autobody materials - lecture 3.pdf

7/29/2019 AUTOBODY MATERIALS - LECTURE 3.pdf

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Automotive Materials

Autobody Materials

Introduction

The ‘body-in white’, a traditional name for the body structure (BIW)

Body in White or BIW refers to the stage or progress of automobile manufacturing in which the car

body sheet metal (including doors, hoods, and deck lids) has been assembled before the

components (chassis, motor ) and trim (windshields, seats, upholstery, electronics, etc.) have

been added.




Autobody Materials

Materials Usage

Auto body frames, windows, chassis, bonnet

Steels

Aluminium alloys

agnes um a oys

Polymer

Ceramics




Autobody Materials

B - I -W : Body in White ; Materials usage




Autobody Materials

Steels

Steel

HSLA – High Strength Low Allow steels

TRIP – Transformation Induced Plasticity steels

IF – Interstitial Free steels

DP – Dual Phase steels

ULSAB – Ultra Light Steel Auto Body

ULSAS - Ultra Light Steel Auto Suspension




Autobody Materials

HSLA : High Strength Low Alloy Steels – Introduction & Composition

High-strength low-alloy (HSLA) steels, or micro alloyed steels.

They were developed primarily for the automotive industry to replace low-carbon steels in order

to improve the strength-to-weight ratio and meet the need for higher-strength construction-grade

materials, particularly in the as rolled condition.

ompos on:

carbon contents (0.50 to ~0.25% C) in order to produce adequate formability and weldability, and

manganese contents up to 2.0%

Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium,

and zirconium are used in various combinations.

Titanium, vanadium, and niobium are added for strengthening purposes




Autobody Materials

HSLA : Properties, Application, & Products

Properties:

better mechanical properties and/or greater resistance to atmospheric corrosion than conventional

carbon steels.

with excellent strength and toughness , high strength-to-weight ratio, abrasion resistance

(HSLA steels have yield strengths of more than, 275 Mpa ).

Application:

oil and gas line pipe, ships, offshore structures, automobiles, off-highway equipment, and pressure

vessels.

Product:

The HSLA steels are commonly furnished in the as-rolled condition.

They may also be supplied in a controlled-rolled, normalized, or precipitation-hardened condition to

meet specific property requirements.




Autobody Materials

HSLA : Production & Heat treatment

Production and Heat treatment:

Product: plates,

structural shapes,

bars, and sheet

[yield strength 290

to 690 Mpa]




Autobody Materials

HSLA : Specification & Types

SAE or ASTM Specification:

The SAE high-strength, low-alloy steels

The ASTM high-strength, low-alloy steels are covered under various specifications including

A242, A440, A441, A572, A588, A606, A607, A618, A633, A656, A690, A709, A714, A715, A808,

A812, A841, A860, and A871.

HSLA alloys can be grouped into four classes:

(i) as-rolled carbon-manganese steels;

(ii) high-strength low-alloy steels;

(iii) heat-treated carbon steels;

(iv) heat-treated low-alloy steels.




Autobody Materials

HSLA : Application

Application:

These HSLA steels have found wide application in areas such as bridge construction (structural

beams), off-shore oil and natural gas platforms, ship hull and deck plate, and electrical transmission

towers and poles.

In the automobile, HSLA steels are used for safety (ultrahigh-strength impact door beams and

energy-absorbing bumper assemblies) and for increasing fuel economy through thinner (lighter

weight) chassis structural sections.

Microalloyed HSLA steels are also employed in large-diameter gas transmission pipelines.




Autobody Materials

HSLA : Application

Application:

in a typical passenger car such as door-intrusion beams, chassis members, reinforcing and

mounting brackets, steering and suspension parts, bumpers, and wheels truck bodies,

other applications include frames, structural members, scrapers, truck wheels, cranes, shovels,

-, , , , , .

Mining equipment and other heavy-duty vehicles use HSLA sheets or plates for chassis

components, buckets, grader blades, and structural members outside the body.

Structural forms are specified in applications such as offshore oil and gas rigs, single-pole

power-transmission towers, railroad cars, and ship construction.




Autobody Materials

HSLA Comparison with Alloy steels & Low Alloy steels,




Autobody Materials

HSLA : SAE Grade

A t ti M t i l




Autobody Materials

HSLA : SAE Grade





Autobody Materials

HSLA : Mechanical Property





Autobody Materials

DP : Dual Phase Steels

DUAL-PHASE STEELS are a new class of high-strength low alloy (HSLA) steels.

This class is characterized by a tensile strength value of approximately 550 MPa (80 ksi) and by

a microstructure consisting of about 20% hard martensite particles dispersed in a soft ductile

ferrite matrix.

The term dual phase refers to the predominance in the microstructure of two phases, ferrite and

martensite. one of which is soft and the other significantly harder.Martensite

Ferrite





Autobody Materials

DP : Alloying

Using thinner sheets of high-strength dual-phase steels for automobile bodies would save weight.

Carbon content of less than 0.1%.

Manganese in amounts of 1 to 1.5% is added to ensure sufficient hardenability.

Chromium and molybdenum have also been added in amounts that are usually under 0.6%.

Silicon is added to provide solid solution hardening.

Small amounts of micro alloying additions, such as vanadium, niobium, and titanium, may be

added to provide precipitation hardening.

Nitrogen may be added to intensify the precipitation-hardening effects of vanadium.




Autobody Materials

DP : Production by Heat treatment

The simplest way of achieving a duplex structure is to use intercritical annealing in which the steel

is heated into the (α+γ) region typically at 790◦C for several minutes to allow small regions of

austenite to form in the ferrite.

As it is essential to transform these regions of austenite into martensite, cooling to ambient

temperature must be sufficiently rapid.

Alternatively, the hardenability of the austenite must be enhanced by adding between 0.2 and

0.4wt% Mo to a steel already containing 1.5wt% manganese.

The required microstructure can then be obtained by air cooling after intercritical annealing.




Autobody Materials

DP : Application

Dual-phase steels are being applied in applications such

as automobile wheel rims and wheel disks.

Because of their energy-absorbing characteristics, dual-phase steels are being used in critical

locations of the automobile for safety to protect the occupants in the event of a crash

autobody materials - lecture 3.pdf

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