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==== Products of the Blast furnace ====

==== Products of the Blast furnace ====

The products obtained from the blast furnace include Pig Iron, Slag and Flue gasses.<ref name=":3" /> Pig iron is the most impure form of iron having impurities. Slag is mostly calcium silicate and some amount of aluminum silicate. Gasses produced in the extraction process are called flue gasses containing CO (carbon monoxide), Nitrogen and hyderogen.

The products obtained from the blast furnace include Pig Iron, Slag and Flue gasses.<ref name=":3" /> Pig iron is the most impure form of iron having impurities. Slag is mostly calcium silicate and some amount of aluminum silicate. Gasses produced in the extraction process are called flue gasses containing CO (carbon monoxide), Nitrogen and hydrogen.

==== Commercial forms of Iron ====

==== Commercial forms of Iron ====

# '''Cast Iron''' - Pig iron when is remelted in a vertical furnace can be poured into moulds. It is then called cast iron. When the pig iron is suddenly cooled, crystalline cast iron is obtained called as white cast iron. In this form carbon is present combined with iron as iron carbide. However, if the molten pig iron is cooled gradually in sand moulds, a graphite coloured iron is formed called grey cast iron. Major part of cast iron is used to manufacture steel and other heavy machinery.

# '''Cast Iron''' - Pig iron when is remelted in a vertical furnace can be poured into moulds. It is then called cast iron. When the pig iron is suddenly cooled, crystalline cast iron is obtained called as white cast iron. In this form carbon is present combined with iron as iron carbide. However, if the molten pig iron is cooled gradually in sand moulds, a graphite coloured iron is formed called grey cast iron. Major part of cast iron is used to manufacture steel and other heavy machinery.

# '''Wrought or Malleable iron''' – It is the purest form of iron. It contains about 0.2 % carbon.

# '''Wrought or Malleable iron''' – It is the purest form of iron. It contains about 0.2 % carbon.

# '''Steel''' – It is an alloy of iron with carbon and other elements like manganese, silicon and phosphorus. It is midway between cast and wrought iron as far as impurities are concerned. It contains 0.1 to 1.5 % carbon.

# '''Steel''' – It is an alloy of iron with carbon and other elements like manganese, silicon and phosphorus. It is midway between cast and wrought iron as far as impurities are concerned. It contains 0.1 to 1.5 % carbon.<ref name=":3" />

== Types of Ferrous Materials ==

== Ferrous Materials - Types and Characteristics ==

The Rasaratnasamucchaya describes three types of ferrous materials.

The Rasaratnasamucchaya describes three types of ferrous materials.<ref name=":6" />

{| class="wikitable"

{| class="wikitable"

|+Classification of iron and its properties as given in Rasa Ratna Samucchaya<ref name=":6">Prakash, B. ''Ancient Iron Making in India'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref>

|+Classification of iron and its properties as given in Rasa Ratna Samucchaya<ref name=":6">Prakash, B. ''Ancient Iron Making in India'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref><ref name=":8">Mookerjee, Bhudeb. (1984 Second Edition) ''Rasa-Jala-Nidhi or Ocean of Indian Chemistry, Medicine and Alchemy'', ''Vol. 3'' Varanasi: Srigokul Mudranalaya</ref>

!Kinds of Iron  

!Kinds of Iron  

(Loha)

(Loha)

|White cast iron

|White cast iron

|}

|}

== Extraction Process in Ancient Times ==

== Extraction Process in Ancient Times ==

# '''Drying, firing and operating the furnace''': After the dried furnace and the raw material were ready the furnace was charged with dried wood chips and then filled with charcoal up to the top. A ritual pooja and havan were performed praying for the successful operation of the furnace and then it was ignited using a little of the sacred fire from the havan. This was introduced inside the furnace through the tuyere pipe. When the wood starts burning, the bellows were operated slowly to build the fire inside the furnace. After the yellow flame appeared at the mouth of the furnace the blowing rate was increased to raise the furnace temperature. As the charcoal got consumed, ore was charged and the blowing was continued till a translucent blue flame appeared at the top. Blue flame indicated that the furnace reached a temperature of > 1000^oC and the charcoal is burning to generate CO gas. At this stage the furnace was charged with alternate layer of ore and charcoal in the ratio 1:2 and the air blowing rate was adjusted and controlled to maintain steady condition. The temperature inside the furnace was visually examined by peeping through the tuyere pipe and after about one hour the first slag was tapped. The fluidity .of the slag, its quantity as well as colour on solidification were indicators of successful operation of the furnace. The slag was either tapped periodically or continuously throughout the furnace operation. When sufficient charges of ore had been made, it was followed by few blank charges of charcoal only, and the air blowing rate was increased to consolidate the reduced iron into a large porous lump and separate it from the FeO rich fayalite (2FeO.SiO₂) slag. The measured temperature at this stage was found to be 1500°C in front of the tuyere. One round took about 5 to 6 hours and preparation is made to take out the hot iron sponge.

# '''Drying, firing and operating the furnace''': After the dried furnace and the raw material were ready the furnace was charged with dried wood chips and then filled with charcoal up to the top. A ritual pooja and havan were performed praying for the successful operation of the furnace and then it was ignited using a little of the sacred fire from the havan. This was introduced inside the furnace through the tuyere pipe. When the wood starts burning, the bellows were operated slowly to build the fire inside the furnace. After the yellow flame appeared at the mouth of the furnace the blowing rate was increased to raise the furnace temperature. As the charcoal got consumed, ore was charged and the blowing was continued till a translucent blue flame appeared at the top. Blue flame indicated that the furnace reached a temperature of > 1000^oC and the charcoal is burning to generate CO gas. At this stage the furnace was charged with alternate layer of ore and charcoal in the ratio 1:2 and the air blowing rate was adjusted and controlled to maintain steady condition. The temperature inside the furnace was visually examined by peeping through the tuyere pipe and after about one hour the first slag was tapped. The fluidity .of the slag, its quantity as well as colour on solidification were indicators of successful operation of the furnace. The slag was either tapped periodically or continuously throughout the furnace operation. When sufficient charges of ore had been made, it was followed by few blank charges of charcoal only, and the air blowing rate was increased to consolidate the reduced iron into a large porous lump and separate it from the FeO rich fayalite (2FeO.SiO₂) slag. The measured temperature at this stage was found to be 1500°C in front of the tuyere. One round took about 5 to 6 hours and preparation is made to take out the hot iron sponge.

# '''Removal of slag and handling of red hot sponge iron bloom''': In case of bowl furnaces, generally the slag was allowed to get collected and solidified at the bottom of the furnace. In the case of other furnaces, it was tapped out through the slag hole known as 'Hagan.' After the smelting period was over, the bellows along with blow pipes were removed and the temporary wall for closing the front opening was removed and the partially melted tuyere was taken out with the help of a tong and a wooden pole. It was placed on a large granite stone anvil and hammered to consolidate and remove the molten slag filled in the pores.

# '''Removal of slag and handling of red hot sponge iron bloom''': In case of bowl furnaces, generally the slag was allowed to get collected and solidified at the bottom of the furnace. In the case of other furnaces, it was tapped out through the slag hole known as 'Hagan.' After the smelting period was over, the bellows along with blow pipes were removed and the temporary wall for closing the front opening was removed and the partially melted tuyere was taken out with the help of a tong and a wooden pole. It was placed on a large granite stone anvil and hammered to consolidate and remove the molten slag filled in the pores.

# '''Secondary refining of the bloom''': This most important and exclusive Indian practice was carried out to remove the slag trapped inside the iron block. For this, the iron bloom was reheated in a smithy forge to almost white hot (>1250°C) condition and silica sand was sprinkled upon it. This reacted with the remaining FeO and helped in forming fluid 2FeO.SiO₂ slag which flowed out of the iron block. The iron block was taken out of the furnace and forged to increase its density. This process was repeated till the bloom was converted into 12 to 15mm square/circular rod. This refined rod containing 0.2 to 0.4% SiO₂ almost free from the slag inclusion was cut into 150 to 180mm long pieces and sold to the blacksmiths or 'Lohars' for reshaping them into useful objects.

# '''Secondary refining of the bloom''': This most important and exclusive Indian practice was carried out to remove the slag trapped inside the iron block. For this, the iron bloom was reheated in a smithy forge to almost white hot (>1250°C) condition and silica sand was sprinkled upon it. This reacted with the remaining FeO and helped in forming fluid 2FeO.SiO₂ slag which flowed out of the iron block. The iron block was taken out of the furnace and forged to increase its density. This process was repeated till the bloom was converted into 12 to 15mm square/circular rod. This refined rod containing 0.2 to 0.4% SiO₂ almost free from the slag inclusion was cut into 150 to 180mm long pieces and sold to the blacksmiths or 'Lohars' for reshaping them into useful objects.<ref name=":6" />

National Metallurgical Laboratory, Jamshedpur, in India made great strides in improving the ancient iron making process and made significant contributions to the iron industry.<ref name=":4" />

 

 

In the 19th century, National Metallurgical Laboratory, Jamshedpur, in India made great strides in improving the ancient iron making process and made significant contributions to the iron industry.<ref name=":4" />

== Wootz Steel ==

== Wootz Steel ==

Wootz is the anglicized version of 'ukku' in the language of the states of Karnataka and Andhra Pradesh, a term denoting steel. Ample literary references suggest that the steel from southern India was the finest and once exported to Europe, China, Arab countries and the Middle East. Though an ancient material, it fulfills the description of advanced material. It is an ultra-high carbon steel of 1-2% exhibiting properties such as super-plasticity and high impact hardness.<ref name=":7">Srinivasan. S and Ranganathan. S. ''Wootz steel: An advanced material of the ancient world'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref>

Wootz is the anglicized version of 'ukku' in the language of the states of Karnataka and Andhra Pradesh, a term denoting steel. Ample literary references suggest that the steel from southern India was the finest and once exported to Europe, China, Arab countries and the Middle East. Though an ancient material, it fulfills the description of advanced material. It is an ultra-high carbon steel of 1-2% exhibiting properties such as super-plasticity and high impact hardness.<ref name=":7">Srinivasan. S and Ranganathan. S. ''Wootz steel: An advanced material of the ancient world'' in Iron & Steel Heritage of India Ed. S. Ranganathan, ATM 97, Jamshedpur</ref>  

Wootz steel spurred developments in modern metallographic studies. Indian wootz ingots are believed to have been used to forge Oriental Damascus swords which were reputed to cut even gauze handkerchiefs and silk. Finest swords and artefacts of Damascus steel are seen in museums today.<ref name=":7" />

Wootz steel spurred developments in modern metallographic studies. Indian wootz ingots are believed to have been used to forge Oriental Damascus swords which were reputed to cut even gauze handkerchiefs and silk. Finest swords and artefacts of Damascus steel are seen in museums today.<ref name=":7" />

Although iron and steel had been used for thousands of years, the role of carbon in steel as the dominant element was found only in 1774 by the Swedish chemist, Tobern Bergman, and was due to the efforts of Europeans to unravel the mysteries of wootz. With the aim of reproducing the South Indian wootz steel on an industrial scale, there was a spurt in interest in many European travellers in early 1800's. By 1918 Belaiew made an important finding concerning wootz steel; he was probably the first to attribute the malleability of it to the spheroidized nature of the forged steel and to recognize that this occurs during forging at a temperature of red heat (700-800^oC).<ref name=":7" />

Although iron and steel had been used for thousands of years, the role of carbon in steel as the dominant element was found only in 1774 by the Swedish chemist, Tobern Bergman, and was due to the efforts of Europeans to unravel the mysteries of wootz. With the aim of reproducing the South Indian wootz steel on an industrial scale, there was a spurt in interest in many European travellers in early 1800's. By 1918 Belaiew made an important finding concerning wootz steel; he was probably the first to attribute the malleability of it to the spheroidized nature of the forged steel and to recognize that this occurs during forging at a temperature of red heat (700-800^oC).<ref name=":7" />

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== References ==

== References ==

[[Category:Shastras]]

[[Category:Shastras]]