Конструкциялық материалдар және термоөңдеу Конструкционные материалы и термообработка Constructional materials and heat treatment Учебное пособие для специальности: 5В071200– «Машиностроение»
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- Annealing and normalization
| Types of heat treatment.
Set of operations of heating, endurance and cooling of firm metal alloys for the purpose of obtaining the set properties at the expense of change of an internal structure and structure is called as heat treatment. Heat treatment is used as intermediate operation for workability improvement by cutting, pressure, etc. and as the final operation of the technological process providing set level of physic-mechanical properties of a detail. Distinguish three main types of heat treatment of metals: - actually heat treatment which provides only temperature impact on metal. - chemical heat treatment at which as a result of interaction with environment when heating the structure of the blanket of metal changes and happens its saturation by various chemical elements. - thermo-mechanical processing at which the structure of metal changes at the expense of thermal and deformation influence. Main types of actually heat treatment steel: - annealing of the first sort - heating, endurance and cooling of a steel product for the purpose of removal of residual tension and distortions of a crystal lattice after previous processing. - annealing of the second sort - heating is higher than temperature of phase transformation and slow cooling, for receiving equilibrium phase composition of steel. - hardening - heating is higher than temperatures of phase transformation with the subsequent fast cooling for receiving structurally non-equilibrium condition. 205 - drawback - heating of the tempered steel is lower than temperatures of phase transformations and cooling for removal of residual tension after training. If drawback is spent at the room temperature or a little exceeding, it is called as aging. Annealing and normalization. Annealing - heat treatment at which steel heats up to a certain temperature, is maintained at it and then slowly cooled in the furnace for receiving equilibrium, less firm structure, free from residual tension. Annealing of 1 sort treat: - diffusive annealing (or homogenization) - heating to 1000-1100 for elimination of the chemical heterogeneity formed at crystallization of metal. To homogenization subject ingots or castings high-alloyed by the steel. - re-crystallization annealing which is applied to cold work removal after cold plastic deformation. Heating temperature most often is in limits 650-700z. - annealing for removal of internal tension. Apply for the purpose of reduction of tension formed in metal at molding, welding, processing by cutting, etc. Temperature of annealing is in limits 200-700zs, is more often 350-600zs. Annealing of 2 sorts (or phase re-crystallization) can be full and incomplete: - full annealing - heating became on 30-50z above the top critical point with the subsequent slow cooling. At this annealing there is a full re-crystallization: when heating the ferritic-pearlitny structure passes in austenitic, and when cooling austenite turns back into ferrite and pearlite. To full annealing subject castings, forgings, hire for crushing of grain, removal of internal tension. Thus plasticity and viscosity increase. - incomplete annealing differs from full that heat steel to lower temperature (on 30-50z higher than temperature of pearlitny transformation). Thus there will be a re-crystallization of only a pearlitny component. It is more economic operation, than full annealing as heating is made up to lower temperatures. At incomplete annealing the workability cutting as a result of decrease in hardness and increase of plasticity of steel improves. Isothermal annealing consists in heating and endurance at a temperature on 30-50z above the top critical point, cooling to 600-700zs, endurance at this temperature before full transformation of austenite into pearlite and the subsequent cooling on air. Normalization - an annealing version. At normalization cooling is carried out on quiet air. Cooling speed is slightly more, than at usual annealing that defines some difference of properties of the annealed and normalized steel. жүктеу/скачать 1,99 Mb. Достарыңызбен бөлісу:
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