Q1: Required properties

Strength

Whilst a certain level of strength is required in order for the body panel not to buckle under minor impact for example this is readily achieved by steel strip. In fact the general objective is to produce low strength steels (between 160 - 300 MPa yield strength) in order to achieve a high level of formability (the properties of strength and formability are linked). So you need to look for a different property.

Toughness

Energy absorption to improve crash resistance is very important in automotive applications. However this is generally achieved through the design of the automotive body, for example side impact bars, crumple zones etc. The overall toughness inherent in most strip steels is therefore sufficient meaning that you need to look for another, more important property.

Corrosion Resistance

Correct, for an automotive body panel corrosion resistance is extremely important and car makers specify pre-coated steels for most body panels (the roof is the main exception) in order to help them meet the corrosion warranties demanded by consumers, currently up to 12 years.

Magnetic properties

Magnetic properties are not really important for this application. Try another property.

Aesthetics

The appearance of the final body panel is very important and would be my fourth choice of property to consider. The roughness, or surface texture, of the finished steel strip influences the image clarity and the quality of the painted finish on the body panel. The steel surface texture is normally controlled within acceptable limits during the final rolling of the steel. Try another property for one of the three most important.

Cost

Correct, cost is always an issue with design and materials selection. In this case cost will be minimised because the steels used are mass produced and, as low strength levels are all that are necessary, the alloying costs will be low. The motor industry is an extremely competitive one and car makers are keen to purchase their steel at the lowest possible price. Cost will act as a driving force for processing and alloy selection for automotive body panels that require higher strength levels.

Steel cleanliness

Steel cleanliness is important as it will control the amount of rejected panels / steel but is not as important for this application as say for strip used in the canning industry. Try another property.

Fatigue resistance

For the body panels fatigue is not a crucial property as the panels do not typically receive significant load fluctuations that would lead to fatigue cracks forming. Fatigue is more of an issue for components such as the connecting rods, drive shafts etc. Try another property.

Formability

Correct, the body panel must be able to be formed into the shape required to give the flowing lines that customers come to expect from the modern car design.

Machinability

Machinability is not a very important property in this case because the strip steels are blanked out and then pressed into shape so machining is not used. Try another property.

Weldability

Certainly weldability is an extremely important property as spot welding is used extensively during assembly of the car. However strip steel is, in general, readily spot welded and therefore does not need to be ranked highly. Spot welding steel is much easier than aluminium alloys and is one added advantage of using steel. Try another property.

Electrical properties

Electrical properties are not really important for this application. Try another property.

Wear resistance

Wear resistance is not really important for this application. Try another property.

Creep

Not really important for this application, as creep only becomes an issue at elevated temperatures and long exposure times (for example in power plant where components may experience temperatures of 400�C+ for 20 years or more.

Recyclability

Recyclability is always important and becoming more so. Fortunately steel is one of the most easily recycled materials which makes its use favourable in this application over polymeric materials. As steel is recyclable in general we not consider this property to any great depth here. Try another property.

When you have correctly identified all three, they will be displayed in a 'Notepad', from where you can link to pages giving more detail.