An alloy is a material having a forward-moving property composed of a metal element and one or more other elements (both metals and non-metals) fused. The most basic and independently present substances that make up the alloy are called components, or simply yuan. In most cases, the components are the elements that make up the alloy. However, there are also compounds as constituents, provided that the compound does not decompose nor undergo any chemical reaction within the scope of the study. According to the number of components, they can be divided into binary alloys, ternary alloys, or multi-element alloys. For example, simple brass is a binary alloy composed of two elements: copper and zinc. Duralumin is composed of aluminum, copper, and magnesium. The composition of the ternary alloy.
â—† Classification of copper alloys Copper alloys are divided into brass, bronze and cupronickel. Cupronickel is a copper-nickel alloy and is mainly used to make corrosion resistant parts, resistors, and thermocouples in precision machinery and precision instruments.
In mechanical production, brass and bronze are mainly used.
â— Alloys known for casting brass, copper and zinc are collectively referred to as brass. The copper-zinc binary alloy is called ordinary brass. In addition to zinc and then adding other elements composed of multi-brass called special brass.
Cast brass has higher mechanical properties, better casting properties and lower price than bronze. Commonly used for general-purpose bearings, bushings, gears and other wear parts and valves and other corrosion parts.
â— Cast bronze can be divided into ordinary bronze (tin bronze) and special bronze (aluminum bronze, lead bronze, silicon bronze, beryllium bronze, etc.).
â—† The crystallization characteristics of the various copper alloys in the copper alloy casting process are different, the casting properties are different, and the casting process characteristics are also different.
1. Tin bronze: Crystallization features a large crystallization temperature range and a wide solidification zone. Poor fluidity in casting performance, easy to produce shrinkage, not easy to oxidation. The process feature is that the wall-thick parts adopt directional solidification (sequential solidification), and the complex thin-wall parts and general wall-thick parts are simultaneously solidified.
2. Aluminum bronze and aluminum brass: The crystallization feature is a small crystallization temperature range, which is a layer-by-layer solidification feature. Good fluidity in casting properties, easy to form a centralized shrinkage cavity, easily oxidized. The process features aluminum bronze casting system as bottom injection type and aluminum brass casting system as open type.
3, silicon brass: crystal characteristics are between bronze and aluminum bronze. Casting performance is best (in special brass). The process features a sequential solidification process, a mid-injection gating system, and a small riser size.
â—† Aluminum Alloy Casting Classification Cast aluminum alloy can be divided into aluminum-silicon alloy, aluminum-copper alloy, aluminum-magnesium alloy and aluminum-zinc alloy according to chemical composition.
â— Casting process of aluminum alloy Casting performance and chemical composition of aluminum alloy are closely related, among them Al-Si alloy is in the vicinity of eutectic composition, casting property is best, and similar to gray cast iron. The Al-Cu alloy is far from the eutectic composition, has a wide range of solidification temperatures and has the worst casting properties. In practical production, aluminum castings are provided with feeders for feeding, Al-Si alloys have a small solidification temperature range, high feeding efficiency for feeders, and easy to obtain dense castings. Other types of cast aluminum alloys have a wide range of solidification temperatures, low feeder feeding efficiency, and poor casting compactness.
Aluminum alloys are very easy to inhale and oxidize, so the pouring system must ensure that the molten aluminum flows in quickly and smoothly, avoiding stirring.
Various casting methods are suitable for aluminum alloy castings. When the production volume is small, sand casting can be used, and fine sand should be used for molding. For mass production of important castings, special casting is used. Metal casting has high efficiency and good casting quality. Low-pressure casting is suitable for pressure-resistant castings requiring high compactness. Pressure casting can be used for thin-walled and complex parts.
◠Melting characteristics of cast aluminum alloy Aluminum alloy is easily oxidized in liquid state. The product is Al2O3, the melting point is as high as 2050°C, the density is slightly larger than aluminum, and the solid inclusions are suspended in the aluminum liquid, so it is difficult to remove, which deteriorates the casting performance. It also reduces the mechanical properties and reduces the compactness of the casting. Aluminum liquid also easily absorbs hydrogen, precipitates when solidified, and forms defects such as pores or pinholes.
1. Refining method In order to slow the oxidation and absorption of aluminum liquid, the aluminum alloy should be melted under the flux layer. KCl, NaCl, etc. may be added to the crucible as a flux to isolate the liquid from the furnace gas. In order to drive off the hydrogen that has been sucked into the aluminum liquid and prevent the generation of pinholes, hydrogen flooding and refining should be performed before the aluminum liquid is discharged. There are various methods, and it is relatively simple to use a bell jar to press a chloride or chloride such as zinc chloride (ZnCl2) or hexachloroethane (C2Cl6) into the aluminum liquid, and the following reaction occurs:
The boiling point of AlCl3 produced by the reaction of 3ZnCl2 + 2Al = 3Zn + 2AlCl33C2Cl6 + 2Al = 3C2Cl4 + 2AlCl3 is 183°C, and the boiling point of C2Cl4 is 121°C. Therefore, bubbles are formed. The gases H2 and Al2O3 in the aluminum liquid are carried out during the floatation process. Liquid level.
2, smelting equipment There are many types of aluminum alloy melting furnaces, which are generally used for coke boilers. Resistor crucible boilers can also be used. In addition, induction furnaces (power frequency, intermediate frequency) are also used.
The structure of the alloy is much more complicated than pure metal. Because the alloy consists of two or more elements, the various elements interact to form different phases. We refer to homogeneous components in metals and alloys that have the same chemical composition, the same structure, and are separated from other parts by the interface.
According to this concept, the structure of pure metals and alloys is analyzed below. When the pure metal is liquid, it is a single phase; the solid state is composed of the same element and the same crystal lattice, so it is a single phase; in the crystallization process, there is both a liquid phase and a solid phase, that is, two phases. When the alloy is in a liquid state, it is an alloy liquid having a uniform chemical composition and is a single phase. After the alloy changes from a liquid state to a solid state, the elements dissolve into each other to form a solid solution; the elements may also react with each other to form a metal compound. Solid solutions and metal compounds are the two basic phases of solid-state alloys. Therefore, in the solid state, the alloy may be a single-phase structure or a multi-phase structure. In the analysis of the alloy structure, the phase structure is analyzed to see if it consists of several solid solutions or metal compounds, that is, several phases.
â—† Solid solution The so-called solid solution is an alloy phase in which the solute atoms are dissolved in the lattice of the metal solvent. The two groups of elements are mutually soluble in the liquid state, and the solid state also dissolves in each other and forms a uniform and uniform substance. When a solid solution is formed, a solvent with a large content is a solvent, and a solvent with a small content is a solute. A lattice of a solvent is a lattice of a solid solution.
â— The classification of solid solutions can be divided into the substitutional solid solution and the interstitial solid solution according to the position of the solute atoms in the crystal lattice.
1. Displacement of solid solution A solute atom occupies the position of a node in the solvent crystal lattice to form a solid solution called substitution solid solution. When the solvent and solute atom diameters are not much different, generally within 15%, the substitutional solid solution is easily formed. The copper-nickel binary alloy forms a substitutional solid solution, and the nickel atom can replace the copper atom at any position of the copper lattice.
2. Interstitial solid solution The solute atoms are distributed in the solvent lattice space and form a solid solution called interstitial solid solution. The solvent of the interstitial solid solution is a transition metal with a larger diameter, and the solute is a non-metallic element such as carbon and hydrogen with a very small diameter. The formation condition is that the ratio of solute atom to solvent atom diameter must be less than 0.59. For example, in iron-carbon alloys, the solid solutions formed by iron and carbon—ferrite and austenite—are interstitial solid solutions.
In addition, according to the solubility of solute elements in solid solution, it can be divided into finite solid solution and infinite solid solution. However, only the replacement solid solution may become an infinite solid solution.
â— Performance of solid solution When the content of solute element is small, the performance of solid solution is basically the same as that of solvent metal. However, as the content of solute elements increases, the strength and hardness of the metal increase, and this phenomenon is called solid solution strengthening. Displacement of solid solution and interstitial solid solution will result in solid solution strengthening.
Appropriate control of the solute content can significantly increase the strength and hardness, while still ensuring a sufficiently high plasticity and toughness, so the solid solution generally has good comprehensive mechanical properties. Therefore, structural materials with comprehensive mechanical properties are required, and almost all of them take a solid solution as a basic phase. This is why solid solution strengthening has become an important enhancement method and has been widely used in industrial production.
â—† Metal compound Metal compound is a new phase formed by the interaction between two groups of elements. Its crystal structure is different from the two groups of elements and has metal properties. There are many kinds of metal compounds, their common feature is high melting point, high hardness, generally as the hardening phase in the alloy. Such as carbon steel Fe3C, alloy steel TiC, VC, W2C and so on.
The presence of a single-phase solid solution or a metal compound in the alloy is reduced, and is mostly present as a two-phase mechanical mixture. For example, pearlite in carbon steel is a mechanical mixture composed of a solid solution (ferrite) and a metal compound (cementite Fe3C).
â—† Determination of alloy phase diagram As mentioned before, the crystallization of pure metals is performed at a constant temperature and can be described by the cooling curve. The transformation of an alloy from a liquid state to a solid state occurs within a certain temperature range and can also be represented by a cooling curve. However, the crystallization process of an alloy system requires the use of phase diagrams to show clearly.
The alloy phase diagram is a graph showing the relationship among the composition, temperature, and structure of the alloy and is an important tool for studying alloys. Alloy phase diagrams are generally obtained by test methods. The Pb-Sb binary alloy is taken as an example to illustrate the measurement process of the binary alloy phase diagram.
(1) Prepare several alloys of different compositions and make their cooling curves separately.
(2) Find the crystallization transition temperatures of the respective alloys, ie, the crystallization starting temperature and the crystallization ending temperature.
(3) The crystallization starting temperature and the crystallization ending temperature of each alloy are respectively indicated in the temperature-component coordinate system.
(4) The crystallization starting point of each alloy is connected, that is, the liquidus; and the end of the crystallization temperature is connected, that is, the solidus. This constitutes a Pb-Sb binary alloy phase diagram. Other alloy phase diagrams can also be determined by this method.
The Pb-Sb alloy constitutes a binary eutectic phase diagram. Other alloys can also constitute binary eutectic phase diagrams, binary phase diagrams that form stable compounds, and binary phase diagrams.
â—† Iron-carbon alloys Iron-carbon alloys are the general name for steel and iron and are the most widely used alloys in the industry. Iron-carbon alloys are iron-based alloys composed mainly of carbon. In the liquid state, iron and carbon can be infinitely soluble. In the solid state, carbon dissolves in iron to form a solid solution. When the carbon content exceeds the solid solubility of carbon in iron, metal compounds appear. In addition, a mechanical mixture consisting of a solid solution and a metal compound can also be formed.
The following sections describe several basic structures of iron-carbon alloys that appear in the solid state.
◠Ferrite ferrite is a solid solution of carbon dissolved in a-Fe, commonly denoted by symbol F. It still maintains a body-centered cubic lattice, which has a very small carbon-solubility. It can only dissolve at 0.0008% carbon at room temperature, and has a maximum carbon-dissolving power of 0.02% at 727°C.
Because the ferrite carbon content is very low, its performance is similar to that of pure iron, and its plasticity and toughness are very good. The elongation δ=45% to 50%. The strength and hardness are lower, σb≈250MPa, and HBS=80.
Austenite austenite is a solid solution of carbon dissolved in γ-Fe, commonly denoted by symbol A. It still maintains a face-centered cubic lattice of γ-Fe. Its carbon-dissolving capacity is relatively large. At 727°C, the dissolved carbon is ωc=0.77%, and the soluble carbon at 2.148°C is 2.11%. Austenite is a stable structure that exists at high temperatures above 727°C. Austenitic plasticity is good, and it is the required structure for most steels under pressure processing at high temperatures. Austenite is not magnetic.
◠Cementite Cementite is a metal compound formed by iron and carbon. Its chemical formula is Fe3C. The carbon content of cementite is ωc=6.69% and the melting point is 1227°C. Its lattice is a complex orthorhombic lattice with a very high hardness of HBW=800, plasticity, toughness almost zero, and brittleness.
There are different forms of cementite in iron-carbon alloys, and their quantity, morphology, and distribution have a direct effect on the properties of iron-carbon alloys.
◠Pearlite pearlite is a ferrite and cementite eutectoid formed by autonomic transformation of austenite. Its morphology is a layered complex of alternating ferrite thin layers and thin layers of cementite, also called pearlite. The symbol P indicates that the carbon content is ωc=0.77%. Its mechanical properties lie between the ferrite and the cementite, which is determined by the pearlite lamellar spacing, which is the average thickness of a layer of ferrite and a layer of cementite.
â—Lefton is a eutectic composed of austenite and cementite formed by eutectic transformation of liquid iron-carbon alloys. Its carbon content is ωc=4.3%. When the temperature is higher than 727°C, the austenite is composed of austenite and cementite and is represented by the symbol Ld. At less than 727°C, beryllite consists of pearlite and cementite and is represented by the symbol Ld' and is called metamorphic beryllite. Due to the fact that the matrix of the lanoid body is a hard and brittle cementite, the hardness is high and the plasticity is poor
â—† Classification of copper alloys Copper alloys are divided into brass, bronze and cupronickel. Cupronickel is a copper-nickel alloy and is mainly used to make corrosion resistant parts, resistors, and thermocouples in precision machinery and precision instruments.
In mechanical production, brass and bronze are mainly used.
â— Alloys known for casting brass, copper and zinc are collectively referred to as brass. The copper-zinc binary alloy is called ordinary brass. In addition to zinc and then adding other elements composed of multi-brass called special brass.
Cast brass has higher mechanical properties, better casting properties and lower price than bronze. Commonly used for general-purpose bearings, bushings, gears and other wear parts and valves and other corrosion parts.
â— Cast bronze can be divided into ordinary bronze (tin bronze) and special bronze (aluminum bronze, lead bronze, silicon bronze, beryllium bronze, etc.).
â—† The crystallization characteristics of the various copper alloys in the copper alloy casting process are different, the casting properties are different, and the casting process characteristics are also different.
1. Tin bronze: Crystallization features a large crystallization temperature range and a wide solidification zone. Poor fluidity in casting performance, easy to produce shrinkage, not easy to oxidation. The process feature is that the wall-thick parts adopt directional solidification (sequential solidification), and the complex thin-wall parts and general wall-thick parts are simultaneously solidified.
2. Aluminum bronze and aluminum brass: The crystallization feature is a small crystallization temperature range, which is a layer-by-layer solidification feature. Good fluidity in casting properties, easy to form a centralized shrinkage cavity, easily oxidized. The process features aluminum bronze casting system as bottom injection type and aluminum brass casting system as open type.
3, silicon brass: crystal characteristics are between bronze and aluminum bronze. Casting performance is best (in special brass). The process features a sequential solidification process, a mid-injection gating system, and a small riser size.
â—† Aluminum Alloy Casting Classification Cast aluminum alloy can be divided into aluminum-silicon alloy, aluminum-copper alloy, aluminum-magnesium alloy and aluminum-zinc alloy according to chemical composition.
â— Casting process of aluminum alloy Casting performance and chemical composition of aluminum alloy are closely related, among them Al-Si alloy is in the vicinity of eutectic composition, casting property is best, and similar to gray cast iron. The Al-Cu alloy is far from the eutectic composition, has a wide range of solidification temperatures and has the worst casting properties. In practical production, aluminum castings are provided with feeders for feeding, Al-Si alloys have a small solidification temperature range, high feeding efficiency for feeders, and easy to obtain dense castings. Other types of cast aluminum alloys have a wide range of solidification temperatures, low feeder feeding efficiency, and poor casting compactness.
Aluminum alloys are very easy to inhale and oxidize, so the pouring system must ensure that the molten aluminum flows in quickly and smoothly, avoiding stirring.
Various casting methods are suitable for aluminum alloy castings. When the production volume is small, sand casting can be used, and fine sand should be used for molding. For mass production of important castings, special casting is used. Metal casting has high efficiency and good casting quality. Low-pressure casting is suitable for pressure-resistant castings requiring high compactness. Pressure casting can be used for thin-walled and complex parts.
◠Melting characteristics of cast aluminum alloy Aluminum alloy is easily oxidized in liquid state. The product is Al2O3, the melting point is as high as 2050°C, the density is slightly larger than aluminum, and the solid inclusions are suspended in the aluminum liquid, so it is difficult to remove, which deteriorates the casting performance. It also reduces the mechanical properties and reduces the compactness of the casting. Aluminum liquid also easily absorbs hydrogen, precipitates when solidified, and forms defects such as pores or pinholes.
1. Refining method In order to slow the oxidation and absorption of aluminum liquid, the aluminum alloy should be melted under the flux layer. KCl, NaCl, etc. may be added to the crucible as a flux to isolate the liquid from the furnace gas. In order to drive off the hydrogen that has been sucked into the aluminum liquid and prevent the generation of pinholes, hydrogen flooding and refining should be performed before the aluminum liquid is discharged. There are various methods, and it is relatively simple to use a bell jar to press a chloride or chloride such as zinc chloride (ZnCl2) or hexachloroethane (C2Cl6) into the aluminum liquid, and the following reaction occurs:
The boiling point of AlCl3 produced by the reaction of 3ZnCl2 + 2Al = 3Zn + 2AlCl33C2Cl6 + 2Al = 3C2Cl4 + 2AlCl3 is 183°C, and the boiling point of C2Cl4 is 121°C. Therefore, bubbles are formed. The gases H2 and Al2O3 in the aluminum liquid are carried out during the floatation process. Liquid level.
2, smelting equipment There are many types of aluminum alloy melting furnaces, which are generally used for coke boilers. Resistor crucible boilers can also be used. In addition, induction furnaces (power frequency, intermediate frequency) are also used.
The structure of the alloy is much more complicated than pure metal. Because the alloy consists of two or more elements, the various elements interact to form different phases. We refer to homogeneous components in metals and alloys that have the same chemical composition, the same structure, and are separated from other parts by the interface.
According to this concept, the structure of pure metals and alloys is analyzed below. When the pure metal is liquid, it is a single phase; the solid state is composed of the same element and the same crystal lattice, so it is a single phase; in the crystallization process, there is both a liquid phase and a solid phase, that is, two phases. When the alloy is in a liquid state, it is an alloy liquid having a uniform chemical composition and is a single phase. After the alloy changes from a liquid state to a solid state, the elements dissolve into each other to form a solid solution; the elements may also react with each other to form a metal compound. Solid solutions and metal compounds are the two basic phases of solid-state alloys. Therefore, in the solid state, the alloy may be a single-phase structure or a multi-phase structure. In the analysis of the alloy structure, the phase structure is analyzed to see if it consists of several solid solutions or metal compounds, that is, several phases.
â—† Solid solution The so-called solid solution is an alloy phase in which the solute atoms are dissolved in the lattice of the metal solvent. The two groups of elements are mutually soluble in the liquid state, and the solid state also dissolves in each other and forms a uniform and uniform substance. When a solid solution is formed, a solvent with a large content is a solvent, and a solvent with a small content is a solute. A lattice of a solvent is a lattice of a solid solution.
â— The classification of solid solutions can be divided into the substitutional solid solution and the interstitial solid solution according to the position of the solute atoms in the crystal lattice.
1. Displacement of solid solution A solute atom occupies the position of a node in the solvent crystal lattice to form a solid solution called substitution solid solution. When the solvent and solute atom diameters are not much different, generally within 15%, the substitutional solid solution is easily formed. The copper-nickel binary alloy forms a substitutional solid solution, and the nickel atom can replace the copper atom at any position of the copper lattice.
2. Interstitial solid solution The solute atoms are distributed in the solvent lattice space and form a solid solution called interstitial solid solution. The solvent of the interstitial solid solution is a transition metal with a larger diameter, and the solute is a non-metallic element such as carbon and hydrogen with a very small diameter. The formation condition is that the ratio of solute atom to solvent atom diameter must be less than 0.59. For example, in iron-carbon alloys, the solid solutions formed by iron and carbon—ferrite and austenite—are interstitial solid solutions.
In addition, according to the solubility of solute elements in solid solution, it can be divided into finite solid solution and infinite solid solution. However, only the replacement solid solution may become an infinite solid solution.
â— Performance of solid solution When the content of solute element is small, the performance of solid solution is basically the same as that of solvent metal. However, as the content of solute elements increases, the strength and hardness of the metal increase, and this phenomenon is called solid solution strengthening. Displacement of solid solution and interstitial solid solution will result in solid solution strengthening.
Appropriate control of the solute content can significantly increase the strength and hardness, while still ensuring a sufficiently high plasticity and toughness, so the solid solution generally has good comprehensive mechanical properties. Therefore, structural materials with comprehensive mechanical properties are required, and almost all of them take a solid solution as a basic phase. This is why solid solution strengthening has become an important enhancement method and has been widely used in industrial production.
â—† Metal compound Metal compound is a new phase formed by the interaction between two groups of elements. Its crystal structure is different from the two groups of elements and has metal properties. There are many kinds of metal compounds, their common feature is high melting point, high hardness, generally as the hardening phase in the alloy. Such as carbon steel Fe3C, alloy steel TiC, VC, W2C and so on.
The presence of a single-phase solid solution or a metal compound in the alloy is reduced, and is mostly present as a two-phase mechanical mixture. For example, pearlite in carbon steel is a mechanical mixture composed of a solid solution (ferrite) and a metal compound (cementite Fe3C).
â—† Determination of alloy phase diagram As mentioned before, the crystallization of pure metals is performed at a constant temperature and can be described by the cooling curve. The transformation of an alloy from a liquid state to a solid state occurs within a certain temperature range and can also be represented by a cooling curve. However, the crystallization process of an alloy system requires the use of phase diagrams to show clearly.
The alloy phase diagram is a graph showing the relationship among the composition, temperature, and structure of the alloy and is an important tool for studying alloys. Alloy phase diagrams are generally obtained by test methods. The Pb-Sb binary alloy is taken as an example to illustrate the measurement process of the binary alloy phase diagram.
(1) Prepare several alloys of different compositions and make their cooling curves separately.
(2) Find the crystallization transition temperatures of the respective alloys, ie, the crystallization starting temperature and the crystallization ending temperature.
(3) The crystallization starting temperature and the crystallization ending temperature of each alloy are respectively indicated in the temperature-component coordinate system.
(4) The crystallization starting point of each alloy is connected, that is, the liquidus; and the end of the crystallization temperature is connected, that is, the solidus. This constitutes a Pb-Sb binary alloy phase diagram. Other alloy phase diagrams can also be determined by this method.
The Pb-Sb alloy constitutes a binary eutectic phase diagram. Other alloys can also constitute binary eutectic phase diagrams, binary phase diagrams that form stable compounds, and binary phase diagrams.
â—† Iron-carbon alloys Iron-carbon alloys are the general name for steel and iron and are the most widely used alloys in the industry. Iron-carbon alloys are iron-based alloys composed mainly of carbon. In the liquid state, iron and carbon can be infinitely soluble. In the solid state, carbon dissolves in iron to form a solid solution. When the carbon content exceeds the solid solubility of carbon in iron, metal compounds appear. In addition, a mechanical mixture consisting of a solid solution and a metal compound can also be formed.
The following sections describe several basic structures of iron-carbon alloys that appear in the solid state.
◠Ferrite ferrite is a solid solution of carbon dissolved in a-Fe, commonly denoted by symbol F. It still maintains a body-centered cubic lattice, which has a very small carbon-solubility. It can only dissolve at 0.0008% carbon at room temperature, and has a maximum carbon-dissolving power of 0.02% at 727°C.
Because the ferrite carbon content is very low, its performance is similar to that of pure iron, and its plasticity and toughness are very good. The elongation δ=45% to 50%. The strength and hardness are lower, σb≈250MPa, and HBS=80.
Austenite austenite is a solid solution of carbon dissolved in γ-Fe, commonly denoted by symbol A. It still maintains a face-centered cubic lattice of γ-Fe. Its carbon-dissolving capacity is relatively large. At 727°C, the dissolved carbon is ωc=0.77%, and the soluble carbon at 2.148°C is 2.11%. Austenite is a stable structure that exists at high temperatures above 727°C. Austenitic plasticity is good, and it is the required structure for most steels under pressure processing at high temperatures. Austenite is not magnetic.
◠Cementite Cementite is a metal compound formed by iron and carbon. Its chemical formula is Fe3C. The carbon content of cementite is ωc=6.69% and the melting point is 1227°C. Its lattice is a complex orthorhombic lattice with a very high hardness of HBW=800, plasticity, toughness almost zero, and brittleness.
There are different forms of cementite in iron-carbon alloys, and their quantity, morphology, and distribution have a direct effect on the properties of iron-carbon alloys.
◠Pearlite pearlite is a ferrite and cementite eutectoid formed by autonomic transformation of austenite. Its morphology is a layered complex of alternating ferrite thin layers and thin layers of cementite, also called pearlite. The symbol P indicates that the carbon content is ωc=0.77%. Its mechanical properties lie between the ferrite and the cementite, which is determined by the pearlite lamellar spacing, which is the average thickness of a layer of ferrite and a layer of cementite.
â—Lefton is a eutectic composed of austenite and cementite formed by eutectic transformation of liquid iron-carbon alloys. Its carbon content is ωc=4.3%. When the temperature is higher than 727°C, the austenite is composed of austenite and cementite and is represented by the symbol Ld. At less than 727°C, beryllite consists of pearlite and cementite and is represented by the symbol Ld' and is called metamorphic beryllite. Due to the fact that the matrix of the lanoid body is a hard and brittle cementite, the hardness is high and the plasticity is poor