What are the effects of elements on steel properties?

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What are the effects of elements on steel properties?

Table of Contents

The influence of various chemical elements on the properties of steel

 

Carbon(C)

Carbon is the main element after iron. It directly affects the strength, plasticity, toughness and welding performance of steel.

When the carbon content in steel is below 0.8%, as the carbon content increases, the strength and hardness of the steel increase, while the plasticity and toughness decrease; but when the carbon content is above 1.0%, as the carbon content increases As the strength increases, the strength of the steel decreases.

As the carbon content increases, the welding performance of steel becomes worse (steel with a carbon content greater than 0.3% has a significant decrease in weldability), cold brittleness and aging sensitivity increase, and atmospheric corrosion resistance decreases.

Silicon (Si)

Silicon is a deoxidizing agent, its deoxidizing effect is stronger than manganese, and it is a beneficial element in steel. When the silicon content is low, the strength of the steel can be increased without significant impact on the plasticity and toughness. However, when the silicon content exceeds 0.8%~1.0%, the plasticity decreases, especially the impact toughness.

Low carbon steel with a silicon content of 1% to 4% has extremely high magnetic permeability and is often used in the electrical industry and silicon steel sheets. However, as the silicon content increases, the welding performance of the steel will be reduced.

Manganese(Mn)

Manganese is added to steel as an element for deoxidation and sulfur removal, and is a beneficial element in steel.

Manganese has strong deoxidation and desulfurization capabilities. It can combine with sulfur to form MnS, thus eliminating the harmful effects of sulfur to a considerable extent and significantly improving the hot processing properties of steel.

At the same time, manganese has a good impact on the mechanical properties of carbon steel. It can improve the hardness, strength and wear resistance of steel. The manganese content is less than 0.8%, which can greatly increase the yield limit and strength limit of carbon steel while maintaining (or only slightly reducing) the original plasticity and impact toughness.

Manganese also affects the welding properties of steel. When the manganese content is very low, manganese mainly plays the role of eliminating hot brittleness. At this time, the impact of manganese on welding performance, especially when the sulfur content is slightly high, is beneficial; but when the manganese content is far more than the elimination of hot brittleness, At the necessary content, excess manganese will significantly increase the supercooling ability of austenite. At this time, manganese mainly plays the role of increasing the formation of cold cracks, which will worsen the welding performance of the steel.

Phosphorus(P)

Phosphorus is a harmful impurity in steel that is difficult to remove. It can cause the cold brittleness of steel to increase and damage the welding performance of steel. The reason for “cold brittleness” is that phosphorus forms a hard and brittle compound Fe2P.

In addition, phosphorus can improve cutting performance and corrosion resistance, so the phosphorus content can be appropriately increased in easy-cutting or weather-resistant steel.

Sulfur(S)

Sulfur mainly comes from steel-making raw materials and is difficult to remove during steel-making. Sulfur exists in the form of sulfide inclusions in steel, which has adverse effects on the plasticity, toughness, welding performance, thickness direction performance, fatigue performance and corrosion resistance of steel.

Among them, the most harmful factor is the formation of FeS with iron and the formation of Fe-FeS binary low melting point eutectic, causing the steel to become brittle and prone to cracking at 800~1200°C, which is called ‘thermal brittleness’.

Oxygen(O)

Oxygen is a harmful impurity element. Oxygen in steel almost entirely exists in the form of oxides. The total amount of various oxides in steel increases as the oxygen content increases. These oxide impurities have a negative impact on the mechanical properties of steel and other aspects. Negative Effects.

As the oxygen content in steel increases, the plasticity and impact toughness of steel decrease, and oxide inclusions reduce the corrosion resistance and wear resistance of steel, making cold stamping, forging processability and cutting processability worse.

Nitrogen(N)

The effect of nitrogen on the properties of steel is similar to that of carbon and phosphorus. As the nitrogen content increases, the strength of the steel can be significantly improved, the plasticity, especially the toughness, is also significantly reduced, the weldability becomes worse, and the cold brittleness is intensified; at the same time, the aging effect is increased Tendency and cold brittleness and hot brittleness, damage the welding performance and cold bending performance of steel. Therefore, the nitrogen content in steel should be minimized and limited. Generally, the nitrogen content should not be higher than 0.018%.

Nitrogen, in combination with aluminum, niobium, vanadium and other elements, can reduce its adverse effects and improve the properties of steel. It can be used as an alloy element in low-alloy steel.

Hydrogen(H)

Hydrogen is also a harmful element in steel. Like oxygen and nitrogen, gas elements have very little solubility in solid steel. They dissolve into the liquid steel at high temperatures and have no time to escape during cooling and accumulate in the structure to form high-pressure micropores, which reduces the plasticity, toughness and fatigue strength of the steel. A sharp decrease may cause cracks and brittle fracture in severe cases. It is a harmful element that must be strictly controlled.

Chromium (Cr)

Chromium can significantly improve the strength, hardness and wear resistance of steel, but at the same time reduce the plasticity and toughness. Chromium can also improve the oxidation resistance and corrosion resistance of steel and is therefore an important alloying element in stainless steel and heat-resistant steel.

Nickel (Ni)

Nickel can increase the strength of steel while maintaining good plasticity and toughness. Nickel has high corrosion resistance to acids and alkalis, and has anti-rust and heat resistance at high temperatures.

Molybdenum (Mo)

Aluminum can refine the grains of steel, improve hardenability and thermal strength properties, and maintain sufficient strength and creep resistance at high temperatures (deformation caused by long-term stress at high temperatures is called creep). Adding molybdenum to structural steel can improve the mechanical properties and inhibit the brittleness of alloy steel caused by fire.

Titanium (Ti)

Titanium is a strong deoxidizer, which can make the internal structure of steel dense and refine the grains; reduce aging sensitivity and cold brittleness, and improve welding performance. Adding an appropriate amount of titanium to some austenitic stainless steels can avoid intergranular corrosion.

Vanadium(V)

Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to steel can refine the structure grains and improve strength and toughness. The carbide formed by vanadium and carbon can improve hydrogen corrosion resistance under high temperature and pressure.

Niobium (Nb)

Niobium can refine grains and reduce the overheating sensitivity of steel, improving strength, but the plasticity and toughness are reduced. Adding niobium to ordinary low alloy steel can improve its resistance to atmospheric corrosion and hydrogen, nitrogen, and ammonia corrosion at high temperatures. Niobium also improves welding properties. Adding niobium to austenitic stainless steel can prevent intergranular corrosion.

Copper(Cu)

Copper can improve strength and toughness and has good resistance to atmospheric corrosion. The disadvantage is that it is prone to thermal brittleness during hot processing, and the plasticity is significantly reduced when the copper content exceeds 0.5%. When the copper content is less than 0.5%, it has no effect on welding performance.

Boron(B)

Adding trace amounts of boron to steel can improve the density and hot-rolling properties of the steel and increase its strength.

Aluminum (Al)

Aluminum is a commonly used deoxidizer in steel. Adding a small amount of aluminum to steel can refine the grains and improve impact toughness. Aluminum also has anti-oxidation and anti-corrosion properties. The combination of aluminum, chromium and silicon can significantly improve the high-temperature peeling performance and high-temperature corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot processing performance, welding performance and cutting performance of steel.

Tungsten(W)

Tungsten has a secondary hardening effect, giving the steel red hardness and improving wear resistance. Its effects on the hardenability, tempering stability, mechanical properties and thermal strength of the steel are similar to those of molybdenum, and it slightly reduces the oxidation resistance of the steel. .

Lead (Pb)

Lead can improve machinability. Lead-based free-cutting steel has good mechanical properties and heat treatability. Due to environmental pollution and harmful effects in the scrap steel recycling and smelting process, lead has a tendency to be gradually replaced.

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