Papers by Keyword: Ferritic Steel

Abstract: Oxide dispersion strengthening steel (ODS) is widely used in high-severity environments in supercritical water gasification (SCWG) due to its high-temperature corrosion resistance and fatigue strength. Nano-oxide can be used as reinforcement for ODS steel to enhance the mechanical properties by retarding dislocation at grain boundaries. This work aims to study the fabrication of Fe-18Cr ODS steels reinforced with 0.5-3.0 wt% nano-Al₂O₃ contents. The microstructure of ODS steels before and after sintering processes was observed by an optical microscope, and the hardness test was conducted by a Micro-Vickers hardness tester. The results showed the mass gain increased by 49.18±10.75 mg cm^-2 due to the formation of Fe₂O₃ during the sintering process. The average porosity of ODS steels after sintering decreased by about 60% due to thermal contraction, resulting in their average densities increased by around 7 %. Moreover, the hardness of Fe-18Cr ODS steels increased up to 120 HV with the increase in nano-Al₂O₃ percentage.

Abstract: ECCC is a voluntary grouping formed in 1991 to co-ordinate Europe-wide development of creep data to be used to design components for high temperature plants, bases on a Memorandum of Understanding, signed by all partners. The ECCC is deeply involved in EU coordination for the development of knowledge on the damage caused by the creep phenomenon and the consequent reliability assessment activities. Strong links exist with the technical committees of the European Standard organizations, giving an efficient network to mutually exchange of technical information relating to current/future activities for the improvement or development of new materials. For several years ECCC (1991-2005) concentrated efforts by EU support. Nevertheless, revitalization of ECCC has been generated by definition of Joint Industrial Project (JIP) started in 2011 and still running (JIP4). ECCC has a very strong link to industrial applications and it is presently organized in four Work Packages: WG1 on common procedures, data generation/assessment and three material specific Working groups: ferritic steels, austenitic steels, nickel-based alloys. Two main outputs are ECCC data sheets and ECCC Recommendation Volumes. The ECCC activities are almost completely carried out by members’ contribution-in-kind. The ECCC plays a part of its role, in term of generation of design properties for new materials introduction into power plant and related applications. It therefore engages a crucial role in assessing and realising the potential of new developments.

Abstract: Alloy design allows to define specific compositions of materials having certain technological requirements as boundary conditions. Moreover increasing interest raised in the last decades on materials for Additive Manufacturing (AM). These new technologies consider a new approach, i.e. bottom up, for component manufacturing and suitable materials in different forms, generally liquid or solid (powders, filaments). One of the most interesting advantages of AM is the potentiality of realizing components with complex geometries and in a single or in few pieces to be assembled. For this reason, in this work a ferritic allow has been designed with the scope of realizing heat exchangers for highly corrosive alkaline environments. Water-ammonia solution are in-fact used in absorption machines for refrigeration and several heat exchangers are required for its thermodynamic cycle. After defining a specific composition, also on the base of thermodynamic simulations, the alloy has been produced by Vacuum Induction Melting (VIM). After suitable thermal treatments microstructural, mechanical and thermal characterizations have been carried out.

Abstract: AISI 441 ferritic stainless steel is a good candidate for metallic interconnects in solid oxide fuel cells (SOFCs). The minor elements Ti and Nb are used to stabilize the ferritic matrix and also to reduce creep by a combination of solid solution strengthening and precipitation of intermetallic Laves phase particles along the grain boundaries. However their influence on the oxidation behavior is not well understood. This study focuses on the early stages oxidation (from 4 to 24 h) at 800 °C of AISI 441 under 5% H₂O in O₂. A relatively smooth micro-crystallized oxide scale and Ti, Nb containing nodules are observed. The internal microstructure of these objects is studied by FIB tomography which allows computing cross sectional views in any direction of interest. FIB study reveals a complex microstructure and a development strongly linked to the presence of niobium and/or titanium in the substrate.

Abstract: Elevated temperature workability of Boron added modified 9Cr-1Mo steel is studied in temperature range 1223-1473K and strain rates of 0.001-10s^-1 using Dynamic Materials Model. Towards this end hot isothermal compression tests are carried out and the experimental results are used to obtain processing map. Extensive microstructural investigation is carried out to validate different domains of processing map. On the basis of the microstructurally validated processing map, parameters for the thermomechanical processing of P91B are recommended.

Abstract: The feasibility of employing the indigenously developed Ferroboron alloy as an alternate neutron shield material in combination with 9Cr-based ferritic steel clad in future Indian Fast Breeder Reactors (FBR), has been investigated from a metallurgical perspective. In this regard, extensive studies have been undertaken to estimate quantitatively the nature of interaction between Ferroboron and P91-ferritic steel at high temperatures. It is found that in the temperature range 550 to 600°C, 9Cr-based ferritic steel is fully compatible with Ferroboron. However, at higher temperatures, Feroboron interacts with ferritic steel; but the maximum estimated loss of clad thickness is restricted to about 250 μm for 60 years of service.

Abstract: The relationship between creep rupture strength and Laves phase precipitation and growth kinetics was investigated at 650 °C for two Fe-9Cr-3Co (wt.%) alloys differing mainly in the amounts of W and Mo added. In the alloy with 3.14 wt.% W added, Laves phase precipitated heterogeneously on grain boundaries and hence had little dispersion strengthening effect. Its stress exponent for rup-ture time became lower in the lower creep stress range tested. In the alloy with 1.31 wt.% W and 3.22 Mo added, Laves phase precipitated both heterogeneously on grain boundaries and homogenously within grains and there was no reduction in stress exponent for rupture time in the whole stress range tested. The Lave phase precipitation kinetics increased with increasing the total amount of W and Mo in the alloys. The differences in stress-rupture time relationship observed between the two alloys were discussed in relation to their differences in the Lave phase precipitation behaviour.

Abstract: In recent years, considerable progress has been made in the simulation of ferritic steel welding processes. The successful validation of a single-pass autogenous TIG beam weld in SA508 Gr.3 Cl.1 steel has identified key simulation variables required for the accurate prediction of post-weld residual stress in ferritic weldments. The present work outlines a sensitivity study performed to examine the influence of austenite grain growth on predicted solid-state phase transformation kinetics and consequently, residual stress predictions.

Abstract: This paper presents the numerical analysis of phase proportions and residual stresses in an autogenous beam edge weld. The thin beam was welded running a heat source along its longer edge using a TIG process. There is no addition of any material so the focus of modelling the process could be concentrated on the thermal analysis and the phase transformations. Temperature dependent material properties and a continuous cooling transformation (CCT) diagram of the base material were provided. The simulations took into account metallurgical effects and used a Goldak-type heat source. Simulations with and without phase transformations were carried out, in order to analyse the effect on the predicted residual stress.

Abstract: FeSi steels with and without addition of Al are widely used as electrical steels. To improve the knowledge of the effects by the addition of Si and Al on the hardening and softening under hot rolling conditions, the behaviour of the flow curves in a wide range of temperatures and deformation velocities have been studied.