Chemical and Mechanical Properties
The mechanical properties of steel is determined by the chemical composition and the manufacturing process used to manufacture the required steel grade. In the case of heat treatment during the manufacturing process, the mechanical properties will differ as the elements will respond differently to the cooling rate from specific temperatures.
The most important mechanical properties, especially for design engineers are the following:
The stress required in order for permanent plastic deformation to take place.
The ability of plastically deforming steel and absorbing energy without fracturing determines the toughness of the steel.
By making use of tensile strength to stretch material, known as elongation, before fracturing commence is is referred to as ductility.
The ability of the steel grade to be welded, the heat affected zone after welding can be harder and its toughness lower than before the welding process.
Durability refers to the ability of the steel to keep its properties for a certain period of time withstanding wear, corrosion, pressure or damage before it starts to deteriorate.
Measurement of mechanical properties
Tensile testing is used to measure the yield strength, stiffness as well as the ductility of steel grades. Impact testing is typically used to determine the toughness of a specific steel grade. Lastly hardness can be measured by using a hard object to determine the resistance of the steel surface against the object breaking or damaging the steel.
Mechanical Properties of Standard Grades
The hardenability and strength of the steel is improved by manganese which is found in the commercial steels.
increasing the carbon content will increase the strength and hardenability while decreasing ductility and machinability. Carbon is the most important alloying element in steel.
Sulphur content should be kept lower than 0.05% to prevent a negative effect. It increases machinability, but decreases the transverse ductility.
The strength and corrosion resistance of low-alloy high strength steels are improved by phosphorous content less than 0.10%, while it has a negative effect on the ductility and toughness.
Silicon improves the strength and hardness of steel while playing the important role of deoxidiser. All steel grades contain silicon.
The primary function is that of a grain refiner. Due to the effectiveness of vanadium only a small amount is required.
Functioning as a grain refiner and a deoxidiser, aluminium improves the toughness of the steel.
The most powerful element in the chemical composition of steel grades, increases the hardenability, yield strength and corrosion resistance.
Forgeability is decreased when the molybdenum content is too high. On the other hand, he tensile strength, heat resistance and weldability of steel increases.
The notch toughness is improved by the addition of Nickel content.
Please see below the basic chemical composition of steel grades.