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The difference between annealing and temperingfor all the mechanical quality of the soul - heat treatment knowledge

The difference is: annealing and tempering (annealing is not simply, still retain certain hardness, tempering hardness).


Tempering:


The high temperature tempering microstructure is tempered sorbite. Tempering is generally not used alone, in the parts after quenching and tempering, the main purpose is eliminate quenching stress, organizational requirements, tempering according to different tempering temperature is low, moderate and high temperature tempering. Tempering martensite, troostite and sorbite respectively. The heat treatment after quenching tempering is called a combination of quenching and tempering, its purpose is to obtain the strength, hardness and plasticity, toughness is good mechanical properties. Therefore, widely used in automobiles, tractors, machine tools and other key components, such as connecting rod, bolts, gears and shafts. The hardness is HB200-330.


Annealing:


Annealing process is pearlite transformation, the primary purpose of annealing is to the internal organization of metal close to equilibrium, preparing for the subsequent processing and final heat treatment. Stress annealing to annealing process to eliminate residual plastic deformation due to machining, welding and casting is caused by the stress of. The internal stress in forging, casting, welding and machining of the workpiece, if not promptly removed, will make the workpiece deformation in the processing and use process, influence the accuracy of workpiece. The internal stress generated stress relief annealing process is very important. To be the heating temperature of annealing is lower than the phase transition temperature, therefore, the organization transition does not occur in the whole process of heat treatment. 


The internal stress is mainly through the workpiece in the insulation and cooling process in the natural elimination. In order to eliminate the internal stress of the workpiece more thoroughly, the heating temperature should be controlled. Generally low temperature into the furnace, and then to 100 degrees Celsius /h heating rate is heated to the specified temperature. The heating temperature should be slightly higher than 600. Holding time as the case may be, usually from 2 to 4h. 


The heat preservation time of the casting stress annealing is the upper limit, and the cooling rate is controlled at (20 ~ 50) /h, cold to 300 degrees Celsius. Aging treatment can be divided into natural and artificial ageing two natural aging is the casting is placed in the open area for more than half a year, then slowly occurs, thereby the residual stress eliminating or reducing artificial aging is heated casting to 550 to 650 DEG C for stress relief annealing, it than natural aging save time, residual stress could be removed more thoroughly.


What is tempering?


Tempering is the quenching metal timber or parts heating to a certain temperature, heat preservation time, in the heat treatment process of cooling, tempering after quenching followed by one operation, the final process of the heat treatment is usually the workpiece. Therefore, the quenching and tempering of the combined process called for the final heat treatment. The main purpose of quenching and tempering is:


1) reduce the internal stress and reduce brittleness, there is a lot of stress and brittleness, such as no timely tempering will often produce deformation and even crack.


2) to adjust the mechanical properties of the workpiece, the workpiece after quenching, high hardness, brittleness, in order to meet the different performance requirements of various parts, can be adjusted by tempering, hardness, strength, plasticity and toughness.


3) stable workpiece size. By tempering, the metallographic structure tends to be stable, so as to ensure that no deformation occurs during the later use.


4) to improve the cutting performance of some alloy steel.


In production, often according to the performance requirements of the workpiece. According to the different heating temperature, tempering for low temperature tempering, temperature tempering and high tempering. The heat treatment process of quenching and subsequent high temperature tempering is called a combination of quenching and tempering, in high strength, good toughness and plasticity. Mainly used for processing machine parts with structure of large load, such as machine tool spindle, automobile rear axle, gear strength etc..


What is called quenching?


Quenching is the metal timber or heating parts to above the phase transition temperature, heat preservation, to greater than the critical cooling rate of the rapid cooling, to obtain martensitic organization heat treatment process. In order to get the quenching martensite, then after tempering, the obtained good performance, in order to give full play to the potential of materials. Its main purpose is to:


1) to improve the mechanical properties of the metal material or parts. For example: to improve the


 hardness and wear resistance of tools, bearings, improve the elastic limit of the spring, to improve the comprehensive mechanical properties of shaft parts etc..


2) material properties or chemical performance improvement of some special steel. As to improve the corrosion resistance of stainless steel, increasing permanent magnetic etc..


During cooling, in addition to the reasonable selection of quenching medium, quenching have the correct methods of quenching methods commonly used, mainly single liquid quenching, quenching, quenching and isothermal quenching, partial quenching etc..


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