 F F1 c2 a a  -  p : Pierels stress pre : Pierels stress s : Solid solution strengtheing ky : Hall-petch constant D : Grain size  : Dislocation density P : Grain size dependent constant [6] K1 : Constant K2 : Constant G : Shear modulus b : Burgers vector
MATERIALS DESIGN LABORATORY  Modeling result at room temperature Exp. Model 0.00 0.05 0.10 0.15 0.20 0.25 0 200 400 600 800 1000 1200 1400 Truestress,MPa True strain Exp. Model 0.00 0.05 0.10 0.15 0.20 0.25 0 1000 2000 3000 4000 5000 d/d,MPa True strain Model Exp._Magnetic saturation Exp._XRD 0.00 0.05 0.10 0.15 0.20 0.25 0.00 0.05 0.10 0.15 0.20 Martensitevolumefraction True strain  Coarse grained d k1 : 0.01 k2 : 1.307  UFG a  UFG g  Martensite k1 : 0.01 k2 : 1.012 k1 : 0.015 k2 : 1.005 k1 : 0.306 k2 : 39.1 Constitutive modeling of medium Mn steel 0.00 0.05 0.10 0.15 0.20 0.25 24 26 28 30 32 34 36 38Temperature,oC True strain Exp. Model Max Min
MATERIALS DESIGN LABORATORY Medium Mn TWIP Steel Design Concept Single phase Two Phase Fe-18%Mn-0.6%C-1.5%Al → Fe-8%Mn-0.4%C-3.0%Al+Si 0 10000 20000 30000 40000 50000 60000 70000 80000 0 25 50 75 100 TensilestrengthxTotalelongation MPa% Volume percentage austenite, % 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 20 22 24 Volumepercentageaustenite,% Mn content, mass-% - +
MATERIALS DESIGN LABORATORY Deformation g gFully austenitic g: Deformation-induced twinning a: Dislocation glide Ferrite/Austenite formation C, Mn partitioning Al, Si partitioning Grain size refinement SFE increase Lowering Ms temperature g a Cooling Retained g a’Mainly martensitic g a C, Mn Al, Si Intercritical annealing Austenite fg: 100% 8% Mn 0.3% C Austenite fg: 50% 16% Mn 0.6% C Medium Mn TWIP Steel Design Concept
MATERIALS DESIGN LABORATORY Deformation g gFully austenitic g: Deformation-induced twinning g: Transformation-induced plasticity a: Dislocation glide g a Cooling g a’Mainly martensitic g aIntercritical annealing a’ C, Mn Al, Si Medium Mn TWIP+TRIP Steel
MATERIALS DESIGN LABORATORY Strain Hardening Engineering of UFG Steel Ultra Fine Grain Size a Multi-phase microstructure g Precipitates VC Bimodal Grain size Distribution Larger grains Martensite reversion + intercritical annealing
MATERIALS DESIGN LABORATORY 10mm d ag d ag d ag 200nm 200nm 50nm 50nm Ferrite Austenite VC SF Strain Hardening Engineering UFG Steel
MATERIALS DESIGN LABORATORY Mn  Lowers Ms  Increases SFE  Increases hardenability C  Lowers Ms  Increases SFE  Increases hardenability Al  Increases Ms  Increases SFE  Required for d ferrite formation  Expands the two phase ag range (higher austenite C content) Si  Lowers Ms  Austenite solid solution strengthening  Ferrite solid solution strengthening  Decreases SFE  Suppression cementite formation g stabilizers a stabilizers Composition Design TWIP+TRIP Quaternary Alloy
MATERIALS DESIGN LABORATORY 5% Mn 4% Mn 2% Mn 3% Mn 1% Mn 0% Mn Temperature,°C Time, s 0.1 1.0 10 100 10000.01 700 800 600 900 500 400 300 200 Ms Fe-0.1%C-x%Mn 2μm 0.10C4Mn1Si 0.10C5Mn1Si 0.10C6Mn1Si Role of Mn in Medium Mn Steel
MATERIALS DESIGN LABORATORY 0 200 400 600 800 10001200 Dilatation Temperature 1200°C 650°C 700°C 750°C 800°C 850°C 900°C 0 200 400 600 800 10001200 Temperature 600°C 650°C 700°C 750°C 800°C Dilatation IAT IAT 1200°C Ms γ γα γ Role of Mn in Medium Mn Steel
MATERIALS DESIGN LABORATORY 5 10 15 Mnmass-% 10Mn0.3C3Al2Si (750°C) 5 10 15 Mnmass-% 8Mn0.3C3Al1Si (750°C) 500 nm 200 nm a a a g g g g a a Partitioning of Mn in Medium Mn Steel
MATERIALS DESIGN LABORATORY 1500 1250 1000 750 500 250 0 0.00 0.25 0.50 0.75 1.00 8Mn-XC-3Al-0.5Si C content, mass-% Temperature,°C Al/Mn=0.375 1500 1250 1000 750 500 250 0 0.00 0.25 0.50 0.75 1.00 10Mn-XC-3Al-0.5Si agM5C2 C content, mass-% Temperature,°C Al/Mn=0.3 d g ag aM5C2 agq agM5C2 g ag aM5C2 agq d Role of Al in Medium Mn Steel
MATERIALS DESIGN LABORATORY γ γ+α+θ γ+α γ+α+(Fe,Mn)5C2 1000 900 800 700 600 500 400 0 0.1 0.2 0.3 0.4 0.5 Mass percent C Temperature(°C) 1000 900 800 700 600 500 400 0 10 20 30 Mass percent 1000 900 800 700 600 500 400 0 10 20 30 SFE* (mJ/m2) γ, Cx10 γ, Mn γ, SFE Microstructure Medium Mn Steel (10%Mn)
MATERIALS DESIGN LABORATORY γ γ+α+θ γ+α γ+α+(Fe,Mn)5C2 1000 900 800 700 600 500 400 0 0.1 0.2 0.3 0.4 0.5 Mass percent C Temperature(°C) 1 μm 1 μm 10 μm γ+α΄ γ+α α+ α΄+(Fe,Mn)5C2 Microstructure at room temperature gaM23C6 Fe-C-10Mn-3Al-2Si 1500 1000 500 0 0.0 0.5 1.0 Temperature,°C Carbon content,mass-% aM23C6 aM23C6 M5C2 aM5C2 g 3 mm g a a a g Fe-0.3C-10Mn-3Al-2Si T:750°C gaM5C2 ga 900 750 gaq (a) (b) Strain Hardening 10-12% Mn Steel EBSD: Phase map Microstructure Medium Mn Steel (10%Mn)
MATERIALS DESIGN LABORATORY Microstructure Medium Mn Steel Example: 12% Mn, nucleation UFGs on twin boundaries After hot rolling After cold rolling  Hot rolled 12%Mn: Austenitic with 2% ferrite.  Cold rolled 12%Mn: Austenitic with martensite + twinning. Ferrite Austenite Martensite Twins After intercritical annealing UFG α+γ (1 < μm)
MATERIALS DESIGN LABORATORY Microstructure Medium Mn Steel Example: 10% Mn, nucleation UFGs on cementite particles 2 μm 1 μm Austenite Cementite C , Mn diffusionC , Mn diffusion Sub-grain boundary
MATERIALS DESIGN LABORATORY Fe-10Mn-0.3C-3Al-2Si S C M -1 3 γn / M =545 426X 30.4 60.5(V )X   400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 -200 -100 0 100 200 Mn C x 10 Mass-% Temperature (C) Stackingfaultenergy(mJ/m 2 ) Temperature (C) Without grain size effect With grain size effect Ms temperature(C) Temperature (C) TWIP SFE↑ Stability ↑ UHS 8%-10% Mn Steel: Composition and Processing
MATERIALS DESIGN LABORATORY S C M -1 3 γn / M =545 426X 30.4 60.5(V )X   TWIP 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 -200 -100 0 100 200 Mass-% Temperature (C) Mn C x 10 Stackingfaultenergy(mJ/m 2 ) Temperature (C) Ms temperature(C) Without grain size effect With graiun size effect Exp. Temperature (C) Fe- 8Mn-0.3C-3Al-1Si SFE↑ Stability ↑ UHS 8%-10% Mn Steel: Composition and Processing
MATERIALS DESIGN LABORATORY 650 700 750 800 850 900 400 500 600 700 800 900 1000 1100 1200 1300 1400 Fe-10Mn-0.3C-3Al-2Si YS UTS UTS Strength(MPa) Annealing temperature (C) YS Fe-8Mn-0.3C-3Al-1Si 650 700 750 800 850 900 10 20 30 40 50 60 70 Totalelongation(%) Annealing temperature (C) Fe10Mn0.3C3Al2Si Fe8Mn0.3C3Al1Si 8%-10% Mn Steel: Mechanical Properties
MATERIALS DESIGN LABORATORY As-annealed 57% Austenite-43% Ferrite As-deformed (~60%) Twin 1 μm 1 μm γ α γα γα Microstructure 8%Mn TWIP+TRIP Steel Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C
MATERIALS DESIGN LABORATORY Microstructure 8%Mn TWIP+TRIP Steel 0.2 μm 21/nm21/nm g a 0.2 μm g a Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C
MATERIALS DESIGN LABORATORY Microstructure 8%Mn TWIP+TRIP Steel Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C As-annealed 57% Austenite-43% Ferrite As-deformed (~60%) 1 μm 1 μm γ α γα α
MATERIALS DESIGN LABORATORY Medium 8% Mn TWIP+TRIP Steel Concept IAT: 700°C IAT: 750°C 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 Engineeringstress,MPa Engineering strain, % 8Mn-0.4C-3Al-2Si-0V 8Mn-0.4C-3Al-2Si-0.1V 8Mn-0.4C-3Al-2Si-0.2V Engineeringstress,MPa Engineering strain, % 8Mn-0.4C-3Al-2Si-0V 8Mn-0.4C-3Al-2Si-0.1V 8Mn-0.4C-3Al-2Si-0.2V Fe18Mn0.6C1.5Al
MATERIALS DESIGN LABORATORY Single phase TWIP steel Multi-phase TWIP-TRIP transition Multi-phase TRIP steel Model for the mechanical properties g →gT TWIP-effect g g →a’ TRIP-effect a’ g g →gT TWIP-effect g g →a’ TRIP-effect a’ g+ 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 8Mn 12Mn 18Mn Eng.stress(MPa) Eng. strain (%) DP980 DP980 10Mn Eng.stress(MPa) Eng. strain (%) Eng.stress(MPa) Eng. strain (%) DP980 6Mn
MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 6Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Medium Mn 3: 8%Mn0.4%C3.0%Al2.0%Si Medium Mn 4: 6%Mn0.3%C3.0%Al1.5%Si Mechanical properties at reduced Mn alloying TWIP TRIP
MATERIALS DESIGN LABORATORY Conclusions New 1GPa UHSS grades for automotive applications: High Mn, Austenitic MBIP-SBIP Steel High Mn, Austenitic TWIP Steel Medium Mn, multi-phase TWIP+TRIP Steel Medium Mn, Multi-phase TRIP Steel Press Hardening Steel Quench and Partitioning Processed Steel Some concepts are “out-of-the-box” in terms of cost, processing, application performance, … and the alloy fundamentals are challenging. Current research focus on selecting and optimizing best concepts: Multi-phase TWIP+TRIP steel with 6-10% Mn Multi-phase UFG TRIP steel with 5-7% Mn Application properties receiving attention: Delayed fracture Hole expansion and stretch forming performance Coatings
MATERIALS DESIGN LABORATORY Thank you for your attention.

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3rd CAMS 2014_TWIP-TRIP Steels_FINAL_2014

  • 1. MATERIALS DESIGN LABORATORY Alloy Design UHS Intercritically Annealed 6%-12%Mn TWIP+TRIP Steel B. C. De Cooman Materials Design Laboratory, Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang, South Korea CAMS 2014 MATERIALS AUSTRALIA November 26th-28th, 2014 Sydney, NSW, AUSTRALIA
  • 2. MATERIALS DESIGN LABORATORY Pohang University of Science and Technology Graduate Institute of Ferrous Technology Pohang
  • 3. MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
  • 4. MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
  • 5. MATERIALS DESIGN LABORATORY The world’s only fully accredited Institute in Steel Science and Technology • Research Areas: Alternative Technology Control & Automation Computational Metallurgy Clean Steel Environmental Metallurgy Microstructure Control Materials Design Material Mechanics Surface Engineering
  • 6. MATERIALS DESIGN LABORATORY Global Trends Automotive Steel Grades The increasing use of AHSS/UHSS use is driven by… • The need for high volume vehicles at competitive prices. • Stringent regulations and corporate goals for: Passenger safety Fuel economy Lower greenhouse gas emissions • Sustained efforts by the steel industry to innovate and create advanced steels, and original, steel-based solutions and methods, which underline the large potential of steel. Car makers test, utilize multi-materials designs, but steel remains dominant… • Steel, the material of choice for BIW: 99% passenger cars have a steel BIW. • 60-70% of the car weight consisting of steel or steel-based parts. • Globalization requires world-wide availability and global procurement of standard materials. • The automotive industry makes excursions in light materials applications but there is only a slight actual increase in the use of Al, Mg and plastics…. but this may change!
  • 7. MATERIALS DESIGN LABORATORY Lightweighting: Mass “Containment”, Mass “Reduction” • Low gas mileage: 0.3l-0.6l/100km fuel use reduction for a 100kg weight reduction • Less greenhouse gas emissions: 2020 target ~100gr/km • NHTSA CAFE Standards for 2017 New mpg target: DOUBLE the average mpg for new cars, trucks 54.5 mpg will cut of gas emissions by HALF Current situation Best US highway mileage 2012: 42 mpg (Chevrolet CRUZE) Other example: 32 mpg (VW Passat ) General situation: 25mpg in US, 45 mpg in EU, better in Japan Passenger Safety: • Low peak deceleration, long crush length, long time duration of crash pulse • High energy dissipation with minimum intrusion • Higher impact strength for A and B Pillars • Anti-Intrusion applications: front and rear crash, side intrusion • Tougher collision and rollover safety test for the 5-star rating Closure Applications: • Dent resistance Coated Products: • Perforation and cosmetic corrosion resistance • Surface quality, visual Other Issues: • Noise and Vibrations • Vehicle Handling, Stiffness and Torsional Rigidity Global Trends Automotive Steel Grades
  • 8. MATERIALS DESIGN LABORATORY Weight spiral: Safety Space Performance Reliability Quality Comfort 1500 1400 1300 1200 1100 1000 900 800 700 600 500 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 Curbweight,kg 88% increase in weight EU mid size vehicles Year CAFE Fuel Economy 40 45 50 55 60 Wheelbase . track Gasmileage,mpg 40 45 50 35 30 Year 2012 2014 2016 2018 2020 2022 Prius Doubling mileage Regulations Influence on Materials Selection
  • 9. MATERIALS DESIGN LABORATORY Weight spiral: Safety Space Performance Reliability Quality Comfort 1500 1400 1300 1200 1100 1000 900 800 700 600 500 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 Curbweight,kg 88% increase in weight EU mid size vehicles Year Regulations Influence on Materials Selection Passive Passenger safety
  • 10. MATERIALS DESIGN LABORATORY Mechanical Properties Yield Strength Tensile Strength Uniform elongation Total Elongation Automotive Sheet Steel Products
  • 11. MATERIALS DESIGN LABORATORY RoughingReheating Finishing Cooling Coiling Conventional HSM, CSM and CA/HDG Processing Cold rolling Continuous Annealing Hot Dip Galvanizing
  • 12. MATERIALS DESIGN LABORATORY Mechanical Properties Yield Strength Tensile Strength Uniform elongation Total Elongation Bake-hardening Springback Normal Anisotropy Planar Anisotropy Deep Drawability Stretch Formability Crashworthiness Geometrical Properties Dimensional Width Thickness Shape Edge Drop Crown Flatness Technical Properties Weldability Phosphatabilty Roughness Waviness Friction Corrosion resistance Phosphatability Paint adhesion Visual appearance Automotive Sheet Steel Products
  • 14. MATERIALS DESIGN LABORATORY 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 IF CMn HSLA Conventional Automotive Steels 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% 10.000MPa.% IF LC CMn HSLA
  • 15. MATERIALS DESIGN LABORATORY MA 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA First Generation Advanced High Strength Steels DP TRIP MACP
  • 16. MATERIALS DESIGN LABORATORY Automotive Body Materials Selection 6% HPF + 5% MA 23% HSS 30% DP / Multi Phase GM AVEO 34% IF +LC +BH Cadillac CTS PHS VW: 6% (GOLF 6) → 28% (GOLF 7)
  • 17. MATERIALS DESIGN LABORATORY Al alloys Polymers Mg alloys Automotive Steel grades CFR-Composites Ti alloys Automotive Body Materials Selection
  • 18. MATERIALS DESIGN LABORATORY Al alloys Polymers CFR-Composites Automotive Body Materials Selection Monocoque: 5754 (Structural) 6111 (External parts) Space frame: Multiple Al products integration High strength die casting Al-extrusion Hydroform extrusion Issues: Strain hardening: low Strain rate sensitivity: negative Cost: 4-6$/kg (1.3$/kg Steel)
  • 19. MATERIALS DESIGN LABORATORY MA 300 400 500 600 700 800 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA Second Generation Advanced High Strength Steels TWIP Fe22Mn0.6C Fe18Mn1.5Al0.6C
  • 20. MATERIALS DESIGN LABORATORY MA 300 400 500 600 900 1000 ElongationA80,% Tensile Strength, MPa 0 20 40 60 80 100 120 140 1100 60.000MPa.% 50.000MPa.% 40.000MPa.% 30.000MPa.% 20.000MPa.% IF LC CMn HSLA Third Generation Advanced High Strength Steels 3rd Generation 0.2µm UFG TRIP Low Mn TWIP SBIP MBIP + 700 800
  • 21. MATERIALS DESIGN LABORATORY Strain Hardening Engineering True strain 0 0 Truestress,strainhardeningrate,MPa )( u   d d
  • 22. MATERIALS DESIGN LABORATORY Strain Hardening Engineering True strain 0 0 Truestress,strainhardeningrate,MPa )( u   d d
  • 23. MATERIALS DESIGN LABORATORY Strain Hardening Engineering 0 0 True strain Truestress,strainhardeningrate,MPa Gain in strength and ductility ! u )(   d d
  • 24. MATERIALS DESIGN LABORATORY 0 0 True strain Truestress,strainhardeningrate,MPa Gain in strength and ductility ! Strain Hardening Engineering u )(   d d Dislocation Accumulation or Storage (Stage II) Dislocation Annihilation or Dynamic recovery (Stage III) ρkρk dε dρ dε dρ dε dρ   21
  • 25. MATERIALS DESIGN LABORATORY  d/d 0 0 0.1 0.2 0.3 0.4 1000 2000 3000 4000 5000 True strain Truestress,strainhardeningrate,MPa TRIP TWIP HS IF TRIP Strain Hardening Engineering
  • 26. MATERIALS DESIGN LABORATORY What is Strain Hardening Engineering? 1. Strengthening mechanisms: • Solid solution strengthening (Alloying) • Grain size refining (Alloying and Processing) • Precipitation strengthening (Alloying) • Bake-hardening (Processing) 2. Plasticity-enhancing mechanisms: • Multi-phase steels: austenite required • TRIP effect: Strain-induced Transformation • TWIP effect: Deformation Twinning g strain g →a’ TRIP-effect a’ g g →gT TWIP-effect g
  • 27. MATERIALS DESIGN LABORATORY High Mn TWIP Steel TWIP: TWinning-Induced Plasticity 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Eng.Stress(MPa) Eng. Strain (%) 20 22 24 26 28 30 700 750 800 850 900 10-4s-1 Fe18Mn0.6C1.5Al g →gT TWIP-effect g 10-3s-1
  • 28. MATERIALS DESIGN LABORATORY Rolling directionTWIP 1000 High Mn TWIP Steel
  • 29. MATERIALS DESIGN LABORATORY HER Diffuse necking No diffuse necking IF steelTWIP LMIE HDF Fe22Mn0.6C Fe15Mn2Al0.7C Zn Zn
  • 30. MATERIALS DESIGN LABORATORY 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C2Al Engineering strain, % YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 SFE** mJ/m2 Fe15Mn0.6C 509 1124 51 12 13 Fe15Mn0.6C1.5Al 480 976 58 26 21 Fe15Mn0.6C2.0Al 488 939 58 30 24 * Saeed-Akbari et al., Metall. Mater. Trans. A 2009 ** Dumay et al., Mater. Sci. Eng. A 2008 YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe15Mn0.6C2.0Al 10% 20% 30% 40% 50% 60% 712 989 1071 1122 1261 2394 991 1167 1319 1407 1590 1737 43 23 15 10 9 7 30 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Engineering strain, % 10% 20% 30% 40% 50% 60%
  • 31. MATERIALS DESIGN LABORATORY YS (MPa) UTS (MPa) Total Elongation (%) SFE* mJ/m2 SFE** mJ/m2 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2.0Al 486 492 478 838 900 915 16 30 41 12 26 30 10 18 21 Fe12Mn0.9C1Si-0.0V Fe12Mn0.9C1Si-0.2V Fe12Mn0.9C1Si-0.5V Fe12Mn0.9C1Si-0.7V 434 614 722 741 1166 1324 1276 1260 45 38 25 22 26 - 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2Al Engineeringstress,MPa Engineering strain, % 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 0.2%V0.7%V 0.5%V Engineeringstress,MPa Engineering strain, % V-free V-additions: increased YS and increased strain hardening
  • 32. MATERIALS DESIGN LABORATORY YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe15Mn0.6C2.0Al 10% 20% 30% 40% 50% 60% 712 989 1071 1122 1261 2394 991 1167 1319 1407 1590 1737 43 23 15 10 9 7 30 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 Engineeringstress,MPa Engineering strain, % 10% 20% 30% 40% 50% 60% 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 1400 1600 0.2%V0.7%V 0.5%V Engineeringstress,MPa Engineering strain, % V-free YS MPa UTS MPa Elongation (total) % SFE* mJ/m2 Fe12Mn0.9C1Si-0.0V Fe12Mn0.9C1Si-0.2V Fe12Mn0.9C1Si-0.5V Fe12Mn0.9C1Si-0.7V 434 614 722 741 1166 1324 1276 1260 45 38 25 22 26
  • 33. MATERIALS DESIGN LABORATORY Classification of the Mn UHSS Steels High Mn Medium Mn %Mn >25 22 - 15 12 - 6 7 - 4 Processing Conventional annealing Intercritical annealing Q & P Cold rolled Shear bands Deformed g Deformed a’ After annealing g UFG g  a Plasticity SBIP TWIP TWIP+TRIP TRIP g-ISFE (mJ/m2) >75 >20 >20 <10 g-stability g-composition g-composition and size Role of Mn g-stability / SFE g-stability / SFE / Hardenability
  • 34. MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 DP980 Truestress,MPa Workhardeningrate,MPa True strain TiIF Ti-IF: standard highly formable steel DP 980: standard 1st generation AHSS Mechanical properties at reduced Mn alloying
  • 35. MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 TWIP1000 DP980 TiIF Truestress,MPa Workhardeningrate,MPa True strain Ti-IF: standard highly formable steel DP 980: standard 1st generation AHSS Mechanical properties at reduced Mn alloying DSA )(   d d
  • 36. MATERIALS DESIGN LABORATORY TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 12Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain Mechanical properties at reduced Mn alloying
  • 37. MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 10Mn Truestress,MPa Workhardeningrate,MPa True strain TWIP1000 TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Mechanical properties at reduced Mn
  • 38. MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 6Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Medium Mn 3: 8%Mn0.4%C3.0%Al2.0%Si Medium Mn 4: 6%Mn0.3%C3.0%Al1.5%Si Mechanical properties at reduced Mn DSA
  • 39. MATERIALS DESIGN LABORATORY Original concept: TWIP Steel Deformation g g Fully Austenitic Low SFE Dislocation plasticity Twinning-induced plasticity Low YS / High Strain Hardening g g High Mn TWIP Steel Design Concept Austenite: e.g. 18% Mn 0.6% C +Al
  • 40. MATERIALS DESIGN LABORATORY YS (MPa) UTS (MPa) Total Elongation (%) SFE* mJ/m2 SFE** mJ/m2 Fe18Mn0.6C Fe18Mn0.6C1.5Al Fe18Mn0.6C3.0Al 484 498 499 1106 960 849 60 59 50 14 28 40 17 25 32 Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C3.0Al 509 480 488 1124 977 939 51 58 58 12 26 30 13 21 24 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2.0Al 486 492 478 838 900 915 16 30 41 12 26 30 10 18 21 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe18Mn0.6C Fe18Mn0.6C1.5Al Fe18Mn0.6C3Al Engineeringstress,MPa 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe15Mn0.6C Fe15Mn0.6C1.5Al Fe15Mn0.6C2Al Engineering strain, % 0 10 20 30 40 50 60 70 0 200 400 600 800 1000 1200 Fe12Mn0.6C Fe12Mn0.6C1.5Al Fe12Mn0.6C2Al
  • 41. MATERIALS DESIGN LABORATORY )(Gb)( o gag  Kocks-Mecking Model [1] P. S. Follansbee, Metall. Mater. Trans. A, 41A (2010), pp. 3080-3090. [2] T. Gladman, Mater. Sci. Tech-Lond, 15 (1999), pp. 30-36. [3] J. G. Speer, B. C. De Cooman, Fundamentals of Steel Product Physical Metallurgy, AIST, 2011. [4] S. Takaki, K. Takeda, N Nakada, T Tsuchiyama,, IAS 2008, Pohang, Korea, p. 107 [5] Y. Estrin, H. Mecking, Acta Metall., 32 (1984), pp. 57-70. [6] O. Bouaziz, Y. Estrin, Y. Brechet, J.D. Embury, Scripta Mater., 63 (2010), pp. 477-479. o )T,(p g  [1] )d,f( preprepre [2] )X( is [3] D ky [4] )(k)( b k b P d d 2 1 gg g  - Ferrite Austenite [5] 0D  gg 111 a D ' ' 0 F F1 c2 a a  -  p : Pierels stress pre : Pierels stress s : Solid solution strengtheing ky : Hall-petch constant D : Grain size  : Dislocation density P : Grain size dependent constant [6] K1 : Constant K2 : Constant G : Shear modulus b : Burgers vector
  • 42. MATERIALS DESIGN LABORATORY  Modeling result at room temperature Exp. Model 0.00 0.05 0.10 0.15 0.20 0.25 0 200 400 600 800 1000 1200 1400 Truestress,MPa True strain Exp. Model 0.00 0.05 0.10 0.15 0.20 0.25 0 1000 2000 3000 4000 5000 d/d,MPa True strain Model Exp._Magnetic saturation Exp._XRD 0.00 0.05 0.10 0.15 0.20 0.25 0.00 0.05 0.10 0.15 0.20 Martensitevolumefraction True strain  Coarse grained d k1 : 0.01 k2 : 1.307  UFG a  UFG g  Martensite k1 : 0.01 k2 : 1.012 k1 : 0.015 k2 : 1.005 k1 : 0.306 k2 : 39.1 Constitutive modeling of medium Mn steel 0.00 0.05 0.10 0.15 0.20 0.25 24 26 28 30 32 34 36 38Temperature,oC True strain Exp. Model Max Min
  • 43. MATERIALS DESIGN LABORATORY Medium Mn TWIP Steel Design Concept Single phase Two Phase Fe-18%Mn-0.6%C-1.5%Al → Fe-8%Mn-0.4%C-3.0%Al+Si 0 10000 20000 30000 40000 50000 60000 70000 80000 0 25 50 75 100 TensilestrengthxTotalelongation MPa% Volume percentage austenite, % 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 16 18 20 22 24 Volumepercentageaustenite,% Mn content, mass-% - +
  • 44. MATERIALS DESIGN LABORATORY Deformation g gFully austenitic g: Deformation-induced twinning a: Dislocation glide Ferrite/Austenite formation C, Mn partitioning Al, Si partitioning Grain size refinement SFE increase Lowering Ms temperature g a Cooling Retained g a’Mainly martensitic g a C, Mn Al, Si Intercritical annealing Austenite fg: 100% 8% Mn 0.3% C Austenite fg: 50% 16% Mn 0.6% C Medium Mn TWIP Steel Design Concept
  • 45. MATERIALS DESIGN LABORATORY Deformation g gFully austenitic g: Deformation-induced twinning g: Transformation-induced plasticity a: Dislocation glide g a Cooling g a’Mainly martensitic g aIntercritical annealing a’ C, Mn Al, Si Medium Mn TWIP+TRIP Steel
  • 46. MATERIALS DESIGN LABORATORY Strain Hardening Engineering of UFG Steel Ultra Fine Grain Size a Multi-phase microstructure g Precipitates VC Bimodal Grain size Distribution Larger grains Martensite reversion + intercritical annealing
  • 48. MATERIALS DESIGN LABORATORY Mn  Lowers Ms  Increases SFE  Increases hardenability C  Lowers Ms  Increases SFE  Increases hardenability Al  Increases Ms  Increases SFE  Required for d ferrite formation  Expands the two phase ag range (higher austenite C content) Si  Lowers Ms  Austenite solid solution strengthening  Ferrite solid solution strengthening  Decreases SFE  Suppression cementite formation g stabilizers a stabilizers Composition Design TWIP+TRIP Quaternary Alloy
  • 49. MATERIALS DESIGN LABORATORY 5% Mn 4% Mn 2% Mn 3% Mn 1% Mn 0% Mn Temperature,°C Time, s 0.1 1.0 10 100 10000.01 700 800 600 900 500 400 300 200 Ms Fe-0.1%C-x%Mn 2μm 0.10C4Mn1Si 0.10C5Mn1Si 0.10C6Mn1Si Role of Mn in Medium Mn Steel
  • 50. MATERIALS DESIGN LABORATORY 0 200 400 600 800 10001200 Dilatation Temperature 1200°C 650°C 700°C 750°C 800°C 850°C 900°C 0 200 400 600 800 10001200 Temperature 600°C 650°C 700°C 750°C 800°C Dilatation IAT IAT 1200°C Ms γ γα γ Role of Mn in Medium Mn Steel
  • 51. MATERIALS DESIGN LABORATORY 5 10 15 Mnmass-% 10Mn0.3C3Al2Si (750°C) 5 10 15 Mnmass-% 8Mn0.3C3Al1Si (750°C) 500 nm 200 nm a a a g g g g a a Partitioning of Mn in Medium Mn Steel
  • 52. MATERIALS DESIGN LABORATORY 1500 1250 1000 750 500 250 0 0.00 0.25 0.50 0.75 1.00 8Mn-XC-3Al-0.5Si C content, mass-% Temperature,°C Al/Mn=0.375 1500 1250 1000 750 500 250 0 0.00 0.25 0.50 0.75 1.00 10Mn-XC-3Al-0.5Si agM5C2 C content, mass-% Temperature,°C Al/Mn=0.3 d g ag aM5C2 agq agM5C2 g ag aM5C2 agq d Role of Al in Medium Mn Steel
  • 53. MATERIALS DESIGN LABORATORY γ γ+α+θ γ+α γ+α+(Fe,Mn)5C2 1000 900 800 700 600 500 400 0 0.1 0.2 0.3 0.4 0.5 Mass percent C Temperature(°C) 1000 900 800 700 600 500 400 0 10 20 30 Mass percent 1000 900 800 700 600 500 400 0 10 20 30 SFE* (mJ/m2) γ, Cx10 γ, Mn γ, SFE Microstructure Medium Mn Steel (10%Mn)
  • 54. MATERIALS DESIGN LABORATORY γ γ+α+θ γ+α γ+α+(Fe,Mn)5C2 1000 900 800 700 600 500 400 0 0.1 0.2 0.3 0.4 0.5 Mass percent C Temperature(°C) 1 μm 1 μm 10 μm γ+α΄ γ+α α+ α΄+(Fe,Mn)5C2 Microstructure at room temperature gaM23C6 Fe-C-10Mn-3Al-2Si 1500 1000 500 0 0.0 0.5 1.0 Temperature,°C Carbon content,mass-% aM23C6 aM23C6 M5C2 aM5C2 g 3 mm g a a a g Fe-0.3C-10Mn-3Al-2Si T:750°C gaM5C2 ga 900 750 gaq (a) (b) Strain Hardening 10-12% Mn Steel EBSD: Phase map Microstructure Medium Mn Steel (10%Mn)
  • 55. MATERIALS DESIGN LABORATORY Microstructure Medium Mn Steel Example: 12% Mn, nucleation UFGs on twin boundaries After hot rolling After cold rolling  Hot rolled 12%Mn: Austenitic with 2% ferrite.  Cold rolled 12%Mn: Austenitic with martensite + twinning. Ferrite Austenite Martensite Twins After intercritical annealing UFG α+γ (1 < μm)
  • 56. MATERIALS DESIGN LABORATORY Microstructure Medium Mn Steel Example: 10% Mn, nucleation UFGs on cementite particles 2 μm 1 μm Austenite Cementite C , Mn diffusionC , Mn diffusion Sub-grain boundary
  • 57. MATERIALS DESIGN LABORATORY Fe-10Mn-0.3C-3Al-2Si S C M -1 3 γn / M =545 426X 30.4 60.5(V )X   400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 -200 -100 0 100 200 Mn C x 10 Mass-% Temperature (C) Stackingfaultenergy(mJ/m 2 ) Temperature (C) Without grain size effect With grain size effect Ms temperature(C) Temperature (C) TWIP SFE↑ Stability ↑ UHS 8%-10% Mn Steel: Composition and Processing
  • 58. MATERIALS DESIGN LABORATORY S C M -1 3 γn / M =545 426X 30.4 60.5(V )X   TWIP 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 0 5 10 15 20 25 30 400 500 600 700 800 900 -200 -100 0 100 200 Mass-% Temperature (C) Mn C x 10 Stackingfaultenergy(mJ/m 2 ) Temperature (C) Ms temperature(C) Without grain size effect With graiun size effect Exp. Temperature (C) Fe- 8Mn-0.3C-3Al-1Si SFE↑ Stability ↑ UHS 8%-10% Mn Steel: Composition and Processing
  • 59. MATERIALS DESIGN LABORATORY 650 700 750 800 850 900 400 500 600 700 800 900 1000 1100 1200 1300 1400 Fe-10Mn-0.3C-3Al-2Si YS UTS UTS Strength(MPa) Annealing temperature (C) YS Fe-8Mn-0.3C-3Al-1Si 650 700 750 800 850 900 10 20 30 40 50 60 70 Totalelongation(%) Annealing temperature (C) Fe10Mn0.3C3Al2Si Fe8Mn0.3C3Al1Si 8%-10% Mn Steel: Mechanical Properties
  • 60. MATERIALS DESIGN LABORATORY As-annealed 57% Austenite-43% Ferrite As-deformed (~60%) Twin 1 μm 1 μm γ α γα γα Microstructure 8%Mn TWIP+TRIP Steel Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C
  • 61. MATERIALS DESIGN LABORATORY Microstructure 8%Mn TWIP+TRIP Steel 0.2 μm 21/nm21/nm g a 0.2 μm g a Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C
  • 62. MATERIALS DESIGN LABORATORY Microstructure 8%Mn TWIP+TRIP Steel Fe-8%Mn-0.4%C-3%Al-1%Si steel intercritically annealed @ 750 °C As-annealed 57% Austenite-43% Ferrite As-deformed (~60%) 1 μm 1 μm γ α γα α
  • 63. MATERIALS DESIGN LABORATORY Medium 8% Mn TWIP+TRIP Steel Concept IAT: 700°C IAT: 750°C 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 Engineeringstress,MPa Engineering strain, % 8Mn-0.4C-3Al-2Si-0V 8Mn-0.4C-3Al-2Si-0.1V 8Mn-0.4C-3Al-2Si-0.2V Engineeringstress,MPa Engineering strain, % 8Mn-0.4C-3Al-2Si-0V 8Mn-0.4C-3Al-2Si-0.1V 8Mn-0.4C-3Al-2Si-0.2V Fe18Mn0.6C1.5Al
  • 64. MATERIALS DESIGN LABORATORY Single phase TWIP steel Multi-phase TWIP-TRIP transition Multi-phase TRIP steel Model for the mechanical properties g →gT TWIP-effect g g →a’ TRIP-effect a’ g g →gT TWIP-effect g g →a’ TRIP-effect a’ g+ 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 0 10 20 30 40 50 60 0 200 400 600 800 1000 1200 1400 8Mn 12Mn 18Mn Eng.stress(MPa) Eng. strain (%) DP980 DP980 10Mn Eng.stress(MPa) Eng. strain (%) Eng.stress(MPa) Eng. strain (%) DP980 6Mn
  • 65. MATERIALS DESIGN LABORATORY 0.0 0.1 0.2 0.3 0.4 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 6Mn TWIP1000 Truestress,MPa Workhardeningrate,MPa True strain TWIP 1000: 18%Mn0.6%C1.5%Al Medium Mn 1: 12%Mn0.3%C3.0%Al Medium Mn 2: 10%Mn0.3%C3.0%Al2.0%Si Medium Mn 3: 8%Mn0.4%C3.0%Al2.0%Si Medium Mn 4: 6%Mn0.3%C3.0%Al1.5%Si Mechanical properties at reduced Mn alloying TWIP TRIP
  • 66. MATERIALS DESIGN LABORATORY Conclusions New 1GPa UHSS grades for automotive applications: High Mn, Austenitic MBIP-SBIP Steel High Mn, Austenitic TWIP Steel Medium Mn, multi-phase TWIP+TRIP Steel Medium Mn, Multi-phase TRIP Steel Press Hardening Steel Quench and Partitioning Processed Steel Some concepts are “out-of-the-box” in terms of cost, processing, application performance, … and the alloy fundamentals are challenging. Current research focus on selecting and optimizing best concepts: Multi-phase TWIP+TRIP steel with 6-10% Mn Multi-phase UFG TRIP steel with 5-7% Mn Application properties receiving attention: Delayed fracture Hole expansion and stretch forming performance Coatings
  • 67. MATERIALS DESIGN LABORATORY Thank you for your attention.