| A football coach walked into the locker room before a big game, looked over to his star player and said, "I'm not supposed to let you play since you failed math, but we really need you in there. So, what I have to do is ask you a math question, and i... Read more of Football player test at Free Jokes.ca |  Informational.caPrivacy |
Steel MakingHardness TestingThe word hardness is used to express various properties of me... Heat Treatment Of Steel Heat treatment consists in heating and cooling metal at defin... The Influence Of Size The size of the piece influences the physical properties obta... Annealing To Relieve Internal Stresses Work quenched from a high temperature and not afterward tempe... William Kelly's Air-boiling Process An account of Bessemer's address to the British Association w... Temperature Recording And Regulation Each furnace is equipped with pyrometers, but the reading an... A Chromium-cobalt Steel The Latrobe Steel Company make a high-speed steel without tun... Hardening Carbon Steel For Tools For years the toolmaker had full sway in regard to make of st... The Packing Department In Fig. 56 is shown the packing pots where the work is packe... Heavy Forging Practice In heavy forging practice where the metal is being worked at... Piston Pin The piston pin on an aviation engine must possess maximum res... Hints For Tool Steel Users Do not hesitate to ask for information from the maker as to t... Placing The Thermo-couples The following illustrations from the Taylor Instrument Compan... Critical Points One of the most important means of investigating the properti... Complete Calibration Of Pyrometers For the complete calibration of a thermo-couple of unknown e... Silicon Silicon prevents, to a large extent, defects such as gas bubb... Case-hardening Treatments For Various Steels Plain water, salt water and linseed oil are the three most co... Heating Of Manganese Steel Another form of heat-treating furnace is that which is used ... Mushet And Bessemer That Mushet was "used" by Ebbw Vale against Bessemer is, perh... Drop Forging Dies The kind of steel used in the die of course influences the he... |
Composition And Properties Of SteelCategory: COMPOSITION AND PROPERTIES OF STEEL It is a remarkable fact that one can look through a dozen text books on metallurgy and not find a definition of the word steel. Some of them describe the properties of many other irons and then allow you to guess that everything else is steel. If it was difficult a hundred years ago to give a good definition of the term when the metal was made by only one or two processes, it is doubly difficult now, since the introduction of so many new operations and furnaces. We are in better shape to know what steel is than our forefathers. They went through certain operations and they got a soft malleable, weldable metal which would not harden; this they called iron. Certain other operations gave them something which looked very much like iron, but which would harden after quenching from a red heat. This was steel. Not knowing the essential difference between the two, they must distinguish by the process of manufacture. To-day we can make either variety by several methods, and can convert either into the other at will, back and forth as often as we wish; so we are able to distinguish between the two more logically. We know that iron is a chemical element--the chemists write it Fe for short, after the Latin word ferrum, meaning iron--it is one of those substances which cannot be separated into anything else but itself. It can be made to join with other elements; for instance, it joins with the oxygen in the air and forms scale or rust, substances known to the chemist as iron oxide. But the same metal iron can be recovered from that rust by abstracting the oxygen; having recovered the iron nothing else can be extracted but iron; iron is elemental. We can get relatively pure iron from various minerals and artificial substances, and when we get it we always have a magnetic metal, almost infusible, ductile, fairly strong, tough, something which can be hardened slightly by hammering but which cannot be hardened by quenching. It has certain chemical properties, which need not be described, which allow a skilled chemist to distinguish it without difficulty and unerringly from the other known elements--nearly 100 of them. Carbon is another chemical element, written C for short, which is widely distributed through nature. Carbon also readily combines with oxygen and other chemical elements, so that it is rarely found pure; its most familiar form is soot, although the rarer graphite and most rare diamond are also forms of quite pure carbon. It can also be readily separated from its multitude of compounds (vegetation, coal, limestone, petroleum) by the chemist. With the rise of knowledge of scientific chemistry, it was quickly found that the essential difference between iron and steel was that the latter was iron plus carbon. Consequently it is an alloy, and the definition which modern metallurgists accept is this: Steel is an iron-carbon alloy containing less than about 2 per cent carbon. Of course there are other elements contained in commercial steel, and these elements are especially important in modern alloy steels, but carbon is the element which changes a soft metal into one which may be hardened, and strengthened by quenching. In fact, carbon, of itself, without heat treatment, strengthens iron at the expense of ductility (as noted by the percentage elongation an 8-in. bar will stretch before breaking). This is shown by the following table: -------------------------------------------------------------------------- Elastic UltimatePercentage. Class by use. Class by Per cent limit strengthelongation hardness. carbon. lb. per lb. per in 8 inches. sq. in. sq. in. --------------------------------------------------------------------- Boiler rivet steelDead soft 0.08 to 0.15 25,000 50,000 30 Struc. rivet steelSoft 0.15 to 0.22 30,000 55,000 30 Boiler plate steelSoft 0.08 to 0.10 30,000 60,000 25 Structural steel Medium 0.18 to 0.30 35,000 65,000 25 Machinery steel Hard 0.35 to 0.60 40,000 75,000 20 Rail steel Hard 0.35 to 0.55 40,000 75,000 15 Spring steel High carbon1.00 to 1.50 60,000 125,000 10 Tool steel High carbon0.90 to 1.50 80,000 150,000 5 -------------------------------------------------------------------------- Just why a soft material like carbon (graphite), when added to another soft material like iron, should make the iron harder, has been quite a mystery, and one which has caused a tremendous amount of study. The mutual interactions of these two elements in various proportions and at various temperatures will be discussed at greater length later, especially in Chap. VIII, p. 105. But we may anticipate by saying that some of the iron unites with all the carbon to form a new substance, very hard, a carbide which has been called cementite. The compound always contains iron and carbon in the proportions of three atoms of iron to one atom of carbon; chemists note this fact in shorthand by the symbol Fe3C (a definite chemical compound of three atoms of iron to one of carbon). Many of the properties of steel, as they vary with carbon content, can be linked up with the increasing amount of this hard carbide cementite, distributed in very fine particles through the softer iron. Next: Sulphur Previous: Classifications Of Steel
Viewed 543 |
||||||||||||||||||||
