Hsla steels

HIGH STRENGTHHIGH STRENGTH
LOW ALLOY STEELSLOW ALLOY STEELS
N. PRAKASAN
ME METALLURGY

HIGH STRENGTH LOW ALLOY STEELSHIGH STRENGTH LOW ALLOY STEELS
INTRODUCTION
 High-strength low-alloy (HSLA) steels, or microalloyed
steels, are designed to provide better mechanical
properties and greater resistance to atmospheric
corrosion than conventional carbon steels.
 They are not considered to be alloy steels in the
normal sense because they are designed to meet
specific mechanical properties rather than a chemical
composition.
 HSLA steels are Low carbon, formable steels
possessing high strength than conventional steels.

INTRODUCTION
 The HSLA steels in sheet or plate form have low carbon
content of 0.05 to 0.25% in order to produce adequate
formability and weldability.
 And they have Manganese content up to 2.0%.
 Small quantities of chromium, nickel, molybdenum, copper,
nitrogen, vanadium, niobium, titanium, and zirconium are
used in various combinations for improving properties.

INTRODUCTION
High-strength low-alloy (HSLA) steels possess,
• High strength to weight ratio
• Improved low temperature toughness
• Fatigue resistance
• High temperature creep resistance
• Atmospheric corrosion resistance
• Improved notch toughness
• Weldability
• Formability

HSLA Steels Categories:
HSLA steels can be divided into six categories:
Weathering steels:
• They contain small amounts of alloying elements
such as Nickel, copper and phosphorus for improved
atmospheric corrosion resistance and solid-solution
strengthening.
 Microalloyed ferrite-pearlite steels:
• They contain very small (less than 0.10%) additions
of strong carbide or carbonitride forming elements
such as niobium, vanadium, and titanium for
precipitation strengthening, grain refinement, and
possibly transformation temperature control

As-rolled pearlitic steels,
• They may include carbon-manganese steels but
which may also have small additions of other alloying
elements to enhance strength, toughness,
formability, and weldability.
Acicular ferrite (low-carbon bainite) steels,
• They are low-carbon (less than 0.05% C) steels with
an excellent combination of high yield strengths, (as
high as 690 MPa) weldability, formability and good
toughness

Dual-phase steels:
• They have a microstructure of martensite dispersed
in a ferritic matrix and provide a good combination of
ductility and high tensile strength
Inclusion-shape-controlled steels:
• They provide improved ductility and toughness by
the small additions of calcium, zirconium, or titanium,
or perhaps rare earth elements so that the shape of
the sulfide inclusions is changed from elongated
stringers to small, dispersed, almost spherical
globules.

Strengthening mechanisms in HSLA
• Refining the ferrite grain size (Grain
size effect)
• Solid solution strengthening
• Precipitation strengthening
• Dislocation strengthening/Work
hardening
• Transformation strengthening

Strengthening mechanisms in HSLA

EFFECT OF ALLOYING ELEMENTS:
 Higher yield strength is achieved by the combined
effects of fine grain size developed during controlled
hot rolling and precipitation strengthening that is due to
the presence of vanadium, niobium, and titanium.

EFFECT OF ALLOYING ELEMENTS:
Vanadium Microalloyed Steels.

Introduction
• Vanadium containing steels up to 0.10% V are
widely used in the hot-rolled condition. Vanadium-
containing steels are also used in the controlled-
rolled, normalized, or quenched and tempered
condition.
Strengthening mechanism
• Vanadium contributes to strengthening by forming
fine precipitate particles (5 to 100 nm in diameter) of
V(CN) in ferrite during cooling after hot rolling.
• The strengthening from vanadium averages between
5 and 15 MPa per 0.01 wt% V, depending on carbon
content and rate of cooling.

Factors affecting strengthening mechanism
• Cooling rate : is determined by the hot-rolling
temperature and the section thickness. Cooling rate
affects the level of precipitation strengthening in a
0.15% V.
• For a given section thickness and cooling medium,
cooling rates can be increased or decreased
• Increasing the temperature results in larger austenite
grain sizes, while decreasing the temperature makes
rolling more difficult.

• Cooling rate : An optimum level of precipitation
strengthening occurs at a cooling rate of about
170°C/min

 Manganese Content:
• A 0.9% increase in manganese content
increases the strength of the matrix by 34
Mpa because of solid-solution strengthening.
• The precipitation strengthening by vanadium
was also enhanced because manganese
lowered the austenite-to-ferrite
transformation temperature, thereby resulting
in a finer precipitate dispersion.

 Ferrite Grain size:
• Finer ferrite grain sizes can be produced by either
lower austenite-to-ferrite transformation
temperatures or by the formation of finer austenite
grain sizes prior to transformation.
• Vanadium steels subjected to recrystallization
controlled rolling require a titanium addition so that a
fine precipitate of TiN is formed that restricts
austenite grain growth after recrystallization.

Grade ASTM A 588 Grades A,B,C,
• Composition : C: 0.10-0.20%; Mn: 0.75-1.35%;
P:0.04%; S: 0.05%; Si:0.15-0.30%; Cr:0.30-0.70%;
Ni: 0.25-0.50%; V: 0.01-0.10%
• Properties: Atmospheric corrosion resistance four
times that of carbon Steels. Yield Strength Minimum
345 Mpa.
• Applications: Structural use – Welded, bolted
structures in buildings and bridges for Weight
savings and Durability.

Grade ASTM A 633 Grade E,
• Composition : C: 0.22%; Mn: 1.15-1.50%; P:0.04%;
S: 0.05%; Si:0.15-0.30%; V: 0.04-0.11%;
N: 0.01-0.03%
• Properties (Normalized) : Enhanced Notch
toughness. Yield Strength Minimum 290-415 Mpa.
• Applications: Structural use – Welded, bolted
structures for service at temperature about -40o
C.

Niobium Microalloyed Steels.
Introduction
• Niobium increases yield strength by
precipitation hardening.
• The usual niobium addition is 0.02 to 0.04%.
• Niobium steels are produced by controlled
rolling, recrystallization controlled rolling,
accelerating cooling and direct quenching.

Strengthening mechanism
• Niobium is more effective grain refiner than
vanadium.
• Thus, the combined effect of precipitation
strengthening and ferrite grain refinement
makes niobium a more effective
strengthening agent than vanadium.
• Strengthening by niobium is 35 to 40 Mpa
per 0.01% addition.

• The magnitude of the increase in Yield strength is
depends on the size and amount of precipitated
niobium carbides.

Grade ASTM A 808
• Composition : C: 0.12%; Mn: 1.65%;
P:0.04%; S: 0.05%; Si: 0.15-0.50%;
Nb: 0.02-0.10%;
• Properties : Improved Notch toughness.
Charpy V - Notch Impact energy 40–60J.
• Applications: Railway Tank Cars.

Grade ASTM A 841
• Composition : C: 0.20%; Mn: 0.70-1.35%; P:0.03%;
S: 0.03%; Si: 0.15-0.50%;
Cr: 0.25%; Ni: 0.25%; Cu: 0.35%; V: 0.06%;
Nb: 0.03%; Al:0.02%
• Properties (produced by Thermo-mechanical
controlled processes) : Yield strength 310-345 Mpa.
• Applications: Welded pressure vessels

 Some commonly used HSLA steel grades and
applications:
 ASTM A533 Grade B
• C:0.22%, Mn:1.25%, Ni:0.50%, Mo: 0.50%
• Yield Strength: 415 Mpa, Tensile strength: 620 Mpa
• Quenched and tempered (620o
C) – Ferrite and
tempered bainite.
• High strength and toughness
• Applications:
• Nuclear vessels,
• Steam generation equipments

applications:
 ASTM A517 Grade F
• C:0.15%, Mn:0.80%, Ni:0.85%, Mo:0.50%, Cr:0.50%
C) – Tempered
Martensite
• Applications:
• Bridge constructions,
• Building constructions

applications:
 ASTM A543 Class 1
• C:0.15%, Mn:0.35%, Ni:3.25%, Mo:0.50%, Cr:1.75%
V: 0.02%
C) – Tempered
Bainite and Martensite
• Applications:
• Nuclear pressure vessel,
• Plates and forgings

applications:
 ASTM A203 Grade D
• C:0.12%, Mn:0.45%, Ni: 3.50%
• Good low temperature toughness
• Impact Transition temperature : -60o
C
• Applications:
• Low temperature service applications

applications:
 ASTM A553 Type I
• C:0.10%, Mn:0.65%, Ni: 9.00%
• Good low temperature toughness
• Impact Transition temperature : -200o
C
• Applications:
• Cryogenic tanks and equipments
• Low temperature service applications

 General Applications:
 Oil and gas pipelines,
 Heavy-duty highway and off-road vehicles,
 Aerospace applications,
 Construction and farm machinery,
 Industrial equipment, storage tanks,
 Mine and railroad cars,
 Passenger car components.
 Bridges, offshore structures,
 Power transmission towers,
 Building beams and panels etc,.

References:
Alloying: Understanding the basics by ASM
International
Structure and properties of Engineering
Materials by Henkel & Pense

Hsla steels

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Hsla steels