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Saxena K.K.,Indian Institute of Technology Roorkee | Saxena K.K.,GLA University | Pancholi V.,Indian Institute of Technology Roorkee | Jha S.K.,Mishra Dhatu Nigam Ltd | And 3 more authors.
Journal of Alloys and Compounds | Year: 2017

Zr-1Nb alloy is normally processed in two phase region to get desirable microstructure and properties for fuel cladding tube application in the nuclear reactor. Thus, it is important to know the deformation behavior of individual phases in the two phase region. However, the conventional approach to develop processing maps is to use flow stress data obtained from hot compression experiments, without accounting for the phases present at different temperatures. This approach fails to bring out the details about the operating deformation mechanism in the individual phases. In order to bring out these details, two new approaches are proposed for developing processing maps. The validity of the approaches is confirmed by performing microstructural analysis using electron backscattered diffraction (EBSD) studies. EBSD analysis of the microstructures obtained after deformation in the two phase region confirmed that α−phase had undergone dynamic recrystallization (DRX) whereas, β−phase exhibited coarse elongated grains. Processing maps developed using the new approaches were able to predict domains of high dissipation efficiency, which is corroborated by microstructural analysis. Also, one of the novel approaches proposed in this work could delineate the contribution of each phase in the two phase region. © 2017 Elsevier B.V.

Jayakumar T.,Indira Gandhi Center for Atomic Research | Mathew M.D.,Indira Gandhi Center for Atomic Research | Laha K.,Indira Gandhi Center for Atomic Research | Albert S.K.,Indira Gandhi Center for Atomic Research | And 6 more authors.
Fusion Science and Technology | Year: 2014

India is one of the countries associated with the development and testing of test blanket modules (TBMs) in ITER. Accordingly, India has taken up development of 9Cr-W-Ta reduced activation ferritic martensitic (RAFM) steel, which is the structural material chosen for TBMs, together with the associated manufacturing technologies required for TBM fabrication. With the objective of developing an India-specific RAFM steel, four heats of RAFM steel with tungsten and tantalum contents varying in the ranges 1 to 2 wt% and 0.06 to 0.014 wt%, respectively, were melted. The steel was melted through vacuum induction melting and vacuum arc refining routes with strict control over the amounts of elements that induce radioactivity (Mo, Nb, B, Cu, Ni, Al, Co, and Ti) and the elements that promote embrittlement (S, P, As, Sb, Sn, Zr, and 0). Extensive characterization of the microstructure and mechanical properties of the steel was carried out. The ductile-to-brittle transition temperature of the steel increased slightly with increasing tungsten and tantalum content. The tensile strength of the steel was found not to change significantly with increasing tungsten content; however, it decreased marginally with increasing tantalum content, with a consequent increase in ductility. The creep rupture strength of the steel at 823 K was found to increase significantly with increasing tungsten content, whereas it decreased with increasing tantalum content. The low-cycle fatigue life of the steel at 823 K was found to increase with increasing tungsten and tantalum content; however, extensive cyclic softening was exhibited when the tungsten content was >1.4 wt%. RAFM steel containing 1.4 wt% tungsten and 0.06 wt% tantalum was found to have a better combination of strength and toughness and is specified as Indian RAFM (INRAFM) steel. The joining technologies adopted for the fabrication of a TBM are hot isostatic pressing to produce the first wall, followed by gas tungsten arc (GTA), electron beam (EB), laser, and laser hybrid welding for joining the rest of the TBM. Welding techniques for joining RAFM steel have been developed and characterized. The properties of the GTA welds met the full specifications of the requirement and were comparable to the properties of the base metal. This consumable has also been used to carry out hybrid laser welding successfully. A procedure for using EB welding to join plates of thicknesses up to 12 mm has been developed. Impact tests conducted on EB welds showed that the toughness of the weld metal in the as-welded condition is comparable to that of the base metal. A box structure that simulates one of the components of a TBM has been fabricated using EB welding to demonstrate the applicability of the process to component fabrication. Laser welding of 6-mm-thick plates of RAFM steel has also been carried out successfully, and the properties of the weld joints have been found to be satisfactory. This paper discusses the development of INRAFM steel and its properties and the current status of the fabrication technologies being developed for fabrication of the Indian TBM to be tested in ITER.

Nageswara Rao M.,Vellore Institute of Technology | Chatterjee M.,Mishra Dhatu Nigam Ltd | Sivasubramanian K.,Mishra Dhatu Nigam Ltd
HTM - Haerterei-Technische Mitteilungen | Year: 2012

Massive rings of 18% nickel maraging steel produced using the ring rolling process do not consistently attain high fracture toughness (K Ic) and tensile ductility values. Due to large section sizes involved, it becomes difficult to suppress precipitation of carbonitride particles and prevent thermal embrittlement. he conventional heat treatment of solutioning at 820 °C followed by aging at 480 °C is not efective in undoing this embrittlement. Diferent multi-stage solution treatments were designed and tried out to improve the mechanical properties. A two-stage (950 °C + 820 °C)/three-stage (950 °C + 950 °C + 820 °C) solution treatment, depending on the section size, proved to be efective. his treatment leads to recrystallisation of the as-hot-worked microstructure and a ine grain size; it is believed that a delinking of grain boundaries and carbonitrides occurs simultaneously. he observed improvement of fracture toughness and tensile ductility can thus be explained. © 2012 Carl Hanser Verlag, München.

Narayana Rao M.,Mishra Dhatu Nigam Ltd
Transactions of the Indian Institute of Metals | Year: 2010

MIDHANI has been producing special stainless steels for different sectors. Production of these steels has posed challenges with respect to control over chemical composition, designing heat treatment parameters to meet the desired properties. The most challenging grades have been SS304L, 13-8 PH and 9Cr1Mo steels to name a few. The melting equipments were selected with utmost care and processing was done to meet the specified properties. In case of 304L grade in order to meet corrosion resistance requirements, elements like Silicon, Carbon and Sulphur were required to be controlled in very low limits. Production of 13-8 PH steels demanded that a combination of high strength and toughness are achieved. © 2010 TIIM, India.

Narahari Prasad S.,Mishra Dhatu Nigam Ltd | Rajasekhar K.,Mishra Dhatu Nigam Ltd | Chatterjee M.,Mishra Dhatu Nigam Ltd
Advanced Materials Research | Year: 2013

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. © (2013) Trans Tech Publications, Switzerland.

Narahari Prasad S.,Mishra Dhatu Nigam Ltd | Narayana Rao M.,Mishra Dhatu Nigam Ltd
Advanced Materials Research | Year: 2013

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 customer's 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. © (2013) Trans Tech Publications, Switzerland.

Gururaja U.V.,Mishra Dhatu Nigam Ltd. | Patra A.,Mishra Dhatu Nigam Ltd. | Mukhopadhyay P.,Mishra Dhatu Nigam Ltd. | Narayana Rao M.,Mishra Dhatu Nigam Ltd.
Advances in Materials Technology for Fossil Power Plants - Proceedings from the 7th International Conference | Year: 2014

Significant development is being carried out worldwide for establishing advanced ultra supercritical power plant technology which aims enhancement of plant efficiency and reduction of emissions, through increased inlet steam temperature of 750°C and pressure of 350 bar. Nickel base superalloy, 50Ni-24Cr-20Co-0.6Mo-1Al-1.6Ti-2Nb alloy, is being considered as a promising material for superheater tubes and turbine rotors operating at ultra supercritical steam conditions. Thermal fluctuations impose low cycle fatigue loading in creep regime of this material and there is limited published fatigue and creep-fatigue characteristics data available. Scope of present study includes behavior of the alloy under cyclic loading at operating temperature. Strain controlled low cycle fatigue tests, carried out within the strain range of 0.2%-1%, indicate substantial hardening at all temperatures. It becomes more evident with increasing strain amplitude which is attributed to the cumulative effects of increased dislocation density and immobilization of dislocation by f precipitates. Deformation mechanism which influences fatigue life at 750°C as a function of strain rate is identified. Hold times upto 500 seconds are introduced at 750°C to evaluate the effect of creep fatigue interaction on fatigue crack growth, considered as one of the primary damage mode. The macroscopic performance is correlated with microscopic deformation characteristics. Copyright © 2014 Electric Power Research Institute, Inc. Distributed by ASM International®. All rights reserved.

Sarkar P.,Mishra Dhatu Nigam Ltd | Narahari Prasad S.,Mishra Dhatu Nigam Ltd | Chatterjee M.,Mishra Dhatu Nigam Ltd | Narayana Rao M.,Mishra Dhatu Nigam Ltd
TMS Annual Meeting | Year: 2013

L605 (equivalent to KC20WN), is a single phase cobalt based superalloy, finding extensive applications in liquid propulsion engines. For optimal performances in service, a uniform fine grained structure is desirable. Controlled thermomechanical treatment was imparted to the material while manufacturing hot forged components. The present paper highlights the influence of the thermo-mechanical treatment on structure and properties of a cobalt based superalloy.

Chatterjee M.,Mishra Dhatu Nigam Ltd | Pani Kishore A.,Mishra Dhatu Nigam Ltd | Sarkar P.,Mishra Dhatu Nigam Ltd | Narayana Rao M.,Mishra Dhatu Nigam Ltd
TMS Annual Meeting | Year: 2013

Nickel base cast superalloys exhibits excellent combination of high temperature strength, creep, fatigue as well as oxidation and corrosion resistance and find wide applications in aerospace gas turbine components. Depending upon the severity of environmental conditions in gas turbine, components are cast in equiaxed (EX) or directionally solidified (DS) modes and subsequently heat treated to achieve a wide variety of structure and properties. Accordingly, a study was undertaken to evaluate the performance of a cast Ni-base superalloy and an attempt has been made to correlate processing conditions, structure and mechanical properties. Under similar heat treatment conditions, the directionally solidified material exhibited 15% to 20% superior high temperature strength and creep properties as compared to the equiaxed product.The superior performance of DS material is attributable to more effective solutionizing of γ/γ1 eutectic, absence of interdendritic microporosity and fineness of microstructural features, which can be correlated to the progressive solidification under steep thermal gradient during vacuum investment casting. The present paper highlights the structure property relations in a Ni- base cast superalloy, which was processed in equiaxed and directionally solidified castings, through investment casting route.

Narayana Rao M.,Mishra Dhatu Nigam Ltd
Energy Procedia | Year: 2011

Materials play very crucial role for a safe, reliable and economic operation of nuclear power plants. Materials used in nuclear reactors encounter hostile environment and aggressive media during service, and are expected to retain their structural and metallurgical integrity over a long period of use. The major challenges are the effect of radiation on embrittlement, creep, erosion, corrosion, radiation induced growth, swelling, stress corrosion cracking, hydrogen embrittlement and radioactivity build up. In order to realize a high degree of reliabilit y and at the same time meet the imposing challenges, material specification and acceptance criteria are extremely stringent and the products have to undergo a detailed testing and characterization prior to their use. To ensure the conformance to the specification, processes need to be developed which involves melting the alloy with stringent chemistry control, optimizing thermo-mechanical treatment and modifying heat treatment schedule suitably to achieve mechanical properties. A typical nuclear power plant makes use of nuclear fuel materials such as uranium, structural materials such as zirconium alloys, stainless steels, nickel base alloys as well as low alloy and carbon steels. The paper outlines processing methodologies and gives an overview of some of the structural materials. © 2011 Published by Elsevie Ltd.

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