Конструкциялық материалдар және термоөңдеу Конструкционные материалы и термообработка Constructional materials and heat treatment Учебное пособие для специальности: 5В071200– «Машиностроение»
part of a product, and the warmth which has remained in other part of a detail
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montaev s h
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- Surface hardening
- Hardening with induction heating
part of a product, and the warmth which has remained in other part of a detail after extraction from the environment, causes holiday of the cooled part. Apply to heat treatment of a percussion instrument like chisels, hammers which have to combine the high hardness and viscosity. - processing by cold consists throughout cooling of the tempered steel below 0?С up to the temperatures of the end of marten site transformation (usually not below - 75?С). As a result of processing by cold hardness increases and the sizes of details are stabilized. Surface hardening. Surface hardening is a heat treatment at which the product blankets on the set depth whereas the core of a product remains not tempered is tempered only. As a result the blanket possesses high durability, and the core of a product remains plastic and viscous that provides high wear resistance and at the same time resistance to dynamic loadings. In the industry apply the following methods of superficial training: - hardening with induction heating by currents of high frequency at mass processing of steel products. - gas-flame surface hardening by a flame gas or oxygen - acetylene torches (flame temperature 2400-3000C) for single large products. - hardening in electrolyte for small details in mass production. - the laser training allowing significantly to increase wear resistance, endurance limit at a bend and a limit of contact endurance. Hardening with induction heating. Hardening with induction heating (TVCh heating) - the most widespread way of surface hardening. Detail place in the inductor which represents copper tubes with water circulating inside for cooling. To the inductor bring an alternating electric current. In the inductor there is a variation magnetic field. The magnetic stream induces the vortex currents causing heating of a surface in product metal. The main quantity of heat is allocated in a thin blanket. Depth of heating depends on properties of metal and current frequency. The more current frequency is thinner the tempered layer turns out. After heating in the inductor the detail is cooled by means of the special cooling device. Through openings available in it on a surface of a detail cooling liquid is sprayed. The hardened products subject to drawback at 160-200zs. Advantages of surface hardening of TVCh: - adjustable depth of the hardened layer. - high efficiency. 208 - possibility of automation. - lack of an decaburation and scale formation. - minimum buckling of a detail. Shortcoming is the high cost of the inductor, individual for each detail. Surface hardening apply for carbonaceous steel, almost not containing about 0,4% of carbon, for alloyed steel almost don't apply. To high-frequency hardening subject necks of cranked shaft, sleeves of cylinders, piston fingers, spring fingers, etc. Thickness of a strengthened layer makes 1,5-3MM if only high wear resistance is required, and increases to the 5-10th in case of high contact loadings and possible regrinding. Fig7.1. The scheme isothermal transformation of austenite eutectoid steel: І – pearlite transformation; ІІ – between transformation: ІІІ – martensitic transformation. Fig 7.2. Influence of austenite carbon steel of temperature transformation: a — the diagram of isothermal transformation; — temperature began transformation in one cooler. 209 Speed of cooling of used environments in the process of chilling , table7.1. № Coolant medium Speed of cooling, % 700-500 0 С 300-200 0 С 1 2 3 4 5 Water t=18ºС t=28ºС In water 10% NaOH solution t=18ºС In water NaCl solution t=18ºС Mineral oil Air 600 500 1200 1100 150 3 270 270 300 300 30 1 жүктеу/скачать 1,99 Mb. Достарыңызбен бөлісу:
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