Strength
A steel product with high strength has many advantages. The higher the steel’s strength, the smaller amounts of material required. Moreover, structures and products of different kinds can be made lighter and thinner, though still equally durable over the long term.
he slender Högakusten suspension bridge is partly made of high strength steel. Photo: Pär K Olsson for SSAB.
The microstructure is of key importance
Steel’s basic properties e.g. its hardness and strength are determined by its microstructure. Changes take place in the steel’s microstructure when it is worked in order to acquire its definitive form e.g. when the steel is rolled, forged or drawn to become plate, bar or wire.
Different processing methods affect the steel’s microstructure in different ways; the effect on the material properties may also be considerable as a consequence. Different types of heat treatment also have a large influence on the final properties of the steel.
The strength of the steel derives, as a rule, from hardening and tempering mechanisms which are controlled by alloying elements and cooling processes. In this context, it is worth noting that two steels, both comprising more than 98 per cent iron and made using the same equipment, may show a difference in strength (tensile strength) of up to ten times. Small differences in alloying additions and, above all, the design of the cooling process yield a big result in terms of material strength.
Mechanical properties
The steel’s strength is determined by mechanical properties:
- static tensile strength
- dynamic strength
- fatigue strength
- impact toughnes
The variety of mechanical properties that steel offers, together with its cost effectiveness, is the main explanation why steel is one of the world’s most common structural materials.
Strong structures
When steel is used as a structural material, its strength is of very great importance. The type of structure determines essential properties, though often there is much to be gained by being able to make thinner and more malleable steel structures but with retained strength.
Freight cars of high strength steel for the transport of iron ore. The weight has been reduced owing to the use of high strength, hot rolled steel in the frame of the freight cars. Lighter freight cars mean that the payload can increase by 20 per cent, thereby increasing the profitability of the iron ore freight. Photo: Lars Jönsson for SSAB.
The higher the strength that can be achieved, the less material consumption is needed to carry into effect the intended function. Lower material amounts lead, in their turn, to fewer transport journeys, less material extraction, lower emissions and energy consumption.
When the high strength steel is used in the structure, additional environmental gains are created. For example, lighter vehicles consume less fuel which means lower emissions.
