Advanced Materials Research Vol. 794

Abstract: Stainless steels, by virtue of their diversity in chemistry, microstructure and properties, find widespread applications ranging from domestic appliances to high technology sectors such as space, aeronautics, power, chemical and ordnance. Midhani has been at the forefront of material development over the past few decades and has produced several stainless steels, tailor made for specific critical applications. Subtle variations in chemistry or processing methodology have been exercised to achieve the desired microstructure and properties. In this context, influence of minor addition of austenitic stabilizing element on structure and properties on conventional ferritic stainless steel SS430 was studied. The chemistry modification changed the structure to dual phase, austenite ferrite structure, that responded to heat treatment by transformation of austenite to martensite. This dual phase structure after tempering enhanced the strength and toughness by 25% and 60% respectively. In the case of 13-8 Mo PH stainless steel, a modified two stage solution treatment and ageing resulted in enhancement of toughness by over 100% as compared to conventional single stage solution treatment and the improvement was attributable to refinement in martensitic sub-structure due to thermal cycling. With respect to SS 440C, a high carbon stainless steel, the performance is closely related distribution of primary carbide. Bearing directly manufactured from forged stock produced from ingot do not perform satisfactorily in view of massive primary carbides present in the form of stringers / bands. This problem was addressed by subjecting the forged stock to further working in the transverse orientation by ring rolling which brought about finer primary carbides. The present paper highlights some of the challenges and the modifications brought about to meet the specific needs.

Abstract: Stainless steel is mostly manufactured by Electric Arc Furnace Argon Oxygen Decarburization route utilising 100% solid charge of steel scrap/DRI/stainless steel scrap and ferroalloys.The process consumes around 415/450 KWH of power per ton of stainless steel.In the state of Odisha, we are endowed with both iron and chromite ores,which offer opportunity for use of molten pig iron and liquid ferrochrome for energy efficient stainless steel making for a plant located there. This paper analyses potential for energy conservation in EAF for three different grades of stainless steel belonging to AISI 200,300,400 series. In this concept, melting is performed in two different furnaces,one EBT type and the other Spout type.In EBT furnace only high ferrous melt with liquid pig iron and DRI/Scrap are charged and dephosphorized. In the spout furnace high carbon ferrochrome which has a tendancy to solidify rapidly due to its high melting point of nearly 1575°C is diluted with scrap which brings down its melting point drastically to enable it to be kept molten.Silicon in the high carbon ferrochrome is gainfully utilised to raise the temperature of molten pool.The diluted ferrochrome is taken in ladle in appropriate portion to which dephosphorised decarburized molten steel is added from EBT furnace for charging into AOD. The material and energy balance have been carried out for the entire charge mix using classical approach of energy calculation. Both variants of DRI and scrap addition to hot metal have been considered for the EBT furnace. Calculations for EBT furnace have been validated using data from an existing carbon steel plant using similar practice of steel making. Calculated values for such energy efficient stainless steel making have been compared with data on existing stainless steel plant using solid charge. Energy usage can be reduced by more than 60% with this approach. Keywords: Electric arc furnace, Stainless steel melting, liquid ferrochrome, energy conservation.

Abstract: Stainless steel bar and wire products that cater to the high technology application in defence, nuclear, aerospace, oil field and chemical engineering is an area poised for rapid growth in India. The advancing capabilities of alloy steel plants in India have enabled mastering of techniques to make a wide variety of stainless steels. However, there are increasing challenges to meet the advanced property requirements, which call for a basic understanding on the structure property relationship that are influenced by appropriate alloy design and down-stream processing. The special steel industry cater to a wide variety of stainless steels namely ferritic, martensitic, austenitic and precipitation hardenable categories for meeting requirements of high technology. One of the process for making the primary stainless steels is Vacuum Oxygen Decarburisation process. For advanced applications, the primary melted steel is again secondary refined using electroslagremelting for the management of solidification structures and control of inclusions. In the austenitic grades, the hot forged and hot rolled heat treated steels, careful choice of chemistry controls the delta ferrite content and ensures uniformity of the grain size in the product during deformation processing and heat treatment. In the martensitic stainless steel grades, focus is given to delta ferrite, grain size control and appropriate tempering treatment. In the precipitation hardenable steels grades the aging reactions and hot deformation range have to be optimised for deriving specified mechanical properties. Special grades are produced using non ESR and ESR routes to meet high temperature applications such as turbine blades and bolting. In these grades control of delta ferrite content, carbides, carbo-nitrides in the matrix has a deep influence on the mechanical and sub zero fracture properties. In the ferritic stainless steel grade grain size control is critical. The presentation would bring forth the correlation between the alloy design, processing and properties that were achieved in the products mentioned above to meet some of the challenging requirements.

Abstract: Accelerating the pace of Nuclear Power Plants construction is critical to the Growth of Indian Economy. It calls for timely and First Time Right manufacturing of various Reactor Equipment. This paper captures the experience of Godrej Precision Engineering Division in successful realization of Calandria, in record time, with First Time Right Quality adhering to very demanding and stringent requirements.

Abstract: This paper presents an overview of development of stainless steel for critical applications and its metallurgical aspects in general. Novel emerging methods of processing of stainless steel are also discussed. Advances in steel making aspects with respect to stainless steel and other specialty steels especially in nuclear applications are presented. Overview of alloy design, physical metallurgical aspects of steel for critical applications is discussed. Advances in manufacturing of stainless steel, strengthening mechanisms, corrosion resistance, challenges in stainless steel applications have also been elaborated.

Abstract: In this work, a comparison study has been performed on the two hot finished manufacturing processes i.e. hot extrusion and hot piercing which are used for manufacturing stainless steel hot finished pipes/tubes. Study is based on different parameters which include raw material, temperature, extrusion ratios, manufacturing process, compressive stresses, shear stresses, friction forces, tooling, etc. The aim of the study is to determine the qualitative difference in the output product which is manufactured through these two processes for hot finished pipes manufactured in austenitic, duplex, super-duplex stainless steels and nickel alloys. The study includes the testing of the hot finished product with non-destructive testing techniques of water immersion ultrasonic testing, Inside Diameter eddy current testing and dye penetrant testing and destructive testing techniques of mechanical testing, microstructure analysis and corrosion testing methods for confirming the qualitative difference in the outputs of both the processes. The products manufactured by hot extrusion are much more superior in terms of defects observed on the inside of the hot finished pipe apart from material soundness, metallurgy and corrosion properties.

Abstract: Prototype Fast Breeder Reactor (PFBR) is liquid sodium cooled, pool type nuclear reactor with generating capacity of 1250 MWt / 500MWe. Reactor assembly consists of many large dimensional components made of special grade austenitic stainless steel material. Safety vessel and Main vessel are torispherical dished end vessels with overall height of 12.8 m and 13.4/12.9 m diameter with thickness ranging from 20 to 40 mm. Vessels approx. 111 / 135 MT with running weld length of 500 & 540 m. Inner vessel and thermal baffles are the internals of reactor assembly made of SS 316LN. Forming of dished end petals, weld overlay on the inside surface, circumference matching between the cylindrical shells, cylindrical shell to dished portion was achieved within the tolerances specified. Due to limitations of transportation, these large sized components were manufactured at PFBR site. This paper discusses the experiences gained during the manufacturing of such over dimensional components at PFBR site in meeting the stringent tolerances on various dimensions and NDE requirements.

Abstract: NPCIL uses stainless steel AISI 403 grade material extensively for very critical nuclear components. A very special application of this material is for manufacturing END FITTING BODY of COOLANT CHANNEL ASSEMBLIES of Pressurized Heavy Water Reactor (PHWR) of Nuclear Power Plants. Presently, two types of PHWR Nuclear Plants viz 220 MWe and 540 MWe are under operation in India. Next higher rating viz 700 MWe PHWR Nuclear Plants are at various stages of construction and due for commissioning in near future. There are number of Pressure Tubes in PHWR Nuclear Plants wherein fuel is loaded and are called coolant channel assemblies. End fitting bodies are assembled on either end of PRESSURE TUBES of coolant channel assembly. The Coolant (Heavy water) flows inside these assemblies and collects the heat produced during nuclear reaction in pressure tubes. This heat is utilized to produce Steam in Steam Generators. After giving up heat in Steam Generator, coolant returns to pressure tube and cycle continues. Material for End Fittings has been selected keeping in mind the mechanical properties at room and at elevated temperatures are compatible with mating component which are manufactured using Zircaloy and SS 410. It is also an essential that coefficient of thermal expansion is also compatible for mating material. Indigenization of the material for manufacturing of End Fittings with short delivery period has always been a challenge for commercial Nuclear Reactors. Inspection of these types of critical nuclear reactor components becomes critical due to the high safety standards and complexity in structures. There are very few manufacturers for this material in India. NPCIL took up a challenge for developing a new supplier in Northern Region of India for developing this material. A leading company in northern region of INDIA came forward and took up the challenge and succeeded for this venture. This paper deals with development of vender to manufacture of AISI 403 grade material by melting, refining ( ESR process), forging, heat treatment, testing & provide the guidelines to tackle the issue faced during this developmental work.

Abstract: Metastable austenitic stainless steel type 301LN is widely used for fabrication of structural components of Metro Coaches. The steel exhibits both high strength and enhanced plasticity due to strain hardening as well as formation of strain-induced martensite (α) during cold deformation (TRIP effect). The current market requirement, as projected by many of the ongoing Metro Rail Projects in India, calls for manufacture of this steel with ultimate tensile strength (UTS) in excess of 1000 MPa and yield (YS/UTS) ratio of less than 0.8, as this would facilitate substantial reductions in tare weight and crash-worthiness of metro coaches. The typical property requirements in high temper (HT) as per one typical Metro Coach specification are: Yield Strength (YS) ~ 751-921 MPa, Ultimate Tensile Strength (UTS) ~ 1001-1151 MPa, Elongation ~ 22% min, Hardness ~ 36 HRC max and YS/UTS ratio <0.8. previous="" plant="" experience="" has="" shown="" that="" the="" maximum="" attainable="" uts="" in="" this="" grade="" through="" cold="" rolling="" is="" only="" to="" tune="" of="" 970="" mpa="" and="" any="" excess="" deformation="" severely="" impairs="" both="" ductility="" 22="" hardness=""> 36 HRC) beyond acceptable limits. In the present work, an innovative thermomechanical processing (TMP) methodology has been evolved for the attainment of this seemingly unlikely combination of properties through experimental cold rolling and short annealing simulations in Gleeble 3500 C thermomechanical simulator. The novel process methodology entails imparting heavy cold reductions (CR) of 45-50% in Sendzimir Mill followed by brief/ short reversion annealing treatments (80-160 s) by means of single furnace operation at 750 °C at standard line operating speeds for 300 series in Annealing Pickling Line-1 (AP Line-1) of Salem Steel Plant (SSP) in India. The improvement in properties (strength-ductility combination) has been attributed to grain refinement through formation of submicron grained austenitic (γ) microstructure by controlled reversion of strain-induced martensite (α) during the short annealing treatment. The process is distinct from conventional long annealing treatments (300-360 s), which are employed to soften the steel after cold rolling by means of recovery and recrystallization processes.

Abstract: Pressure Housing, used in the Grid Mechanisms Motor, is manufactured from ferritic stainless steel, SS430 bar of 120mm diameter. The application demands an alternative non-magnetic and magnetic material (austenitic and ferritic) on the outside. This is manufactured by making longitudinal machined slots on the outside surface of SS430 bar which is ferritic and magnetic and the machined slots are filled up by depositing SS347 which is an austenitic and non-magnetic stainless steel material. In order to weld SS430 # SS430 with SS347, welding procedure was to be qualified as per ASME Sec IX with additional requirements of impact specimens from weld and HAZ at temperature +20°C, microstructure examination and intergranular corrosion test as per ASTM A763 Pr.Z. It was the first time, SS430 # SS430 welding procedure qualification with SS347 was to be carried out as no earlier cases required this qualification. SS430 ferritic stainless steel bar exhibits stringers of ferrite and martensite and in cases of stingers of two phase structures like duplex stainless steel, it has been reported that the transverse impact properties drops to half to two-third the longitudinal values. In the welded coupon, the impact property on the HAZ was located in the transverse direction and extremely difficult to meet the requirements. Welding qualification with impact requirement in transverse direction in HAZ was a challenging task and this paper addresses the issues encountered and the work carried out in literature study on the metallurgy, heat treatment and experimental trials to meet the specification requirement.