Automakers are using more and more high-strength steel, but what does that term even mean?
Aluminum is not the only light-weight material well suited for the construction of Automobiles. Car-makers have been turning to increased use of high-strength steel in vehicles for many years. The objectives of using high-strength steel include better performance of critical safety parts, such as A-pillars, lower weight from key structural components in both space-frame and unit-body constructed vehicles, and of course, lower cost for manufacturers and consumers who make and buy the vehicles.
A recent report by Markets and Markets says that the high-strength steel market is to grow by about 8% per year through 2021. By then, the market should be about 21 billion U.S. dollars globally. The report says that the automotive market is the number one user of high-strength steels and that Asia Pacific is the largest user by region. Let’s look at what this material is, and why so many car makers are trumpeting its use.
High Strength Steel – What Exactly Is It?
Steel is an iron alloy. That means it is a mixture of more than one metal and other elements; unlike say the metal we know of as copper, which is just the element copper. Steel is almost all iron by weight, but it has small amounts of carbon and other materials in it.
At the atomic level, the additional elements change the way the material behaves in dramatic fashion. The way the carbon is managed during the production of steel is also key to its properties. One way to think of high-strength steel is to think of it as low-carbon steel. In conventional steel, the carbon content is about 1.4%. In high-strength steel it is about 1/6th that amount.
Engineering students who study materials science spend years gaining a full understanding of what “strength” of a metal means. The material’s resistance to being pulled and how well it performs in shear are key to this. The specific strength of a material is where the term high-strength steel (also called high-tensile strength steel) comes from. In a nutshell, a high-strength steel is an alloy that has better performance per unit of weight.
Another way to think about it is high-strength steel alloys can do what lower strength (sometimes call mild steel) steel alloys can do, but with less material, or with a lower weight. In our top graphic Mazda brags that its steel is “…the thinnest in its class.” Can you imagine an automaker doing that back in the 1960s?
Where is High Strength Steel Used and Why Use Low-Strength Steel At All?
The above graphic is a perfect illustration of how automakers use varying materials and varying grades of steel throughout a vehicle. Can you guess which automaker created this handy guide? Yes, it is Ford, who has become so well known for its advertisements touting its use of aluminium in its trucks.
As you can see, the high-strength, more expensive steel is used primarily in the structural parts of this unit-body hatchback car. Think of the high-strength steel as a sort of skeleton, onto which less expensive, easier to work with materials are hung, joined, or mated to.
Lower weight is always a benefit for automakers, so high-strength steels are used in parts of a car where automakers can get the best bang for the buck.
What Are the Downsides of High Strength Steel?
High-strength steel alloys cost more to manufacture. Not only is the alloy harder to create in its raw form, it is also harder to work with. Stamping it and forming it is harder. More energy and stronger tools, dies, and presses are required, and those tools and dies wear out faster.
So automakers use it sparingly, but as fuel economy and safety levels continue to be set higher, more of the steel, or more accurately the metal, in a vehicle is becoming specialized.
Aside from being more expensive as a base material, and also more expensive to work with, the high-strength steel alloys generally used in a vehicle are not inert, meaning they can and will rust. So special care in their anti-corrosion preparation is required.
This is also the reason why automakers don’t usually use expensive steel alloys in places prone to rust. Body panels and floor pans, for example, would be a poor choice for the material.
High-strength alloys are also much harder to reform after an accident. If you find yourself in an accident that bends the difficult to re-shape A-pillar, the B-pillar, or the roof, the vehicle is very likely totaled.
Notice that in the front of the example vehicle above, the front bumper component is an individual part. It would be replaced in a minor crash.
The on-going debate between GM and Ford about which metal is best for a truck bed in the F-150 or Silverado is sort of silly. Other automakers have already moved on to corrosion-free, high-strength plastics.
Carbon fiber is becoming less expensive and is finding its way into more mainstream and more affordable cars. GM has, and still does, use non-metallic body panels for cars, and that trend will return to popularity as consumers come to expect rust-free and easy to repair body panels on longer-lasting vehicles.
Fun fantasy note: The Valyrian steel mentioned in Game of Thrones, would likely be special not because of its raw materials, but because of how it was forged and worked. The ripples would be from varying types of steel forged into one blade that were strong in the middle, to prevent breaking, and hard at the edges, to stay sharp and resist chipping.
Melt down a Valyrian steel blade and re-make it the way other swords are made at “modern Kings Landing”, and the special advantages should be lost, but in the show, they’re retained.
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