Modern Concepts of Steel making through Induction Furnaces
R.R Varshney Executive Director, All India Induction Furnaces Association
Jitendra Singh President of All India Induction Furnaces Association
l . Introductions
The various types of Induction Furnaces used for Steel making are medium frequency and high frequency. Mild steel, Stainless Steel and low and high alloy Steel can be made from this furnaces. Raw materials used are Steel melting Scrap and Direct Reduced Iron. Alloying elements added as per requirement.
2. Brief history of making steel by Induction Furnaces route
2.1 In India we started using Mains Frequency Induction Furnaces from mid?sixties and medium frequency imported induction furnaces from mid-seventies but a sudden growth took place from early eighties upto mid?nineties when indigenous manufacture of Induction Furnaces commenced. Initially we were using them for melting and making Stainless steels by using imported stainless steel scrap but market condition from mid-eighties encouraged entrepreneurs to make mild steel. However, after liberalisation there was considerable increase in the number of induction furnaces and also capacity per charge. Now-a-days, furnaces upto a maximum of 16-tonne/charge are being used.
3. Current status of Induction Furnaces
3.1 Modernisation has been carried out by using refining, equipment as well as continuous casting of billets. To make good quality of mild steel, refining by using (LRF) ladle refining furnaces are in use and for manufacture of stainless steel, AOD refining vessels are used. It is advisable to use pedigree chemical composition medium and heavy steel melting scrap. Prior to production of Direct Reduced Iron (DRI), it was difficult to control chemistry of melt but now the technology of using DRI to adjust chemistry has been mastered. Carbon can he adjusted as per specification and tramp elements are controlled because DRI does not have tramp metals and elements.
4. Why steel in India is made from I.F. route ?
4.1 India is the first country using Induction Melting Furnaces for making mild steel. As a matter of fact, EAFs are not making mild steel of structural quality for over a decade now. The bulk of structural quality mild steel for long products is manufactured by Induction Melting Furnaces. During 2001?2002 period over 4.5 million tonnes of steel were produced by Induction Furnaces. The EAF units have also installed Induction Melting Furnaces. There are several reasons for the popularity of Induction Melting Furnaces for making steel. They consume less power comparing EAFs. Expenditure on electrode is nil. They use lesser quantity of refractory. Initial investment is less on plant and equipment. Thus, there are economic advantages in making steel through Induction Furnaces route. The only snag is that at present bulk quantity steel cannot be produced through Induction Furnace route. May be that in future it may be possible to do so.
5. Mini-integrated steel plant concept
5.1 A new trend of making steel in India is emerging. This new technology is using Direct Reduced Iron (DRl) - Induction Melting Furnaces (large capacity) Continuous Casting of Billets or Rolling Mills to Make Billets and Bars, Fods and Sections.
5.2. Initially M/s Essar Gujarat installed DRI unit and used EAF (150 tonnes) to make steel for flat products. Some more such steel plants have been installed. Some prominent DRI manufacturers have also installed Induction Melting Furnaces to make mild steel ingots or billets. During the last two to three years many DRI making plants have been installed in States like Chattisgarh (carved Out of Madhya Pradesh), Jharkhand (carved out of Bihar), Orissa and West Bengal varying from 20,000 tonnes upwards. These states are rich in Iron ore and coal. During DRI making from coal, waste gases coming out are rich in carbon monoxide/dioxide, Methane?Ethane, etc., and hence have lot of calorific values to generate power taking and by quantity of power from State Electricity Boards and using its own generated power, DRI plants are installing various capacity Induction Furnaces. Some have also downward fabricating units like concast or rolling mills. Thus a sort of Mini Integrated Steel Plants are coming up. This technology is fast becoming popular and may revolutionise our old and established concept of making steel. The mild steel produced by such plants is cheap and of good duality. However, much will depend upon economies of production and market forces. Many, other technologies are coming up which all have orientation to local conditions and resources availability. Induction Furnaces industry has to face many challenges in this era of emerging new technologies for making steel.
6. Various types of steel and cast iron production by I.F.
6.1 Mild Steels: In order to control chemistry of end product, chemical analysis of all input metallic is taken before snaking the charge-mix. After 50% charging is completed a bath sample is sent to laboratory. The chemical analysis is examined, calculations made tin further additions are made of input metallics. If it has high carbon, Sulphur and phosphorous, percentage Sponge iron in the charge is increased. When 80% melting is completed a final bath sample is taken. If carbon is still high more of sponge iron fines are charged in case carbon is less, cast iron scrap and turnings are charged. Thus, the chemistry is controlled. Since no
vigorous arcing like Electric Arc Furnace:; takes place in Induction Melting Furnaces, the oxidation of iron much less and losses are also minimal. Silicon an Manganese in metal are oxidized by FE2 O3 and FeO Carbon is reduced by iron oxide of DRI. Sulphur and phosphorous are diluted by DRI. There are no tram elements in the final product.
6.2 Low Alloy Steels
6.2.1 At present Low alloy steels are being regularly produced by Induction Furnace Units in India. The include EN18, EN19, EN8, EN9, etc. Chemical composition is strictly controlled by using spectrometer. Size of ingots varies 3½ x 4½ to as much
6 ½" x 7½". So far none of the Induction Furnaces units have produced these steels by concast process but some Induction Furnaces units are installing ladle refining and concast equipment to make concast billets.
6.3 Stainless Steels
6.3.1 Induction Melting Furnaces before making Mild Steel ingots started producing Stainless Steel since 1979?80 period using small size Induction Furnaces. The raw material was imported-SS scrap and casting ingots by purging liquid metal in ladle, adding alloying elements etc. and melting mild steel scrap and adding ferro?allow and transferring the liquid metal to AOD vessels for refining. After AOD treatment some units carry out further refining in LRF and then producing billet by concast process. All units having ladle refining system have installed spectrometer for accurate and quicker bath analysis. Gas levels such N2H2 & O are also determined by the newly installed instruments. Most of the Induction Furnaces units are producing utensils grade SS. Two Induction Furnaces units making SS have exported bars rods and wires. More anal more Induction Furnace units are modernizing as well as diversifying to value added products.
6.4 Grinding Media
6..1.1 Five Induction Furnace units are producing Grinding Media MnCr5, 20 MnCr5, etc. located at Ghaziabad. Jhansi, Ahmedabad and Bangalore. and exporting. It meets the quality requirements of world standard.
6.5 Special Cast Iron & S.G. Iron castings:
6.4.1 While many cast iron casting foundries have installed mains frequency Induction Furnaces to make special cast irons, some have installed medium frequency Induction furnaces to make S.G. iron. These foundries have chemical testing, sand testing and physical testing equipment along with ultrasonic testing equipments. It is learnt that these Induction Furnace units have exported special Cast iron and SG iron worth crores of rupees over the years.
7.1 Steel making process is tinder going considerable changes, New processes are being developed to use various types of Iron ores, coal and gas. Iron ore fines are used for making Pig Iron. These are developed by European Countries, In India National Mineral Development Corporation have an agreement with Russia to adopt Romalt process by using fines of Iron ores. Hopefully the production will commence shortly. Jindal's have purchased a technology called Corex process. Steel has been produced successfully by Jindal's. It is to be seen whether new processes are econornicaly viable comparing to old systems i.e. Coke over, Blast furnaces, steel making by BOF converters' M/s Usha Martin company are making pig iron in cupela and it is charged hot in Electric Arc Furnace to mak steel. All these processes trim to make cheaper steel and conversation of energy. Duplexing and Tripplexing process is may become necessary to make steel in future.