How do steel elements affect steel?
This material technology script describes the influence of different alloying elements on steel. It should be noted that in addition to iron (Fe), so-called unalloyed steel always contains the elements carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulfur (S). Alloying elements can have a very different influence on the properties of the steel.
Alloying element aluminum
In iron, aluminum acts as a strong deoxidizer to calm the steel (during the casting process). Aluminum also forms nitrides (=> nitriding steel) with nitrogen, it increases the scale resistance and increases the coercive force. In addition, aluminum has a ferrite-stabilizing effect in high-alloy steels.
Alloying element beryllium
The γ region (austenite) is pinched off by the effect of beryllium as an alloying element in iron. Beryllium acts as a powerful deoxidizer in steel making and it increases precipitation hardening.
As an alloying element in iron, beryllium lowers the toughness as a negative effect.
Alloying element boron
Boron acts as an alloying element in iron as a strong neutron absorber. This type of alloy is therefore used in steels for building nuclear power plants. Boron also increases the yield strength and strength of the steel.
A negative effect of boron as an alloy partner is that it reduces the corrosion resistance and leads to embrittlement of spheroidal graphite cast iron.
Alloy element cerium
Cerium acts as a deoxidizer in iron and increases its resistance to scaling. In cast iron with spheroidal graphite (GGG) it promotes the formation of spheroidal graphite. In addition, iron alloys with up to 30% iron are pyrophoric (used as flint in lighters).
Alloying element chromium
As an alloying element in iron, chromium lowers the critical cooling rate, increases wear resistance, heat resistance, and scale resistance. It increases tensile strength as it acts as a carbide former. Since it increases the corrosion resistance from a mass content of 12.2%, it is used for the production of stainless steel (V2A, V4A). It also has a ferrite-stabilizing effect and constricts the γ-area.
Chromium has an adverse effect in that it reduces impact energy and weldability. It lowers thermal and electrical conductivity.
Chromium shifts point S (eutectoid) in the iron-carbon diagram further up into the area of higher temperature and point E upwards to the left in the area of higher temperature and lower carbon content.
Alloying element carbon
The effect of carbon is very important for materials technology. On the one hand, carbon as an alloying element in iron lowers the melting point, while it increases the hardness and tensile strength through the formation of Fe3C. An iron alloy is also called steel if the carbon content is between 0.002% and 2.06%. However, steel can only be hardened with a carbon content of 0.3% or more.
If carbon is present in the alloy in large quantities, it increases the brittleness and thus lowers forgeability, weldability, elongation at break and impact energy.
Alloying element copper
As an alloying element in iron, copper increases resistance to weathering and strength, while it significantly reduces elongation at break.
Alloying element manganese
If manganese is added to steel, it improves forgeability, weldability, strength and wear resistance. In addition, manganese in iron has the positive effect of reducing the tendency to break red.
Manganese shifts point S (eutectoid) in the iron-carbon diagram further up into the area of higher temperature and point E upwards to the left in the area of higher temperature and lower carbon content. Manganese also has a ferrite-stabilizing effect in high-alloy steels.
Alloy element molybdenum
In iron alloy, molybdenum improves hardenability, tensile strength and weldability.
The negative is that the breakpoint A1 is shifted slightly upwards. In addition, molybdenum lowers forgeability and ductility.
Molybdenum shifts point S (eutectoid) in the iron-carbon diagram further upwards into the area of higher temperature and point E to the top left in the area of higher temperature and lower carbon content.
Alloy element nickel
Nickel increases the tensile strength and the yield point in steel. From a proportion of 8%, nickel makes a steel corrosion-resistant.
A disadvantageous influence of nickel on steel is that it shifts the stopping point A1 downwards by 10 K for every 1% Ni. In addition, nickel has a ferrite-stabilizing effect in high-alloy steels.
Alloying element phosphorus
Phosphorus increases tensile strength, hardness and corrosion resistance in iron alloys.
However, it raises the stopping point A1 slightly and leads to embrittlement.
Alloying element sulfur
As an alloying element of iron, sulfur increases machinability, but reduces ductility.
Alloy element silicon
In iron alloys, silicon increases the resistance to scaling; it is a solid solution hardener and prevents the formation of carbides. In steel production, it has the positive effect of making the melt thinner and serves as a deoxidizer. Another positive influence of silicon on steel is that it increases tensile strength, yield strength and resistance to scaling.
In addition, silicon shifts the stopping point A1 upwards (by 20 - 30 K per 1% Si, but only up to 3%). It moves the point S (eutectoid) in the iron-carbon diagram further upwards into the area of higher temperature and point E upwards to the left in the area of higher temperature and lower carbon content. In addition, silicon has a ferrite-stabilizing effect in high-alloy steels.
Alloy element titanium
As an alloying element in iron alloys, titanium prevents intergranular corrosion through the formation of TiC.
Alloying element vanadium
Vanadium increases the tensile strength in iron alloys.
However, it moves the breakpoint A1 slightly upwards
Alloying element tungsten
Tungsten acts as a carbide former and thus significantly increases the tensile strength.
However, it slightly shifts breakpoint A1 upwards.
Moves point S (eutectoid) in the iron-carbon diagram further up into the area of higher temperature and point E to the top left in the area of higher temperature and lower carbon content.
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