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Steel MakingRate Of CoolingAt the option of the manufacturer, the above treatment of gea... Heat Treatment Of Gear Blanks This section is based on a paper read before the American Gea... Annealing There is no mystery or secret about the proper annealing of d... Flange Shields For Furnaces Such portable flame shields as the one illustrated in Fig. 1... Liberty Motor Connecting Rods The requirements for materials for the Liberty motor connecti... Using Illuminating Gas The choice of a carburizing furnace depends greatly on the fa... The Modern Hardening Room A hardening room of today means a very different place from ... Properties Of Steel Steels are known by certain tests. Early tests were more or l... Detrimental Elements Sulphur and phosphorus are two elements known to be detrimen... Vanadium Vanadium has a very marked effect upon alloy steels rich in c... Alloying Elements Commercial steels of even the simplest types are therefore p... Calibration Of Pyrometer With Common Salt An easy and convenient method for standardization and one whi... Heat Treatment Of Milling Cutters Drills Reamers Etc THE FIRE.--Gas and electric furnaces designed for high heats ... High-carbon Machinery Steel The carbon content of this steel is above 30 points and is ha... Making Steel Balls Steel balls are made from rods or coils according to size, st... Chrome-nickel Steel Forging heat of chrome-nickel steel depends very largely on ... Mushet And Bessemer That Mushet was "used" by Ebbw Vale against Bessemer is, perh... Introduction Of Carbon The matter to which these notes are primarily directed is the... Blending The Compound Essentially, this consists of the sturdy, power-driven separa... Heavy Forging Practice In heavy forging practice where the metal is being worked at... |
The Theory Of TemperingCategory: HARDENING CARBON STEEL FOR TOOLS Steel that has been hardened is generally harder and more brittle than is necessary, and in order to bring it to the condition that meets our requirements a treatment called tempering is used. This increases the toughness of the steel, i.e., decrease the brittleness at the expense of a slight decrease in hardness. There are several theories to explain this reaction, but generally it is only necessary to remember that in hardening we quench steel from the austenite phase, and, due to this rapid cooling, the normal change from austenite to the eutectoid composition does not have time to take place, and as a consequence the steel exists in a partially transformed, unstable and very hard condition at atmospheric temperatures. But owing to the internal rigidity which exists in cold metal the steel is unable to change into its more stable phase until atoms can rearrange themselves by the application of heat. The higher the heat, the greater the transformation into the softer phases. As the transformation takes place, a certain amount of heat of reaction, which under slow cooling would have been released in the critical range, is now released and helps to cause a further slight reaction. If a piece of steel is heated to a certain temperature and held there, the tempering color, instead of remaining unchanged at this temperature, will advance in the tempering-color scale as it would with increasing temperature. This means that the tempering colors do not absolutely correspond to the temperatures of steels, but the variations are so slight that we can use them in actual practice. (See Table 23, page 158.) Next: Temperatures To Use Previous: Quenching Tool Steel
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