Association Article

R.P. Varshney, Executive Director, AIIFA,Delhi

Introduction

The world at present is witnessing technology up-gradation in regard to input materials and technology for steel making and pig iron production. Good quality iron ores are depleting all over the world and in the same way good quality coking coal needed for reduction of iron ores in blast furnace is also becoming scarce. Big hills of iron ore fines can be seen at the iron ore mine heads because in Blast Furnaces only certain weight and size of iron ore grits can be used. Thus, to reclaim the fine iron ores several technologies have been developed to make pig iron.

Romalt Process for Pig Iron

Russians have developed a technology of using iron ore fines by making agglomerate of fines and then charging them in a furnace where ordinary coal can carry out reduction of iron ore and make pig irons. It is closed chamber furnace. National Mineral Development Corporation (NMDC) who mine iron ore and export it to other countries have a tie-up with Russia for installing the ROMALT process at Bailadila in the State of Chhattisgarh. Similar plants have been developed by Austria, etc. which can be used according to the types of iron ore fines availability and the reduction i.e. Carbon content material availability.

COREX Process

COREX Process was developed by the Austrian firm who utilizes good quality iron ore with poor quality of coal. In a closed vessel, the reaction takes place and the ore gets reduced. In India, the COREX process plant has been installed by M/s Jindal Vijaynagar Steel Limited in the State of Karnataka. The pig iron produced in the plant is sent to LD converters for production of Steel. The Pig iron has been made by COREX process, ROMALT process and by HYSMELT process. Low shaft Blast Furnaces are also being used.

Manufacturing Steel - Continuous Casting Process

More and more International Steel plants are at present using continuous casting machines for the manufacture of long as well as flat products of steel. India is also not lagging behind. Over two dozen Electric Induction Furnaces are using continuous casting process.

Manufacture of Sponge Iron/Direct Reduced Iron - As Input Material to Steel Making

As stated earlier, the iron ore has to be reduced to remove the Oxygen content. Carbonaceous materials are to be used but for smelting the carbonaceous materials do not have the property to carry out sufficient reduction of iron ores. The technology was developed in Germany known as SLRN process in Sixties to use iron ore, mix it with limestone and then use ordinary coal. These are fired in horizontal kilns of 60 ft. to 90 ft. long which are kept rotating to allow the input to mix up. From various points and zones firing is done. It will bring the temperature to near about 1350ºC to 1400ºC. At this temperature, the carbonaceous material reacts with FeO, Fe²O³, etc. and removes the oxygen from the ores. This contains iron upto 90% and rest is gauge material. The reduction of iron ore is also carried out by using Compressed Natural Gas (CNG). For this purpose pellets of iron ore are taken from palletizing plants. Coal is added in the kilns. Here again at a temperature of 1350ºC, the carbon content of the gases react with the iron ore and reduce the Oxygen of the ore. The product is called Hot Briquetted Iron (HBI). The HBI are considered to be superior than the coil based sponge iron. Sponge iron is input material not only for Electric Steel making but also in big Integrated Steel Plants who charge it in the blast furnaces or at any point where it is necessary to increase the productivity. For the production of Steel by Electric Steel making route, Sponge Iron/HBI is a good substitute because it contains least tramp elements. The steel melting scrap is rendered from Steel products, which may contain Copper, Chromium and other metals, and non-metals, which will make the steel, produced dirty. Thus due to absence of tramp elements, sponge iron is gaining popularity in steel making.

Electric Process of Making Steel

Due to shortage of Steel in the Country, Government of India allowed a member of Electric Arc Furnaces (EAFs) to produce steel in the Secondary Steel Sector by recycling the steel scrap. Since early 70"s to 1985, nearly 150 EAFs were installed with a capacity of over 9 million tones in various parts of the country. However, in the meanwhile the Medium Frequency Induction Furnaces technology came into the country in early 80's. Electric Induction Furnaces have been installed in all states in India and India is perhaps the only country in the World using Induction Furnaces on a large scale to manufacture secondary steel.

Electric Arc Furnaces of bigger capacities say 150 tones/charges have been developed. The recent developments in EAF technology are the increased oxygen consumption, reducing power consumption and decrease in tap to tap time and the increased hot metal proportion to reduce power consumption and control 'Cu' content which comes from steel melting scrap to produce higher grades of steel. At present nearly 30% of steel is produced by EAF route in the world. This is because of more and more availability of steel scrap.

Electric Arc Furnaces

Electric Arc Furnaces installed in India were of small capacities ranging from 5 tonne to 20 tonne per charge in early seventies. The reason was (a) non availability of big size furnaces (b) to cater the need of shortage of steel for construction industry as the product of Arc furnaces was not under Government control of prices unlike steel produced by integrated steel plants. (c) Facilities provided by Government such as less excise duty of Arc furnace product. Thus EAFs were installed in J & K, Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Rajasthan, M .P., Bihar, West Bengal, Orissa, Andhra Pradesh, Tamil Nadu, Karnataka, Maharashtra & Gujarat. There was some slump in 1975 to 77 and to rehabilitate them the banks reduced interest rates, excise duty was reduced. Finding shortage of steel melting scrap in the country, import of steel scrap was allowed at concessional custom duty rate. From1978 to 1985 EAF s did very well.. some of them started diversifying the product-mix made by them. Some installed balancing equipment and continuos casting equipments. In mid eighties the profitability of EAFs up to 15 tone/charge decreased particularly who were producing pencil ingots only. Some of EAFs did not take action to reduce power consumption etc. When the Induction Furnaces started producing steel from 84-85 using less power, the competitiveness of EAFs became less and less despite steel Ministry not giving license to Induction Furnaces to make steel and import scrap. However, EAFs were still favoured by Steel Ministry in giving steel melting scrap, which was canalized by Government of India, through MSTC and allotted to EAFs only. But Induction Furnaces got import duty concession for importing steel melting scrap in 1998 through MSTC. This made the production of EAFs for making only pencil ingots uneconomical. Only 35 EAFs are in operation at present who have diversified their production or have started flat production - colour coating or galvanizing them, etc.

Electric Induction Furnaces

Induction Melting Furnaces in India were first installed to make Stainless Steel from imported Stainless Steel Scrap. But in years 1981-82, some entrepreneurs who were having small size Induction Furnaces, and making Stainless Steel experimented in making Mild Steel from steel melting scrap. It succeeded. More firms in northern India produced Steel (Pencil Ingots) by using 500 kg to 1 tonne Induction Furnaces. The power consumption was found to be about 650 Kwh/tone, which were nearly 100 units less than EAFs. Bigger size Induction Furnaces were then installed first in North India and then in other states of India. By 1985-86, the technology of making Mild Steel by Induction Furnace route was mastered by Indian Technologists. Induction Furnace manufacturers saw the potential and started installing bigger size/capacity Furnaces. By 1988-89 period 3 tonne per charge Induction Furnaces were installed (became standard) all over India. The chemistry of melt was adjusted by adding mill scale if opening carbon of bath was more. Good quality of steel melting scrap was used. In 1991-92, the Government license and control on steel making and rolling was removed. Then more Induction Furnaces were installed all over India. Backward and forward integration took place. The use of sponge iron made it possible to adjust chemistry of melt. Thus good quality of Mild Steel pencil ingots are being produced with no tramp elements.

Technological Upgradation

The fact that Electric Induction Furnaces are producing Mild Steel of structural quality in considerable quantities indicates both quality-wise and price-wise, they are competitive and will become still better if Government of India adopts a more pragmatic policy with regard to cost of Energy. Improvements are taking place in the Panel Circuit design and in Power factor. It is hoped that by improved panel circuit design, power consumption can be achieved below 600 Kwh per tonne. While many Electric Induction Furnace units have started processing steel melting scrap so that it not only improves the quality of products but also consumes less power. The other area, which can be improved in Induction Furnaces working, is in material handling, i.e. materials and also finished goods. Continuous feeding and heating of raw materials, i.e. Sponge iron and steel melting scrap in the Furnace is used by many companies in Maharashtra and Gujarat.

Inputs in the Induction Furnaces

Induction Furnaces are using Steel-melting scrap, Sponge Iron & Pig Iron/Cast Irons. On an average the ratio of these items is 40% sponge Iron + 10% Cast Irons or Pig Iron. The technology of melting these input materials varies according to the availability of raw materials and location of the plant. Quality of products made by Induction Melting Furnaces depends on the quality of input materials charged in the furnace. The various input materials used are given below:-

  • Shredded Steel Melting Scrap - mostly imported from USA
  • Heavy Steel Melting Scrap -mill cut ends or old steel components and some quality importer
  • Light Steel Melting Scrap such as turnings brooding or the steel sheets cutting
  • Old Cans & coated steel sheet cuttings
  • Railway scrap
  • Pig Iron/Cast Iron
  • Direct reduced Iron (Coal based)
  • Direct reduced Iron (Gas based)
  • Ship-breaking steel scrap

The shredded Steel scrap is at present considered to be a better input material due to its higher density and low melting losses. However, it has some tramp elements such as Copper, Nickel, Chromium, Zinc and Aluminium etc. While Zinc and Aluminium, chromium gets removed during melting but they make bath sluggish. Copper and Nickel remain in the metal. Over size steel scrap used need sizing and processing before charging, but very few units are doing so, thereby tap to tap time is more and Power consumption is higher, Railway scrap is good if it is of Mild Steel. Pig Iron and Cast iron can be used in certain proportions only. Direct reduced iron ores coal based or gas based have occupied a premier position in the secondary melting industry. It is a boon to Induction Melting Furnaces. It has no tramp element and is very low is Sulfur and Phosphorous contents. It is reported that some Induction Melting Furnace units are using as high as 85% DRI. A judicious blending of charge is needed to produce Steel of particular specification to meet quality requirement of customer/Annexure I gives a guidance of charge-blending etc. Therefore, quality management for steel production in Induction Melting Furnaces commences from input material stage. Ship breaking scrap is of Mild Steel and very good for Induction Furnaces.

Quality Management

With such a large producing capacity 8.5 million tonne and estimated production amounting to nearly 16% of Steel semi production in the country, Government of India has now realized the potential of this sector, which it neglected for over a decade. The industry on its own has initiated several schemes to meet the challenge it faces in regard to Quality Management. All the Induction Melting Furnace units have chemical testing laboratory and 20% have sophisticated testing equipment for alloying elements by using spectrometers. They have instruments for gas analysis. Casting units have Ultrasonic testing equipment or get such castings tested by independent laboratories as per requirement of the customer. Proper testing records are maintained by all Induction Furnace units. Over 30 number of Induction Furnace units have taken BIS Certification mark. The products of Induction Furnace units are meeting the BIS Certification mark. The products of Induction Furnace units are acceptable to ISRO; BHEL; NTPC; Railways and Defence and other users/customers. Product of Induction Melting Furnace units is exported to USA; Germany and other developed countries. It is expected that Induction Melting Furnace industry will in the next two years have elaborate quality assurance regime.

Quality Control of Low Alloys Special Steels and Stainless Steel made by Induction Melting Furnaces

Some Induction Furnace units are producing electrode grade steel. The production is carried out under strict control. The chemical composition of the steel as noted from the company's records is as follows: -

Heat No

C

Mn

Si

S

P

01

0.037

0.45

0.04

0.020

0.024

02

0.058

0.50

0.03

0.0186

0.019

03

0.04

0.55

0.05

0.020

0.23

04

0.03

0.48

0.03

0.017

0.023

Size of ingots produced is 3 ½ X 4 ½. All bath sample and final samples are tested using Spectrometer. The steel produced by this company is acceptable to electrode manufacturers.

At present many Induction Furnace units in India are regularly producing Low alloy Steels. These include En18, En19, En24, En8, En9 etc. Size of ingots varies 3 ½ " x 4 ½" to as much as 6 ½ " x 7 ½ ". So far none of the Induction Furnace units have produced these Steels by Concast process but three Induction Furnace units are installing Ladle Refining and Concast equipment to make Concast billets soon.

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 stainless scrap of 304 grade. At present stainless steel is produced by (a) melting SS scrap and casting ingots by gas purging the liquid metal in ladle, adding alloying elements etc. and (b) melting Mild steel scrap and adding ferro alloys 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 quicker bath analysis. Gas levels such as N, H & O are also determined by the newly installed instruments. Most of the induction furnace units are producing utensils grade stainless steel. Two induction furnace units making SS have exported bars and rods and forged flanges. More and more Induction furnace units are modernizing as well as diversifying to value added products.

Five Induction Melting Furnace units are producing Grinding Media on Mncr5; 20 MnCr5, etc. located at Ghaziabad, Jhansi, Ahmedabad, Mumbai and Bangalore and exporting. It meets the quality requirement of World standard.

At least 40 Induction Melting furnace units are producing steel castings for Railways, Sugar Mills, Tractor units and Machine tool companies. Four Units are producing heat resistant casting. The metallurgical tests are carried out as per specification, Ultrasonic testing, water Pressure test, tensile testing etc. Such units have all in-house testing equipment to control quality of products. More and more induction furnace units are going for special steel castings. At least five induction furnace units are exporting steel & alloy steel castings.

While many cast iron casting foundries have installed Mains Frequency Induction Furnaces to make quality cast irons, some have installed Medium Frequency Induction Furnaces to make SG Iron. These foundries have chemical testing, Sand testing and Physical testing equipments along with Ultrasonic testing equipments. It is learnt that these Induction furnace units have exported special cast iron & S G Iron castings worth Rs. 350/- crore in 1997-98.

It was felt that Induction Melting Furnace industry should develop Micro-Alloy structural steels. This idea was mooted by AIIFA and the development project was given to National Institute of Secondary Steel Technology (NISST), which prepared a feasibility report submitted to Ministry of Steel, Government of India in 2002. A sum of Rs. 4.0 lakh was granted by the ministry for this project. The melting & rolling has been completed. The Micro-Alloy Steel was produced by varying additions of vanadium, niobium and titanium for rolling 12 mm bars was carried out. Physical and Chemical tests were done. The semis of 12 mm bars so produced were made in normalized condition. Some were water quenched. The 12 mm bars produced with about 0.04% vanadium with carbon content nearly 0.25% was having strength and ductility superior to TMT bars in normalized condition. Mass production is being carried out. AIIFA is, therefore, taking up R&D projects to help the Induction Furnace industry.

  • Electrode Quality Steel
  • Low Alloy Steels
  • Stainless Steels
  • Grinding Media
  • Production of Steel & Alloy Steel Castings
  • Special Cast Iron & Sponge Iron Castings
  • Micro-Alloy Structural Steel

Present Scenario

After 2 years of depressed market the steel market suddenly showed competitiveness. It is noted that induction-melting furnaces in various parts of the country are at present operating to near full capacity depending on power availability. However, the power is not supplied to the units fully. Against a capacity of 8.5 million tonne in the year 2003-04, the induction furnaces are likely to produce nearly 5.2 million tonne of mild steel ingots. The production of stainless steel may also be 3.5 lakh tonne. There are nearly 890 units of induction melting furnaces installed in various parts of the country and laboratories to produce cast iron, special cast iron, mild steels stainless steels and high & low alloy castings. There are nearly 650 induction furnaces installed in the country to manufacture the mild steel and stainless steel. Out of this nearly 560-induction furnace units are in operation at present.

Due to demand of steel increased during the last one year, Mini Integrated steel plants are come up in some states of India. These plants, according to our information have been installed at Durgapur zone in West Bengal, Chhattishgarh, Jharkhand , and in a big way in Orissa. The route followed by these units are to have sponge iron plant, use sponge iron in melting it in induction melting furnaces of various capacities using Waste gas of sponge iron kiln in generating Power and use it in melting Sponge Iron and Steel melting scrap. The molten metal is put in Concast continuous machine and produce billets. According to our information nearly 1 million tonne of steel is being produced by this route. It is expected that this system of manufacturing steel by this Mini Integrated Steel Plants will shortly present a scenario totally new.

It is also noted that many units are installing furnaces of 16 tonne per charge to 22 tone per charge. Induction melting furnaces use over 60% sponge, and have iron installed mechanical devises to remove slag, then use LRF to make better quality steel. The refined steel will be poured in the Concast machine to produce steel billets. Revolution is taking place to make steel in India by utilizing various technologies. India is therefore, emerging as a country with innovative idea to make steel, which is not followed by other countries in the world. Our technologists are at present exporting this technology to various countries in Asia and Africa.