Dr. Dinesh Kumar Lekhi,
Director (Production & Marketing)
Mishra Datu Nigam Limited
A Government of India Enterprise, Hyderabad, INDIA
Special Steels Through Induction Melting Furnaces: Vision 2020
Growth in Steel production performance has been largely contributed by Blast Furnace (BF) and Electric Arc Furnace (EAF) process routes. However in India, Steel making through induction furnace has emerged as one of the key driver for steel production (with increased share of 30% compared to 25% through EAF) in small steel plants due to the key economic benefits over EAF. It is also evident that the growth of induction furnace based production may be contributed due to following factors:
- Low requirement of electricity.
- Suitable for power supplied through generators driven by diesel or gas.
- Little expenditure for environment compatibility and clean workplace.
- High yields from input raw materials and alloying elements.
- High alloy content steel can also melted.
- Less loss of chromium.
- No electrode costs.
- Relatively low investment cost and small space requirements.
- Largely automatic operations in simple manner
Apart from above it is also a fact that operation of induction furnace is largely acceptable over EAF in small steel plant due to low refractory cost, less amount of slag and exact chemical composition.
In India there are approximately 1000 induction furnaces in various capacities with an annual capacity of producing about 25 million Tonnes per annum. The growth recorded in the increased usage of induction melting route is mostly with processing of carbon steel and alloy steels. In order to increase the production of steels through induction furnace route it is required to adopt the following strategies:
- Cost reduction:
Cost always has been a challenging task for any metallurgical industry since it is governed by the many fixed and variable factors. Sustainability of cost component in induction Furnace will depend on:
- Raw Material input cost
- Raw Material Mix
- Tap-to-Tap time.
- Process sequence.
- Refectory performance.
Firstly, raw material cost factor depends on selection of raw material like scrap or virgin type, its availability in the market and their prices will decide the cost of final product. Also, one of the best practices in induction melting of stainless steel suggest that the required raw materials such as low carbon steel or stainless steel scrap, Ferro – Molybdenum, Nickel, Low carbon Ferro – Chromium, Ferro – Silicon, and Manganese etc. are estimated in such a way that the final composition is achieved without much refining.
Secondly, process sequence steps such as optimum Tap – to – tap time also decide the cost of production and its yield.
Equipment availability factor depend on the type of refectory lining used in the crucible. Studies show that the High alumina refectories for stainless steel making have delivered a life about 30 heats for austenitic steels and 50 heats for Cr – stainless steels.
From the above it is the fact that the product viability of the induction furnace industry is possible only if some cost reduction takes place in the existing.
- Value added products:
Growing application demands in various industries for steels will be the key necessity for new product development. The term “Stainless” was coined early in the development of new product called stainless steels for cutlery products. Stainless steel are materials with Cr> 12% and are graded as austenitic, ferritic, martensitic, duplex and precipitation hardened varieties involving variety of alloying elements. Also, metallurgical studies were carried out in stainless steels components for its wide application in corrosion or oxidation atmosphere. Increasing demand in the areas of Stainless Steels containing high Nitrogen, low carbon, Borated steel etc. are the current markets to be tapped by induction furnace industries.
- Technological changes in equipment or processes:
One of the key advantage part of induction melting in its close control of chemical composition and when coupled with vacuum systems (well known as VIM) can make high end technology products for various critical applications. Even though VIM technology delivers high quality stainless steels, cost of production is higher as compared to air induction melting. Modified processes in the form of argon oxygen de – carburizing (AOD), Vacuum Oxygen de - carburizing (VOD) being followed for production of stainless steel in some industries which is cheaper and also have high rate of production. Sometimes it is also studied that the melted ingots from the induction melting are further refined in vacuum Arc Re – melting(VAR) and Electro slag refining (ESR) furnaces as per the customer requirements. Finally, the ingots are processed further to mill products ranging from bars, flats, rings, sheets wires, tubes and foils.
Analysis from above three strategies shows that it is difficult to reduce the cost of production significantly for carbon steels and low alloys steel in induction melting route due to lower capacities of such furnace. Only way of increasing the induction melting process route is suggested to focus on the emerging product demand through melting of special steel such as stainless steels aiming with high quality and more value addition.
- Moving forward for the year 2020:
Growing energy demand in the country made power equipment manufacturers to set up ultra mega power projects with superior technology. Also, by nuclear industry requirements for stainless steels used in structural components of pressured water reactor(PWR), fast breeder reactor(FBR), International thermonuclear experimental reactor(ITER) and forth coming gen IV fission reactors. Materials required for such super critical steam generators, turbines etc. will be the future challenge in this country with the availability of capacities and technologies. Induction furnace industries must gear up to fulfill the need of the nation by augmentation, modernization and bringing of new facilities.
It is evident that every process has advantages and disadvantages with increased output requirement the induction furnace alone can’t fulfill the requirements of the country and it has to depend on the electric arc furnace for some more period of time. With the addition of some critical metallurgical requirements such as Sulphur, Nitrogen, Oxygen levels induction furnace has to be added with addition refining facility such as ESR, VAR for its existence.