International Zinc Association
Advanced High Strength Steels
Frank E. GoodwinInternational Zinc Association
Hot-Dip Galvanized Sheet Production CourseJanuary 26-28, 2021
International Zinc Association
The Light-Weighting ChallengePassenger car results normalized to USA CAFE
A. Abraham, GDIS 2019
International Zinc Association
CO2 & MPG Compliance Showing Significant Progress
A. Abraham, GDIS 2019
International Zinc Association
“There will be no cars made of aluminum in the future. Press hardened steels (PHS) will play a special role in this development. PHS are at the core of a car’s occupant cell, which protects the driver and passengers in case of a collision. If you compare the stiffness-weight ratio, PHS is currently ahead of aluminum.” Dr. Bernd Mlekusch, head of Audi’s Leichtbauzentrum
International Zinc Association
What is the role of mass reduction in meeting economy/emissions requirements?
A. Abraham, GDIS 2019
International Zinc Association
Where is the mass in a vehicle? And how to reduce it?
A. Abraham, GDIS 2019
International Zinc Association
Body-In-White & Closure Steel Content Pounds Per Vehicle By GradeGrade Percentage & Total Pounds
Net steel content for body in white and closures will see declines; however, AHSS, UHSS and 3rd Gen AHSS materials will grow at a tremendous pace
A. Abraham, GDIS 2019
International Zinc Association
2018 - 2020 NA Light Vehicle Material ContentSteel remains the primary share of automotive materials; however, from a content perspective, steel will decline by approximately 65 pounds between 2018 and 2020 due to the increased use of thinner gage AHSS and UHSS as opposed to Mild or HSS.
A. Abraham, GDIS 2019
International Zinc Association
Auto continues to be the largest user of galvanized sheet in the USA.The fraction of steel sheet that is galvanized continues to grow.
GalvInfo Center
International Zinc Association
AISI Statistical Review
Sheet is a vital product for the USA steel industry
International Zinc Association
Bagley GDIS 2019
International Zinc Association
2019 Silverado
Geeraerts and Sulik GDIS 2018
International Zinc Association
Geeraerts and Sulik GDIS 2018
International Zinc Association
Geeraerts and Sulik GDIS 2018
International Zinc Association
2019 Dodge Ram 1500 Improvements
Reed & Belanger GDIS 2018
International Zinc Association
Ram 1500 Steel-IntensiveLight-weighting
Reed & Belanger GDIS 2018
International Zinc Association
Body Structure Weight Comparison
Reed & Belanger GDIS 2018
International Zinc Association
Gestamp (Supplier) Innovations for Dodge Ram 1500
Reed & Belanger GDIS 2018
International Zinc Association
2020 Hyundai Palisade59% AHSS
International Zinc Association
Continued evolution of Ford F150 pickup frame for 2020: 12% mass reduction
Shahidi GDIS 2019
International Zinc Association
Zinc Protecting Automotive Steel
• 207,600t = US made galvanized sheet
• 70,000t = imported galvanized sheet
• 277,600t = total zinc consumption for USA automotive sheet in 2017
International Zinc Association
Categorization of HSS/AHSS
HSS
� Tensile Strengths: 280 – 650 MPa� Formability decreases as TS increases
AHSS
� Multiphase steels― Tensile Strengths: 500 – 1000 MPa― Better formability for specific strengths
� Ultra High Strength Steels (UHSS)― Tensile Strengths: 700 – 1600 MPa― Low formability
Traditional strength-formability relationships
But: Third generation steels permit both high strength and high formability
International Zinc Association
Early Changes: Emergence of HSS – 1970s
� Solid solution strengthened steels― IF HS―Rephosphorized
Bake hardening―C-Mn
� High Strength Low Alloy (HSLA) steels―Nb, V and Ti steels 350 – 800 MPa
� Low formability� Low energy absorption
Elon
gatio
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
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
Two categories
Issues:
270 – 600 MPa
Ref: Peter Mould
International Zinc Association
Requirements of AHSS El
onga
tion
(%)
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
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
Better:― formability― energy absorption
Better deformation resistance
Ref: Peter Mould
International Zinc Association
Application of HSS — General
Ref: Peter Mould
International Zinc Association
First Generation AHSS — DP, TRIP, CP, Martensitic El
onga
tion (
%)
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, CP
TRIPAHSS
MART
HSLA
IF
MildIF-HS
BHCMn
ISO
Conventional HSS
Ref: Peter Mould
International Zinc Association
AHSS — Types and Description
Typical applicationsCrush structures: Rails, pillarsDent resistance: Exposed Body panels
Dual Phase (DP)
� O.1C-Mn-Si/Aℓ� Ferrite-Martensite structure� 500 – 1000 MPa Tensile Strengths
� High work hardening� High elongation� Good TS – Elongation — Energy absorption� High bake hardening
Ref: Peter Mould
International Zinc Association
Typical applicationsCrush structures: Rails, pillars
TRansformation Induced Plasticity (TRIP) steels
� O.15C-Mn-Si/Aℓ (Mo)� 500 – 1000 MPa Tensile Strengths
� About 4 – 12% retained austenite� Deformation transforms the austenite
• high work hardening• high energy absorption
� Welding issues
AHSS — Types and Description continued
Ref: Peter Mould
International Zinc Association
A3A1
F-B-ATRIP
Temperature
Time
- Carbon enrichment during bainite transformation- Suppression of Fe3C formation (Si, Al, P…)
TRIP: Stabilizing Austenite
International Zinc Association
0.19C- 1.5Mn- 1.5Si TRIP Steel After 2nd stage tint etching
Before tensile straining After 20% strainingVγ : ~17% Vγ : ~ 4%
1000X
TRIP Transformation on Deformation
TRIP Deformation Martensite
International Zinc Association
Complex Phase (CP) steels
� O.1C-Mn-Si-Nb/Ti steels
� Complex phases – very fine microstructuresBainite (green)Martensite (black)Austenite (yellow)Ferrite (white)
� 700 – 1000 MPa
� High work hardening
� High energy
Typical applications� Deformation resistance
• Bumper reinforcements• Rockers• Impact beams
� Crush structures• Rails, pillars
AHSS — Types and Description-continued
Ref: Peter Mould
International Zinc Association
Martensite steels 2 types . . .
(1) As supplied by steel supplier� Carbon steels with hardenability elements
-
Limited formability/weldingTypical applications
• Roll formed rockers, cross beams
• Simple reinforcements
AHSS — Types and Description-continued
Ref: Peter Mould
International Zinc Association
The Hot Stamping Process
Figure source: Voestalpine
Table source: H. Güler, “Investigation of Usibor 1500 Formability in a Hot FormingOperation”, ISSN 1392–1320 Materials Science (Medžiagotyra). Vol. 19, No. 2. 2013
International Zinc Association
(Martensite steels (continued)2)Post-form strengthened steels
� Carbon – Boron steels� Hot stamped > 900°C� Good formability – complex shapes
Strength / Workability
Source: Hard Tech
AHSS — Types and Description-continued
Ref: Peter Mould
International Zinc Association
• Additional 10% mass reduction (projecting over 35%)
For 2017-2025, new formable AHSS grades will enable more steelmass reduction
3rd Generation AHSS
Elo
ngat
ion
(%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200300 900 1600
DP, CP
TRIP
MART
HSLA
IF
MildIF-HS
BHCMn
ISO-
BH
TWIPAUST. SS
L-IP
Future Opportunity
Third Generation AHSS
International Zinc Association
•Quenching and Partitioning Produced New AHSS Microstructures with High Retained Austenite and Martensite
O.2 C, 1.5 Mn, 1.2 Si (also Al, Ni, Cr can be added)Quench and Partition Compositions
David Matlock and John Speer, 2010
International Zinc Association
CAL CR+ EG/EGA(2015)
CGL GA or GI GEN3 (2017)
\Coated AHSS GEN1, GEN1+, GEN3 Materials
Actual Production Coil Data on a “Banana Plot” *
* J. Stechschulte, New CAL at PRO-TEC, Galvanizers Assoc. Proc., 2015
780G3CGL GA & GI 980 GEN3
25,000 UTS * El
International Zinc Association
Actual MicrostructureSchematic Illustration
Dual Phase
Actual Microstructure
Martensite
TRIP
Actual Microstructure Schematic Illustration
Metallurgy of AHSS - Summary
International Zinc Association
Optimization of CGL Processing to Improve GA Hole Expansion Ratio
(HER, λ)
High Yield Ratio AHSS with optimized:• CGL Annealing Heat Treatment• CGL Skin Pass Temper Rolling
effect, changing GA micro-cracks frequency and steel threshold for crack initiation
Normal GA AHSS with 65% HER
18.5 mm
Optimized GA AHSS with 85% HER
Goodwin & Silva, Galvatech 2017
International Zinc Association
Processing to Optimize Fracture Resistance of AHSS
• Iso-contour lines show boundaries of very good, good, fair, and poor formability.
• Zones are also shown with balanced versus local or global behavior of the ten steels, which had application-specific material designs.
• The limiting bend ratio (r/t) required by applications is a combined function of both local and global formability parameters
Hance Diagram showing true fracture versus true uniform strains for several coated and uncoated 980 MPa AHSS, one new GEN3 780
B. Hance , IABC 2016M. Davenport, TheFabricator.com Oct.2017
GEN3 980
GEN3 980-HY
TBF 980
MP 980 (LCE)
CP 980
DP 980
DP 980 (LC)
DP 980 (LSi)
DP 980-HY (LSi)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.00 0.05 0.10 0.15 0.20
True
Frac
ture
Stra
in (T
FS)
True Uniform Strain (εu)
GEN3TBFMP/CPDP
Balanced/Local
V. Good
Good
FairPoor
Local
Global GEN3 780
Balanced/Global
International Zinc Association
Zn Coating of AHSS: Reduction of Oxides and Furnace Gas Dewpoints
International Zinc Association
Schematic diagram of the oxidation kinetics mechanism of high strength steel
International Zinc Association
Effect of Furnace Dewpoint and Use of Preoxidation Section (DFF, DFI) on Steel Surface
Wuttke et al., Galvatech 2015
International Zinc Association
Steel Composition 6%Mn and 3.5% (Al+Si)
Kang et al., Galvatech 2015
International Zinc Association
Kang et al., Galvatech 2015
International Zinc Association
Depth profile of annealed steel surface using Glow Discharge Optical Emission Spectroscopy
Kang et al., Galvatech 2015
International Zinc Association
Granular MnO forms on surface at -10 and +5C dewpoints
Kang et al., Galvatech 2015
International Zinc Association
Kang et al., Galvatech 2015
International Zinc Association
Kang et al., Galvatech 2015
International Zinc Association
Kang et al., Galvatech 2015
International Zinc Association
Kang et al., Galvatech 2015
International Zinc Association
Conclusions
• HDG of AHSS is a balance between:-developing correct phase makeup (and therefore mechanical properties) and-developing a galvanizable surface (granular or reducible surface oxides that allow Zn-Al wetting or reactivity with the steel/oxide surface