| Tommy Fox kept a sharp look-out to see what he could capture to eat. But he could discover nothing at all. To be sure, there were birds in the trees, and birds' nests too, and Tommy was very fond of birds' eggs. But he couldn't climb trees. T... Read more of TOMMY FOX IS HUNGRY at Children Stories.ca |  Informational.caPrivacy |
Steel MakingThe Quenching TankThe quenching tank is an important feature of apparatus in c... Surface Carburizing Carburizing, commonly called case-hardening, is the art of pr... Effects Of Proper Annealing Proper annealing of low-carbon steels causes a complete solu... Effect Of A Small Amount Of Copper In Medium-carbon Steel This shows the result of tests by C. R. Hayward and A. B. Joh... Using Illuminating Gas The choice of a carburizing furnace depends greatly on the fa... Heat-treating Department The heat-treating department occupies an L-shaped building. ... Double Annealing Water annealing consists in heating the piece, allowing it to... Instructions For Working High-speed Steel Owing to the wide variations in the composition of high-speed... The Forging Of Steel So much depends upon the forging of steel that this operation... Preventing Cracks In Hardening The blacksmith in the small shop, where equipment is usually ... High Speed Steel For centuries the secret art of making tool steel was handed ... Judging The Heat Of Steel While the use of a pyrometer is of course the only way to hav... Pyrometry And Pyrometers A knowledge of the fundamental principles of pyrometry, or th... Sulphur SULPHUR is another element (symbol S) which is always found i... Annealing Of High-speed Steel For annealing high-speed steel, some makers recommend using g... S A E Heat Treatments The Society of Automotive Engineers have adopted certain heat... Knowing What Takes Place How are we to know if we have given a piece of steel the ver... Tungsten Tungsten, as an alloy in steel, has been known and used for a... Quenching It is considered good practice to quench alloy steels from th... Oil-hardening Steel Heat slowly and uniformly to 1,450 deg.F. and forge thorough... |
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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