According to the different added elements and appropriate processing technology,alloy steel can obtain corresponding high strength,high toughness,wear resistance,corrosion resistance,low temperature resistance,high temperature resistance,non-magnetic and other special properties.
In addition to iron and carbon, an iron-carbon alloy formed by adding an appropriate amount of one or more alloying elements on the basis of ordinary carbon steel is called alloy steel.
There are many types of special performance steels. In machinery manufacturing, stainless steel, heat-resistant steel and wear-resistant steel are mainly used.
Special performance steel has special physical or chemical properties. In addition to certain mechanical properties, it also requires special properties.
Tool steel has high hardness, maintains high hardness and red hardness at high temperature, as well as high wear resistance and appropriate toughness.
Alloy tool steel is the steel used to manufacture cutting tools, measuring tools, molds and wear-resistant tools.
Generally divided into structural steel for construction and engineering which is used as engineering components (pipes and brackets, etc.) and structural steel for machinery manufacturing, used as various mechanical parts (shafts, gears, springs, impellers, etc.)
Structural alloy steels are steels that meet specific strength and formability grades. Formability is expressed as elongation after break in tensile test. Structural steel is generally used for load bearing and other applications where the strength of the steel is an important design criterion.
Classification By Type of Commonly Used Alloying Eelements
There are various classification systems for alloy steel. At present, the mainstream classifications mainly include the following:
The main alloying elements of alloy steel are silicon, manganese, chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, aluminum, copper, boron, rare earth, etc.
Vanadium, titanium, niobium, and zirconium are strong carbide-forming elements in steel. As long as there is enough carbon, their respective carbides can be formed under appropriate conditions.When carbon is deficient or under high temperature conditions, they enter into solid solution in atomic state.
Manganese, chromium, tungsten, and molybdenum are carbide-forming elements, some of which enter the solid solution in atomic state, and the other form replacement alloy cementite.
Aluminum, copper, nickel, cobalt, and silicon are elements that do not form carbides and generally exist in solid solutions in an atomic state.
Silicon(Si)
Silicon is used as one of the main deoxidizers in the steelmaking process.Once the silicon content in steel exceeds 0.50-0.60%, silicon is considered an alloying element.
Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, so it is widely used as spring steel.If 1.0-1.2% silicon is added to the quenched and tempered structural steel, the material strength can be increased by 15-20%.
Silicon can be combined with molybdenum, tungsten, and chromium alloying elements, which can improve corrosion resistance and oxidation resistance,so it is used to manufacture heat-resistant steel.
Low carbon steel containing 1-4% silicon, with extremely high magnetic permeability, used for silicon lamination in electrical industry.
However, increasing the amount of silicon will reduce the weldability of the steel.
Manganese (Mn)
In the process of steelmaking, manganese is a good deoxidizer and desulfurizer.Generally, the content of manganese in steel is 0.30-0.50%.Once adding more than 0.70% Mn to carbon steel, it is considered “manganese steel”.
Manganese not only gives the steel higher strength, better hardness, and more resistance to wear,but also improves the hardenability and the hot working performance.
Steel containing 11-14% manganese has extremely high wear resistance which is used for excavator buckets, ball mill lining plates, etc.
However, the increase of manganese content weakens the corrosion resistance of steel and reduces the welding performance.
Chromium (Cr)
In structural steels and tool steels, chromium can significantly improve strength, hardness, hardenability and wear resistance, but at the same time reduce ductility and toughness.
Chromium can also improve the oxidation resistance and corrosion resistance of steel, so it is the most important alloying element of stainless steel and heat-resistant steel.
Nickel (Ni)
Nickel can improve the strength of steel while maintaining good plasticity and toughness. Nickel has high corrosion resistance to acid and alkali, rust and heat resistance at high temperature.
When a proper amount of nickel is introduced into high chromium (stainless steel) steel, it will become austenitic stainless steel which is tougher,maintains good ductility,and has strong corrosion resistance.
However, since nickel is a relatively scarce resource, other alloying elements should be used instead of nickel-chromium steel.
Molybdenum (Mo)
Related links:Molybdenum can refine the grains of steel, improve hardenability and thermal strength, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperature, deformation occurs, called creep).
Molybdenum is added to structural steel to improve strength,hardness,hardenability,and toughness. Molybdenum can inhibit the temper brittleness of alloy steel due to quenching.
In hot-work steels and high speed steels, Molybdenum increases red-hardness properties.
Titanium (Ti)
Titanium is a strong deoxidizer in steel. Titanium can make the internal structure of steel compact, refine grains, and reduce aging sensitivity and cold brittleness.
Adding appropriate titanium to austenitic stainless steel can be used as a stabilizing element which fixes carbon in inert particles, improving corrosion resistance and weldability.
Since Titanium is a rare element on Earth, this alloying element can be up to 200 times more expensive than regular carbon steel.
Vanadium (V)
Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to the steel can refine the grain structure which can improve the strength,toughness,wear resistance and resistance to shock impact.
Carbides formed by vanadium and carbon can improve the resistance to hydrogen corrosion under high temperature and high pressure.
Vanadium is most commonly used in high-speed metal cutting tools because of its enhanced red hardness property.
Tungsten (W)
As a precious alloying element, tungsten has a high melting point and a large specific gravity.Tungsten carbide formed from tungsten and carbon has high hardness and wear resistance.
Adding tungsten to high-speed steel and hot working tool steel can significantly improve the red hardness and thermal strength,and have superior hot-working and greater cutting efficiency at elevated temperatures.
Copper (Cu)
Copper can improve strength and toughness, especially atmospheric corrosion performance (copper content between 0.2%-0.4%).
However, copper has a negative effect on forging and welding and is prone to hot embrittlement during hot working.
The plasticity decreases significantly when the copper content exceeds 0.5%. When the copper content is less than 0.50%, it has no effect on the weldability.
Aluminum (Al)
Aluminum is the most effective and commonly used deoxidizer in steel.Adding a small amount of aluminum to the steel can refine the grains and improve the impact toughness.
Aluminum also has anti-oxidation and anti-corrosion properties. When used in combination with chromium and silicon, it can significantly improve the high-temperature corrosion resistance of steel.
Aluminum is often added to nitrided steels because it forms hard aluminum nitride with nitrogen.Such as EN41B, 41CrAlMo7 steel.
However, aluminum affects the hot workability, weldability and machinability of the steel.
Cobalt (Co)
Cobalt is a rare precious metal that is mostly used in high-speed steels,hot forming tool steels,and high temperature materials.
Cobalt improves red hardness,high temperature strength,and permits higher quenching temperatures.
However,Cobalt does not form any carbides.
Alloy steel and carbon steel both have very useful properties. Carbon steel is an alloy of iron and carbon, typically containing up to 2% carbon by weight. It is often utilized in the production of: machines, tools, steel buildings, bridges, and other infrastructure. Alloy steel, on the other hand, is a type that contains one or more alloying elements (usually other metals such as: manganese, chromium, and nickel) in addition to carbon. Alloy steel is often used in high-strength parts such as gears, shafts, and axles.
When choosing the right steel for a project, it is important to consider what properties the final product will need to have. For example, if strength and hardness are key requirements, alloy steel may be the better choice. If weldability is a key concern, carbon steel may be the better option. This article will take a detailed look at some of the key differences between alloy steel and carbon steel.
Alloy steel is a type of steel that contains alloying elements (e.g. aluminum, chromium, copper, manganese, nickel, silicon, and titanium) in addition to the carbon found in ordinary carbon steel. These alloying elements enhance the steel’s mechanical properties. Some alloys improve: strength, hardness, wear resistance, and/or corrosion obstruction. Alloy steel is widely used in a variety of applications, especially in the construction, automotive, and aerospace industries.
Carbon steel is a type of steel that contains carbon as the main alloying element. It typically has a higher carbon content than alloy steel. Carbon steel can be used for a variety of applications including automotive parts, construction materials, and hand tools. It is known for its strength and durability and can be heat-treated to increase hardness. Carbon steel is also more susceptible to rust than other types of steel. Carbon steel parts may be manufactured by forging, casting, and machining.
Alloy steel can contain a wide variety of elements that enhance its properties. Table 1 highlights some physical and chemical properties of alloy steel:
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