Advanced High Strength Steels - Home - GalvInfo

International Zinc Association

Advanced High Strength Steels

Frank E. GoodwinInternational Zinc Association

Hot-Dip Galvanized Sheet Production CourseJanuary 26-28, 2021


The Light-Weighting ChallengePassenger car results normalized to USA CAFE

A. Abraham, GDIS 2019


CO2 & MPG Compliance Showing Significant Progress



“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


What is the role of mass reduction in meeting economy/emissions requirements?



Where is the mass in a vehicle? And how to reduce it?



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



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.



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


AISI Statistical Review

Sheet is a vital product for the USA steel industry


Bagley GDIS 2019


2019 Silverado

Geeraerts and Sulik GDIS 2018






2019 Dodge Ram 1500 Improvements

Reed & Belanger GDIS 2018


Ram 1500 Steel-IntensiveLight-weighting



Body Structure Weight Comparison



Gestamp (Supplier) Innovations for Dodge Ram 1500



2020 Hyundai Palisade59% AHSS


Continued evolution of Ford F150 pickup frame for 2020: 12% mass reduction

Shahidi GDIS 2019


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


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


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


Requirements of AHSS El

onga

tion

(%)


0

10

20

30

40

50

60

70

0 600 1200



300 900

High StrengthSteels

1600

HSLA

IF

MildIF-HS

BHCMn

ISO

Conventional HSS

Better:― formability― energy absorption

Better deformation resistance

Ref: Peter Mould


Application of HSS — General

Ref: Peter Mould


First Generation AHSS — DP, TRIP, CP, Martensitic El

onga

tion (

%)


0

10

20

30

40

50

60

70

0 600 1200



300 900

High StrengthSteels

1600

DP, CP

TRIPAHSS

MART

HSLA

IF

MildIF-HS

BHCMn

ISO

Conventional HSS

Ref: Peter Mould


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


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


A3A1

F-B-ATRIP

Temperature

Time

- Carbon enrichment during bainite transformation- Suppression of Fe3C formation (Si, Al, P…)

TRIP: Stabilizing Austenite


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


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


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


Ref: Peter Mould


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


(Martensite steels (continued)2)Post-form strengthened steels

� Carbon – Boron steels� Hot stamped > 900°C� Good formability – complex shapes

Strength / Workability

Source: Hard Tech


Ref: Peter Mould


• 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

(%)


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


•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


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


Actual MicrostructureSchematic Illustration

Dual Phase

Actual Microstructure

Martensite

TRIP

Actual Microstructure Schematic Illustration

Metallurgy of AHSS - Summary


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


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


Zn Coating of AHSS: Reduction of Oxides and Furnace Gas Dewpoints


Schematic diagram of the oxidation kinetics mechanism of high strength steel


Effect of Furnace Dewpoint and Use of Preoxidation Section (DFF, DFI) on Steel Surface

Wuttke et al., Galvatech 2015


Steel Composition 6%Mn and 3.5% (Al+Si)

Kang et al., Galvatech 2015




Depth profile of annealed steel surface using Glow Discharge Optical Emission Spectroscopy



Granular MnO forms on surface at -10 and +5C dewpoints











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

Documents

Advanced High Strength Steels - Home - GalvInfo