Advanced High Strength Steels - LBCG · PDF fileAdvanced High Strength Steels ! Emmanuel De...
Transcript of Advanced High Strength Steels - LBCG · PDF fileAdvanced High Strength Steels ! Emmanuel De...
Advanced High Strength Steels
Emmanuel De Moor Advanced Steel Processing and Products Research Center*
Colorado School of Mines Global Automotive Lightweight Materials Detroit 2015
August 20th, 2015 Novi, MI
*An NSF Industry/University Cooperative Research Center - Est. 1984
Outline
2
Provide an overview of advanced high strength sheet steels Metallurgical strategies enabling high strength and ductility Microstructures of interest to enable next generation AHSS properties
Overview
3
Higher strength with ductility/formability to enable downgauging. Processing and alloying to tailor microstructures resulting in attractive properties e.g. high strength phases can be introduced
AHSS Development
4 AISI: www.steel.org (2006)
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
HSLA
IF
Mild IF - HS
BH
Elo
ngat
ion
(%)
600
-
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
HSLA
IF
Mild IF - HS
BH ISO
Elo
ngat
ion
(%)
600
- ISO
AISI: www.steel.org (2006)
Dual Phase Steels
Dual Phase Steels
“Typical Compositions:” C: 0.05 - 0.15 Mn: 1.0 - 2.0 Others: Si, Cr, Ni, Mo, Nb, V
0.15C, 1.5 Mn, 1.5 Si WQ from 775oC
A. De et al., Adv. Mat. Proc., 2003
“Dual Phase:” High Strength Martensite Ductile Ferrite Processing: Intercritical Annealing
Strengthening in DP Steels
Davies (1978)
Strength increase follows rule of mixtures: σT = Vfσf + VMσM
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
HSLA
IF
Mild IF - HS
BH ISO
Elo
ngat
ion
(%)
600
- ISO
AISI: www.steel.org (2006)
TRIP Steels
TRIP Steels
“Typical Compositions:” C: 0.20 Mn: 1.5 Si, Al 1.5 TRansformation Induced Plasticity: Austenite transforms to martensite with deformation
Significant strain hardening resulting in high strength and ductility
Time
Tem
pera
ture
Ferrite-Bainite-Austenite
"TRIP"
"Dual Phase"Ferrite +Martensite
A1
A3
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
HSLA
IF
Mild IF - HS
BH ISO
Elo
ngat
ion
(%)
600
- ISO
AISI: www.steel.org (2006)
Martensitic Steels
Hot Stamping-Press Hardening
Formability at elevated temperature Blanks heated to > 900 ºC Forming and accelerated cooling in dies Complex geometry and high strength Alloying for hardenability - Boron
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
HSLA
IF
Mild IF - HS
BH ISO
600
- ISO
Before hardening Press-hardened
Hot Stamping
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
HSLA
IF
Mild IF - HS
BH ISO
Elo
ngat
ion
(%)
600
-
First Generation AHSS
Second Generation AHSS
ISO
Properties: “1st and 2nd Generation AHSS”
AISI: www.steel.org (2006)
Advanced High Strength Sheet Steels
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Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
HSLA
IF
Mild IF - HS
BH ISO
-
BH
“3rd Generation AHSS”
AISI: www.steel.org (2006) 13
Current Status of AHSS • Conventional High Strength
Bake Hardenable (BH) HSLA
• “1st Generation”: (ferrite-based) Dual Phase (DP) TRIP Complex Phase (CP) Martensitic
• “2nd Generation”: (austenite-based) Austenitic stainless steels TWIP - Twinning Induced Plasticity (TWIP) L-IP® - Lighter Weight Steels with Induced Plasticity
• “3rd Generation”: New (?) multiphase 14
Predictive Model: Ferrite + Martensite
Increase MVF Matlock and Speer: ICASS 2006
200 400 600 800 1000 1200 1400 1600Ultimate Tensile Strength (MPa)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Uni
form
Eng
inee
ring
Stra
inFerrite + Martensite
50%
40%
70%
% MVF
60% Constituent UTS (MPa)
Uniform True
Strain Ferrite 300 0.3
Martensite 2000 0.08
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Composite modeling to predict properties of hypothetical mixtures Ferrite + Martensite
Constituent properties from the literature
Comparison to “3rd Generation” AHSS
Matlock and Speer: ICASS 2006 Tensile Strength (MPa)
Elo
ngat
ion
(%)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
IF
Mild IF - HS
BH ISO
-
BH
HSLA Ferrite + Martensite Ferrite + Martensite 50% 40% 60%
% MVF
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Predictive Model: Austenite + Martensite
Increase MVF Matlock and Speer: ICASS 2006
Constituent UTS (MPa)
Uniform True
Strain Ferrite 300 0.3
Martensite 2000 0.08
Austenite 640 0.6
200 400 600 800 1000 1200 1400 1600Ultimate Tensile Strength (MPa)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Uni
form
Eng
inee
ring
Stra
inFerrite + Martensite
Austenite + Martensite
50%
30%
40%
60%
% MVF
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Composite modeling to predict properties of hypothetical mixtures Martensite + Austenite
Comparison to “3rd Generation” AHSS
Matlock and Speer: ICASS 2006
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
IF
Mild IF - HS
BH ISO
-
BH
HSLA
Austenite + Martensite
Ferrite + Martensite Ferrite + Martensite
50% MVF
Stable Austenite + Martensite
desired 3rd generation microstructures: High strength phase + ductile austenite 18
Quenching and Partitioning
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Future AHSS: Martensite/Austenite µstr
Quenching and Partitioning (Q&P) process
Speer et al., 2003 53Speer et al., 2003 Acta Mater., 51, p. 2611
Stabilize austenite in a martensitic matrix Alloying to suppress cementite: Si additions
Example Proper,es Q&P Steels
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C Mn Si 0.20 3.00 1.60 0.29 2.95 1.59
0 2 4 6 8 10 12 14 16 18600700800900
100011001200130014001500160017001800
Engi
neer
ing
stre
ss, M
Pa
Engineering strain, %
450°C/10s400°C/100s
400°C/30s
400°C/10s
0.3C‑3Mn‑1.6Si QT of 200°C
800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800789
10111213141516171819202122
0.3C-3Mn-1.6Si
0.2C-3Mn-1.6Si
Tota
l elo
ngat
ion,
%Tensile strength, MPa
De Moor et al., ISIJ, vol. 51, pp. 137-‐144, 2011
Q&P Steels Proper,es Overview
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800 1000 1200 1400 1600 1800 2000 2400
5
10
15
20
25
30
35
40
45
50 Austempered TRIP Sakuma et al. Matsumura et al.
Bainite Bhadeshia-Edmonds Miihkinen-Edmonds Caballero et al.
Mixed Microstructures Sugimoto et al. Jun-Fonstein Cobo et al.
Quenching & Partitioning Jun-Fonstein Streicher et al. De Moor et al.Thomas et al. Li et al. Wang et al.- ind. trial Santofimia et al.Martins et al.
Lower Mn TWIP/TRIP Merwin Gibbs et al. Jun et al.
To
tal E
lon
gat
ion
, %
Tensile Strength, MPa
data plotted with literature-reported elongations
800 1000 1200 1400 1600 1800 2000 24002468
101214161820222426283032
Tota
l Elo
ngat
ion,
%
Tensile Strength, MPaReferences detailed in: E. De Moor, P.J. Gibbs, J.G. Speer, D.K. Matlock, J.G. Schroth, AIST Trans., Vol. 7, No.11, 2010, pp. 133-44
Model predic-ons Martensite + Austenite
Strategies
Desired microstructures consisting of a high strength phase and ductile austenite through: Quenching and Partitioning Carbide free bainite TRIP bainitic ferrite-TBF Medium Manganese steels Others..
Medium Manganese Steels
Fine grained ferrite and austenite Austenite stabilization by manganese enrichment during intercritical annealing Amount and stability of austenite Example: 0.1C-7.1Mn
P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, Met. and Mat. Trans., Vol. 42, pp. 3691-02 2011.
0.1C-7.1Mn-0.1Si Annealed for 1 week
Medium Manganese Steels
(33 %)
(26%)
(40%)
(43.5%) (< 2%) • ASTM E-8 sub-sized
samples 32 mm reduced section
• Initial austenite contents in (%)
• Annealing temperatures in ºC
P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, Met. and Mat. Trans., Vol. 42, pp. 3691-02 2011.
• Neutron diffraction in-situ, under load • Deformation paused for each diffraction measurement
Strain-dependent Austenite Transformation
7.1 Mn 600 oC
P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, Met. and Mat. Trans., Vol. 42, pp. 3691-02 2011.
Strain-dependent Austenite Transformation
P. J. Gibbs, E. De Moor, M. J. Merwin, B. Clausen, J. G. Speer, D. K. Matlock, Met. and Mat. Trans., Vol. 42, pp. 3691-02 2011.
Amount and stability of austenite
Summary
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Overview of Advanced High Strength Steels
Multiphase microstructures consisting of a high strength and a ductile phase such as austenite of interest for next generation properties development Promising metallurgical strategies
Acknowledgements
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Innovative Manufacturing Initiative by the Advanced Manufacturing Office, US Department of Energy Award Number DE-EE0005765 Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
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