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Product selection guide

ArcelorMittal offers a wide range of steel grades and coatings to help its automotive sector customers design and produce vehicle bodies and components meeting the requirements of an increasingly demanding market.

Several elements define a steel product:

  • metallurgical grade, often broken down into several qualities, determining the mechanical strength and formability required for the part;
  • coating, to meet corrosion resistance and surface appearance specifications;
  • surface condition, determining friction behavior during forming as well as adhesion properties and post-paint appearance.

This catalogue is thus organized in dedicated technical sheets:

  • metallurgical grades: products are defined according to their metallurgy and their mechanical strength, often involving specific applications,
  • coatings, including hot-dipped and electrodeposited metal and organic coatings,
  • aluminized steels, specific to exhaust systems, fuel tanks and heat shields. These are covered in a separate chapter,
  • composite products such as sound-absorption sheet and thick polymer core sheet.

This catalogue has been designed as a working tool and reflects the range of products and services available from ArcelorMittal at a given point in time. The range is subject to ongoing development and will be expanded in coming years to include new grades offering improved strength-formability combinations and coatings for a wider range of substrates. All product range extensions and product renewals will be directly accessible from the customer's usual technical or sales contact and posted on the ArcelorMittal catalogue website.

The following section explains the approach to be used to identify the ArcelorMittal product which will best suit a given application, system or component. The reader thus has the benefit of the experience ArcelorMittal has built up with its customers in the area of product selection for the main automotive systems.

Choice of steel grade

The choice of a steel grade is generally a compromise between two more or less conflicting objectives:

1. Part performance in service.

The design office calculates the minimum strength (yield and/or tensile strength) level required. These must be guaranteed for each component in order to meet the relevant performance requirements, especially in terms of impact strength (deformation resistance or energy absorption in crash conditions) and durability (fatigue strength).

It should be emphasized that the move to save mass (in order to reduce CO2 emissions) is prompting manufacturers to reduce thickness as much as possible, which in turn means that strength levels need to be increased.

2. Industrial feasibility under economically acceptable conditions, generally at high production rates.

To meet this objective, good ductility, generally expressed as high ultimate elongation, is required.

ArcelorMittal steel grades are therefore ranked in the following tables by strength level.

Specifications

Choice of coatings

Product/coating availability

The final mechanical properties of a steel are determined by all of the mechanical (hot rolling, cold rolling, skin pass, tension leveling, etc,) and thermal (hot rolling, continuous or batch annealing, galvanizing, etc.) treatments that the steel strip undergoes throughout the manufacturing process.

During hot dip coating (zinc or aluminum), the strip passes through a liquid coating bath held at approximately 460°C in the case of galvanizing and 680°C in the case of aluminizing. For Galvannealed type coatings and organic coatings, a further baking stage is required in order to:

  • achieve Fe-Zn alliation at between 500 and 550°C in the case of Galvannealed,
  • cross-link resins and evaporate solvents at between 150 and 250°C in the case of organic coatings.

Clearly, the thermo-mechanical processing plan must include the coating phase to ensure that the required final product mechanical properties are achieved. This means that the choice of a steel grade and the choice of coating are linked. The detailed product sheets provided later on in this catalogue give the combinations of grades and coatings that are currently possible.

In the case of thin organic coatings (TOC), the grade/coating/TOC combinations are too complex to be summarized in a simple table and customers are asked to consult us.

Coating properties in service

Apart from the question of availability in the chosen grade (this applies mainly to external body parts), the choice of coating is a compromise between:

1. coating compatibility with the process employed:

  • drawing behavior
  • influence on welding
  • phosphating aptitude

2. coating characteristics in service:

  • appearance after painting
  • corrosion resistance

The tables below give a comparative evaluation of the most common coatings in terms of these criteria:

Extragal®

Galvannealed

Galfan

Electrogalvanized

Treated electrogalvanized

Drawing behavior

++

[] (1)

++

+

++

Influence on welding

[]

++

#

+

+ (2)

Aptitude for phosphating

[] (3)

+

#

++

+

Appearance after painting

++

[] (4)

#

++

+

Corrosion resistance

++

+

++

++

++

++ Excellent

+ Very good

[] Good

# Good, but with reservations

(1) Risk of powdering, based on Fe-Zn alliation rate

(2) On electrogalvanized substrate

(3) Compatibility to be verified, particularly in the case of Ni-free cataphoresis

(4) Prone to cratering

Extragal®

Galvannealed

Galfan

Alusi®

Electrogalvanized

TOC

Visible parts

 

 

•*

Structural parts

 

 

suspension system components

 

Exhaust system

Heat screens

Under-hood parts

Fuel tanks

* Resin deposited on the non-visible side only.

As indicated, all automotive manufacturing sectors are called upon to make coating choices; no optimum solution can be identified across the board, since the options selected are determined by each manufacturer's specific constraints, know-how and judgment.

Currently options are under review as a result of three significant trends:

  1. The ongoing extension of anti-corrosion guarantees is prompting automakers and equipment manufacturers to seek products offering the best possible corrosion performance; this has notably resulted in the widespread use of sheet coated on both sides.
  2. Environmental protection standards are being stepped up; this has a number of implications, including discontinuation of the use of heavy metals (especially Chromium VI) in coatings (particularly in zones liable to undergo sanding) and in surface treatments.
  3. Surface appearance has been improved by better control of "dedicated automotive" hot-dip coating processes, enabling these coatings to be used for the majority of visible parts and providing an opportunity for cost savings.

ArcelorMittal can supply an optimum coating for each system: alloyed and non-alloyed hot-dip and electrolytic metal coatings in thicknesses ranging from approximately one micron to over 10 microns, with and without thin organic resin films and paint.

As part of the technical support service ArcelorMittal offers its customers, experts are available to help you make the best possible choice.

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