1 Grain and grain boundary Crystals formed after the metal crystallizes are inconsistent and the internal character is arranged in the same direction is called a crystal grain. The interface between grains and grains, known as the grain boundary
Phase and phase boundaries In metals or alloys, homogeneous components that have the same composition, the same structure, and separate interfaces are called phases. The interface between phase and phase, called the phase boundary
3 Solid solution The solid phase formed by the atom of another element dissolved in the crystal of a metal element constituting the alloy is called a solid solution. Solid solution generally has higher strength, good plasticity, corrosion resistance, and higher resistance and magnetic properties
4 Metal Compounds Solid phases formed by the interaction of different elements in the alloy, whose lattice types and properties are completely different from their constituent elements and have metallic properties, are called metal compounds.
5 Austenite Austenite is a solid solution in which carbon and other elements are dissolved in y-Fe. Austenitic has face-centered cubic crystals, good plasticity, generally exists at high temperatures
6 Iron Wire Ferrite is a solid solution of carbon and other elements dissolved in a-Fe. Ferrite has a body-centered cubic lattice with a very low carbon content. Its properties are very similar to that of pure iron, also called pure iron.
7 Cementite Cementite is a compound of iron and carbon, also known as tri-carbonate (Noc), which has a carbon content of 6.69% and has a complex character structure. Its performance is hard and brittle, almost no plasticity
8 Pearlite Pearlite is a lamellar structure between iron wire and cementite. It is named for its fingerprint-like pearl luster. Its properties lie between ferrite and cementite, moderate strength, hardness, and good plasticity and toughness
9 Sorbite, also known as fine pearlite, is a mixture of ferrite and cementite that austenite decomposes below the pearlite formation temperature. The layer is thinner than the pearlite and can only be distinguished under a high power microscope. Hardness, strength and impact toughness are higher than pearlite
10 troostite Also known as fine pearlite, a mixture of ferrite and cementite decomposed from austenite below the pearlite formation temperature. Its layer is thinner than sorbite. Its hardness and strength are higher than sorbite
11 Bainite Bainite is a mixture of supersaturated ferrite and cementite. Bainite is divided into upper bainite and lower bainite. The upper bainite formed at a higher temperature is feather-like; the lower bainite formed at a lower temperature is needle-like or bamboo-leaf. Lower bainite is higher in hardness and strength than upper bainite, and maintains a certain degree of toughness and plasticity
12 Martensite Martensite usually refers to a supersaturated solid solution of carbon in a-Fe. The hardness of martensite in steel increases with the increase of carbon content. High-carbon martensite has high hardness and brittleness, while low-carbon martensite has higher toughness. Martensite has the highest hardness in austenite transformation products
13 Laymanite is a eutectic structure in carbon alloys. It consists of austenite and cementite at high temperatures and consists of pearlite and cementite at low temperatures (below 727°C). The carbon content is 4.3%, the organization contains a lot of cementite, so high hardness, low plasticity, toughness
14 Fractography Inspection Fracture organization is one of the quality indicators of steel. After the specimen is grooved or broken, the fracture condition is checked with the naked eye or lO-magnifier. This is called the fracture test. Metal defects can be seen from the fracture
15 Tower-Turning Hairline Inspection Steel car into a predetermined tower-shaped or ladder-shaped sample, and then use acid etching or magnetic powder test hairline, referred to as tower test Note: Carbon content refers to the mass fraction.
2. General heat treatment of iron and steel materials General heat treatment name for steel materials Heat treatment process Heat treatment purpose
1. Annealing Steel will be heated to a certain temperature, heat for a certain period of time, and then slowly cooled to room temperature 1 Reduce the hardness of the steel, improve the plasticity, in order to facilitate cutting and cold deformation processing 2 refine the grain, uniform steel structure, improve the steel The performance and preparation for the subsequent heat treatment 3 eliminate the internal stress in the steel. Prevent deformation and cracking of parts after processing Annealing Category (1) Fully annealed to heat steel to critical temperature (different steel critical temperature is also different, usually 710-750 °C, individual alloy steel critical temperature up to 800-900oC) above 30 -50oC, incubate for a certain period of time, then cool slowly with the furnace (or immersed in the sand to cool) Refine grains, uniform organization, reduce hardness, fully eliminate internal stress Complete annealing applies to carbon content (mass fraction) below 0.8% Forging or steel castings
(2) Spheroidizing annealing The steel is heated to a temperature above the critical temperature of 20 to 30oC. After heat preservation, it is slowly cooled to below 500oC. Then the air cooling of the furnace reduces the hardness of the steel, improves the cutting performance, and prepares for the subsequent quenching to reduce After deformation and cracking after quenching, spheroidizing annealing is applicable to carbon steel and alloy tool steel with carbon content (mass fraction) of more than 0.8%
(3) Stress-relief annealing: The steel is heated to 500-650oC for a certain period of time, then slowly cooled (usually with furnace cooling) to eliminate the internal stress generated when the steel welding and cooling is straightened, and to eliminate the production of precision parts. The internal stress is applied to various castings, forgings, weldments, cold extrusions, etc. to prevent future processing and deformation during the process.
2. Normalizing steel to a temperature above the critical temperature of 40 ~ 60oC, heat for a certain period of time, and then cooled in the air 1 to improve the organizational structure and cutting performance 2 parts of the mechanical properties are not high, common normalizing as the final heat treatment 3 Eliminate internal stress
3. Quench the steel to the quenching temperature, hold for a period of time, and then rapidly cool in water, brine or oil (individual material in the air) 1 to obtain high hardness and wear resistance of the steel 2 steel in the After tempering get some special properties, such as higher strength, elasticity and toughness quenching category (1) single-liquid quenching steel will be heated to the quenching temperature, after insulation, in a quenching agent cooling single-liquid quenching only Applicable to carbon steel and alloy steel parts with relatively simple shapes and low technical requirements. When quenching, for steel pieces with a diameter or thickness greater than 5 to 8 mm, brine or water is used for cooling; alloy steel is selected for oil cooling
(2) Double-liquid quenching After the steel is heated to the quenching temperature, it is cooled in the water to 300-400oC after it is kept warm, and then it is cooled in the oil.
(3) Flame surface quenching Flames mixed with acetylene and oxygen are sprayed on the surface of the part to quickly heat the part to the quenching temperature, and then immediately sprayed on the part surface with water. The flame surface quenching is suitable for single or small batch production and the surface is hard. Heavy-duty medium and medium-carbon steel parts such as crankshafts, gears, and guide rails that are resistant to wear and can withstand impact loads
(4) Induction hardening on the surface The steel part is placed in the inductor. The inductor generates a magnetic field under the action of the alternating current of a certain frequency. The steel part generates the induced current under the action of the magnetic field, so that the surface of the steel part is rapidly heated (2-10 min). Quenching temperature, when the water is immediately sprayed to the surface of the steel.
Surface-hardened parts have a hard and wear-resistant surface, while the heart maintains good strength and toughness.
Surface induction hardening for medium carbon steel and medium carbon steel alloy steel parts
4. Tempering Heat the quenched steel below the critical temperature, hold for a certain period of time, and then cool in the air or oil. Tempering is carried out immediately after quenching. It is also the last step of the heat treatment to obtain the required mechanical properties. . Under normal circumstances, the strength and hardness of the parts after quenching are greatly improved, but the plasticity and toughness are significantly reduced, and the actual working conditions of the parts require good strength and toughness. After selecting the appropriate tempering temperature for tempering, the desired mechanical properties can be obtained 2 Stable structure, stable size 3 Elimination of internal stress
(1) Low temperature tempering Hardened steel parts are heated to 150-50oC, and held at this temperature for a certain period of time, then cooled in the air. Low temperature tempering is used for cutting tools, measuring tools, molds, rolling bearings, carburizing parts, etc. Elimination of internal stress caused by quenching of steel Category (1) Medium temperature tempering Quenched steel parts are heated to 350-450%, cooled for a certain period of time after being kept warm, generally used for various types of springs and hot stamping parts to make steel parts Obtain higher elasticity, certain toughness and hardness
(1) High temperature tempering After quenching, the steel part is heated to 500-650oC and cooled after heat preservation. It is mainly used for important structural parts requiring high strength and high toughness, such as spindle, crankshaft, cam, gear, and connecting rod. The steel has better comprehensive mechanical properties, namely higher strength and toughness and sufficient hardness, eliminating the internal stress of the steel due to quenching
5. Quenching and tempering Quenched steel parts are subjected to high temperature (500-600oC) tempering. They are mostly used for important structural parts, such as shafts, gears, connecting rods, etc. The quenching and tempering is generally performed after the rough machining, To make the steel higher toughness and sufficient strength, so that it has good comprehensive mechanical properties
6. Aging treatment
(1) Artificial aging Heat-quenched steel parts are heated to 100-160°C for a long period of time, followed by cooling to eliminate internal stresses, reduce part deformation, stabilize dimensions, and are more important for parts with higher precision requirements.
(2) Natural aging Put castings on the open air; steel parts (such as long shafts, lead screws, etc.) are placed in seawater or suspended for a long time or lightly beat parts that are to be subjected to natural aging. It is best to perform rough machining first.
7. Chemical heat treatment The steel is placed in a chemical medium containing certain active atoms (such as carbon, nitrogen, chromium, etc.), and some of the atoms in the medium penetrate into the surface of steel by heating, heat preservation, and cooling. , in order to change the chemical composition of the steel surface, so that the steel surface has a special performance
Chemical heat treatment
(1) Carbon infiltrated carbon Infiltrates carbon atoms into the surface of steel parts and is often used for wear-resistant and impact-resistant parts, such as wheels, gears, shafts, piston pins, etc., to make the surface have high hardness (HRC60-65) and wear resistance. , while the center still maintains high resilience
(2) Nitrogen infiltrated by steel Infiltrating nitrogen atoms into the surface of steel parts is often used for important bolts, nuts, pins, etc. to improve the hardness and wear resistance of the steel surface.
Corrosion resistance category (3) Cyanidation of steel The simultaneous penetration of carbon and nitrogen atoms into the surface of steel parts is suitable for low-carbon steel, medium-carbon steel or alloy steel parts. It can also be used for high-speed steel tools to increase the hardness of the steel surface and Wear resistance
8. Blackening The metal parts are placed in a very concentrated solution of alkali and oxidant to heat and oxidize, so that the surface of the metal parts generates a layer of magnetic Fe3O4 thin film commonly used in low carbon steel, low carbon alloy tool steel due to the material and Influence of other factors, the film thickness of the black layer is blue black, black, reddish brown, tan, etc., its thickness is 0.6 ~ 0.8μm rust, increase the appearance and gloss of the metal surface, eliminate the stress during the quenching process
Phase and phase boundaries In metals or alloys, homogeneous components that have the same composition, the same structure, and separate interfaces are called phases. The interface between phase and phase, called the phase boundary
3 Solid solution The solid phase formed by the atom of another element dissolved in the crystal of a metal element constituting the alloy is called a solid solution. Solid solution generally has higher strength, good plasticity, corrosion resistance, and higher resistance and magnetic properties
4 Metal Compounds Solid phases formed by the interaction of different elements in the alloy, whose lattice types and properties are completely different from their constituent elements and have metallic properties, are called metal compounds.
5 Austenite Austenite is a solid solution in which carbon and other elements are dissolved in y-Fe. Austenitic has face-centered cubic crystals, good plasticity, generally exists at high temperatures
6 Iron Wire Ferrite is a solid solution of carbon and other elements dissolved in a-Fe. Ferrite has a body-centered cubic lattice with a very low carbon content. Its properties are very similar to that of pure iron, also called pure iron.
7 Cementite Cementite is a compound of iron and carbon, also known as tri-carbonate (Noc), which has a carbon content of 6.69% and has a complex character structure. Its performance is hard and brittle, almost no plasticity
8 Pearlite Pearlite is a lamellar structure between iron wire and cementite. It is named for its fingerprint-like pearl luster. Its properties lie between ferrite and cementite, moderate strength, hardness, and good plasticity and toughness
9 Sorbite, also known as fine pearlite, is a mixture of ferrite and cementite that austenite decomposes below the pearlite formation temperature. The layer is thinner than the pearlite and can only be distinguished under a high power microscope. Hardness, strength and impact toughness are higher than pearlite
10 troostite Also known as fine pearlite, a mixture of ferrite and cementite decomposed from austenite below the pearlite formation temperature. Its layer is thinner than sorbite. Its hardness and strength are higher than sorbite
11 Bainite Bainite is a mixture of supersaturated ferrite and cementite. Bainite is divided into upper bainite and lower bainite. The upper bainite formed at a higher temperature is feather-like; the lower bainite formed at a lower temperature is needle-like or bamboo-leaf. Lower bainite is higher in hardness and strength than upper bainite, and maintains a certain degree of toughness and plasticity
12 Martensite Martensite usually refers to a supersaturated solid solution of carbon in a-Fe. The hardness of martensite in steel increases with the increase of carbon content. High-carbon martensite has high hardness and brittleness, while low-carbon martensite has higher toughness. Martensite has the highest hardness in austenite transformation products
13 Laymanite is a eutectic structure in carbon alloys. It consists of austenite and cementite at high temperatures and consists of pearlite and cementite at low temperatures (below 727°C). The carbon content is 4.3%, the organization contains a lot of cementite, so high hardness, low plasticity, toughness
14 Fractography Inspection Fracture organization is one of the quality indicators of steel. After the specimen is grooved or broken, the fracture condition is checked with the naked eye or lO-magnifier. This is called the fracture test. Metal defects can be seen from the fracture
15 Tower-Turning Hairline Inspection Steel car into a predetermined tower-shaped or ladder-shaped sample, and then use acid etching or magnetic powder test hairline, referred to as tower test Note: Carbon content refers to the mass fraction.
2. General heat treatment of iron and steel materials General heat treatment name for steel materials Heat treatment process Heat treatment purpose
1. Annealing Steel will be heated to a certain temperature, heat for a certain period of time, and then slowly cooled to room temperature 1 Reduce the hardness of the steel, improve the plasticity, in order to facilitate cutting and cold deformation processing 2 refine the grain, uniform steel structure, improve the steel The performance and preparation for the subsequent heat treatment 3 eliminate the internal stress in the steel. Prevent deformation and cracking of parts after processing Annealing Category (1) Fully annealed to heat steel to critical temperature (different steel critical temperature is also different, usually 710-750 °C, individual alloy steel critical temperature up to 800-900oC) above 30 -50oC, incubate for a certain period of time, then cool slowly with the furnace (or immersed in the sand to cool) Refine grains, uniform organization, reduce hardness, fully eliminate internal stress Complete annealing applies to carbon content (mass fraction) below 0.8% Forging or steel castings
(2) Spheroidizing annealing The steel is heated to a temperature above the critical temperature of 20 to 30oC. After heat preservation, it is slowly cooled to below 500oC. Then the air cooling of the furnace reduces the hardness of the steel, improves the cutting performance, and prepares for the subsequent quenching to reduce After deformation and cracking after quenching, spheroidizing annealing is applicable to carbon steel and alloy tool steel with carbon content (mass fraction) of more than 0.8%
(3) Stress-relief annealing: The steel is heated to 500-650oC for a certain period of time, then slowly cooled (usually with furnace cooling) to eliminate the internal stress generated when the steel welding and cooling is straightened, and to eliminate the production of precision parts. The internal stress is applied to various castings, forgings, weldments, cold extrusions, etc. to prevent future processing and deformation during the process.
2. Normalizing steel to a temperature above the critical temperature of 40 ~ 60oC, heat for a certain period of time, and then cooled in the air 1 to improve the organizational structure and cutting performance 2 parts of the mechanical properties are not high, common normalizing as the final heat treatment 3 Eliminate internal stress
3. Quench the steel to the quenching temperature, hold for a period of time, and then rapidly cool in water, brine or oil (individual material in the air) 1 to obtain high hardness and wear resistance of the steel 2 steel in the After tempering get some special properties, such as higher strength, elasticity and toughness quenching category (1) single-liquid quenching steel will be heated to the quenching temperature, after insulation, in a quenching agent cooling single-liquid quenching only Applicable to carbon steel and alloy steel parts with relatively simple shapes and low technical requirements. When quenching, for steel pieces with a diameter or thickness greater than 5 to 8 mm, brine or water is used for cooling; alloy steel is selected for oil cooling
(2) Double-liquid quenching After the steel is heated to the quenching temperature, it is cooled in the water to 300-400oC after it is kept warm, and then it is cooled in the oil.
(3) Flame surface quenching Flames mixed with acetylene and oxygen are sprayed on the surface of the part to quickly heat the part to the quenching temperature, and then immediately sprayed on the part surface with water. The flame surface quenching is suitable for single or small batch production and the surface is hard. Heavy-duty medium and medium-carbon steel parts such as crankshafts, gears, and guide rails that are resistant to wear and can withstand impact loads
(4) Induction hardening on the surface The steel part is placed in the inductor. The inductor generates a magnetic field under the action of the alternating current of a certain frequency. The steel part generates the induced current under the action of the magnetic field, so that the surface of the steel part is rapidly heated (2-10 min). Quenching temperature, when the water is immediately sprayed to the surface of the steel.
Surface-hardened parts have a hard and wear-resistant surface, while the heart maintains good strength and toughness.
Surface induction hardening for medium carbon steel and medium carbon steel alloy steel parts
4. Tempering Heat the quenched steel below the critical temperature, hold for a certain period of time, and then cool in the air or oil. Tempering is carried out immediately after quenching. It is also the last step of the heat treatment to obtain the required mechanical properties. . Under normal circumstances, the strength and hardness of the parts after quenching are greatly improved, but the plasticity and toughness are significantly reduced, and the actual working conditions of the parts require good strength and toughness. After selecting the appropriate tempering temperature for tempering, the desired mechanical properties can be obtained 2 Stable structure, stable size 3 Elimination of internal stress
(1) Low temperature tempering Hardened steel parts are heated to 150-50oC, and held at this temperature for a certain period of time, then cooled in the air. Low temperature tempering is used for cutting tools, measuring tools, molds, rolling bearings, carburizing parts, etc. Elimination of internal stress caused by quenching of steel Category (1) Medium temperature tempering Quenched steel parts are heated to 350-450%, cooled for a certain period of time after being kept warm, generally used for various types of springs and hot stamping parts to make steel parts Obtain higher elasticity, certain toughness and hardness
(1) High temperature tempering After quenching, the steel part is heated to 500-650oC and cooled after heat preservation. It is mainly used for important structural parts requiring high strength and high toughness, such as spindle, crankshaft, cam, gear, and connecting rod. The steel has better comprehensive mechanical properties, namely higher strength and toughness and sufficient hardness, eliminating the internal stress of the steel due to quenching
5. Quenching and tempering Quenched steel parts are subjected to high temperature (500-600oC) tempering. They are mostly used for important structural parts, such as shafts, gears, connecting rods, etc. The quenching and tempering is generally performed after the rough machining, To make the steel higher toughness and sufficient strength, so that it has good comprehensive mechanical properties
6. Aging treatment
(1) Artificial aging Heat-quenched steel parts are heated to 100-160°C for a long period of time, followed by cooling to eliminate internal stresses, reduce part deformation, stabilize dimensions, and are more important for parts with higher precision requirements.
(2) Natural aging Put castings on the open air; steel parts (such as long shafts, lead screws, etc.) are placed in seawater or suspended for a long time or lightly beat parts that are to be subjected to natural aging. It is best to perform rough machining first.
7. Chemical heat treatment The steel is placed in a chemical medium containing certain active atoms (such as carbon, nitrogen, chromium, etc.), and some of the atoms in the medium penetrate into the surface of steel by heating, heat preservation, and cooling. , in order to change the chemical composition of the steel surface, so that the steel surface has a special performance
Chemical heat treatment
(1) Carbon infiltrated carbon Infiltrates carbon atoms into the surface of steel parts and is often used for wear-resistant and impact-resistant parts, such as wheels, gears, shafts, piston pins, etc., to make the surface have high hardness (HRC60-65) and wear resistance. , while the center still maintains high resilience
(2) Nitrogen infiltrated by steel Infiltrating nitrogen atoms into the surface of steel parts is often used for important bolts, nuts, pins, etc. to improve the hardness and wear resistance of the steel surface.
Corrosion resistance category (3) Cyanidation of steel The simultaneous penetration of carbon and nitrogen atoms into the surface of steel parts is suitable for low-carbon steel, medium-carbon steel or alloy steel parts. It can also be used for high-speed steel tools to increase the hardness of the steel surface and Wear resistance
8. Blackening The metal parts are placed in a very concentrated solution of alkali and oxidant to heat and oxidize, so that the surface of the metal parts generates a layer of magnetic Fe3O4 thin film commonly used in low carbon steel, low carbon alloy tool steel due to the material and Influence of other factors, the film thickness of the black layer is blue black, black, reddish brown, tan, etc., its thickness is 0.6 ~ 0.8μm rust, increase the appearance and gloss of the metal surface, eliminate the stress during the quenching process
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