STEELS USED IN AUTOMOBILES

Muhammed Labeeb

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Steels used in automobiles

▪ Steel for use in automotive applications ranges from the most formable grades with a low yield strength of 140 N/mm² to ultra-high-strength tyre-cord steel with a strength of 2,500 N/mm²

▪ Steel grades fall into a number of general types, each suitable for different categories of component in automobiles

▪ Steel manufacturers can use a range of techniques like solid-solution strengthening, grain refinement, work hardening, precipitation hardening and heat treatment to make higher-performance steels.

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Steels used in automobiles

range of formability (elongation) and yield strength

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Steels used in automobiles

▪ Selection of steel is primarily depended on the strength required and formability

▪ Ultra High Strength Steels, for safety-critical parts, especially for maintaining a passenger survival space in crash events like B-Pillar and front crossmemeber

▪ High Strength Steels with a good balance of strength, formability, energy absorption and durability for chassis and platform

▪ Steels with excellent formability for sheet metal works like roofs and side panel

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Common grades of steel used

AISI 1010

▪ AISI 1010 carbon steel is a plain carbon steel with 0.10% carbon content. This steel has relatively low strength but it can be quenched and tempered to increase strength

▪ AISI 1010 carbon steel has good formability and ductility, and can be easily formed using conventional methods

▪ AISI 1010 carbon steel can be welded using all the conventional welding techniques

▪ AISI 1010 carbon steel is mostly used in the annealed or case hardened condition. However, it can also be heat treated, quenched and tempered but the cost for performing these processes are very high

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Cont.Annealing

▪ A full anneal process can be performed for AISI 1010 carbon steel at 871 to 982°C, which is followed by slow

cooling process in the furnace. A stress relief anneal process can also be done at 538°C (1000°F) and then

gradually cooled.

Tempering

▪ Tempering can be performed on AISI 1010 carbon steel, after hardening process is completed, at 316 to 593°C.

This depends upon the strength level that is required.

Hardening

▪ AISI 1010 carbon steel can be hardened by both cold working and heat treatment.

Applications

▪ AISI 1010 carbon steel is primarily used for applications such as automotive panels cold headed fasteners and

bolts

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Common grades of steel used

AISI 1020

▪ AISI 1020 is a low hardenability and low tensile carbon steel with Brinell hardness of 119 – 235 and tensile strength of 410-790 Mpa

▪ It has high machinability, high strength, high ductility and good weldability

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Annealing

▪ AISI 1020 steel is heated at 870°C - 910°C followed by holding for certain time until the temperature remains constant all over the section. It is then cooled in a furnace.

Carburizing

▪ AISI 1020 is heated to between 880°C - 920°C in a suitable carburizing atmosphere followed by holding for sufficient amount of time to produce the needed carbon content and case depth. After this, refining/hardening and tempering processes are carried out to optimize the core and case properties.

Core Refining

▪ AISI 1020 steel is slowly cooled and re-heated at 870°C - 900°C followed by holding until the temperature remains constant all over the section and quenching in water, oil or brine

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Case Hardening

▪ After performing the core refining process, it is re-heated to 760°C - 780°C followed by holding until the temperature is consistent all over the section. It is then quenched in water.

Tempering

▪ AISI 1020 steel is re-heated at 150°C - 200°C followed by holding for certain time until the temperature remains constant throughout the section. It is soaked for 1 hour per 25 mm of section and then cooled under normal atmosphere. By performing the tempering process, the toughness of the case will be improved and grinding cracks will be reduced.

Normalizing

▪ AISI 1020 steel is heated at 890°C - 940°C followed by holding until the temperature remains constant throughout the section. It is soaked for 10 - 15 minutes and then cooled in still air

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Stress Relieving

▪ AISI 1020 steel is heated to 650°C - 700°C followed by holding until the temperature remains constant all over the section and soaking for 1 hour per 25 mm of section. It is then cooled in still air.

▪ Applications

▪ It is used for simple structural application such as cold headed bolts.

▪ Axles general engineering parts and components

▪ machinery parts shafts

▪ Camshafts ratchets

▪ light duty gears worm gears and spindles

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Common grades of steel used

ASTM A656

▪ ASTM A656 is High-strength low-alloy (HSLA) steel

▪ ASTM A656 is Standard Specification for Hot-Rolled Structural Steel

▪ It is hot rolled according to a predetermined rolling schedule, designed to develop a highly deformed austenite structure that will transform to a very fine equiaxed ferrite structure on cooling

▪ They provide better mechanical properties than conventional carbon steels in the normal sense because they are designed to meet specific mechanical properties rather than a chemical composition

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Composition

Mechanical Properties

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Applications

▪ The excellent strength to weight ratios make them useful in structural applications where weight is an issue. Because these plates are stronger than mild steel, they can provide high strength in thinner sections at a lower weight

▪ Used for chassis components.

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Common grades of steel used

AISI 409

▪ Grade 409 stainless steel is a Ferritic steel that offers good mechanical properties and high-temperature corrosion resistance

▪ It is commonly considered as a chromium stainless steel, with applications in exhaust systems of automobiles and applications that demand weldability

Heat Treatment

▪ Annealing of grade 409 steels is carried out at temperatures ranging from 790 to 900°C, followed by air-cooling. Thermal treatment does not harden grade 409 steels

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Heat Treatment

▪ Annealing of grade 409 steels is carried out at temperatures ranging from 790 to 900°C, followed by air-cooling. Thermal treatment does not harden grade 409 steels

Applications

▪ The typical applications of grade 409 stainless steels are listed below:

▪ Automotive exhaust tubing

▪ Catalytic converter systems

▪ Mufflers

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Common grades of steel used

TRIP (Transformation Induced Plasticity) steels

▪ The microstructure of TRIP steels is retained austenite embedded in a primary matrix of ferrite

▪ TRIP steels offer an outstanding combination of strength and ductility as a result of their microstructure

▪ Austenite is transformed into martensite during plastic deformation making it possible to achieve greater elongations and lending these steels their excellent combination of strength and ductility

▪ They are thus suitable for structural and reinforcement parts of complex shape

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Applications

▪ As a result of their high energy absorption capacity and fatigue strength, TRIP steels are particularly well suited for automotive structural and

▪ safety parts such as cross members, longitudinal beams, B-pillar reinforcements, sills and bumper reinforcements

REFERENCES

▪ http://en.wikipedia.org/wiki/SAE_steel_grades

▪ http://en.wikipedia.org/wiki/Steel#Uses

▪ http://www.azom.com/article.aspx?ArticleID=6817