Advanced High Strength Steels and their Heat Treatment processes

Prepared by
Sudarshan S
Dept. of M.M.E
NIT Trichy
June 2017
IIT Madras

INTRODUCTION TO AHSS
• AHSS are complex, sophisticated materials, with carefully selected chemical
compositions and multiphase microstructures resulting from precisely
controlled heating and cooling processes. Various strengthening mechanisms
are employed to achieve a range of strength, ductility, toughness, and fatigue
properties.
• AHSS family has unique microstructures utilizing complex deformation and
phase transformation processes to achieve strength and ductility
combinations that were never-before realized
• By definition, steels with yield strengths (YS) greater than 550 MPa are called
AHSS
• AHSS with YS> 780 MPa are called ULTRA HIGH STRENGTH STEELS.
• AHSS with YS> 1000 MPa are called GIGAPASCAL STEELS

WHY AHSS ?
• High strength to weight ratio – Gauge reduction – Mass, Material and Fuel Saver.
Stronger than conventional steels
• Offer high work-hardening rates & bake hardening capability, which allows
increased formability.
• Greater part complexity - Fewer individual parts - Time, mass and cost
effective.
• Steel is the most recycled material – Used in new automotive or other products.
• Improved crash performance – Improved passenger safety.
• Leave minimum carbon footprint – Environment friendly
• When considering AHSS application benefits for vehicles, the steel industry has
adopted the acronym given below :
• SAFE—for crash protection (Safety), for Affordability and cost, for Fuel
efficiency, and for the Environment.

MATERIAL SELECTION
• Several key considerations drive material selection for automotive applications,
including safety, fuel efficiency, environmental performance, manufacturability,
durability, and quality.
• These factors manifest themselves differently in each component of the vehicle,
and materials are selected to match each set of performance requirements in the
most efficient means possible.
 CRASH PERFORMANCE
The ability to carry the required static and dynamic loads, particularly in a crash
event, is one of the key design considerations for vehicle structures.
(i) Passenger safety cage – Structure should prevent any deformation that
compromises the integrity of the cage and impinge on space around passengers
(ii) Crumpled Zones (front& rear)- Cushions the impact and preserves structure of
passenger compartment.

MATERIAL SELECTION
 CRASH PERFORMANCE

MATERIAL SELECTION
 STIFFNESS
• Modulus of elasticity (E) and geometry of material have direct linkage with
stiffness of a component.
• As E value has been constant for all steel grades, so geometry can only be
changed to improve stiffness.
• But, the load carrying capacity of the component can suffer from the gauge
reduction of the component.
• For high strength steel reduction in gauge can be counterbalanced by changes
in geometry or by using continuous joining techniques such as laser welding
or adhesive bonding
• The use of AHSS offers many advantages in this process because high work
hardening rates increase formability, allowing for improved shapes for optimal
efficiency

MATERIAL SELECTION
 FORMABILITY
• AHSS were developed partly to address decreased formability with increased
strength in conventional Steels.
• As steels became increasingly stronger, they simultaneously become
increasingly difficult to form into automotive parts.
• AHSS, although much stronger than conventional low- to high-strength steel,
also offer high work hardening and bake hardening capabilities that allow
increased formability and opportunities for optimization of part geometries.
• Hence, a combination of both strength and ductility is required to effectively
use a material in manufacturing of auto parts.
• When considering ductility, both overall and local elongation properties needs
to be considered. For some difficult-to-form parts, high stretchability at
sheared edges are examined.

1994, ULSAB program- light weight
design, meets-safety and performance.
Gave rise to AHSS family
ULSAB- AVC (Advanced vehicle
concepts)- refined fabrication method-
even greater mass reduction
2008, FSV program- Application of
Gigapascal strength AHSS- reduced life
cycle emissions- 39% body mass
reduction
STEEL EVOLUTION IN AUTO INDUSTRY
WorldAutoSteelGuidelinesV5.0

TYPES OF AUTOMOTIVE STEELS
Automotive steels can be classified in 3 different designations as follows :
(i) Metallurgical designation
Low Strength steels Interstitial free steels (IF)
Mild steels
Conventional HSS
C-Mn steels
Bake hardenable steels
HSLA steels
New AHSS
Dual Phase steels (DP)
Ferritic Bainitic steels (FB)
Complex phase steels (CP)
Martensitic steels (MS/MART)
Transformation-induced plasticity steels (TRIP)
Twinning-induced plasticity steels (TWIP)

(ii) Strength designation
- Yield strength(Ys) > 550 Mpa === Advanced high strength steels
- Yield strength(Ys) > 780 Mpa=== Ultra high strength steels
- Yield strength(Ys) > 1000 Mpa=== Gigapascal steels
(iii) Formability designation
Classification is based on mechanical or forming parameters of different steels, such as
total elongation, work hardening exponent (n-value), or hole expansion ratio (λ)
TYPES OF AUTOMOTIVE STEELS
This graph compares total
elongations (a steel property related
to formability) – to the tensile
strength for the current types of
steel. These properties are
important for press shop operations
and virtual forming analyses.
AHSS_Guidelines V5.0

(i) Mild Steel
- Very low strength but extremely high
formability (due to minimal alloying
elements)
- Inexpensive, widely produced, used
and often serve as baseline for
comparison with other materials.
- Commonly used in body structures,
closures, and other ancillary parts
- Example: AISI 1010 - ideal for the
automobile industry, where it
frequently is used for auto bodies,
fenders, and smaller parts including
pans and transmission covers.
LOW STRENGTH STEELS
Image Source @ automotive.arcelormittal.com

(ii) IF Steel
- Ultra low carbon content,
achieved by vacuum degassing
of CO, H2, N2, and other gases
during steel making.
- Lack of interstitial atoms
enables IF steels to have high
ductility values, ideal for deep
drawing.
- Low strength, but high work
hardening rates and excellent
formability.
- Commonly Used in elements
of body structures and
closures.
LOW STRENGTH STEELS
Microstructure of Interstitial free steelSource @ ispatguru.com/interstitial-free-steels

LOW STRENGTH STEELS
ConventionalVsInterstitialfreeSteelProcessroute
Source @ sustainableinsteel.eu

(i) Bake hardening Steel
- "Bake hardening" is a controlled aging phenomenon
related to the presence of carbon and/or nitrogen in solid
solution in the steel
- The steel is soft during forming stage, but picks up
strength during subsequent paint baking stage. This
increases the YS of the BH steel
- The BH2 parameter is used to evaluate the resulting
increase in dent resistance. It is given by: BH2 = LYS - 2%
PS, in which LYS is the lower yield stress measured after
heat treatment and PS is the yield stress after initial 2%
plastic pre-strain.
- The diagram here illustrates the Bake hardening
mechanism and shows the displacement of carbon atoms
in solution during heat treatment-typically 20 minutes at
170°C to block the dislocations generated by forming. This
ultimately increases the metal's yield strength.
- Commonly Used in closure panels like door outer,
hoods, and deck lids.
CONVENTIONAL HSS
Bake hardening process
Source @http://automotive.arcelormittal.com/europe/products/HYTSS/BH/EN

CONVENTIONAL HSS
BakehardeningSteelapplicationin Autoindustry
Metal
Grade
YS(Mpa) UTS(Mpa) n BH2(Mpa) C (Max) Mn (Max) Si (Max)
180 BH 180-230 300-360 ≥ 0.17 ≥ 35 0.04 0.7 0.5
260 BH 260-300 370-430 ≥ 0.15 ≥ 35 0.08 0.8 0.5
Microstructure of grade 180 BH
Hood in 180 BH Door in 260 BH

(ii) HSLA Steel
- HSLA steels are hardened by a
combination of precipitation and grain
size refining, resulting in high strength
with low alloy content. This enhances
weldability and choice of coatings, since
these steels exhibit neither weld zone
softening nor grain coarsening.
- The mechanical properties of hot rolled
HSLA steels and their excellent cold
forming performance and low-
temperature brittle fracture resistance
support cost-effective solutions for many
parts and sub-assemblies for which
weight, thickness and size reduction are
sought, such as: Chassis components;
wheels; side rails; cross members.
CONVENTIONAL HSS
Rear cross member in
Extragal®-coated HSLA 300
Shock absorber in HSLA 300

CONVENTIONAL HSS
PropertiesofHSLAsteelsusedin AutoIndustry
Metal Grade YS(Mpa) UTS(Mpa) C (Max) Mn (Max) Si (Max) Welding
Range(kA)
HSLA 300 300-360 390-450 0.08 0.6 0.04 3.5 (t=2)
HSLA 340 340-400 420-490 0.08 0.7 0.04 1.1 (t=2)
Microstructure of cold rolled
HSLA 340
t= thickness
Formability: Draw-ability declines progressively with increasing yield
strength.
Weldability: Weldability is determined according to the ISO 18278-2
method. Cold rolled HSLA steels can be readily welded using all
common welding processes.
Fatigue strength: Because of their high endurance limits, these steels
are particularly well suited to parts subject to fatigue stress. To
restore the base metal endurance limit adjacent to welds in areas
subjected to severe cyclic loading, a post-weld treatment such as TIG
melting, hammering, peening or grinding should be applied to the
weld toe.
Data from World autosteel_GuidelinesV5.0

(i) Dual Phase (DP) Steel
- Dual Phase steels offer an outstanding combination
of strength and drawability as a result of their
microstructure, in which a hard martensitic or
bainitic phase is dispersed in a soft ferritic matrix.
- Due to high strain hardenability, they posses good
strain redistribution capacity. So drawability as well
as finished part mechanical properties including
yield strength, are far superior to those of the initial
blank. The yield strength of Dual Phase steels is
further increased by the paint baking (BH) process.
- The strain hardening capacity of these steels
combined with a strong bake hardening effect gives
them excellent potential for reducing the weight of
structural parts
- Alloy additions- Si, P strengthen the steel, but must
be balanced for weldability, while Mn, Cr, V, Nb
increase the hardenability.
ADVANCED HIGH STRENGTH STEELS
DP schematic microstructure
Microstructure of DP 600 steel
Source @ worldautosteel.org

DualPhaseSteelProductionProcess
The most common way of producing DP steels is by cold rolling of low alloy (LA) steels
followed by inter critical annealing in a continuous annealing line, referred to as CAL
Applications: DP allows broad range of applications from crumple zone to body structures. Hence used in
1. Beams, cross members and structural components
2. Crash energy absorption in crumple zone
3. tailored blanks, and hydroformed tubes
Source @ worldautosteel.org

PropertiesofDPsteelsusedin AutoIndustry
Metal
Grade
YS(Mpa) UTS(Mpa) n BH2 C (Max) Mn (Max) Si (Max)
DP 600 330-410 600-700 0.14 30 0.14 2.1 0.4
DP 780
Y450
450-500 780-900 0.1 30 0.17 2.2 0.6
Wheel web in hot rolled DP 600 B-pillar reinforcement in DP 780 Y450
Given their high energy absorption capacity and fatigue strength, cold rolled Dual Phase
Steels are particularly well suited for automotive structural and safety parts
Source @ automotive.arcelormittal.com

(ii) Ferritic Bainitic (FB) Steel
- The microstructure of FB Steel consists of
a softer ferrite matrix, with fine bainite as
second phase. The microstructure is finer
than the typical DP steel.
- The primary advantage of FB steels over
HSLA and DP steels is the improved
stretchability of sheared edges as
measured by the hole expansion test (λ).
Compared to HSLA steels with the same
level of strength, FB steels also have a
higher strain hardening exponent (n-value)
and increased total elongation.
- Commonly used in cross beams and
reinforcements, and wheels
- Because FB has good fatigue properties in
dynamic load conditions, it is an
outstanding candidate for shock towers
and control arms.
Formability curve representation for FB
steel
Microstructure of FB 540 steel

Ferritic BainiticSteelProductionProcess
TTT diagram of corresponding high
strength steel grades
- The first step is to cool from finishing temperature in
austenitic region down to an intermediate
temperature in ferritic region.
- At intermediate temperature air cooling for some
seconds allows 80-90% of the austenite to transform
to the polygonal ferrite or irregular ferrite.
- In the third step, fast cooling to a coiling temperature
in the bainitic region is applied to fully transform the
retained austenite into bainite.
- FB steels show more transformation hardening than
HSLA steels, but less than Dual Phase steels. Hence,
yield ratios lie between HSLA and DP steels.
- High Hole Expansion (HHE) grade, is recommended
for parts with sheared edge stretch ability
requirements (stretch flange ability, edge flanging,
edge stress during secondary processing, etc) HHE behavior of FB 590 (ISO standard)

PropertiesofFBsteelsusedinAutoIndustry
Metal Grade YS(Mpa) UTS(Mpa) C (Max) Mn (Max) Si (Max)
FB 540 400-485 540-610 0.17 1.5 0.15
FB 560 450-530 560-640 0.1 1.6 0.15
Suspension arm FB 540 (t=4mm) Pillar reinforcement galvanized
FB 560 (t=1.8mm)
Front and rear underseat cross member
galvanized FB 560 (t=1.8mm)

(iii) Complex Phase (CP) Steel
- CP steels have a mixed microstructure with ferrite/bainite
matrix containing bits of martensite, retained austenite,
and pearlite. Grain refinement is essential to obtaining the
desired properties from CP steel; delayed recrystallization
is often employed to develop very small grains for a very
fine microstructure.
- The Complex Phase family, was specially designed for
exceptional stretch flangeability and has higher hole
expansion values.
- CP steel has several automotive applications, particularly in
body structure, suspension, and chassis components. The
high YS and elongation enables high energy absorption,
also making it a good choice for crash safety components,
such as fender beams, door impact beams, and
reinforcements for B-pillar, etc.
- According to ThyssenKrupp Steel, replacing conventional
microalloyed steel with CP in a B-pillar reinforcement can
double its strength
Microstructure of hot rolled CP 1000
HHE behavior of CP steels (ISO 16630)
Source @ worldautosteel.com

PropertiesofCPsteelsusedin AutoIndustry
Metal Grade
(Hot rolled)
YS(Mpa) UTS(Mpa) C (Max) Mn (Max) Si (Max)
CP 800 680-830 ≥ 780 0.1 2.0 0.25
CP 1000 800-950 ≥ 950 0.14 1.7 0.25
Tunnel stiffener CP 800 (t-=1.6mm) Door bar CP 1000 (t=2mm)
Formability: Although UTS is
lower than DP steels, formability
is good for their high strength
level.
Weldability: Good response to
resistance spot welding.
Impact strength: As a result of
their very high YS and UTS
values, they particularly well
suited for anti-intrusion parts.Image Source @ automotive.arcelormittal.com

(iv) Martensitic ( MS) Steel
- In MS steels, nearly all austenite is converted to
martensite. The resulting martensitic matrix
contains a small amount of very fine ferrite and/or
bainite phases. This structure typically forms
during a swift quench following hot-rolling,
annealing, or a post-forming heat treatment.
- Increasing the carbon content and alloying with
Mn, Si, Cr, Mo, B, V and Ni in various combinations
increases hardenability. MS steel is typically roll
formed and may be bake hardened and
electrogalvanized for applications requiring
corrosion resistance, but heat-treating MS
decreases its strength.
- Because MS steel has such high strength to weight
ratio, it is weight and cost effective. It is often
selected for body structures, ancillary parts, and
tubular structures.
- MS grades are recommended for bumper
reinforcement and door intrusion beams, rocker
panel inners and reinforcements, side sill and
belt line reinforcements, springs, and clips.
Typical parts for MS steels
HHE behavior of MS steels (ISO 16630)

PropertiesofMSsteelsusedin AutoIndustry
Metal
Grade
YS(Mpa) UTS(Mpa) C (Max) Mn (Max) S Form
M 1500 1370 1629 0.25 0.45 0.015 CR, EG
M 1700 1520 1820 0.3 0.45 0.015 CR
Microstructure of M1700 (1000X) Microstructure of M1500
Limitation:
- Low elongation
- High springback
They can be overcome
by multiple operations in
Roll forming and over
bending.

(v) Hot Formed (HF) Steel
- The use of HF boron steel, called ultra-high-
strength steel (UHSS) by some automakers, has
grown rapidly in Europe; other materials for hot
forming are also being investigated, as well as new
coatings to improve corrosion resistance.
- HF steel is typically boron-based (0.002-0.005% B).
Microstructure is similar to martensite. There are
two types of forming processes- Direct and Indirect
hot forming.
- Applications for HF steels include reinforcements
for and A- and B-pillars, roof bows, side-wall
members, and beams for crash management
structures and other parts that carry severe loads.
Volvo was one of the early adopters of hot-formed
steels, as they call UHSS (YS of 1500 MPa).
- Parts made from HF steel benefit from several
material advantages, including high strength and
improved (reduced) spring back.
Application of Usibor& Ductibor HF grades
Microstructure of Usibor1500
HF steels
World Auto steel Guidelines _V5.0

DirectHotFormedSteelProductionProcess
In direct hot-forming, the boron-based steel is blanked at room temperature and then heated to high
enough temperature for austenization. The steel is then formed while hot and quenched in the forming tool,
developing the martensitic microstructure. Some special post-forming work may be required to finish the
pieces, which are exceptionally high strength.
Direct hot forming process
Usibor®-AS and -GA were specially developed for a direct hot
stamping process consisting of austenitization of blanks in
the heat treatment oven, hot stamping of these hot blanks
in a press and martensitic quenching in the water-cooled
stamping tool. All strain during forming occurs at high
temperature.
Hot-stamped Usibor®-AS and Ductibor®-AS parts have no
micro-cracks inside the steel substrate.
Direct HF process for Usibor and Ductibor
grades produced by Arcelor mittal

In-directHotFormedSteelProductionProcess
In indirect-hot forming, the steel is blanked and pre-formed at room temperature. The part is then
heated and forming is completed while the steel is in this low strength, high elongation state. A final
quench in the die produces the final properties and shape.
In direct hot forming process
Transitions in HF STEEL:
1: Initial, room temperature state
where the steel is blanked.
2: Raised temperature state where
forming is completed.
3: Final strength-elongation achieved
after rapid cooling.

PropertiesofHF steelsusedinAutoIndustry
Metal Grade YS(Mpa) UTS(Mpa) C (Max) Mn (Max) B (Max)
Ductibor 1000 ≥800 ≥1000 0.12 2.0 0.005
Usibor 1500 1100 1500 0.25 1.4 0.005
Laser welded blanks Ductibor 1000 B- pillar Usibor (t= 1.8 mm) Potential applications of HF in
automobile

(vi) TRIP Steels
- TRIP benefits from a multi-phase microstructure with a
soft ferrite matrix embedded with hard phases. The
matrix contains a high amount of retained austenite
(at least 5 percent), plus some martensite and bainite
- The amount of strain required to initiate this
transformation may be managed by regulating the
stability of the austenite by controlling its carbon
content, size, morphology or alloy content. With less
stability, the transformation begins almost as soon as
deformation transpires. With more stability, the
austenitic transformation to martensite is delayed
until higher levels of strain are reached
- TRIP, as a result of its high work hardening rates, has
excellent formability and a high capacity for stretch.
Complex shapes are possible because TRIP exhibits
good bendability and resists the onset of necking.
- Common applications: Cross members, Longitudinal
beams, sills and bumper reinforcements
Schematic of typical TRIP
microstructure
Cold rolled TRIP 780 microstructureSource @ ispatguru.com/trip-steels

PropertiesofTRIPsteelsusedinAutoIndustry
- A two-stage heat treatment with intercritical annealing in the temperature range 780–880
°C followed by cooling and isothermal annealing in the range 350–450 °C and cooling to
ambient temperature is applied .
-After bainitic transformation, the microstructure contains around 50–60% of ferrite, 25–40%
of bainite and 5–15% of retained austenite.
Transformation is delayed until high
strain values are reached , beyond
forming process, usually in a crash
eventSource from ‘Physical Metallurgy’ by Vijecndra Singh

PropertiesofTRIPsteelsusedinAutoIndustry
Metal Grade YS(Mpa) UTS(Mpa) n C (Max) Mn (Max)
TRIP 690 410-510 690-800 ≥ 0.19 0.2 2.0
TRIP 780 450-550 780-900 ≥ 0.18 0.25 2.0
Limitaitons:
- poor local and edge stretchability
- high alloying requirement
Bumper cross member TRIP 780 B- pillar reinforcement TRIP 780

(vii) TWIP Steels
- TWIP steels offers extremely high strength (>1000
MPa) with extremely high stretch ability. It is
developed by adding high manganese content (17-
24%) which causes the steel to be fully austenitic at
room temperatures. A large amount of deformation
is driven by the formation of deformation twins.
- The twinning causes a high value of the
instantaneous hardening rate (n value) as the
microstructure becomes finer and finer.
- Commonly used in in A-Pillar, wheelhouse, front
side member, wheel, lower control arm, front and
rear bumper beams, B-pillar, wheel rim, floor
cross-member, wheelhouse, door impact beam.
- Mechanism: deformation twinning, where slip
causes symmetric twin boundaries, which are
much like grain boundaries in their functionality,
restricting the movement of dislocations through
the material.
Microstructure of as annealed
TWIP steel
Formability curve for TWIP steel

GradesofTWIPsteelsusedin AutoIndustry
TWIP 500/900 A-Pillar, wheelhouse, front side member
TWIP 500/980 Wheel, lower control arm, front and rear bumper
beams, B-pillar, wheel rim
TWIP 600/900 Floor cross-member, wheelhouse
TWIP 750/1000 Door impact beam
TWIP 950/1200 Door impact beam
Summary of TWIP steel properties
Use of TWIP steel in
shock absorber casing

(i) Post Forming Heat treatable steels (PFHT)
- Post-forming heat treatment is a general method to
develop an alternative higher strength steel. The major
issue holding back widespread implementation of HSS
typically has been maintaining part geometry during
and after the heat treatment process. Fixturing the part
and then heating (furnace or induction) and immediate
quenching appear to be a solution with production
applications. In addition, the stamping is formed at a
lower strength (ellipse 1) and then raised to a much
higher strength by heat treatment (ellipse 2).
- Another process is air-hardening of alloyed tempering
steels that feature very good forming properties in the
soft-state (deep-drawing properties) and high strength
after heat treatment (air-hardening). Apart from direct
application as sheet material, air-hardening steels are
suitable for tube welding. These tubes are excellent for
hydroforming applications
- Third option: heating to 900 ºC and water quench to
form Martensite. This is called ‘Form hardening’.
ADDITIONAL HIGH STRENGTH STEELS
PFHT 340/480 As receiver@ Room
temperature
PF 1050/1500 Heat treated after
forming
PF 1200/1900 Heat treated after
forming
Examples of PFHT grades used in AutomobilesSource @ automotive.arcelormittal.com

(ii) Quenched and Partitioned steels (QP)
- Q&P steels are a series of C-Si-Mn, C-Si-Mn-Al or
other likely compositions subjected to the
quenching and partitioning (Q&P) heat treatment
process. With a final microstructure of ferrite (in
the case of partial austenitization), martensite and
retained austenite, Q&P steels exhibit an excellent
combination of strength and ductility
- This high strength martensitic grade is produced by
controlled low temperature partitioning of Carbon
from as-quenched martensite laths to retained
inter-lath austenite under conditions where both
low temperature transition carbide formation and
cementite precipitation are suppressed.
- The potential automotive applications are very
likely to be in the area of anti-intrusion barriers.
Q&P processing capability is believed to exist in
some existing facilities for hot-rolled, cold-rolled,
and hot-dip coated products
ADDITIONAL HIGH STRENGTH STEELS
QP microstructure of AISI 9260 steels.
Quenched at 190 ºC. Partiontioned at
400 ºC. Nital etchedLi Wang, John G Speer ASM international (2013) 2:268-281

SCHEMATIC PROCESS FOR QP&QPT
T.Y. Hsu (Xu Zuyao), Materials science Forum (2007)

COMBINATION OF QP & HOT STAMPING
Test specimen grade: 22SiMn2TiB steel
Ms temperature : 378ºC
Mf temperature : 265ºC
Finer microstructure of
the test specimen
Showing martensite ==
H. P. Liu and X. J. Jin* et al, Scripta Mater 64 (2011) 749-752

DESIGN STRATEGY WITH PROPER ALLOYING
FOR AUTOMOBILE (AHSS)
Development in multiphase steels over the years

(iii) Super Bainitic steels (Novel development)
- Designed to overcome brittleness and cracking of
traditional Bainite in service during armor
applications. Steel crystals of this type, contain
just one tenth the size of those in standard steel,
making it much stronger. And by carefully
adjusting the quantities of the alloying elements
including Mn, Si, Cr and Mo, the level of carbides
could be reduced, making it less prone to
cracking.
- The new derivative was found to have a tensile
strength of around 2.5 gigapascals, much stronger
than similar metals used in military applications,
absorbing a large amount of energy by
deformation without allowing ingress of
projectiles. Super bainite could be used to give
increased stiffness to roll cages within car
manufacture while reducing weight. Obtaiend by
Isothermal hardening (200 ºC) followed by heat
treatment(250 ºC).
RECENT HIGH STRENGTH STEELS
Steel crystals with fewer carbides
SB steel in British army’s ‘Foxhound’
Image Source @ General Dynamics

CURRENT EXAMPLES
2010 Mercedes E-class
- 72% HSS in body. YS > 180Mpa. Achieved more than 30% rigidity
2011 Honda CR-Z
- 1st to introduce AHSS. They advertise ACE (Advance compatibility Engineering) to
improve crashworthiness.
2011 Porsche Cayenne
- Mass reduction by 180kg, Body structure predominantly fabricated from HSS,
AHSS(DP&TRIP) steels. 25% reduction in fuel consumption. Cayenne S-hybrid will be the cleanest
Porsche version.
2011 Jeep Grand Cherokee
- increased its HSS and AHSS steel content from 28 to 50 percent.
2013 Cadillac ATS
- Light design coefficient

• L. Wang, H.Dong, J. Shi, J.F.Wang, X.C. Xiong (2010) High Strength Steels Treated by Quenching
and Partitioning Process. Science direct Vol: 527 Issue: 15
• Mayank kumar singh (2016) Application of steels in Automotive industry. IJETAE journal Vol:6
Issue:7
• B.C. De Cooman, John G. Speer (2006) Quenching and Partitioning steel: A new AHSS concept for
Automobile application. Steel research int. No-9-10
• Advanced High strength steels Guidelines V 5.0 (2014)
• Carrie M. Tamarelli (2011) The evolving use of AHSS in automobile aplications . Steel Market
Development Institute
• H. P. Liu and X. J. Jin* et al, Scripta Mater 64 (2011) 749-752
WEBSITES
www. Automotive.arcelormittal.com
www.ispatguru.com
www.army-technology.com
REFERENCES

Advanced High Strength Steels and their Heat Treatment processes

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