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GENERAL PROPERTIES OF ALLOY STEELS.

Alloy or “special” steels are combinations of iron and carbon with some other element, such as nickel, chromium, tungsten, vanadium, manganese and molybdenum. All of these metals give certain distinct properties to the steel, but in all cases the principal quality is the increase in hardness and toughness.

            Nickel steel usually contains from 3 to 3.5 percent nickel (ordinarily not over 5 percent), and from 0.20 to 0.40 percent carbon. This steel is used for armor plate, ammunition, bridge construction, rails, etc. One of the reasons why nickel steel is adapted for armor plate is that it does not crack when perforated by a projectile.

            Chromium steel is well adapted for armor-piercing projectiles, owing to its hardness, toughness and stiffness, and is extensively used for this purpose. Chromium steel is also used in the construction of safes and for casting subjected to unusually severe stresses, such as those used in rock-crushing machinery, etc. The percentages of chromium used in chromium steels varies over quite a wide range in the low-chromium and high-chromium steels.

            Tungsten steel is largely employed for high speed metal cutting tools and magnet steels. It has also been used in the manufacture of armor plate and armor-piercing projectiles, in which case it is combined either with nickel or chromium or with both of these metals. The property that tungsten imparts to steel is that of hardening in the air, after heating to the required temperature. This steel usually contains from 5 to 15 percent tungsten) although the percentage is sometimes as high as 24 percent) and from 0.4 to 2 percent carbon.

            Vanadium steels ordinarily contain from o.16 to 0.25 percent vanadium. The effect of vanadium is to increase the tensile strength and elastic limit, and it gives the steel the valuable property of resisting, to an unusual degree, repeat44d stresses. Vanadium steel is especially adapted for springs, car axles, gears subjected to severe service, and for all parts which must withstand constant vibration and varying stresses.

            Manganese steel contains about 12 per cent manganese and from o.8 to 1.25 per cent carbon. If there is only 1.5 per cent manganese, the steel is very brittle, and additional manganese increases this brittleness until the quantity has reached 4 to 5.5 per cent, when the steel can be pulverized under the hammer. With a further increase of manganese, the steel becomes ductile and very hard, these qualities being at their highest degree when the manganese content is 12 per cent. The ductility of the steel is brough out by sudden cooling, the process being opposite that employed for carbon steel

            Molybdenum steels have properties similar to tungsten steels, except that a smaller quantity of molybdenum than to tungsten is required to secure similar results.

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