Heat Treatment
All
Experiment Ways
Nickel Based Alloy
Steelmaking
Metal Forming
Heat Treatment
Metal Cutting
Surface Treatment
Company Policy
Another Downstream Industry Technology
Carbon Steel
Stainless Steel
Alloy Steel
Springs Industry
Cutting Tool Industry
Tool Steel
High Speed Steel
Drill Tool Industry
Oil and Gas
Boiler Industry
Bearing Industry
Auto Parts Industry
Fasteners Industry

Heat Treatment

Heat treatment of steel - general definitions and terms

Heat treatment of steel - general definitions and terms Without heat treatmentRolled, forged or cast steel without heat treatment Controlled coolingCooling from an elevated temperature (after hot plastic deformation) in a  predetermined way. Tnis process produces a definite microstructure and mechanical properties and it prevents strain hardening, cracking and internal damages Soft annealingAnnealing at the temperature range A1 or oscillating around A1 foolowed by slow cooling. The purpose is to obtain the struture of spheroidized  perlite and to reduce hardness for further machining or cold forming. This ensures the most suitable structure for further heat treatment. Soft annealing with recrystallizationHeating just above A3 and rapid cooling to lower perlite or upper bainite range with spheroidizing just below Ac1. The process diminishes austenite grains and leads to a 100% spheroidizing of perlite which is most suitable for further heat treatment. Grain coarseningThis is used especially for low-carbon steels which are machined after heat treatment. The temperature range of this annealing is 100-200°C above Ac3. Cooled to ferritic-perlitic range. The purpose is to produce large ferritic-perlitic grains with lamellar perlite improving machinability of heat-treatable steel. Annealing to a definite strenghtHeating to 800-950°C, adequate cooling, then tempering at 500-650°C. The purpose is to produce heat-treatable steel and case-hardening steel of a definite strength. Annealing to ferritic-perlitic structureAfter austenitizing, steel is cooled down to temperature of perlite transformation and is then held isothermally. Cooling rate depends on hardness requirement. The purpose of this annealing is to produce a ferrite-perlite structure of case-hardening steel. Stress-relief annealingAnnealing at a suitable temperature followed by a very slow cooling (to reduce and prevent internal stresses). Steel should be stress-relived at least 25°C below the tempering temperature. This annealing reduces internal stresses induced by rolling, forging, casting, cold forming, irregular cooling, welding, machining. HomogenizingAnnealing at high temperatures just below solidus (1000-1300°C), depending on steel grade. This process diminishes inhomogeneity in steel and equlizes local diffrences in concentrations of chemical elements in crystal segregation. DehydrogenationA long anneal cycle of steel containing hydrogen which is therefore subjected to form "flakes" or temperature oscillating above A1, followed by slow cooling down to room temperature. The purpose is to reduce hydrogen content and to avoid the danger of "flakes". RecrystallizationAnnealing after cold work to renew the ability of steel for cold work. Recrystallization temperature is above 600°C. The purpose is to obtain polygonal grains suitable for further cold plastic deformation. NormalizingHeating the hypoeutectoid steel just above Ac3 and hypereutectoid steel above Ac1 followed by air cooling. The purpose is to obtain a small anduniform perlitic structure throughout the whole piece (after rolling, forging and casting) improving mechanical properties. In casting, it eliminates a rough cast structure. Structure is conditioned for further heat treatment. Quench hardeningHeat treatment comprised of austenitzing followed by cooling in air, oil, water or some other medium that allows the transformation of austenite to martensite or bainite with the highest possible hardness. Austempering/MartemperingAustempering-Steel cooling from austenitizing temperature to the bainte transformation temperature where it is held until a suitable isothermal transformation into bainite is implemented, followed by cooling down to the ordinary temperature. Martempering-Heat treatment comprised of austenitizing followed by step quenching at a rate fast enough to avoid the formation of ferrite, perlite or bainite, to a temperature slightly above Ms and soaking for long enough to ensure that the temperature is uniform but short enough to avoid the formation of bainite. Case hardening, surface hardeningQuench hardening treatment after surface heating. According to the type of heating, we destnguish between flame hardening and induction hardening. The purpose is to achieve and abrasive resistant surface and to retain the tough core part. Step quenchingQuenching during which the process of cooling is temporarly interrupted by soaking in a medium at a suitable temerature. The purpose is to reduce the danger of deformation and cracking in quenching process. Hardening after case hardeningBlank hardeningHerdening of uncarburized case-hardening steels to determine mechanical properties of ucarburized regions of parts. Direct quenchingHardening of a carburized part directly after carburization (or after cooling) from the temperature suitable for a carburized layer. Single quenchingSingle hardening of case or core after carburizing Double quenchingDouble hardening of carburized steels. The first hardening from the austenitizing temperature of core, the second one from the temperature which is suitable for case hardening. The purpose is to obtain an abrasive resistant case. TemperingIt consists of heating to specific temperatures below Ac1 for one or more times and holding at these temperatures. Followed by appropriate cooling rate. It should be temperd immediately after quenching. The purpose is to transform a hardend structure, to improve mechanical properties and to reduce internal stresses. Quenching and temperingQuench hardening followed by tempering at high temperature with aim of obtaining the desired mechanical properties and, in particular, good ductility. QuenchingHeating to a definite temperature depending on steel composition without changing its ferritic or austentic structure, holding at that temperature and rapid cooling. The result is a homogeneous structure (dissolved carbides), maximum toughness and an improved corrosion resistance. Precipitation hardeningHeating to a definite temperature (determined by the cemical composition of steel), holding at thet temperature for several hours and cooling. The aim is to reach the  percipitation of special phases to obtain higher hardnes. Thermomechanical treatmentCombination of hot plastic deformation of heat treatment. The purpose is to obtain special mechanical properties. Change in resistance to deformation and cracks. AgingAge hardening-Hardening at room temperature after rapid cooling or cold working. Artificial hardening-Aging above room temperature. The purpose is to stabilaze structure stresses and dimension.

How does heat-treatment the steel affects properties?

How does heat-treatment the steel affects properties? Heat can affect the electrical, magnetic, and structural properties of steels. Since steel has a wide range of uses, various conditions emphasize different attributes. Toughness is required in industrial applications, whereas low electrical density is significant in electronic applications.There are many methods of heating steel that are widely used to change these properties. To obtain the desired result, the temperature at which the steel is heated and the rate at which it cools is closely regulated. The following are the most critical ways that steels are converted by heat:MagnetismElectrical ResistanceThermal ExpansionMagnetismIron, nickel, and cobalt are the three steels that have magnetic properties. It is referred to as ferromagnetic steel. Heating these steels reduces their magnetism to the point that magnetism is no longer there. The Curie temperature is the temperature at which this happens. This temperature is 626 ° Fahrenheit for nickel, 2,012 degrees Fahrenheit for cobalt, and 1,418 ° Fahrenheit for iron. Electrical ResistanceThe electrical resistance of a steel is an indicator of how deeply it obstructs the flow of electrical current. Electrons scatter when they collide with the steellic structure as they flow through the steel. Electrons consume more energy and travel faster while the steel is heated. This causes further scattering, which raises the sum of the resistance. Thermometers typically calculate temperature by measuring the difference of electrical resistance in a piece of wire. Thermal ExpansionWhen heated, steel expands. Temperature causes an increase in length, surface area, and thickness. Thermal expansion is the technical name for this. The degree of thermal expansion varies depending on the steel. Thermal expansion happens as a result of heat increasing the motions of the steel’s atoms. When building steellic structures, it is critical to account for thermal expansion. A simple example is the construction of household pipes, which must allow for expansion and contraction as the seasons shift. Heat Treatment on steelsHeat treatment is a method of altering the characteristics of steel in order to make it more suitable for its desired applications. The following are the most common methods of heat treatment:AnnealingNormalisingHardeningTemperingAnnealingMaterials such as iron, steel, copper, brass, and silver are commonly softened by annealing. The procedure entails heating the material to a certain degree and then allow to cool slowly and steadily. Annealing changes the steel’s physical and chemical characteristics to make it more ductile and less rigid. This makes for easier carving, stamping, and formation methods, as well as easier cutting of the steel. Electrical conductivity is also improved by annealing. NormalizingNormalizing also known as normalization is a process used to achieve uniformity of grain size and composition in alloys. The steel is heated to a certain degree before being cool by air. The resulting steel is free of impurities and has increased strength and hardness. Normalizing is often used to manufacture harder and tougher steel, but it is less ductile than annealing. Since the procedure improves this attribute, the normalizing process is typically done on products that may be exposed to machining. HardeningSteel and other alloys are hardened to enhance their mechanical property. During hardening, the steel is heated to a high temperature and kept there until a proportion of the carbon has been melted. The steel is then put out, which means it is quickly cooled in oil or water. Hardening results in an alloy with high strength and wear-resistant. Hardening, on the other hand, makes it more brittle and is thus unsuitable for industrial application. Surface hardening is used where the surface of a part has to be hard enough to prevent wear and degradation while preserving ductility and resilience to withstand impact and shock loading. TemperingTempering is used to increase the ductility of steel. Untempered steel is very strong, but it is too porous for the majority of practical applications. Tempering is a low-temperature heat treatment technique used to achieve a desired hardness/toughness ratio after hardening (neutral hardening, double hardening, ambient carburizing, carbonitriding, or induction hardening). To reduce some of the excess hardness, steel is heated to a lower temperature. After that, the steel is able to cool in still air, resulting in a harder and less brittle material.

Difference between Annealing and Tempering

Difference between Annealing and Tempering The difference between annealing and tempering is determined by how it is treated. Tempering the steel entails heating it to a certain heat below a certain threshold and then cooling it at a very slow and regulated rate, while annealing involves heating the steel to a given temperature and then cooling it at a very slow and controlled rate, and is often performed in air, vacuum, or inert atmospheres. What is Heat Treatment on steels?Heat treatments are used to modify the Mechanical-Property, Physical-Property of the steel steels without altering their appearance. They are critical processes in steel production that improve the favorable properties of steel while allowing for more processing.The heat and temperature of steel are closely regulated in various heat treatment processes. For instance, steel is a steel that mostly goes under heat treatment for various commercial uses.Common objectives of heat treatment are to:Increase strengthImprove elasticityImprove machiningIncrease hardnessImprove formabilityIncrease ductilityImprove toughnessThe cooling stage has varying results depending on the steel and phase. Steel hardens as it is easily cooled, while aluminum softens during the fast cooling stage of solution annealing. There are various methods through which steels are given heat treatment, but Annealing and Tempering are commonly used methods. What Is Annealing?Annealing is the process in which the steel is heated at a certain degree and then cooled slowly at a regulated pace.Annealing is sometimes used to: Prepare steel for cold working by softening it.Increase electrical conductivity.Increase machinabilityFor restoring the steel ductility annealing is done. Cold welding hardens the steel in such a way that, excessive work on it, which may break or crack the steel. Since annealing releases mechanical stresses created during machining or grinding, cold working may take place without the risk of cracking. Annealing is mostly used for steel, but some steels such as copper, aluminum, and brass may be solution annealed. For the annealing process of steel, huge ovens or heaters are used. There must be enough space in the ovens so that it allows proper air to flow through the steel. Gas fire conveyor-furnace are utilized for huge steels parts, and Cars bottoms furnace is used for the small parts of steels. The steel is heated to a certain temperature during the annealing process, where recrystallization can occur. Any imperfection found due to distortion is fixed at this level. The steel is been allowed to set to a certain degree and been cooled at room temperatures. To achieve a refined microstructure and thus maximize softness, the cooling process must be carried out very slowly. This is often accomplished by immersing the hot steel in sand, ashes, or other low heat conductivity materials, or by turning off the oven and allowing the steel to cool with the furnace. What is tempering?Tempering is a technique applicable to improve the hardness of alloys having alloys, especially steel. While steel which is not tempered is extremely stiff, it is too fragile for most applications. Tempering is widely used to reduce excess stiffness after hardening.Tempering is used to modify: FortitudeThe degree of difficultyStability of the structureDuctility is a term that refers to the ability to tenacity. Tempering is the process of heating a steel to a specific temperature less than the critical points, which is mostly found in air, vacuum, or inert atmospheres. The temperature is changed based on how much hardness has to be minimized. Although it varies depending on the steel, in general, low temperatures decrease brittleness while retaining the majority of the hardness, while higher temperatures reduce hardness, increasing elasticity and plasticity while causing some yield and tensile strength to be lost. It is necessary to keep on heating steadily which does not crack steel or other steels. The steel is held to a certain degree for a fixed time. The interior pressure within the steels is been relaxed at the time. Then the steel soon cools in the air or in room temperature.

WHAT IS TEMPERING?

WHAT IS TEMPERING?Tempering is a heat treatment process that alters the mechanical properties (typically ductility and hardness) and relieves internal stresses of a steel. Tempering allows carbon trapped in a martensitic microstructure to disperse, and enables the internal stresses to be released from the steel that may have been created from prior operations. The Tempering ProcessTempering is performed by elevating the steel to a set point below its lower critical temperature, typically following a hardening operation. Once this temperature is reached, it is held there for a specified amount of time. The exact temperature and time depend on several factors such as the type of steel and desired mechanical properties. To get the steel to its critical temperature, some type of heating device must be used. Common devices include gas furnaces, electrical resistance furnaces, or induction furnaces. Often, this heating is done in a vacuum or with an inert gas to protect the steel from oxidation. Once the furnace achieves the desired temperature, a dwell time occurs. Following the dwell time, the furnace is shut off and the steel is allowed to cool at predetermined rate. Why Is Steel Tempered?Tempering steel after a hardening process allows for a middle ground of hardness and strength. This is achieved by allowing the carbon diffusion to occur within a steel microstructure. When steel is hardened, it can become excessively brittle and hard. However, when not hardened, the steel may not have the strength or abrasion resistance needed for its intended application. Tempering also improves the machinability and formability of a hardened steel, and can reduce the risk of the steel cracking or failing due to internal stresses. When Is Tempering Used?Tempering is most commonly used following a quenching operation. Heating a carbon steel and rapidly quenching it can leave it too hard and brittle. Tempering it can restore some of its ductility.Tempering can reduce the hardness and relieve the stress of a welded component. Welds can create a localized zone that has been hardened due to the heat of the welding process. This can leave undesirable mechanical properties and residual stress that can promote hydrogen cracking. Tempering helps prevent this.Work hardened materials often require tempering. Materials can become work hardened through processes such as punching, bending, forming, drilling, or rolling. Work hardened materials have a high amount of residual stresses that can be alleviated through a tempering process.

WHAT IS NORMALIZING?

WHAT IS NORMALIZING?It is important that the material used for any project possesses the correct mechanical properties for the specific application. Heat Treatment processes are often used to alter the mechanical properties of a metal, with one of the more common heat treatment processes being Normalizing. What Is Normalizing?Normalizing is a heat treatment process that is used to make a metal more ductile and tough after it has been subjected to thermal or mechanical hardening processes. Normalizing involves heating a material to an elevated temperature and then allowing it to cool back to room temperature by exposing it to room temperature air after it is heated. This heating and slow cooling alters the microstructure of the metal which in turn reduces its hardness and increases its ductility. Why Is Normalizing Used?Normalizing is often performed because another process has intentionally or unintentionally decreased ductility and increased hardness. Normalizing is used because it causes microstructures to reform into more ductile structures. This is important because it makes the metal more formable, more machinable, and reduces residual stresses in the material that could lead to unexpected failure. What Is The Difference Between Annealing and Normalizing?Normalizing is very similar to annealing as both involve heating a metal to or above its recrystallization temperature and allowing it to cool slowly in order to create a microstructure that is relatively ductile. The main difference between annealing and normalizing is that annealing allows the material to cool at a controlled rate in a furnace. Normalizing allows the material to cool by placing it in a room temperature environment and exposing it to the air in that environment. This difference means normalizing has a faster cooler rate than annealing. The faster cooler rate can cause a material to have slightly less ductility and slightly higher hardness value than if the material had been annealed. Normalizing is also generally less expensive than annealing because it does not require additional furnace time during the cool down process. The Normalizing ProcessThere are three main stages to a normalizing process. Recovery stageRecrystallization stageGrain growth stageRecovery Stage During the recovery stage, a furnace or other type of heating device is used to raise the material to a temperature where its internal stresses are relieved. Recrystallization Stage During the recrystallization stage, the material is heated above its recrystallization temperature, but below its melting temperature. This causes new grains without preexisting stresses to form. Grain Growth Stage During the grain growth, the new grains fully develop. This growth is controlled by allowing the material to cool to room temperature via contact with air. The result of completing these three stages is a material with more ductility and reduced hardness. Subsequent operations that can further alter mechanical properties are sometimes carried out after the normalizing process. What Metals Can Be Normalized?To be normalized, a metal needs to be receptive to normalizing, meaning its microstructure can be altered by heat treatment. Many types of alloys can be normalized, including: Iron based alloys (tool steel, carbon steel, stainless steel, and cast iron)Nickel-based alloysCopperBrassAluminumCommon Applications for NormalizingNormalizing is used in many different industries for many different materials. Examples include: Ferritic stainless steel stampings in the automotive industry may be normalized following the work hardening that occurs during their forming process.Nickel-based alloys in the nuclear industry may be normalized following the thermal microstructure alteration that occurs following welding.Carbon steel may be normalized after it is cold-rolled to reduce the brittleness caused by work hardening.

WHAT IS ANNEALING?

WHAT IS ANNEALING?While the chemical composition of a metal determines much of the mechanical properties, many metals can have their mechanical properties altered through heat treatment. There are many different types of heat treatment used today, and one of the most popular methods is annealing. What Is Annealing?Annealing is a heat treatment process used mostly to increase the ductility and reduce the hardness of a material. This change in hardness and ductility is a result of the reduction of dislocations in the crystal structure of the material being annealed. Annealing is often performed after a material has undergone a hardening or cold working process to prevent it from brittle failure or to make it more formable for subsequent operations. Why Is Metal Annealed?As mentioned above, annealing is used to reduce hardness and increase ductility. Changing these mechanical properties through annealing is significant for many reasons: Annealing improves the formability of a material. Hard, brittle materials can be difficult to bend or press without creating a material fracture. Annealing helps eliminate this risk.Annealing can also improve machinability. A material that is extremely brittle can cause excessive tool wear. Reducing the hardness of a material via annealing can reduce the wear on the tool being used.Annealing removes residual stresses. Residual stresses can create cracks and other mechanical complications, and it is often best to eliminate them whenever possible.What Metals Can Be Annealed?To perform an annealing process, a material that can be altered by heat treatment must be used. Examples include many types of steel and cast iron. Some types of aluminum, copper, brass and other materials may also respond to an annealing process. The Annealing ProcessThere are three main stages to an annealing process. Recovery stage.Recrystallization stageGrain growth stageRecovery StageDuring the recovery stage, a furnace or other type of heating device is used to raise the material to a temperature where its internal stresses are relieved. Recrystallization StageDuring the recrystallization stage, the material is heated above its recrystallization temperature, but below its melting temperature. This causes new grains without preexisting stresses to form. Grain Growth StageDuring the grain growth, the new grains fully develop. This growth is controlled by allowing the material to cool at a specified rate. The result of completing these three stages is a material with more ductility and reduced hardness. Subsequent operations that can further alter mechanical properties are sometimes carried out after the annealing process. When Are Annealed Metals Used?Common applications for annealed metals include: Work-hardened materials such as sheet metal that has undergone a stamping process or cold drawn bar stock.Metal wire that has been drawn from one size to a smaller size may also undergo an annealing process.Machining operations that create high amounts of heat or material displacement may also warrant an annealing process afterward.Welded components can create residual stresses in the area of the material exposed to elevated temperatures; to recreate uniform physical properties, annealing is often used.

Heat treatment of steel - general definitions and terms

Heat treatment of steel - general definitions and terms Without heat treatmentRolled, forged or cast steel without heat treatment Controlled coolingCooling from an elevated temperature (after hot plastic deformation) in a  predetermined way. Tnis process produces a definite microstructure and mechanical properties and it prevents strain hardening, cracking and internal damages Soft annealingAnnealing at the temperature range A1 or oscillating around A1 foolowed by slow cooling. The purpose is to obtain the struture of spheroidized  perlite and to reduce hardness for further machining or cold forming. This ensures the most suitable structure for further heat treatment. Soft annealing with recrystallizationHeating just above A3 and rapid cooling to lower perlite or upper bainite range with spheroidizing just below Ac1. The process diminishes austenite grains and leads to a 100% spheroidizing of perlite which is most suitable for further heat treatment. Grain coarseningThis is used especially for low-carbon steels which are machined after heat treatment. The temperature range of this annealing is 100-200°C above Ac3. Cooled to ferritic-perlitic range. The purpose is to produce large ferritic-perlitic grains with lamellar perlite improving machinability of heat-treatable steel. Annealing to a definite strenghtHeating to 800-950°C, adequate cooling, then tempering at 500-650°C. The purpose is to produce heat-treatable steel and case-hardening steel of a definite strength. Annealing to ferritic-perlitic structureAfter austenitizing, steel is cooled down to temperature of perlite transformation and is then held isothermally. Cooling rate depends on hardness requirement. The purpose of this annealing is to produce a ferrite-perlite structure of case-hardening steel. Stress-relief annealingAnnealing at a suitable temperature followed by a very slow cooling (to reduce and prevent internal stresses). Steel should be stress-relived at least 25°C below the tempering temperature. This annealing reduces internal stresses induced by rolling, forging, casting, cold forming, irregular cooling, welding, machining. HomogenizingAnnealing at high temperatures just below solidus (1000-1300°C), depending on steel grade. This process diminishes inhomogeneity in steel and equlizes local diffrences in concentrations of chemical elements in crystal segregation. DehydrogenationA long anneal cycle of steel containing hydrogen which is therefore subjected to form "flakes" or temperature oscillating above A1, followed by slow cooling down to room temperature. The purpose is to reduce hydrogen content and to avoid the danger of "flakes". RecrystallizationAnnealing after cold work to renew the ability of steel for cold work. Recrystallization temperature is above 600°C. The purpose is to obtain polygonal grains suitable for further cold plastic deformation. NormalizingHeating the hypoeutectoid steel just above Ac3 and hypereutectoid steel above Ac1 followed by air cooling. The purpose is to obtain a small anduniform perlitic structure throughout the whole piece (after rolling, forging and casting) improving mechanical properties. In casting, it eliminates a rough cast structure. Structure is conditioned for further heat treatment. Quench hardeningHeat treatment comprised of austenitzing followed by cooling in air, oil, water or some other medium that allows the transformation of austenite to martensite or bainite with the highest possible hardness. Austempering/MartemperingAustempering-Steel cooling from austenitizing temperature to the bainte transformation temperature where it is held until a suitable isothermal transformation into bainite is implemented, followed by cooling down to the ordinary temperature. Martempering-Heat treatment comprised of austenitizing followed by step quenching at a rate fast enough to avoid the formation of ferrite, perlite or bainite, to a temperature slightly above Ms and soaking for long enough to ensure that the temperature is uniform but short enough to avoid the formation of bainite. Case hardening, surface hardeningQuench hardening treatment after surface heating. According to the type of heating, we destnguish between flame hardening and induction hardening. The purpose is to achieve and abrasive resistant surface and to retain the tough core part. Step quenchingQuenching during which the process of cooling is temporarly interrupted by soaking in a medium at a suitable temerature. The purpose is to reduce the danger of deformation and cracking in quenching process. Hardening after case hardeningBlank hardeningHerdening of uncarburized case-hardening steels to determine mechanical properties of ucarburized regions of parts. Direct quenchingHardening of a carburized part directly after carburization (or after cooling) from the temperature suitable for a carburized layer. Single quenchingSingle hardening of case or core after carburizing Double quenchingDouble hardening of carburized steels. The first hardening from the austenitizing temperature of core, the second one from the temperature which is suitable for case hardening. The purpose is to obtain an abrasive resistant case. TemperingIt consists of heating to specific temperatures below Ac1 for one or more times and holding at these temperatures. Followed by appropriate cooling rate. It should be temperd immediately after quenching. The purpose is to transform a hardend structure, to improve mechanical properties and to reduce internal stresses. Quenching and temperingQuench hardening followed by tempering at high temperature with aim of obtaining the desired mechanical properties and, in particular, good ductility. QuenchingHeating to a definite temperature depending on steel composition without changing its ferritic or austentic structure, holding at that temperature and rapid cooling. The result is a homogeneous structure (dissolved carbides), maximum toughness and an improved corrosion resistance. Precipitation hardeningHeating to a definite temperature (determined by the cemical composition of steel), holding at thet temperature for several hours and cooling. The aim is to reach the  percipitation of special phases to obtain higher hardnes. Thermomechanical treatmentCombination of hot plastic deformation of heat treatment. The purpose is to obtain special mechanical properties. Change in resistance to deformation and cracks. AgingAge hardening-Hardening at room temperature after rapid cooling or cold working. Artificial hardening-Aging above room temperature. The purpose is to stabilaze structure stresses and dimension.

Why are there quenching cracks?

1 Quenching crackThe quenching process is mainly used for steel parts, which is to heat the steel to a temperature above the critical temperature Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel), hold it for a period of time to make it fully or partially austenitized, and then The cooling rate of the critical cooling rate is quickly cooled to below Ms (martensitic transformation starting temperature) (or isothermal near Ms) to perform a martensite (or bainite) transformation heat treatment process. Quenching cracking refers to the cracks generated during quenching or during room temperature after quenching. The latter is also called aging cracks. The distribution of cracks does not have a certain rule, but it is generally easy to form at the sharp corners and abrupt cross-sections of the workpiece. The root cause of quenching cracking is that the tensile stress exceeds the fracture strength of the material, or although the fracture strength of the material is not exceeded, the material will also crack due to internal defects. There are many specific reasons for quenching cracking, and the analysis should be based on the characteristics of the crack. 2 Causes of quenching cracksThe essential brittleness of martensite is the internal cause of quenching cracks, and the crystal structure, chemical composition, metallurgical defects, etc. of martensite are the influencing factors of the essential brittleness of martensite; the macroscopic internal stress caused by various process conditions, part sizes and shapes, etc. The size, direction, distribution, etc. are the external causes of quenching cracks. The quenching cracks of steel parts will be analyzed from micro to macro, from inside to outside.

The main disadvantages of water as a quenching cooling medium for forgings?

1) In the code area of the austenite isothermal transformation diagram, that is, about 500-600 ℃, the water is in the vapor film stage, and the cooling rate is not fast enough, which often results in "soft spots" formed by uneven cooling of the forgings and insufficient cooling rate. . In the martensite transformation system, that is, about 300-100 ° C, the water is in the boiling stage, the cooling rate is too fast, and it is easy to make the martensite transformation speed too fast and generate great internal stress, which causes severe deformation and even cracking of the forging.2) Water temperature has a large effect on cooling capacity, so it is sensitive to changes in ambient temperature. When the water temperature increases, the cooling capacity drops sharply, and the temperature range of the maximum cooling rate moves to low temperatures. When the water temperature exceeds 30 ° C, the cooling rate decreases significantly in the range of 500-600 ° C, which often results in hardening of the forging, but has a small effect on the cooling rate in the martensitic transformation range. When the water temperature increases to 60 ° C, the cooling rate will drop by about 50%.

Forging’s quenching and normalizing?

In the heat treatment of forgings, due to the high power of the electric furnace and the long holding time, the energy consumption is huge throughout the process. For a long period of time, how to save energy during heat treatment of forgings has always been a problem.The so-called "zero heat preservation" quenching refers to the heat treatment process in which the surface and core of the forging are quenched and cooled immediately after reaching the quenching heating temperature, without the need for heat preservation. Traditional austenite theory holds that forgings must have a long holding time during heating in order to complete the nucleation, growth of austenite grains, dissolution of residual cementite, and homogenization of austenite. The current quenching and heating processes of forgings are all produced under the guidance of this theory. Compared with the current quenching process, "zero heat preservation" quenching eliminates the heat preservation time required for homogenization of the austenite structure, which can not only save energy by 20% -30%, improve production efficiency by 20% -30%, but also It can reduce or eliminate the defects such as oxidation, decarburization and deformation during the heat preservation process, which is conducive to the improvement of product quality.When carbon steel and low alloy structural steel are heated above Ac1 or Ac2, the homogenization process of austenite and the dissolution of carbides in pearlite are relatively fast. When the size of the steel part belongs to the range of thin parts, there is no need to consider heat preservation when calculating the heating time, that is, to achieve zero heat preservation quenching. For example, when the diameter or thickness of the 45 steel workpiece is not more than 100mm, the surface and core temperature are reached at the same time when heated in an air furnace, so the uniform time can be ignored, and the traditional production process with a large heating coefficient ( r = aD), it can shorten the quenching heating time by nearly 20% -25%.Relevant theoretical analysis and experimental results show that it is completely feasible to use "zero insulation" for structural steel quenching and normalizing heating. In particular, 45, 45Mn2 carbon structural steel or single-element alloy structural steel, the use of "zero insulation" process can ensure its mechanical performance requirements; 45, 35CrMo, GCrl5 and other structural steel workpieces, using "zero insulation" heating can save more than traditional heating Heating time 50%. The total energy saving is 10% -15%, and the work efficiency is improved by 20% -30%. At the same time, the "zero insulation" quenching process helps to refine the grains and improve the strength.

What is the purpose of annealing?

1. Improve or eliminate various structural defects and residual stress caused by steel during casting, forging, rolling and welding, and prevent deformation and cracking of the workpiece.2. Soften the workpiece for cutting.3. Refine the grains and improve the structure to improve the mechanical properties of the workpiece.4. Prepare the structure for final heat treatment (quenching, tempering).

What is the purpose of tempering?

1. Improve the stability of the organization, so that the workpiece no longer undergoes structural transformation during use, so that the geometry and performance of the workpiece remain stable.2. Eliminate internal stress in order to improve the performance of the workpiece and stabilize the workpiece geometry.3. Adjust the mechanical properties of steel to meet the requirements of use.

What is the purpose of quenching?

1) Improve the mechanical properties of metal products or parts. For example: improve the hardness and wear resistance of tools, bearings, etc., increase the elastic limit of springs, and improve the comprehensive mechanical properties of shaft parts.2) Improve the material properties or chemical properties of some special steels. Such as improving the corrosion resistance of stainless steel and increasing the permanent magnetism of magnetic steel.

What elements will effect heat treatment for forgings?

What elements will effect heat treatment for forgings?1, size effect:The mechanical properties of forged steel vary with the shape and size. Generally, the larger the size, the shallower the depth of heat treatment in the same cooling medium, and the lower the mechanical properties.2. Mass effect:The quality (weight) of the forgings is different, and the final result of the heat treatment is different, especially in the quenching process. Generally, the thicker the workpiece, the harder it is to harden. The larger the workpiece, the harder it is to quench. The difference in heat treatment results due to the difference in quality is large.The mass effect is to analyze the quenching effect from the perspective of the size of the workpiece. Hardenability is the analysis of the quenching effect from the material perspective of the steel. The mass effect of a workpiece with good hardenability is small, that is, the hardenability improves the mass effect.3, shape effect:The quenching effect of the forgings is affected by the shape of the parts. The shapes of the rods, plates and balls are different, and their quenching effects are different. In addition, the cooling methods of different quenching parts on the same parts are different, and the quenching effect is also different.The size, quality and shape of the forging are the three elements of the forging. When formulating the heat treatment process specification, the three elements of the heat treatment process must be combined with the three elements of the heat treatment workpiece, and cannot be divided. When referring to the heat treatment CCT, TTT and other curves in various manuals, the three elements of the heat treatment forgings and the surface and workpiece of the forgings cannot be ignored. The difference in temperature between heating and cooling of the heart.