Materials

Ferrous alloys, those in which iron is the principal constituent, include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel). Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

Types of Ferrous Metals – Classification Based on Composition

• 

  Pig Iron. In general, the pig iron is an intermediate product of the iron industry. Pig iron, known also as crude iron, is produced by the blast furnace process and contains up to 4–5% carbon, with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. The high level of carbon makes it relatively weak and brittle. Reducing the amount of carbon to 0.002–2.1% by mass produces steel, which may be up to 1000 times harder than pure iron.

• Wrought Iron. Wrought iron is an iron alloy with very low carbon content (less than 0.08%) with respect to cast iron (2.1% to 4%). The microstructure of wrought iron shows dark slag inclusions in ferrite. It is soft, ductile, magnetic, corrosion-resistant and easily welded. It has high elasticity and tensile strength. It can be heated and reheated and worked into various shapes. Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are actually made of mild steel. For example, the Eiffel Tower is a wrought-iron lattice tower.

• 

  Steel. Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. There are thousands of alloys that have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. According ot AISI classification, carbon steel is broken down into four classes based on carbon content:

  • Low-carbon Steels. Low-carbon steel, also known as mild steel is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications. Low-carbon steel contains approximately 0.05–0.25% carbon making it malleable and ductile. Mild steel has a relatively low tensile strength, but it is cheap and easy to form; surface hardness can be increased through carburizing.
  • Medium-carbon Steels. Medium-carbon steel has approximately 0.3–0.6% carbon content. Balances ductility and strength and has good wear resistance. This grade of steel is mostly used in the production of machine components, shafts, axles, gears, crankshafts, coupling and forgings and could also be used in rails and railway wheels.
  • High-carbon Steels. High-carbon steel has approximately 0.60 to 1.00% carbon content. Hardness is higher than the other grades but ductility decreases. High carbon steels could be used for springs, rope wires, hammers, screwdrivers, and wrenches.

  • 

    Ultra-high-carbon Steels. Ultra-high-carbon steel has approximately 1.25–2.0% carbon content. Steels that can be tempered to great hardness. This grade of steel could be used for hard steel products, such as truck springs, metal cutting tools and other special purposes like (non-industrial-purpose) knives, axles or punches. Most steels with more than 2.5% carbon content are made using powder metallurgy.

• Cast Iron. Cast irons also comprise a large family of different types of iron, depending on how the carbon-rich phase forms during solidification. The microstructure of cast irons can be controlled to provide products that have excellent ductility, good machinability, excellent vibration damping, superb wear resistance, and good thermal conductivity. The most common cast iron types are:
  • Gray cast iron. Grey cast iron is the oldest and most common type of cast iron. Grey cast iron is characterised by its graphitic microstructure, which causes fractures of the material to have a grey appearance.
  • White cast iron. White cast irons are hard, brittle, and unmachinable, while gray irons with softer graphite are reasonably strong and machinable. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron.
  • Malleable cast iron. Malleable cast iron is white cast iron that has been annealed. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form.

  • 

    Ductile cast iron. Ductile iron, also known as nodular iron, is very similar to gray iron in composition, ductile iron is stronger and more shock resistant than gray iron. In fact, ductile iron has mechanical characteristics approaching those of steel, while it retains high fluidity when molten and lower melting point.

• Alloy Steels. Steel is an alloy of iron and carbon, but the term alloy steel usually only refers to steels that contain other elements— like vanadium, molybdenum, or cobalt—in amounts sufficient to alter the properties of the base steel. In general, alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups:
  • Low-alloy Steels.
  • High-alloy Steels.
• Stainless Steel. Stainless steels are defined as low-carbon steels with at least 10% chromium with or without other alloying elements. Strength and corrosion resistance often make it the material of choice in transportation and processing equipment, engine parts, and firearms. Chromium increases hardness, strength, and corrosion resistance. Nickel gives similar benefits but adds hardness without sacrificing ductility and toughness. It also reduces thermal expansion for better dimensional stability.
• Superalloys.

Special Ferrous Metals

• Tool Steels
• High-speed Steels
• Shock-resisting Steels
• Silver Steel

See above:
Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Hardness of Metal Alloys

In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Hardness is probably the most poorly defined material property because it may indicate resistance to scratching, resistance to abrasion, resistance to indentation or even resistance to shaping or localized plastic deformation. Hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness.

Brinell hardness test is one of indentation hardness tests, that has been developed for hardness testing. In Brinell tests, a hard, spherical indenter is forced under a specific load into the surface of the metal to be tested. The typical test uses a 10 mm (0.39 in) diameter  hardened steel ball as an indenter with a 3,000 kgf (29.42 kN; 6,614 lbf) force. The load is maintained constant for a specified time (between 10 and 30 s). For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball.

The test provides numerical results to quantify the hardness of a material, which is expressed by the Brinell hardness number – HB. The Brinell hardness number is designated by the most commonly used test standards (ASTM E10-14[2] and ISO 6506–1:2005) as HBW (H from hardness, B from brinell and W from the material of the indenter, tungsten (wolfram) carbide). In former standards HB or HBS were used to refer to measurements made with steel indenters.

The Brinell hardness number (HB) is the load divided by the surface area of the indentation. The diameter of the impression is measured with a microscope with a superimposed scale. The Brinell hardness number is computed from the equation:

There are a variety of  test methods in common use (e.g. Brinell, Knoop, Vickers and Rockwell). There are tables that are available correlating the hardness numbers from the different test methods where correlation is applicable. In all scales, a high hardness number represents a hard metal.

Example – Hardness of Low-carbon Steel

Brinell hardness of low-carbon steel is approximately 120 MPa.

Example – Hardness of High-carbon Steel

Brinell hardness of high-carbon steel is approximately 200 MPa.

Example – Hardness of Damascus Steel

Rockwell hardness of Damascus steel depends on the current type of the steel, but it may be approximately 62-64 HRC Rockwell.

See above:
Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Ferrous Alloys

Ferrous alloys, those in which iron is the principal constituent, include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel). Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques.
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

See above:
Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Types of Alloys

Metal alloys, by virtue of composition, are often grouped into two classes:

• Ferrous alloys. Ferrous alloys, those in which iron is the principal constituent, include steel, stainless steel, carbon steel, cast iron. Ferrous alloys are known for their strength.
• Non-ferrous alloys. Non-ferrous alloys those that does not contain iron (ferrite) in appreciable amounts thus they are based on non-ferrous metals (i.e. aluminium, copper, chromium, titanium, gold, nickel, silver, tin, lead, zinc, etc.) Other common properties of non-ferrous metals are non-magnetic, malleable, and lightweight.

Ferrous Alloys

Ferrous alloys, those in which iron is the principal constituent, include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel). Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

Strength of Metal Alloys

In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. Strength of a material is its ability to withstand this applied load without failure or plastic deformation.

Ultimate Tensile Strength

The ultimate tensile strength is the maximum on the engineering stress-strain curve. This corresponds to the maximum stress that can be sustained by a structure in tension. Ultimate tensile strength is often shortened to “tensile strength” or even to “the ultimate.”  If this stress is applied and maintained, fracture will result. Often, this value is significantly more than the yield stress (as much as 50 to 60 percent more than the yield for some types of metals). When a ductile material reaches its ultimate strength, it experiences necking where the cross-sectional area reduces locally. The stress-strain curve contains no higher stress than the ultimate strength. Even though deformations can continue to increase, the stress usually decreases after the ultimate strength has been achieved. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material. Ultimate tensile strengths vary from 50 MPa for an aluminum to as high as 3000 MPa for very high-strength steels.

Example – Ultimate Tensile Strength – Low-carbon Steel

Ultimate tensile strength of low-carbon steel is between 400 – 550 MPa.

Example – Ultimate Tensile Strength – Ultra-high-carbon Steel

Ultimate tensile strength of ultra-high-carbon steel is 1100 MPa.

Yield Strength

The yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. Some steels and other materials exhibit a behaviour termed a yield point phenomenon. Yield strengths vary from 35 MPa for a low-strength aluminum to greater than 1400 MPa for very high-strength steels.

Example – Yield Strength – Low-carbon Steel

Yield strength of low-carbon steel is 250 MPa.

Example – Yield Strength – Ultra-high-carbon Steel

Yield strength of ultra-high-carbon steel is 800 MPa.

Young’s Modulus of Elasticity

The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests. Up to a limiting stress, a body will be able to recover its dimensions on removal of the load. The applied stresses cause the atoms in a crystal to move from their equilibrium position. All the atoms are displaced the same amount and still maintain their relative geometry. When the stresses are removed, all the atoms return to their original positions and no permanent deformation occurs. According to the Hooke’s law, the stress is proportional to the strain (in the elastic region), and the slope is Young’s modulus. Young’s modulus is equal to the longitudinal stress divided by the strain.

Example – Young’s modulus of elasticity – Low-carbon Steel

Young’s modulus of elasticity of low-carbon steel is 200 GPa.

Hardness of Metal Alloys

In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Hardness is probably the most poorly defined material property because it may indicate resistance to scratching, resistance to abrasion, resistance to indentation or even resistance to shaping or localized plastic deformation. Hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness.

Brinell hardness test is one of indentation hardness tests, that has been developed for hardness testing. In Brinell tests, a hard, spherical indenter is forced under a specific load into the surface of the metal to be tested. The typical test uses a 10 mm (0.39 in) diameter  hardened steel ball as an indenter with a 3,000 kgf (29.42 kN; 6,614 lbf) force. The load is maintained constant for a specified time (between 10 and 30 s). For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball.

The test provides numerical results to quantify the hardness of a material, which is expressed by the Brinell hardness number – HB. The Brinell hardness number is designated by the most commonly used test standards (ASTM E10-14[2] and ISO 6506–1:2005) as HBW (H from hardness, B from brinell and W from the material of the indenter, tungsten (wolfram) carbide). In former standards HB or HBS were used to refer to measurements made with steel indenters.

The Brinell hardness number (HB) is the load divided by the surface area of the indentation. The diameter of the impression is measured with a microscope with a superimposed scale. The Brinell hardness number is computed from the equation:

There are a variety of  test methods in common use (e.g. Brinell, Knoop, Vickers and Rockwell). There are tables that are available correlating the hardness numbers from the different test methods where correlation is applicable. In all scales, a high hardness number represents a hard metal.

Example – Hardness of Low-carbon Steel

Brinell hardness of low-carbon steel is approximately 120 MPa.

Example – Hardness of High-carbon Steel

Brinell hardness of high-carbon steel is approximately 200 MPa.

Example – Hardness of Damascus Steel

Rockwell hardness of Damascus steel depends on the current type of the steel, but it may be approximately 62-64 HRC Rockwell.

See above:
Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Strength of Metal Alloys

In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. Strength of a material is its ability to withstand this applied load without failure or plastic deformation.

Ultimate Tensile Strength

The ultimate tensile strength is the maximum on the engineering stress-strain curve. This corresponds to the maximum stress that can be sustained by a structure in tension. Ultimate tensile strength is often shortened to “tensile strength” or even to “the ultimate.”  If this stress is applied and maintained, fracture will result. Often, this value is significantly more than the yield stress (as much as 50 to 60 percent more than the yield for some types of metals). When a ductile material reaches its ultimate strength, it experiences necking where the cross-sectional area reduces locally. The stress-strain curve contains no higher stress than the ultimate strength. Even though deformations can continue to increase, the stress usually decreases after the ultimate strength has been achieved. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material. Ultimate tensile strengths vary from 50 MPa for an aluminum to as high as 3000 MPa for very high-strength steels.

Example – Ultimate Tensile Strength – Low-carbon Steel

Ultimate tensile strength of low-carbon steel is between 400 – 550 MPa.

Example – Ultimate Tensile Strength – Ultra-high-carbon Steel

Ultimate tensile strength of ultra-high-carbon steel is 1100 MPa.

Yield Strength

The yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. Some steels and other materials exhibit a behaviour termed a yield point phenomenon. Yield strengths vary from 35 MPa for a low-strength aluminum to greater than 1400 MPa for very high-strength steels.

Example – Yield Strength – Low-carbon Steel

Yield strength of low-carbon steel is 250 MPa.

Example – Yield Strength – Ultra-high-carbon Steel

Yield strength of ultra-high-carbon steel is 800 MPa.

Young’s Modulus of Elasticity

The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests. Up to a limiting stress, a body will be able to recover its dimensions on removal of the load. The applied stresses cause the atoms in a crystal to move from their equilibrium position. All the atoms are displaced the same amount and still maintain their relative geometry. When the stresses are removed, all the atoms return to their original positions and no permanent deformation occurs. According to the Hooke’s law, the stress is proportional to the strain (in the elastic region), and the slope is Young’s modulus. Young’s modulus is equal to the longitudinal stress divided by the strain.

Example – Young’s modulus of elasticity – Low-carbon Steel

Young’s modulus of elasticity of low-carbon steel is 200 GPa.

 

See above:
Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

Types of Alloys

Metal alloys, by virtue of composition, are often grouped into two classes:

• Ferrous alloys. Ferrous alloys, those in which iron is the principal constituent, include steel, stainless steel, carbon steel, cast iron. Ferrous alloys are known for their strength.
• Non-ferrous alloys. Non-ferrous alloys those that does not contain iron (ferrite) in appreciable amounts thus they are based on non-ferrous metals (i.e. aluminium, copper, chromium, titanium, gold, nickel, silver, tin, lead, zinc, etc.) Other common properties of non-ferrous metals are non-magnetic, malleable, and lightweight.

See above:
Alloys

Metal alloys, by virtue of composition, are often grouped into two classes:

• Ferrous alloys. Ferrous alloys, those in which iron is the principal constituent, include steel, stainless steel, carbon steel, cast iron. Ferrous alloys are known for their strength.
• Non-ferrous alloys. Non-ferrous alloys those that does not contain iron (ferrite) in appreciable amounts thus they are based on non-ferrous metals (i.e. aluminium, copper, chromium, titanium, gold, nickel, silver, tin, lead, zinc, etc.) Other common properties of non-ferrous metals are non-magnetic, malleable, and lightweight.

Ferrous Alloys

Ferrous alloys, those in which iron is the principal constituent, include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel). Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

Types of Ferrous Metals – Classification Based on Composition

• Pig Iron. In general, the pig iron is an intermediate product of the iron industry. Pig iron, known also as crude iron, is produced by the blast furnace process and contains up to 4–5% carbon, with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. The high level of carbon makes it relatively weak and brittle. Reducing the amount of carbon to 0.002–2.1% by mass produces steel, which may be up to 1000 times harder than pure iron.
• Wrought Iron. Wrought iron is an iron alloy with very low carbon content (less than 0.08%) with respect to cast iron (2.1% to 4%). The microstructure of wrought iron shows dark slag inclusions in ferrite. It is soft, ductile, magnetic, corrosion-resistant and easily welded. It has high elasticity and tensile strength. It can be heated and reheated and worked into various shapes. Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are actually made of mild steel. For example, the Eiffel Tower is a wrought-iron lattice tower.
• Steel. Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. There are thousands of alloys that have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. According ot AISI classification, carbon steel is broken down into four classes based on carbon content:
  • Low-carbon Steels. Low-carbon steel, also known as mild steel is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications. Low-carbon steel contains approximately 0.05–0.25% carbon making it malleable and ductile. Mild steel has a relatively low tensile strength, but it is cheap and easy to form; surface hardness can be increased through carburizing.
  • Medium-carbon Steels. Medium-carbon steel has approximately 0.3–0.6% carbon content. Balances ductility and strength and has good wear resistance. This grade of steel is mostly used in the production of machine components, shafts, axles, gears, crankshafts, coupling and forgings and could also be used in rails and railway wheels.
  • High-carbon Steels. High-carbon steel has approximately 0.60 to 1.00% carbon content. Hardness is higher than the other grades but ductility decreases. High carbon steels could be used for springs, rope wires, hammers, screwdrivers, and wrenches.
  • Ultra-high-carbon Steels. Ultra-high-carbon steel has approximately 1.25–2.0% carbon content. Steels that can be tempered to great hardness. This grade of steel could be used for hard steel products, such as truck springs, metal cutting tools and other special purposes like (non-industrial-purpose) knives, axles or punches. Most steels with more than 2.5% carbon content are made using powder metallurgy.
• Cast Iron. Cast irons also comprise a large family of different types of iron, depending on how the carbon-rich phase forms during solidification. The microstructure of cast irons can be controlled to provide products that have excellent ductility, good machinability, excellent vibration damping, superb wear resistance, and good thermal conductivity. The most common cast iron types are:
  • Gray cast iron. Grey cast iron is the oldest and most common type of cast iron. Grey cast iron is characterised by its graphitic microstructure, which causes fractures of the material to have a grey appearance.
  • White cast iron. White cast irons are hard, brittle, and unmachinable, while gray irons with softer graphite are reasonably strong and machinable. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron.
  • Malleable cast iron. Malleable cast iron is white cast iron that has been annealed. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form.
  • Ductile cast iron. Ductile iron, also known as nodular iron, is very similar to gray iron in composition, ductile iron is stronger and more shock resistant than gray iron. In fact, ductile iron has mechanical characteristics approaching those of steel, while it retains high fluidity when molten and lower melting point.
• Alloy Steels. Steel is an alloy of iron and carbon, but the term alloy steel usually only refers to steels that contain other elements— like vanadium, molybdenum, or cobalt—in amounts sufficient to alter the properties of the base steel. In general, alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups:
  • Low-alloy Steels.
  • High-alloy Steels.
• Stainless Steel. Stainless steels are defined as low-carbon steels with at least 10% chromium with or without other alloying elements. Strength and corrosion resistance often make it the material of choice in transportation and processing equipment, engine parts, and firearms. Chromium increases hardness, strength, and corrosion resistance. Nickel gives similar benefits but adds hardness without sacrificing ductility and toughness. It also reduces thermal expansion for better dimensional stability.
• Superalloys.

Special Ferrous Metals

• Tool Steels
• High-speed Steels
• Shock-resisting Steels
• Silver Steel

See above:
Alloys

Historically, metalworking posses one of key domains in materials science. It is the process of working with metals to create individual parts, assemblies, or large-scale structures. Materials science is one of the oldest forms of engineering and applied science and the material of choice of a given era is often a defining point (e.g. Stone Age, Bronze Age, Iron Age). Processing of metals in the solid state can be divided into two major stages:

• Cold working. Cold working is a metalworking process, which occurs below the recrystallization temperature. Because plastic deformation results from the movement of dislocations, metals can be strengthened by preventing this motion. When a metal is plastically deformed, dislocations move and additional dislocations are generated. Dislocations can move if the atoms from one of the surrounding planes break their bonds and rebond with the atoms at the terminating edge. The dislocation density in a metal increases with deformation or cold work because of dislocation multiplication or the formation of new dislocations. The more dislocations within a material, the more they will interact and become pinned or tangled. This will result in a decrease in the mobility of the dislocations and a strengthening of the material. This process is known as cold working because the plastic deformation must occurs at a temperature low enough that atoms cannot rearrange themselves. It is a process of making a metal harder and stronger through plastic deformation. Cold forming techniques are usually classified into four major groups:
  • Squeezing
  • Bending
  • Drawing
  • Shearing

See above:
Metalworking

An alloy is a mixture of two or more materials, at least one of which is a metal. Alloys can have a microstructure consisting of solid solutions, where secondary atoms are introduced as substitutionals or interstitials in a crystal lattice. An alloy may also be a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within the metal). Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms respectively.

Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials. Many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent.

Alloying is a common practice because metallic bonds allow joining of different types of metals. For example, austenitic stainless steels, including Type 304 stainless steel (containing 18%-20% chromium and 8%-10.5% nickel), have a face-centered cubic structure of iron atoms with the carbon in interstitial solid solution.

Characteristics of Metal Alloys

Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. Strength is the most important criterion by which many structural materials are judged. Therefore, alloys are used for engineering construction. Steel, probably the most common structural metal, is a good example of an alloy. It is an alloy of iron and carbon, with other elements to give it certain desirable properties.

It is sometimes possible for a material to be composed of several solid phases. The strengths of these materials are enhanced by allowing a solid structure to become a form composed of two interspersed phases. When the material in question is an alloy, it is possible to quench the metal from a molten state to form the interspersed phases. The term quenching refers to a heat treatment in which a material is rapidly cooled in water, oil or air to obtain certain material properties, especially hardness. In metallurgy, quenching is most commonly used to harden steel by introducing martensite.

Types of Alloys

Metal alloys, by virtue of composition, are often grouped into two classes:

• Ferrous alloys. Ferrous alloys, those in which iron is the principal constituent, include steel, stainless steel, carbon steel, cast iron. Ferrous alloys are known for their strength.
• Non-ferrous alloys. Non-ferrous alloys those that does not contain iron (ferrite) in appreciable amounts thus they are based on non-ferrous metals (i.e. aluminium, copper, chromium, titanium, gold, nickel, silver, tin, lead, zinc, etc.) Other common properties of non-ferrous metals are non-magnetic, malleable, and lightweight.

Ferrous Alloys

Ferrous alloys, those in which iron is the principal constituent, include steel and pig iron (with a carbon content of a few percent) and alloys of iron with other metals (such as stainless steel). Ferrous alloys are known for their strength. Alloys are usually stronger than pure metals, although they generally offer reduced electrical and thermal conductivity. The simplest ferrous alloys are known as steels and they consist of iron (Fe) alloyed with carbon (C) (about 0.1% to 1%, depending on type). Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. Their widespread use is accounted for by following factors:

1. Iron containing compounds exist in abundant quantities within the Earth’s crust.
2. Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques
3. Ferrous alloys are extremely versatile, in that they may be tailored to have a wide range of mechanical and physical properties.

The principal disadvantage of many ferrous alloys is their susceptibility to corrosion. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel, while adding silicon will alter its electrical characteristics, producing silicon steel.

Types of Ferrous Metals – Classification Based on Composition

• Pig Iron. In general, the pig iron is an intermediate product of the iron industry. Pig iron, known also as crude iron, is produced by the blast furnace process and contains up to 4–5% carbon, with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. The high level of carbon makes it relatively weak and brittle. Reducing the amount of carbon to 0.002–2.1% by mass produces steel, which may be up to 1000 times harder than pure iron.
• Wrought Iron. Wrought iron is an iron alloy with very low carbon content (less than 0.08%) with respect to cast iron (2.1% to 4%). The microstructure of wrought iron shows dark slag inclusions in ferrite. It is soft, ductile, magnetic, corrosion-resistant and easily welded. It has high elasticity and tensile strength. It can be heated and reheated and worked into various shapes. Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are actually made of mild steel. For example, the Eiffel Tower is a wrought-iron lattice tower.
• Steel. Steels are iron–carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength. Due to its very-high strength, but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloy in modern use. There are thousands of alloys that have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. According ot AISI classification, carbon steel is broken down into four classes based on carbon content:
  • Low-carbon Steels. Low-carbon steel, also known as mild steel is now the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications. Low-carbon steel contains approximately 0.05–0.25% carbon making it malleable and ductile. Mild steel has a relatively low tensile strength, but it is cheap and easy to form; surface hardness can be increased through carburizing.
  • Medium-carbon Steels. Medium-carbon steel has approximately 0.3–0.6% carbon content. Balances ductility and strength and has good wear resistance. This grade of steel is mostly used in the production of machine components, shafts, axles, gears, crankshafts, coupling and forgings and could also be used in rails and railway wheels.
  • High-carbon Steels. High-carbon steel has approximately 0.60 to 1.00% carbon content. Hardness is higher than the other grades but ductility decreases. High carbon steels could be used for springs, rope wires, hammers, screwdrivers, and wrenches.
  • Ultra-high-carbon Steels. Ultra-high-carbon steel has approximately 1.25–2.0% carbon content. Steels that can be tempered to great hardness. This grade of steel could be used for hard steel products, such as truck springs, metal cutting tools and other special purposes like (non-industrial-purpose) knives, axles or punches. Most steels with more than 2.5% carbon content are made using powder metallurgy.
• Cast Iron. Cast irons also comprise a large family of different types of iron, depending on how the carbon-rich phase forms during solidification. The microstructure of cast irons can be controlled to provide products that have excellent ductility, good machinability, excellent vibration damping, superb wear resistance, and good thermal conductivity. The most common cast iron types are:
  • Gray cast iron. Grey cast iron is the oldest and most common type of cast iron. Grey cast iron is characterised by its graphitic microstructure, which causes fractures of the material to have a grey appearance.
  • White cast iron. White cast irons are hard, brittle, and unmachinable, while gray irons with softer graphite are reasonably strong and machinable. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron.
  • Malleable cast iron. Malleable cast iron is white cast iron that has been annealed. Through an annealing heat treatment, the brittle structure as first cast is transformed into the malleable form.
  • Ductile cast iron. Ductile iron, also known as nodular iron, is very similar to gray iron in composition, ductile iron is stronger and more shock resistant than gray iron. In fact, ductile iron has mechanical characteristics approaching those of steel, while it retains high fluidity when molten and lower melting point.
• Alloy Steels. Steel is an alloy of iron and carbon, but the term alloy steel usually only refers to steels that contain other elements— like vanadium, molybdenum, or cobalt—in amounts sufficient to alter the properties of the base steel. In general, alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups:
  • Low-alloy Steels.
  • High-alloy Steels.
• Stainless Steel. Stainless steels are defined as low-carbon steels with at least 10% chromium with or without other alloying elements. Strength and corrosion resistance often make it the material of choice in transportation and processing equipment, engine parts, and firearms. Chromium increases hardness, strength, and corrosion resistance. Nickel gives similar benefits but adds hardness without sacrificing ductility and toughness. It also reduces thermal expansion for better dimensional stability.
• Superalloys.

Special Ferrous Metals

• Tool Steels
• High-speed Steels
• Shock-resisting Steels
• Silver Steel

See above:
Metals

Metal is a material (usually solid) comprising one or more metallic elements (e.g., iron, aluminium, copper, chromium, titanium, gold, nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, oxygen) in relatively small amounts. The unique feature of metals as far as their structure is concerned is the presence of charge carriers, specifically electrons. This feature is given by the nature of metallic bond. The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized.

Joining Processes

Metal joining is a controlled process used to fuse metals. There are several techniques of metal joining of which welding is one of the more basic forms.

• Welding. In welding, one of most common joining processes, two or more metal parts are joined to form a single piece by using high heat to melt the parts together and allowing them to cool causing fusion.
• Brazing. Brazing is a metal-joining process in which a filler metal is melted and drawn into a capillary formed by the assembly of two or more work pieces. The filler metal has a lower melting point than the adjoining metal. Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering.
• Soldering. A technique for joining metals using a filler metal alloy that has a melting temperature less than about 425°C (800°F). Because of this lower temperature and different alloys used as fillers, the metallurgical reaction between filler and work piece is minimal, resulting in a weaker joint. In electronics assembly, the eutectic alloy with 63% tin and 37% lead (or 60/40, which is almost identical in melting point) has been the alloy of choice.
• Riveting. Riveting is one of the most ancient metalwork joining processes. A rivet is essentially a two-headed and unthreaded bolt which holds two other pieces of metal together. Currently riveting still retains important uses in industry and construction. Solid rivets are used in applications where reliability and safety count. A typical application for solid rivets can be found within the structural parts of aircraft. Hundreds of thousands of solid rivets are used to assemble the frame of a modern aircraft.

See above:
Metals