Thursday, 27 April 2017

ENGINEERING METALLURGY - APPLIED PHYSICAL METALLURGY BY RAYMOND A. HIGGINS FREE DOWNLOAD PDF

ENGINEERING METALLURGY

APPLIED PHYSICAL METALLURGY 

BY RAYMOND A. HIGGINS 





CONTENTS

  1. Some Fundamental Chemistry
  2. The Physical and Mechanical Properties of Metals and Alloys
  3. The Crystalline Structure of Metals
  4. Mechanical Deformation and Recovery
  5. Fracture of Metals
  6. The Industrial Shaping of Metals
  7. An Introduction to Steel
  8. The Formation of Alloys
  9. Thermal Equilibrium Diagrams
  10. Practical Metallography
  11. The Heat-treatment of Plain Carbon Steels – (I)
  12. The Heat-treatment of Plain Carbon Steels – (II)
  13. Alloy Steels
  14. Complex Ferrous Alloys
  15. Cast Irons and Alloy Cast Irons
  16. Copper and the Copper-base Alloys
  17. Aluminium and Its Alloys
  18. Other Non-ferrous Metals and Alloys
  19. The Surface Hardening of Steels
  20. Metallurgical Principles of the Joining of Metals
  21. Metallic Corrosion and Its Prevention




INTRODUCTION TO ENGINEERING METALLURGY BY RAYMOND A HIGGINS

Towards the end of the fifteenth century the technology of shipbuilding was sufficiently advanced in Europe to allow Columbus to sail west into the unknown in a search for a new route to distant Cathay. Earlier that century far to the east in Samarkand in the empire of Tamerlane, the astronomer Ulug Beg was constructing his great sextant—the massive quadrant of which we can still see to-day—to measure the period of our terrestrial year. He succeeded in this enterprise with an error of only 58
seconds, a fact which the locals will tell you with pride. Yet at that time only seven metals were known to man—copper, silver, gold, mercury, iron, tin and lead; though some of them had been mixed to produce alloys like bronze (copper and tin), pewter (tin and lead) and steel (iron and carbon).
By 1800 the number of known metals had risen to 23 and by the beginning of the twentieth century to 65. Now, all 70 naturally occurring metallic elements are known to science and an extra dozen or so have been created by man from the naturally occurring radioactive elements by various processes of 'nuclear engineering'. Nevertheless metallurgy, though a modern science, has its roots in the ancient crafts of smelting, shaping and treatment of metals or several hundreds of years smiths had been hardening steel using heat-treatment processes established painstakingly by trial and error, yet it is only during this century that metallurgists discovered how the hardening process worked. Likewise during the First World War the author's father, then in the Royal Flying Corps, was working with fighter aeroplanes the engines of which relied on 'age-hardening' aluminium alloys; but it was quite late in the author's life before a plausible explanation of age-hardening was forthcoming. Since the days of the Great Victorians there has been an upsurge in metallurgical research and development, based on the fundamental sciences of physics and chemistry. To-day a vast reservoir of metallurgical knowledge exists and the metallurgist is able to design materials to meet the ever exacting demands of the engineer. Sometimes these demands are over optimistic and it is hoped that this book may help the engineer to appreciate the limitations, as well as the expanding range of properties, of modern alloys. Whilst steel is likely to remain the most important metallurgical material available to the engineer we must not forget the wide range of
relatively sophisticated alloys which have been developed during this century. As a result of such development an almost bewildering list of alloy compositions confronts the engineer in his search for an alloy which will be both technically and economically suitable for his needs. Fortunately most of the useful alloys have been classified and rigid specifications laid down for them by such official bodies as the British Standards Institution  (BSI) and in the USA, the American Society for Testing Materials(ASTM). Now that we are in Europe' such bodies as Association Frangaise de Normalisation (AFNOR) and Deutscher Normenausschuss (DNA) also become increasingly involved. Sadly, it may be that like many of our public libraries here in the Midlands, your local library contains proportionally fewer books on technological matters than it did fifty years ago, and that meagre funds have been expended on works dealing with the private life of Gazza—or the purple passion publications of Mills and Boon. Nevertheless at least one library in your region should contain, by national agreement, a complete set of British Standards Institution Specifications. In addition to their obvious use, these are a valuable mine of information on the compositions and properties of all of our commercial alloys and engineering materials. A catalogue of all Specification Numbers will be available at the information desk. Hence, forearmed with the necessary metallurgical knowledge, the engineer is able to select an alloy suitable to his needs and to quote its relevant specification index when the time comes to convert design into reality.




Atoms, Elements and Compounds : It would be difficult to study metallurgy meaningfully without relating mechanical properties to the elementary forces acting between the atoms of which a metal is composed. We shall study the structures of atoms later in the chapter but it suffices at this stage to regard these atoms as tiny
spheres held close to one another by forces of attraction. 1.21 If in a substance all of these atoms are of the same type then the substance is a chemical element. Thus the salient property of a chemical element is that it cannot be split up into simpler substances whether by mechanical or chemical means. Most of the elements are chemically reactive, so that we find very few of them in their elemental state in the Earth's crust—oxygen and nitrogen mixed together in the atmosphere are the most
common, whilst a few metals such as copper, gold and silver, also occur uncombined. Typical substances occurring naturally contain atoms of two or more kinds.



Oxidation and Reduction

Oxidation is one of the most common of chemical processes. It refers, in its simplest terms, to the combination between oxygen and any other element—a phenomenon which is taking place all the time around us. In our daily lives we make constant use of oxidation. We inhale atmospheric oxygen and reject carbon dioxide (CO2)—the oxygen we breathe combines with carbon from our animal tissues, releasing energy in the process. We then reject the waste carbon dioxide. Similarly, heat energy can be produced by burning carbonaceous materials, such as coal or petroleum. Just as without breathing oxygen animals cannot live, so without an adequate air supply fuel cannot burn. In these reactions carbon and oxygen have combined to form a gas, carbon dioxide (CO2), and at the same time heat energy has been released—the 'energy potential' of the carbon having fallen in the process. 

Oxidation, however, is also a phenomenon which works to our disadvantage, particularly in so far as the metallurgist is concerned, since a large number of otherwise useful metals show a great affinity for oxygen and combine with it whenever they are able. This is particularly so at high temperatures so that the protection of metal surfaces by means of fluxes is often necessary during melting and welding operations. Although corrosion is generally a more complex phenomenon, oxidation is always involved and expensive processes such as painting, plating or galvanising must be used to protect the metallic surface. 



Complex Ferrous Alloys
 
High-speed Steels

The development of high-speed steel had its origins in 1861 when Robert Mushet of Sheffield was investigating the value of manganese in the production of Bessemer steel. He made Henry Bessemer's process viable by deoxidising the 'wild' steel with manganese, and discovered that one composition containing rather a large amount of manganese hardened when it was cooled in air. Analysis showed approximately 6% tungsten to be present in addition, and this alloy subsequently found its way on to the market under the name of air-hardening steel. It was discovered soon afterwards that cooling from 11000C in an air blast gave better results for tools. Some twenty years later Messrs. Maunsel White and Fredrick Taylor, both of the Bethlehem Steel Company, replaced the manganese in Mushet's steel by chromium, and also increased the tungsten content. These changes in composition enabled the steel to be forged readily and produced a superior tool steel. Production engineers will already be
familiar with the name of Taylor, who devoted a great deal of attention to time-study and machine-shop methods. Modern high-speed steel was first introduced to the public at the Paris Exposition in 1900. The tools were exhibited cutting at a speed of about 0.3 m/s with their tips heated to redness. It was found later that maximum efficiency was obtained with a chromium content of 4% and about 18% tungsten, the carbon content having been reduced from 2.0%, in the original Mushet steel, to between 0.6 and 0.8%. In 1906 vanadium was first added to high-speed steel. Molybdenum was investigated as a substitute for some of the tungsten, but increases in the price of molybdenum in the 1920s suspended this development, particularly since molybdenum steels were regarded as being inferior in properties. Only in more recent years has molybdenum replaced much of the tungsten in many grades of highspeed steel. This is particularly true in the USA, the World's leading producer of molybdenum, where the greatest annual tonnage of high-speed steel is of the molybdenum type. 

The main features of a high-speed steel are its great hardness in the heat-treated condition, and its ability to resist softening at relatively high working  temperatures. Thus, high-speed steel tools can be used at cutting speeds far in excess of those possible with ordinary steel tools, since high-speed steel resists the tempering effect of the heat generated. In high-speed steels ordinary cementite, Fe3C, is replaced by single or double carbides of three different groups based on the general formulae M6C; M23C6 and MC, where 'M' represents the total metallic atoms. Thus M6C is represented by Fe4WiC and Fe4Mo2C, whilst M23C6 is present as
O"23C6 and MC as WC and VC. Vanadium Carbide is very abrasion resistant and so improves cutting efficiency with abrasive materials. Since vanadium is also an important grain-refiner, this effect is very useful in high-speed steels because of the very high heat-treatment temperatures involved. It also increases the tendency towards air hardening by retarding transformation rates. Vanadium tends to stabilise the 6-ferrite phase (13.11) at high temperatures and this leads to carbide precipitation so that high-vanadium steels may be somewhat brittle. Nevertheless vanadium is now added in amounts up to 5.0% to modern high-speed steels. Up to 12.0% cobalt is also added to 'super' high-speed steels. Not being a carbide former it goes into solid solution and raises the solidus temperature, thus allowing higher heat-treatment temperatures to be used with a consequent increase in the solution of carbides and, hence, hardenability and wear-resistance. Since cobalt promotes excellent red-hardness these super-high-speed steels are useful for very heavy work at high speeds. As mentioned above, high-speed steels containing greater proportions of molybdenum are now widely used. Generally these alloys require greater care during heat-treatment, being more susceptible to decarburisation than the tungsten varieties. With modern heat-treatment plant, however, this is not an unsurmountable difficulty. Molybdenum high-speed steels are considerably tougher than the  corresponding tungsten types and are widely used for drills, taps and reamers. All of the metallic carbides mentioned above are harder than ordinary cementite, Fe3C, but the most important feature of high-speed steel is its ability to resist softening influences once it has been successfully hardened. This 'red' hardness, or resistance to softening at temperatures approaching red-heat, is due to tungsten, molybdenum, cobalt, etc being taken into solid solution in the austenite along with carbon before the steel is quenched. Further transformations in the resultant martensite are very sluggish as a result of the large quantities of alloying elements in solid solution, so that the steel can be raised to quite high temperatures before softening sets in due to carbide precipitation.





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