Advanced Materials Research Vol. 794

Abstract: Stainless steels (SS) have earned a unique position as a widely accepted class of alloys with track record of steadily improving the performance and increasing applications from 1913 till date. This distinction is attributed to R&D, innovations and applications leading to harnessing the rare combination of properties of stainless steels, since its discovery hundred years back. Though the initial discovery of stainless steel is basically serendipity, and based on previous work, its indispensable position today, in many a wide range of applications is due to intense R&D efforts in understanding its physical, chemical, thermal and thermo-mechanical response for various chemistries and microstructures. A deliberate attempt to extend its application spectrum through various routes of manufacturing in the last century is another crucial aspect of the success story. The first part of the presentation would briefly review this exciting journey of unravelling the mysteries of stainless steels.The second part of the presentation would highlight the evolution of stainless steels in the nuclear industry, especially for the sodium cooled fast reactors. Early 70s have seen the application of stainless steels in first generation water based nuclear power plants and AISI types 304 and 316 SS was recommended for structural and core applications in fast spectrum reactors (FSR). Failure of some of the components even in the manufacturing stage and quest for improving mechanical properties and sensitisation and intergranular corrosion resistances resulted in the development of 304L, 304LN, 316L, 316LN SS during 1980-90 for further applications in FSRs. Towards core applications in intense radiation environments, three generations of stainless steels namely 20% cold worked 316 SS, D9, and D9I have been developed to yield high burnup and to triple the lifetime of the core components of the fast reactors. Towards closing the fuel cycle, again 304L SS was the workhorse material which was upgraded with newer varieties like nitric acid grade alloys for improved corrosion resistance and longer life. Manufacturing of special grades of SS and the developments in fabrication technologies was necessary in order to enhance the performance of components and to avoid failures. Welding, inspection, quality assurance and structural integrity of various components of SS for FSRs and fuel cycle facilities resulted in developments in areas like modelling, devices, methodologies and analysis. An opportunity existed for the development and application of innovative non-destructive testing techniques for robust examination of critical components.Nuclear industry is embarking a state of the art fourth generation reactors. The consequent newer generation of SS are evolving with improved properties to match the expectations of performance in increased temperature, pressure, chemical and other physical constraints. It is of paramount importance to consider the extension of the lifetime of the current reactors from 40-60 to 60-80 years for economic considerations, and in this regard innovations are necessary in the development of newer varieties of stainless steels with respect to modelling and life prediction, manufacturing, fabrication, testing and evaluation. Thus the management approach to knit a network of industry-research-academia is a key approach for way forward. A development of roadmap for robust science based technology development with foresight is a desired management strategy.

Abstract: Indian Stainless Steel Development Association (ISSDA) was formed in 1989 with the explicit objective of diversifying and expanding the domestic market of stainless steel. At that time, more than 90% of stainless used in the country was kitchenware but over the last two decades, stainless steel has undergone tremendous changes in perception and its increasingly growing end use application in areas such as architecture building & construction, automotive transport, process and engineering. The world production of stainless steel in 2012 is estimated at 35.4 million tonne. Asia has strongly emerged as both the worlds largest stainless steel producer and user. Among countries, China dominates the world production of stainless steel accounting for almost 45% share. However, India has outpaced global growth rates consistently over last 10 years with its stainless steel melt production in 2012 reaching almost 3 million tonnes to propel the country as 4^th largest producer after China, Europe and Japan. The potential growth of stainless steel in India is enormous, considering the fact that the per capita consumption at 1.9kg is still much lower than world average of almost 4.85kg. The per capita consumption of stainless steel has strong co-relation with per capita GDP and India is expected to more than double its per capita income over next 10 years. In addition increased urbanization, high demographic dividends and governments manufacturing policy seeking to enhance the share of manufacturing in GDP to 25% within a decade augurs well for the future growth of the stainless steel in India. This paper focuses on the growth story of Indian Stainless Steel industry and its market sector vis-à-vis world and further explores on the strategy to increase the consumption domestically considering the fact that world is going through recession cycles resulting in excessive capacity especially China posing a major challenge to Indian Stainless industry. Keywords: Stainless Steel, Indian Industry, Growth Prospects, Present Status

Abstract: The major route for SS production has been via EAF. The challenge of decarburising the melt with oxygen in the presence of high levels of chromium has been handled through AOD and VOD processes. In plants manufacturing other alloys as well as SS, high carbon liquid steel is produced in the EAF, without any chromium addition. All Chrome addition takes place in the AOD, increasing the process time, cost, temperature and refractory wear. EAF has high oxygen consumption and foaming arc allowing long arcs. In SS plants, the EAF charge consists of SS/MS scrap high C ferrochrome. Minimal oxygen is used and 85% of energy is electrical. Foaming slag practice has not been successful till now. Short arc lengths are used. Proper choice of Electrode Regulation System and Smart Furnace Melt program are essential. Modern Electrode Regulators are similar in regulation speeds. Hence the choice must be based on the diagnostic and analytic features and other special features which can eliminate VCB trippings and Electrode breakages. Improvements can be achieved in some areas. Electromagnetic Stirring will help in reducing arcing time, lining wear and allow longer arcs. Possibilities of modifications to the shell to allow foaming slag practice should be explored. Waste heat recovery using high temperature quenching and evaporative cooling to generate steam can be adapted.

Abstract: Stainless Steel is a family of versatile materials that has been put into a wide variety of application by mankind. Stainless steels are iron-based alloys containing minimum 12% chromium and upto 25% nickel with minor additions of carbon, nitrogen, molybdenum, tungsten, titanium, niobium, copper and selenium. It has a wide range of applications from small pins to the construction of automobiles, petrochemical, space, aeronautical, ship building industries, nuclear and thermal power stations. Certain grades of stainless steels, because of their biocompatibility are used for manufacture of biomedical implants. In fact steel touches every sphere of our daily life. By and large stainless steel family consists of hundreds of grades with varieties of compositions and a large spectrum of mechanical properties. The corrosion and oxidation resistance of stainless steels have been significantly improved through fine-tuned chemical compositions and microstructural constituents, leading to the evolution of super stainless steels. Stainless steel development from design to application is a long-term continuous effort. The recent advances in stainless steels are mainly due to new ways of manufacture, processing and usage of advanced equipments. In spite of inroads by a range of competing materials, stainless steels occupy an important place as structural materials, because of their outstanding strength to weight ratios, ductility, fracture toughness, repairability, corrosion, etc for a given cost. Over the years, MIDHANI has catered to the requirements of Indian Space, Nuclear, Thermal, aeronautical and Defence sector for many high performance materials. A wide range of special stainless steels many of them being tailor made to customers specific needs have been developed and supplied. This has been possible with the help of state of the art facility and excellent quality assurance system available in MIDHANI. The presentation will high light MIDHANI role in development and commercial production of different varieties of stainless steels for critical applications.

Abstract: A new dynamic control model based on simultaneous mass transfer of C, Cr, and Mn and dynamic heat balance is developed. It allows dynamic adjustment of argon-oxygen ratio. The model is implemented through Level II control system. The total operating period of one heat is divided into five different stages: charge calculation, first blow period, second blow period, third blow period and, lastly, the reduction stage. The charge calculation model, based on heat balance, mass balance and the costs decided the optimum charge mix to start with. Both linear and non-linear regression models are used to predict the temperature and composition of bath at the end of first blow period. The second blow and the third blow periods use the dynamic models for predicting the chemical composition and temperature. In the model for reduction stage (final stage) the amount of reduction mixture is determined for obtaining maximum recovery of Cr and Mn from slag. On-line testing of the dynamic models was carried out on the shop floor. The integration of models with the Level II control system using Supervisory Control and Data Acquisition System (SCADA) are discussed. User friendly HMI are developed such that the operators can easily use it during the regular operation on shop-floor. This is the first time that a full dynamic control system was implemented in India for the AOD process.

Abstract: Recent advances in continuous casting have facilitated remarkable improvement in the quality of cast steel. The focus of the present paper is directed towards understanding of the influence of chemistry and intrinsic solidification behaviour on the different quality issues of stainless steel. An attempt has been made, wherever possible in quantitative terms , to correlate the chemistry and the process parameters with the quality factors. The relevant theoretical background has been touched upon. Understanding has been developed on the role of the ratio of nickel equivalent and chromium equivalent. This factor can be used to represent the chemistry of any stainless steel grade. Under similar casting conditions, specific problem of mould sticking , strand bulging , or depression formation has been explained invoking this chemistry factor. Each quality issue owes its genesis to interaction between the high-temperature strength and ductility of the solidifying shell during casting. The important roles of micro-segregation , the effective shell thickness during the early stage of casting , and the temperature range of transformation for δ-ferrite to austenite have been highlighted. An approach of grade-specific casting practice has been suggested to formulate the specific casting parameters. The developed understanding has been utilised to address specific quality problems in continuously cast slabs and rolled products of different stainless steel grades. This integrated understanding can be useful for ensuring the quality of stainless steel of any chemistry.

Abstract: Mould flux was invented for bottom poured ingots using fly ash as raw material. It transited subsequently to synthetic raw materials. As continuous casting of steel developed, Fluxes in fine powder form evolved culminating to the development of environment friendly fluxes in granular form. As continuous casting of stainless steel commenced different powders were developed for different Stainless qualities like austenitic, ferritic etc. Powders developed from interface with users were not only to satisfy demand of lubrication in the mould but also for adequate heat transfer and better surface quality. Shrinkage in mould, interplay of the elements in steel during casting with mould slag, tendency of the steel grades towards cracking or sticking and influence of various casting parameters determined mould powder development and usage. In-mould Powder performance dynamically reacts to changes in casting parameters and conditions and appropriate changes in powder chemistry can overcome or minimise detrimental effects of such changes. Future demands of overall cost control, better surface quality, minimal grinding, stable meniscus will guide powder research and development alongwith focus on environmental concerns.

Abstract: Specialty stainless steels designed with higher levels of Chromium, Nickel and Molybdenum than the general austenitic grades AISI 304 and AISI 316 have distinctly superior corrosion resistance properties. The commercial production of such high alloyed stainless steels came with advent of improved steel melting, refining and casting technologies. These technological improvements made it possible to produce such steels with low carbon levels and close control of chemical composition necessary to achieve the desired phase balance and avoid formation of undesirable intermetallic phases. Further, ability to achieve low sulphur levels combined with freedom from undesirable level of tramp elements improved the hot workability characteristics. Thermodynamic aspects of steelmaking and refining in Vacuum Oxygen Decarburization ( VOD) process for manufacture of specialty grades 904L (24% Ni, 20% Cr, 4% Mo, 1.2%Cu) , 317LM ( 19% Cr, 14.5% Ni, 4% Mo,) , 2205 ( 22.5% Cr, 5% Ni, 3% Mo) at Mukand through the Triplex process route ( Ultra High Power Furnace Oxygen Top and Bottom Blown Convertor VOD) are outlined. The effects of undesirable intermetallic phases, particularly sigma phase, on mechanical and corrosion properties are discussed. Application areas for such specialty grades are reviewed. Keywords: High alloyed Stainless steels, triplex process, sigma phase, intermetallic phases, tramp elements, hot workability, corrosion properties, vacuum oxygen decarburization.

Abstract: Developed over last six decades, Chrome-Manganese stainless steels now comprise a whole family of lustrous products in a variety of compositions and properties to facilitate optimal selection of most appropriate grades for a large number of applications .This paper describes properties of some of these steels and how they compare with Chrome-Nickel austenitic stainless steels. Due to their attributes, these stainless steels constitute the fastest growing family of stainless steels in the globe. Some of the applications where these grades have been successfully used are covered. Their advantage in terms of cost effectiveness and material saving is outlined.