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ADVANCES IN HIGH STRENGTH STEELS
FOR AUTOMOTIVE APPLICATIONS
Shrikant P. BhatAutomotive Product Applications
ArcelorMittal Global R&D – East Chicago
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Presentation Outline
• Introduction - Material Choice in Automobiles
• Sheet Steel and the Automobile – General Introduction
• Fundamentals of Sheet Steel Metallurgy
• Product Characteristics and Application Trends• Hot Rolled Products• Cold Rolled Products• Coated Products
Hot Stamping
• Q&A
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Steel – Material of Choice for Modern Living
• “Most Large Metal Structures are made of Carbon Steel – the World’s Most Useful Structural Material”
– Kennedy Space Center website
• Integral Material for modern buildings, medicine, homeland security, food packaging, transportation and infrastructure.
• In today’s cars, Steel makes up about 62% weight- Steel is the Backbone of the entire vehicle(Protect occupants, Provide positive driving experience,
React to road loads, Provide comfort, and attachment points to other components of the vehicle)
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Automobile Weight Trend - VW
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Reasons for Weight Gain
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Sheet Steel and the Automobile
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Sheet Steel and the Automobile
Design ManufacturingTensile Stress(MPa)
Elon
gatio
n(%
)
200 400 1200600 1000 14008000
10
30
20
40
50
60
UHHSUHHS
Conventional HSS
Mild Steel
Materials
Safety
PerformanceLight Weight
Environment
Cost
Customer Satisfaction
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SHEET STEEL AND THE AUTOMOBILE
Dent resistant Ultra-high strengthHigh strength
Forming Grade
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Automotive Sheet SteelsE
long
atio
n (%
)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200
Low StrengthSteels (<270MPa)
Ultra High StrengthSteels (>700MPa)
300 900
High StrengthSteels
1600
DP
AHSS
MARTENSITE
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
TWIP
TRIP
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Steels – Alloys based on Iron
Fundamentals of Sheet Steel Metallurgy
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Strengthening Mechanisms
• Work Hardening (Dislocation Strengthening)• Solid Solution Strengthening• Grain Refinement• Precipitation Strengthening• Phase Transformations
Strength/Ductility in Steel obtained by a combination of strengthening mechanisms
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Fe - Fe3C Phase Diagram
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Processing of HiTen SteelsTime-Temperature-Transformation (TTT) Diagram
Time
AUSTENITE
BAINITE
PEARLITEFERRITE
MARTENSITE
Tem
pera
ture
Ms
Ar3
MARTENSITE DUALPHASE
TRIP COMPLEXPHASE
BainiteFerrite
AusteniteMartensite
MicrostructureLegend
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Sheet Steel Microstructures
Ferrite (F) Martensite (M)
TRIP (F + B/M + RA)Dual Phase (F + M)
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Strengthening Mechanisms in Sheet Steels - Summary
Tensile Strength,
MPa
Carbon Level Solid Solution
Hardening
Grain Refinement Precipitation
HardeningPhase
Transformation
270 Low C √ √
340 ULC - L C, Mn, P √ √
440 ULC - L C, Mn, Si √ Nb, Ti, V √
600Low -
Medium C, Mn, Si √Nb, Ti, V,
Mo √
800Low-
Medium C, Mn, Si √Nb, Ti, V,
Mo √
1000 DPLow -
MediumC, Mn, Si,
Mo √Nb, Ti, V,
Mo √
900 – 1500 MMedium -
High C, Mn, Si√ √
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Facilities for High Strength Steels
Time (18-36 hrs)
Tem
pera
ture
Soak 600-700°C
Slow coolingSlow
heating
Time (3-4 min)
Tem
pera
ture
Soak >720°C
Overage 200-400°C
Rapid cooling 500-1000 °C/s
T>820o
C
Cooling5 ∼ 10
oC/sec
Coating
Tem
pera
ture
(o C)
4-6 minutes
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Sheet Steel Applications
Formability of Sheet SteelsStress – Strain Curves as
Surrogates
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PRODUCT CHARACTERISITCSHOT ROLLED STEELS
ENGINEERING STRESS -STRAIN CURVES HR GRADES
100
200
300
400
500
600
700
800
0 5 10 15 20 25 30 35 40
ENGINEERING STRAIN, %
ENG
INEE
RIN
G S
TRES
S, M
Pa
HSLA 250
HSLA 350
HSLA 550
HSLA 590TS
HSLA 700
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PRODUCT CHARACTERISTICSCOLD ROLLED STEELS
ENGINEERING STRESS -STRAIN CURVES CR STEEL GRADES
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30 35 40 45 50ENGINEERING STRAIN, %
EN
GIN
EER
ING
STR
ESS,
MPa
270
DIFORM140T (965 MPa TS)
M190 (1300 MPa )
440
590 590DU
980DU
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PRODUCT CHARACTERISTICSGALVANNEALED STEELS
100
200
300
400
500
600
700
800
900
1000
1100
0 10 20 30 40 50 60
ENGINNERING STRAIN, %
ENG
INEE
RIN
G S
TRES
S, M
P
2 7 0 E
3 4 0 HR3 4 0 B H
4 4 0
5 9 0 D U5 9 0
9 8 0 D U
ENGINEERING STRESS - STRAIN CURVESGA STEEL GRADES
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TYPICAL STRESS STRAIN CURVES FOR 590 MPa FAMILY OF STEELS
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30Engineering Strain, %
Engi
neer
ing
Stre
ss, M
Pa
GA 590TRIP
GA 590 DU
GA 590
GA590
GA 590DU
GA 590TRIP
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Automotive Sheet SteelsE
long
atio
n (%
)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200
Low StrengthSteels (<270MPa)
Ultra High StrengthSteels (>700MPa)
300 900
High StrengthSteels
1600
DP
AHSS
MART
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
TWIP
USIBOR
USIBOR
TRIP
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Typical Hot Stamping Process Steps
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Example Parts made with Usibor 1500P
Fuel Tank Guard
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Main Properties After Hot Stamping
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SHEET STEEL APPLICATION TRENDS
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SHEET STEEL APPLICATION TRENDS
2007 North American Light Vehicle Steel Content for Body, Bumper and Closures
(Extracted from the Ducker 2007 Report)
9,341 Million Pounds of Content for 9.9 Million Vehicles
GM, Ford and DCX- Segmented by Type of Steel -
Foreign Domestics- Segmented by Type of Steel -
4,305 Million Pounds of Content for 5.394 Million Vehicles
56.0%
6.9%
12.0%
2.2%6.2%
16.7%Low Strength (270)
5,234MHSS (340)1,562
CHSS(440)1,122
AHSS(590-980)
644
UHSS (Over 980)203
Bake Hard576
45.3%11.0%
15.0%
1.5%8.9%
18.3%
Low Strength(270)1,952
MHSS (340)472
CHSS (440)646
AHSS (590-980) 787(Includes wheels)
UHSS (Over 980)63
Bake Hard385
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SHEET STEEL APPLICATION TRENDS
51.5%12.4%
36.1%
55.0%9.4%
35.6%59.5%
5.8%34.7%
2007 Body and Closure Steel Content by Type
Mild Steel
HSS
976 Pounds
Advanced HSS
Total Body on Frame
Mild Steel
HSS
763 Pounds
Advanced HSS
Total Unibody Total
842 Pounds
Mild Steel
HSS
Advanced HSS*
*AHSS is 73.6 pounds of Dual Phase , 5.8 pounds of martensitic, boron, complex phase, recovery annealed steels and TRIP steel not including door intrusion or bumper beams
There is a significant difference between the percent of AHSS in vehicles using a body on frame type architecture versus vehicles using a unibody type architecture.
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SHEET STEEL APPLICATION TRENDS
2007 North American Light Vehicle Flat Rolled AHSS and UHSS Steel Content
17%
75%
8%
DP 500/600 Including 590R
DP 980
DP 780
665,000 Tons
Dual Phase Steels
31.1%
40.7%28.2%
Boron Steels75,000 tons
Recovery Annealed TRIP and CP Steels
52,000 Tons
Martensitic Steels57,200 Tons
184,200 Tons
Other Steel Grades
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Predicted Growth of AHSS Usage - VW
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AHSS usage to grow significantly
• Advance of Japanese OEMs in AHSS implementation
• AHSS Growth currently limited by transformation constraints
• Future Emerging markets needs calculated as if required AHSS were available.
AHSS gathersall MultiPhaseSteels above450MPa Ts
BIW AHSS Usage (%)
05
10152025303540
2000 2006 2012 2020
NaftaJapan EU EM
Source AM Global Auto Marketing Studies
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Automotive Sheet SteelsE
long
atio
n (%
)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200
Low StrengthSteels (<270MPa)
Ultra High StrengthSteels (>700MPa)
300 900
High StrengthSteels
1600
DP
AHSS
MART
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
TWIP
USIBOR
USIBOR
TRIP
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QUESTIONS?
THANK YOU
ADVANCES IN HIGH STRENGTH STEELS
FOR AUTOMOTIVE APPLICATIONS