Up-Scaling of Thermomechanically Induced Laves Phase Precipitation in High Performance Ferritic (HiperFer) Stainless Steels

Fully ferritic stainless steels, strengthened by Laves phase precipitates, were developed for high-temperature application in the next generation of ultra-super-critical thermal power plants. Based on the rapid occurrence of thermomechanically induced precipitation in strengthening Laves phase particles, a novel thermomechanical process route for this class of steels was developed. A controlled precipitation of particles, in a desired morphology and quantity, and an optimization of the corresponding forging parameters was achieved on a laboratory scale. This article outlines the very first up-scaling experiment with these optimized forging parameters from the laboratory scale to the industrial scale. The precipitation behavior was analyzed, utilizing digital particle analysis of scanning electron microscopy (SEM) images, to estimate and compare the phase fraction of the precipitated Laves phase, as well as the particle size and distribution. Due to the up-scaling in the forging process, the behavior of the precipitation changed and the precipitation strengthening effect was decreased, in comparison with the laboratory scale

Application of DFT Simulation to the Investigation of Hydrogen Embrittlement Mechanism and Design of High Strength Low Alloy Steel

In this work, first-principles methods were performed to simulate interactions between hydrogen and common alloying elements of high strength low alloy (HSLA) steel. The world has been convinced that hydrogen could be one of the future clean energy sources. HSLA steel with a balance of strength, toughness, and hydrogen embrittlement susceptibility is expected for application in large-scale hydrogen storage and transportation. To evaluate the property deterioration under a hydrogen atmosphere, hydrogen embrittlement (HE) of HSLA steel attracts attention. However, due to the small size of hydrogen atoms, the mechanism of HE is challenging to observe directly by current experimental methods. To understand the HE mechanism at an atomic level, DFT methods were applied to simulate the effects of alloying elements doping in bcc-Fe bulk structure and grain boundary structure. Furthermore, the potential application of DFT to provide theoretical advice for HSLA steel design is discussed

NO Reduction Reaction by Kiwi Biochar-Modified MnO2 Denitrification Catalyst: Redox Cycle and Reaction Process

NO is a major environmental pollutant. MnO2 is often used as a denitrification catalyst with poor N2 selectivity and weak SO2 resistance. Kiwi twig biochar was chosen to modify MnO2 samples by using the hydrothermal method. The NO conversion rates of the biochar-modified samples were >90% at 125–225 °C. Kiwi twig biochar made the C2MnO2 sample with a larger specific surface area, a higher number of acidic sites and Oβ/Oα molar ratio, leading to more favorable activity at high temperatures and better SO2 resistance. Moreover, the inhibition of the NH3 oxidation reaction and the Mn3+ → Mn4+ process played a crucial role in the redox cycle. What was more, Brønsted acidic sites present on the C1MnO2 sample participate in the reaction more rapidly. This study identified the role of biochar in the reaction process and provides a reference for the wide application of biochar

Compositional Optimization of High-Performance Ferritic (HiperFer) Steels : Effect of Niobium and Tungsten Content

The combined addition of Nb and W provides increased solid solution and precipitation strengthening by (Fe,Cr,Si)2(Nb,W)-Laves phase particles of ferritic, 17 wt.% Cr stainless high-performance ferritic (HiperFer) steel. Based on alloy modifications and the obtained hardness, tensile, and creep testing results; a new high alloying variant is proposed as a candidate steel for future structural application up to approximately 680 °C in power engineering and the process industry

Thermomechanically Induced Precipitation in High-Performance Ferritic (HiperFer) Stainless Steels

Novel high-performance fully ferritic (HiperFer) stainless steels were developed to meet the demands of next-generation thermal power-conversion equipment and to feature a uniquely balanced combination of resistance to fatigue, creep, and corrosion. Typical conventional multistep processing and heat treatment were applied to achieve optimized mechanical properties for this alloy. This paper outlines the feasibility of thermomechanical processing for goal-oriented alteration of the mechanical properties of this new type of steel, applying an economically more efficient approach. The impact of treatment parameter variation on alloy microstructure and the resulting mechanical properties were investigated in detail. Furthermore, initial optimization steps were undertaken

Compositional Optimization of High-Performance Ferritic (HiperFer) Steels—Effect of Niobium and Tungsten Content

The combined addition of Nb and W provides increased solid solution and precipitation strengthening by (Fe,Cr,Si)2(Nb,W)-Laves phase particles of ferritic, 17 wt.% Cr stainless high-performance ferritic (HiperFer) steel. Based on alloy modifications and the obtained hardness, tensile, and creep testing results; a new high alloying variant is proposed as a candidate steel for future structural application up to approximately 680 °C in power engineering and the process industry

Low-temperature Fe-MnO2 nanotube catalysts for the selective catalytic reduction of NOx with NH3

Exhaust gas from the sintering process in the iron and steel industry contains NOx and SO2 at low temperature. Therefore, the corresponding denitration catalyst should have favorable low-temperature activity and SO2 resistance. In this study, an Fe-doped MnO2 nanotube catalyst with the (211) crystal face synthesized using a one-step hydrothermal synthesis method demonstrated favorable pore structure and many weak acidic sites, which improved its low-temperature activity (>90% at 125-225 degrees C), N-2 selectivity (>90%), and SO2 resistance. The NO conversion rate reached 94% when the Fe0.5%MnO2 catalyst was used in the presence of SO2. Moreover, the Fe in the Fe0.5%MnO2 catalyst improved the reducibility of the surface Mn sites and reduced the oxidizing properties of bridging oxygen, resulting in easier conversion of Mn4+ to Mn3+ and affecting the regeneration of oxygen vacancies in the selective catalytic reduction of NOx with NH3 process. In situ diffuse reflectance infrared spectroscopy showed that the reduction of NOx in the MnO2 nanotubes and Fe0.5%MnO2 sample involved the Eley-Rideal mechanism, whereas the NH3-SCR process of the Fe5%MnO2 sample involved both Langmuir-Hinshelwood and Eley-Rideal mechanisms

Science and Technology of High Performance Ferritic (HiperFer) Stainless Steels

Future, flexible thermal energy conversion systems require new, demand-optimized high-performance materials. The High performance Ferritic (HiperFer) stainless steels, under development at the Institute of Microstructure and Properties of Materials (IEK-2) at Forschungszentrum Jülich GmbH in Germany, provide a balanced combination of fatigue, creep and corrosion resistance at reasonable price. This paper outlines the scientific background of alloy performance development, which resulted in an age-hardening ferritic, stainless steel grade. Furthermore, technological properties are addressed and the potential concerning application is estimated by benchmarking versus conventional state of the art materials