Martensitic Stainless steel And Ferrite Stainless Steel

MARTENSITIC STAINLESS STEEL :

This group often termed plain chromium types of stainless steel , which contain 10 to 14 per cent chromium and with the old exception , have no other major alloying element. These steels are all harden-able by heat treatment.

FERRITE STAINLESS STEEL :

This group contains mainly 14 to 18 or 23 to 30 percent chromium again with no other major alloying element. They cannot be hardened by heat treatment.

Stainless Steels have great strength and toughness and extremely good resistance to corrosion and heat. The heat resisting properties are increased by the addition of about 3 percent of silicon. They find wide application in the brewery, diary and chemical industries , in making cutlery, all types of surgical and dental instruments, household appliances such as kitchen utensils, sinks, saucepans, and many others. Considerable amounts of these steels are used for components in power stations, particularly in the field of nuclear power-production because of the excellent combination of resistance to heat and corrosion, and maintenance of high strength at elevated temperatures, which they provide.

When the carbon content is reduced as low as 0.90 per cent the produce is called stainless iron. Irons of this classification usually have chromium in excess of 23 per cent. They are highly resistant to corrosion and they may be used in parts for heat exchangers, conveyer chains, furnaces, strokers, and other similar high temperature applications

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THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

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Mechinopedia For Mechanical Engineers

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