3 GREATEST ADVANCEMENTS IN THE FIELD OF METALLURGY

INTRODUCTION

Without any doubt, I can clearly say that the skeleton of the developing world is laid by metals and their alloys. Metals have their significant application since Mesolithic age. Metals and alloys have significant history, amazing present and definitely a brilliant future. From greatest architectures and structures to micro-chips and nano-chips metals have their remarkable presence. They are given so much of importance that the time passage of history is being divided on their names. As:

a.) Copper age( 4500 B.C. to 3500 B.C.)

b.) Bronze age( 4,000 B.C. to 1,200 B.C)

c.) Iron age( began around 1,500 B.C.)

Metals are playing a very vital role in development of any other industry of the world, as they are either the raw material for final product or are used to produce machinery. As there is a widespread application of metals and alloys in almost every sector of the world, the advancements are the must needed for this sector. Due to these demands the people around the world had been very busy in development of the field of metallurgy. Now-a-days we have reached an efficiency of nearly 95% in blast furnace. As the needs are growing so are the advancements, but to match the pace of both, is one of the biggest challenges of metallurgy. In this journey of advancements we have achieved many milestones and I am going to discuss about the three which has lead us to reach different heights in metallurgy world.

They are

A.) Stainless steel

B.) Hall–Héroult process

C.) Age Hardening

A.) STAINLESS STEEL

Stainless steel is also known as inox. Invention or discovery of stainless steel becomes an ambiguous topic to discuss on. As stainless steel is an alloy of iron with minimum of 10.5% (by mass) of chromium content which forms an oxide layer, this layer is also known as passive layer. So at different instances there had been significant claims about the different compositions. Like there were these two people Englishmen Stoddard and Farraday circa in 1820 and this man Frenchman Pierre Berthier in 1821 who said that certain iron-chromium alloys are resistant to attack of acids. Again, in 1872 another pair of Englishmen, Woods and Clark, filed for patent of an acid and weather resistant iron alloy containing 30–35% chromium and 2% tungsten, effectively the first ever patent on what would now be considered a stainless steel. In 1875 the importance of carbon was discovered. This discovery claimed that carbon content must be near 0.15% or less than this amount to bind sufficient amount of chromium. There are many such claims of it’s discovery. Let’s look into other aspects.

Stainless steel is used across the world in almost every industry. It is a suitable material to be used at those places where strength of steel and corrosion resistance both are required together. As for basic examples in daily life we have

1. ) Domestic uses as in cutlery, saucepans, utensils etc.
2. ) Architectural uses as in lighting columns, lintels, masonry supports etc.
3. ) It is used to make different types of engines and in locomotives.

and many more.

stainless steel rods

Stainless steel has a corrosion resistance uses. Along with the chromium other alloying elements are also added for example nickel, molybdenum, titanium and copper. Also certain amount of non metals are added, carbon and nitrogen are examples.

As the name suggest that this is stainless so it remains stainless for a period of time but it don’t claim no signs of corrosion. Stainless steel corrodes, too, but the effect of corrosion is relatively seen after a long period of time.The best thing about stainless steel is that it is 100% recyclable.

B.) Hall–Héroult process

Hall–Héroult process is an electrochemical process. It comes under the ‘smelting’ category under broader classification of metallurgical processes. In this process alumina is dissolved in cryolite bath with in a cage of carbon linings. A powerful electric current is passed through the bath that separates the aluminium from the molten solution.

Now-a-days aluminium is one of the most common metal. It is the third most abundant element in the earth crust. It is obtained from a reddish brown ore called bauxite. But before 1886 the scenario was not the same. Aluminium was considered as a semi-precious metal and it’s prices were comparable to that of silver. Aluminium is difficult to extract because of its high affinity to combine with oxygen. The story of aluminium changed on February 23, 1886 when Charles Martin Hall succeeded in producing aluminum metal by passing an electric current through a solution of aluminum oxide in molten cryolite. And at nearly the same time Paul L.T. Héroult was granted a French patent on April 23, 1886, for a comparable process based on cryolite and aluminum oxide. It is really amazing that these two people without knowing anything about each other discovered the same methods at nearly the same time. It is because of this, that we get the name Hall-Héroult process.

Hall made a crucible of graphite to line the clay crucible. He then added the bauxite and also aluminium fluoride to lower the melting point of system. Then the electricity was allowed to pass for several hours then the molt was taken out and broken, certain silvery globules were observed. These globules were then tested with hydrochloric acid and a new benchmark in the field of metallurgy generated right there.

C.) Age Hardening

This is also known as precipitation hardening or particle hardening. This is a heat treatment technique used to increase the yield strength of malleable materials. Precipitation hardening relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the movement of dislocation or defects in a crystals’s lattice. The metal is aged by either heating it or keeping it stored at lower temperatures so that precipitates are formed. The process of age hardening was discovered by Alfred Wilm. Age Hardening is performed on alloys of nickel, Magnesium, Titanium and low Carbon Steels.

Precipitation hardening relies on formation of finer impure particles which is a result of change in solid solubility and change in solid temperature. Precipitaionin solids can produce many different sizes of particles, which have radically different properties. Unlike ordinary tempering , alloys must be kept at elevated temperature for hours to allow precipitation to take place.

Age hardening has proved to be a major milestone in development of metals and alloys as it enhances the properties drastically. Age hardening improves :

1. tensile strength
2. yield strength
3. wear resistance

If age hardening would not have been there we would not have been using ball bearings, valves in engines, turbine blades etc. Without all these how do you see our overall development?

Many aluminum based alloys, copper-tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age hardening processes. Duralumin is a name known to all, after cast iron, in 19th century the better known alloy was duralumin which was enhanced and developed using age hardening. This method enhanced the strengthening characteristics so drastically that this developed material was now used for making aircraft.

Age hardening is done in three steps:

Step 1: Solution treatment

Step 2: Quenching

Step 3: Ageing

After these process certain properties develop, which have proved to play a major role in different kinds of development throughout the world.

There had been many such advancements and developments which had lead humankind towards directions of developments. But these developments had made us a little dizzy towards the environment and nature. We, in the name of development, are ruining and overloading our mother nature. Although many steps are taken yet many are needed to be taken.