Metallurgy in depth Explanation : Introduction, Classification, What and How?

 

Introduction of Metallurgy

Metallurgy is the science and technology of metals. The worker of metals is mentioned in the Bible, Greek and Norse mythology. It is an art that has been practiced since ancient times. The ancient men knew and used many native metals.

Gold was used for ornaments, plates and utensils as early as 3500 B.C. The art of smelting, refining and shaping metals was highly developed by both the Egyptians and the Chinese. The ancient Egyptians knew how to separate iron from its ore and that steelhead the ability to harden. But iron was not used widely before 1000 B.C. Iron was not popular with ancient people because of its tendency to rust and they preferred working with gold, silver, copper, brass and bronze.

Knowledge of dealing with metals was generally passed directly from master to apprentice in the Middle Ages, leading to an aura of superstition surrounding many of the processes. Very little was written on the metallurgical processes until Biringuccio published his “Pirotechnia” in 1540 followed by Agricola’s “De Re Metallurgica” in 1556. In succeeding years, much knowledge was added to the field by people trying to duplicate the composition and etched structure of Damascus steel.

Until the beginning of the last quarter of the nineteenth century, most of the investigations of metal structure had been macroscopic (by eye) and superficial. The science of the structure of metals was almost nonexistent. The situation was ripe for the detailed attention of individuals whose background was more scientific than practical. The individual was responsible for the period of rapid development that followed was Henry Clifton Sorby. 

Sorby was an amateur English scientist who started with a study of meteorites and then went on to study metals. In September 1864, Sorby presented a paper to the British Association for the Advancement of Science in which he exhibited and described a number of microscopical photographs of various kinds of iron and steel. This paper marks the beginning of the metallography, the field concerned with the use of the microscope to study the structure of metals. It seems that while many people appreciated the value of Sorby’s studies at the time they were done, none of them had sufficient interest to develop the technique independently and metallography lay dormant for almost twenty years.

Additional work by Martens in Germany (1878) revived Sorby’s interest in metallurgical problems and in 1887 he presented a paper to the Iron and Steel Institute which summarized all his work in the field. Considerable attention was now generated by both scientists and industrial metallurgists in other countries. In the early part of the twentieth century, Albert Sauveur convinced American steel companies that the microscope was a practical tool to aid in the manufacture and heat treatment of steel.

About 1922, more knowledge of the structure and properties of metals was added by the application of x-ray diffraction and wave mechanics.

Metallurgy is really not an independent science since many of its fundamental concepts are derived from physics, chemistry and crystallography.

The metallurgist has become increasingly important in modern technology. Years ago, the great majority of steel parts were made of cheap, low-carbon steel that will machine and fabricate easily. Heat treatment was reserved largely for tools. Designers were unable to account for structural inhomogeneity, surface defects etc. It was considered good practice to use large factors of safety. Consequently, machines were much heavier than they should have been and the weight was considered a mark of quality. This attitude has persisted to some extent, to the present time but has been discouraged under the leadership of the aircraft and automotive industries. They have emphasized the importance of the strength-weight ratio in good design and this has led to the development of new high-strength, lightweight alloys.

New technical applications and operating requirements pushed to higher levels have created a continued need for the development of new alloys. For example, an exciting development has been the Wankel rotary engine. It is an internal combustion engine of unusual design that is more compact, lighter and mechanically far simpler than the ordinary reciprocating piston motor of equivalent horsepower. A particularly bothersome problem has been the seals between the rotor and the metal wall. Originally, the seals were made of carbon and seldom lasted more than 20,000 miles. Research developed a new sintered titanium-carbide alloy seal which has given life-times of up to 100,000 miles.

The metallurgical field may be divided in two large groups. They are:

1.      Process or Extractive metallurgy- The science of obtaining metals from their ores, including mining, concentration, extraction and refining metals and alloys.

2.      Physical metallurgy- The science concerned with the physical and mechanical characteristics of metals and alloys. This field studies the properties of metals and alloys as affected by three variables.

a.       Chemical composition- The chemical constituents of the alloy.

b.      Mechanical treatment- Any operation that causes a change in shape such as rolling, drawing, stamping, forming or machining.

c.       Thermal or Heat treatment- The effect of temperature and rate of heating and cooling.