For alloying elements, it is essential to distinguish whether they form carbide, austenite or ferrite or, as the case may be, what is the purpose of steel alloying. Each individual element gives the steel specific qualities.
This is the strongest and also frequently used deoxidizing element. Improving the resistance to ageing.
In small amounts, it refines the grain structure.
Together with nitrogen, aluminium forms extremely hard nitrides, therefore, it is the most frequently used alloying element for nitrided steels. Apart from this, aluminium reduces generation of scales, consequently, it is added to ferritic heat resistant steels.
The essential alloying element in steel. Apart from carbon, each non-alloy steel contains silicon (Si) , manganese (Mn), phosphorus (P) and sulphur (S). These elements are added in the course of manufacturing.
By adding another alloying elements as well as increasing content of manganese and silicon, alloy steel will be obtained. Along with increasing the carbon content, strength and hardenability, but also ductility, weldability and machinability of steel will be enhanced.
Higher carbon content reduces toughness and thermal conductivity.
It does not form any carbides. At higher temperatures, cobalt prevents the grains from growing and improves heat strength.
Used for permanent magnets.
Carbide-forming element. The carbides increase wear resistance. Chromium steels can be hardened in air and also in oil. The higher chromium content, the lower weldability.
Each per cent of chromium increases tensile strength by 80 – 100M Pa. Higher chromium content reduces formation of scales. In order to guarantee corrosion resistance, more than 13% Cr are required.
Cr reduces thermal and electrical conductivity and also thermal expansion, increasing tempering brittleness.
Copper will be added only to some types of steel, since it reduces the ability of being machined.
For this reason, it is considered harmful component.
In non-alloy steels, copper causes significant increase of weather resistance of the material.
It is a harmful component increasing the brittleness.
Deoxidising agent. In combination with sulphur, manganese causes formation of manganese sulphates abating undesirable effects of sulphur. This property is important in free-machining steels (improved machinability).
Reduces the risk of red heat fracture. Manganese enhances hardenability, yield point and breaking strength of steel. Positive effect on formability and weldability.
If any steel contains more than 4% of manganese, its structure becomes brittle, even at slow cooling. The steels containing more than 12% of manganese and, at the same time, high amount of carbon are austenitic, i. e. highly resistant against impact. The steels containing more than 18% of manganese are non-magnetic, event after cold forming. They are used for works at low temperatures.
Manganese increases thermal expansion coefficient of steel and reduces its thermal and electrical conductivity.
Used in combination with other alloying elements. Enhances weldability, significantly reducing tempering brittleness and improving grain fineness and weldability.
Higher content of molybdenum reduces formability and influences formation of carbides. Hence, it is added to high-speed and tool steels. Molybdenum is one of the elements increasing corrosion resistance.
High content of molybdenum increases resistance to pitting corrosion.
Harmful element, however it can also be used in alloying. Its harmful effects include reduction of toughness, increasing of sensitivity to ageing as well as brittleness at blue heat (300-350°C).
As an alloying element, nitrogen stabilises the austenitic structure. In austenitic steels, it increases strength and improves mechanical properties at high temperatures.
Nitrogen, and more specifically the nitrides increase surface hardness (nitriding).
These elements are always found together, since they are difficult to separate from each other.
They cause formation of carbides, therefore, they are used as stabilising agents in chemically resistant steels.
These elements are always found together, since they are difficult to separate from each other.
They cause formation of carbides, therefore, they are used as stabilising agents in chemically resistant steels.
This element causes significant increase of notch toughness, even at low temperatures. Added to case-hardened and heat-treated steel.
Carbide-forming element.
If its content is higher than 7%, austenitic structure will be produced. At temperatures over 600°C, austenitic steels will have higher toughness. Nickel also improves corrosion resistance.
And undesirable element, since it affects mechanical properties of steel, predominantly notch toughness. It also increases ageing brittleness of steel.
Phosphorus is considered harmful, since it results in rough crystalline structure of steel. It causes increasing of strength and atmospheric corrosion resistance, but also brittleness of steel.
In austenitic Cr-Ni steels, phosphorus may increase the yield point.
In amount of 0.2-0.5%, lead will be used in alloyed free-cutting steels, since its fine distribution results in short chips and fine surface structure after machining.
The content of lead as indicated does not affect mechanical properties.
Sulphates in steel structure reduce toughness and forgebility at red heat. Therefore, sulphur is considered undesirable.
Increases welding joint brittleness potential.
Will be added to free-cutting steels to increase friction between the workpiece and the cutting tool, owing to its lubrication effects.
Residual element from chemical composition of iron ore. Silicon steel contains more than 0.4% of silicon.
Accelerates deoxidation and increases wear resistance, while substantially increasing the limit of steel elasticity. This is why silicon is used in coil steel. Increases thermal resistance and fatigue limit.
Moderate increasing of hardenability and tempering resistance. No carbides. Silicon reduces electric conductivity, therefore, it is used for transformer steel.
Harmful element, owing to its accumulation below the scale layer, thus causing surface cracks (similarly to copper).
Causes strong deoxidation, owing to high affinity to oxygen, nitrogen, sulphur and carbon.
Will be used for refinement of grain structure.
Refinement of grain structure and, consequently, also the casting piece structure. Forming of carbides, thus increasing wear resistance.
Increasing hot brittleness of steel.
Causes forming of carbides, even at increased temperature, thus increasing the tempering resistance. In larger amount, it supports forming of residual austenite.
In larger amount, it reduces toughness and plasticity of steel. Tungsten carbides can hardly be dissolved by austenization, therefore, tungsten steels are hardened at high temperatures (as a rule, higher than 1000°C).
Tungsten increases wear resistance and cutting properties of steel, therefore, it is frequently added to high-speed steels, steels intended for hot processing as well as extremely hard steels.
Used for deoxidation, dentridation, and desulphurisation. Carbide-forming element.
Zircon will be added to completely killed free-cutting steels. Vytváří karbidy.
Positive effect on forming sulphides.