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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Influence of defect characteristics on tensile deformation of an additively manufactured stainless steel: Evolutions of texture and intergranular strain

The micromechanics of plastic deformation behavior of a selective laser melt processed austenitic stainless steel were studied by investigating the evolutions of texture and intergranular strain using in situ high-energy synchrotron x-ray diffraction (sXRD). The effects of defect characteristics on tensile behavior were studied using three different samples: a near full-density sample with elliptical closed voids and two samples with lack-of-fusion (LOF) defects tensile loaded either perpendicular or parallel to their major axes. The evolutions of pole figures and inverse pole figures show that the full-density specimen develops a strong (111)/(200) fiber texture along the loading direction. For both LOF specimens, the evolution of texture is qualitatively similar to the full-density counterpart, but the development of the fiber texture was much slower, indicating a limited plasticity at a given macroscopic strain. The intergranular strain evolution in the full-density specimen is similar to that of a wrought 316L stainless steel. Conversely, a significantly different intergranular strain development was observed in a LOF specimen, where tensile strain development was observed in both the axial and transverse directions. Finally, the influence of defect type, density, and orientation on the local stress states in the steel matrix and the evolutions of intergranular strains is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Creep of MARBN-type 9Cr martensitic steel in gaseous CO 2 environment

Here, with an interest in moving from steam to supercritical CO 2 as the working fluid in advanced energy systems, it is important to study the mechanical response of structural alloys to CO 2 -containing environments. MARBN-type 9Cr martensitic steel was originally developed for application in boilers for supercritical and ultra-supercritical power plants where the steam temperature reaches 650 °C. In this research, a MARBN-type 9Cr martensitic steel designed and manufactured at NETL was creep tested in a gaseous CO 2 environment (i.e., 0.1 MPa at 650 °C), and the results are directly compared to creep tests conducted in air. It was found that environmentally-assisted cracking facilitated by carbide formation beneath the growing oxide accelerated failure in gaseous CO 2 . This work indicates that creep-oxidation interactions in advanced martensitic steels represent an important consideration for materials selection in supercritical CO 2 power cycles. Furthermore, this work confirms that more oxidation-resistant alloys will be required for the highest temperature portions of these systems.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The mechanism of twin thickening and the elastic strain state of TWIP steel nanotwins

A Twinning Induced Plasticity (TWIP) steel with a nominal composition of Fe-16.4Mn-0.9C-0.5Si-0.05Nb-0.05V was deformed to an engineering strain of 6%. The strain around the deformation twins were mapped using the 4D-STEM technique. Strain mapping showed a large average elastic strain of approximately 6% in the directions parallel and perpendicular to the twinning direction. However, the large average strain comprised of several hot spots of even larger strains of up to 12%. These hot spots could be attributed to a high density of sessile Frank dislocations on the twin boundary and correspond to shear stresses of 1–1.5 GPa. The strain and therefore stress fields are significantly larger than other materials known to twin and are speculated to be responsible for the early thickness saturation of TWIP steel nanotwins. The ability to keep twins extremely thin helps improve grain fragmentation, i.e. the dynamic Hall–Petch effect, and underpins the large elongations and strain hardening rates in TWIP steels.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Friction surfacing and cold spray deposition for surface crack repair in austenitic stainless steels

Two technologies, friction surfacing (FS) and cold spray deposition (CSD), have been investigated for field repair of cracks in 304L austenitic stainless steel. Both technologies are low-heat-input, solid-state technologies that do not introduce the detrimental effects of solidification, such as compositionally segregated microstructures and shrinkage stresses. Friction surfacing was performed using a 304L stainless steel rod over the substrate of the same material. Further, the process was performed at a high spindle speed of 20,000 RPM allowing for process forces below 500N to be used effectively. Spherical gas-atomized 304L stainless steel powder, in size range of 25–44 µm, was used as feedstock powder for the cold spray process for deposition on 304L substrates. Both technologies showed leak-tight crack repair capabilities on ~30–50 µm wide simulated through-crack specimens based on helium leak tests.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Influence of fatigue precracking and specimen size on Master Curve fracture toughness measurements of EUROFER97 and F82H steels

EUROFER97 and F82H steels are two leading reduced-activation ferritic-martensitic (RAFM) steels for fusion first wall and blanket applications. Exposure to the harsh environment of fusion reactors can result in severe degradation of fracture toughness. Thus, the post-irradiation evaluation of fracture toughness is critical for understanding the material behavior. Due to the space constraints of irradiation facilities and challenges in controlling a uniform irradiation condition for large size specimens, the development of small specimen test techniques (SSTT) is indispensable to evaluate the performance of irradiated materials. In this study, we evaluated specimen size effects on the Master Curve fracture toughness of EUROFER97 and F82H steels. A wide variety of specimens, including 0.5 T compact tension (C(T)) specimens, 0.16 T mini-compact tension (miniC(T)) specimens, and 1.65 mm miniature bend bar specimens, were tested. The testing methodology was based on the Master Curve method in the ASTM E1921 standard. No specimen size effect was observed in 0.5 T C(T) and 0.16 T miniC(T) specimens on the Master Curve reference temperature T0, while 1.65 mm miniature bend bar specimens yielded a higher T 0Q . A strong effect of fatigue precracking on T 0 for 0.5 T C(T) and 0.16 T miniC(T) specimens was observed, such that testing on specimens with skewed fatigue precrack fronts resulted in lower T 0 than for specimens with ASTM standard qualified straight fatigue precrack fronts. The results highlight the importance of experimental quality control in developing SSTT for Master Curve fracture toughness testing. Lastly, we also evaluated and provided recommendations on the minimum number of specimens needed for each specimen type for yielding reliable T 0Q values.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Morphology and elemental composition of a new iron-rich ferrite phase in highly irradiated austenitic steel

Here, elemental composition and morphology of a previously unidentified radiation-induced ferrite phase were investigated in a 300-series steel irradiated by neutrons in-service up to 57.6 dpa. Specimens of 18Cr-10Ni-Ti stainless steel (AISI 321 analog) were cut from a hexagonal wrapper of a fuel assembly irradiated in the BN-350 sodium-cooled fast reactor. An Fe-rich bcc-phase was observed primarily on grain boundaries. In this phase, the concentration of Cr is ~8–12% (compared to ~19% in the matrix), the concentration of Ni is ~1.5–3% (~9% in the bulk material), and the concentration of Mn is ~0.23% (1.3% in the matrix). This Fe-rich phase is distinctly different from the retained-ferrite phase, commonly found in commercial austenitic steels. The extensive appearance of this Fe-rich ferrite on grain boundaries suggests that enhanced surface–intergranular corrosion may occur in water-cooled power reactors, arising from the low Ni, Mn, and Cr concentrations in this phase.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The role of excess vacancies in stabilizing solute clusters in low-alloy steels

The formation of solute clusters in irradiated low-alloy steels, such as reactor pressure vessel steels, is a critical cause of radiation hardening and embrittlement. However, the chemical interactions among solute elements and excess vacancies remain to be fully understood. This study employs density functional theory, cluster expansion, and lattice-based Monte Carlo simulations to examine the stability and morphology of nano-size coherent solute clusters with excess vacancies. The findings reveal that excess vacancies are crucial in stabilizing and promoting the growth of Mn-Ni-Si-vacancy clusters. A minimum of seven vacancies is required for stable nucleation and growth of these clusters. These Mn-Ni-Si clusters act as defect sinks, effectively trapping and absorbing mobile vacancies generated under irradiation. Furthermore, phosphorus (P) preferentially dissolves in Mn-Ni-Si clusters due to chemical coupling with vacancies. In conclusion, this study offers new insights into solute-vacancy interactions, enhancing our understanding of solute-defect cluster formation and embrittlement in low-alloy steels.

36 - MATERIALS SCIENCE↗
DOE OSTI2025

Rapid tempering to enhance dynamic performance of high and ultra-high strength steels

This study employed rapid, short-time duration (1 s) tempering to improve the dynamic performance of high-strength steel (HSS) and ultra-high-strength steel (UHSS), compared to quenched and conventionally (1800 s) tempered microstructures. Rapid tempering significantly improved the Charpy toughness of both steels compared to the conventionally tempered condition at an equivalent tempering parameter (TP) or hardness level. For conventionally tempered conditions, tempered martensite embrittlement was observed within the tempering temperature range of 200–400 °C, whereas rapid tempering exhibited increased Charpy toughness with increasing tempering temperature across all tempering conditions. Dynamic compression experiments indicated that rapid tempering led to improved ductility compared to the conventionally tempered condition at an equivalent TP. This work shows that the same rapid tempering strategy used for HSS is directly transferable to a higher-carbon UHSS and provides the first systematic evidence of improved strength-ductility combinations and cracking resistance under dynamic compression, supported by Kolsky bar experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Influence of Microstructure on the Absorption of Tritium into Gold-Plated 316 Stainless Steel

The interaction of tritium with metal surfaces is the initial step in the overall absorption of tritium by the substrate metal. As a result, limiting the adsorption of tritium to the surface may effectively reduce the quantity of tritium absorbed by a metal when it is in contact with tritium gas. To limit tritium adsorption, many tritium users electroplate gold onto the substrate metal. The gold layer is expected to reduce tritium adsorption, and subsequently absorption, by reducing water adsorption. The present work shows a comparison between tritium inventories in nonplated 316 stainless steel to the inventories in 316 stainless-steel samples electroplated with gold by various commercial vendors and laboratories. Of the various gold-plated samples, only one type of plating shows ~25% reduction in tritium inventory, relative to non-plated steel samples. The degree of tritium absorption appears to be significantly influenced by the porosity, texture, and completeness of the gold layer. Incomplete and/or porous layers lead to increased absorption, while gold layers with smaller surface features lead to similar tritium inventories as non-plated samples. Furthermore, reduced tritium absorption was observed only for complete gold layers with small surface features.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Mitigated Dissimilar Mass Transfer with Aluminized RAFM Steels in Flowing PbLi at 650°C

To evaluate dissimilar material interactions in flowing eutectic Pb-16at. %Li between fusion-relevant materials and to establish a maximum operating temperature of future blanket designs, a series of thermal convection loop (TCL) experiments with flowing PbLi have been conducted. Following a 1000-h, 550°C to 650°C TCL experiment, a thin reaction product was observed on the surface of monolithic, high-purity SiC. To identify the source of the observed dissimilar material interaction and to understand the reaction kinetics, an identical 2000-h TCL exposure was conducted, but less reaction of the SiC specimen was observed. Characterization of the FeCrAlMo (alloy APMT) loop tubing and the PbLi-exposed austenitic stainless steel (SS) assembly parts suggested that the formation of the reaction layer on the surface of the PbLi-exposed SiC did not originate from the coated reduced activation ferritic martensitic (RAFM) steel, but from the dissolved loop materials (liquid metal exposed APMT tubing and type 316 SS fittings). Here, the results, after 2000 h, suggest that the dissimilar material reaction between the Al-coated RAFM steel and the SiC has very slow reaction kinetics within a temperature gradient of 550°C to 650°C.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Nondestructive Evaluation of Stress Corrosion Cracking in a Welded Steel Plate Using Guided Ultrasonic Waves

Stress corrosion cracking (SCC) had occurred in early-generation high-level nuclear waste tanks constructed by welding carbon steel. This paper describes an ultrasonic inspection system and its fundamental ability to detect and quantify the length of SCC on thick welded steel plates. The finite element method (FEM) was applied to simulate the welding process to estimate the welding residual stress field. Growth of stress corrosion cracks is driven by crack stress intensities exceeding the subcritical cracking threshold intensity. The subject plate was experimentally inspected with ultrasonic nondestructive evaluation (NDE) techniques to characterize the extent of SCC. The NDE system uses a piezoelectric transducer to generate guided waves in the thick steel plate, and a scanning laser Doppler vibrometer (SLDV) to measure multidimensional time–space wavefield data over a user-defined scanning area in the plate surface. The measured wavefield data can show wave interactions in a localized area in the plate due to the presence of the discontinuities of the SCC. To generate an inspection image that can precisely show the crack’s location and/or the dimension, the wavefield data are further processed to generate inspection image that maps the entire sample plate so the crack can be clearly identified in the plate while its length can be readily estimated. In conclusion, the ultrasonic test results for crack length agree well with the visually estimated length and are close to that predicted by the FEM for cracks in the weld residual stress field.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Forming Limits of Thin Ferritic Stainless Steel for Fuel Cell Application

To lower the cost of fuel cell bipolar plate (BPP), less expensive ferritic stainless steel (FSS) BPP substrate materials are investigated. A series of tensile tests and multistage microchannel-forming tests were conducted on 85-µm-thick ferritic stainless steel foils, 439L, 444, and Chromeshield® 22, to understand the effect of the forming temperatures, tooling geometry, and processes on their formability. Three microchannel-forming processes were conducted, which are 1-Hit (single-stage forming), 2-Hit (two-stage forming) with 50% preform, and 2-Hit with 80% preform. FLC o s at various microchannel-forming conditions were obtained to address the formability of the ferritic stainless steel foils under plane strain conditions. It has been found that the larger the microchannel radius, the better the formability, two-stage forming is superior to the single-stage process, and a larger draw percentage in preform (stage I) leads to a higher FLC o or better formability. It has also been found from tensile tests that the thermal effect (higher temperature) has a negative impact on the failure strains. A similar phenomenon was also observed through channel-forming tests conducted at room temperature, 100 °C, and 200 °C.

08 HYDROGEN↗
DOE OSTI2020

Cost Effective 6.5% Silicon Steel Laminate for Electric Machines

Iowa State University teamed with United Technologies Research Center and the University of Delaware and demonstrated a high switching frequency non-rare earth permanent magnet motor. A prototype motor with 400 Hz switching frequency, dummy MnBi permanent magnet with 8 MGOe energy density, and 6.5%Si steel as the laminate materials was designed, built, and tested. The performance of the prototype met the expectations showing a higher frequency motor enabled by 6.5%Si steel is a viable approach to meet DOE 2022 cost and performance targets for electric vehicle drive. Adoption of 6.5%Si steel will result in 3% improvement in energy conversion efficiency of the soft magnetic materials. In addition, the ability to use non-rare earth magnet for high power density application effectively mitigate the risk of EV traction motor from the rising rare earth price.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Combined modeling and experiments to predict corrosion and embrittlement in dual-phase stainless steels within the MARMOT framework

Extending service of Light Water Reactors (LWRs) to beyond 60 years will demand high integrity of materials and components in the reactors. The accurate evaluation and prediction of materials performance under anticipated operating conditions are of particular importance for ensuring the safety of nuclear power plants over their extended lifetime. Stainless steels are extensively used as structural alloys in light water reactor (LWR) systems because of their excellent combination of mechanical properties and corrosion resistance. Austenitic stainless steel welds and cast austenitic stainless steels (CASS) contain significant amounts of ferrite ~5-30% and are ubiquitous in LWR piping (elbows, pump casings, valves) and internal structural components. During their lifetime, these components are subjected to thermal aging at the temperature range of 288-327°C for pressurized water reactors (PWR). A phase transformation within the ferrite phase of these materials leads to embrittlement and degradation in corrosion resistance, which undermines the materials selection criteria.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Maximizing Scrap Recycling by Designing Cu Tolerant Steel Compositions

Residual elements from scrap steel recycling, most notably copper, are known to result in hot shortness during thermomechanical processing and casting. As the concentration of copper and other residuals in steel scrap streams increases, Electric Arc Furnace (EAF) scrap recycling heats commonly use pig iron to dilute residuals below current limits. This work focuses on establishing residual element tolerant compositions and concomitant processing windows that can simultaneously mitigate issues from residuals during thermomechanical processing and, if possible, use these residuals to improve properties, yielding a more sustainable steel manufacturing pathway with a substantially smaller carbon footprint.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Energy Requirements for Integration of Nuclear Reactors with Iron and Steel Plants

This report identifies energy needs of heavy energy users within the domestic iron and steel industry and suggests solutions for integrating nuclear energy. The iron and steel industry, composed of several types of plants which perform different processes with varied energy demands and vectors, is a heavy consumer of electric power and fossil fuels including coke and natural gas. Almost all major process temperatures exceed the temperatures of direct heat available from advanced reactors, and so electricity and hydrogen were considered instead. Reference units were adopted and estimated energy demands computed for the blast furnace (BF), direct reduced iron (DRI) unit, electric arc furnace (EAF), and reheat furnaces. By utilizing production capacity data from industry reports, the ranges of power demands were estimated, including for hydrogen production by high temperature steam electrolysis (HTSE). For the EAF and DRI unit, more detailed integration studies with thermodynamic modeling were also conducted and determined a possible solution with a specific reactor design and number of modules. Furthermore, because many unit processes are co-located, entire plants were considered by adding the energy demands of the unit processes to form four hypothetical reference plants. The range of power needs for the reference plants is compatible with multi-unit banks of microreactors at the low end, and would create a need for multiple larger-capacity SMRs at the high end (1 GWe plus 0.14 GWt). Although the overall power need at the high end is well-matched with one present-day large reactor offering (1.1 GWe), redundancy considerations may require a minimum of two reactors, potentially eliminating the single large reactor from consideration. Auxiliary or house loads would increase the reference plant estimates. Finally, the report provides total estimated energy needs under integration of all U.S. units of each process (BF, DRI, EAF, and reheat furnaces), representing a national potential for nuclear energy in the industry. U.S. iron and steel plants may be candidates for integration with nuclear reactors via electricity and hydrogen, and many sites have energy requirements that correspond well to the capacities of several advanced nuclear power designs.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Enhancing NDE Reliability for Grade 91 Steel Welds: Ultrasonic Imaging and Microstructural Correlations

Ensuring the integrity of Grade 91 (9Cr-1Mo-V) steel welds is vital for the safe and reliable operation of fossil fuel–fired and nuclear power plants. Here, this study applies an imaging technique for the ultrasonic characterization of two Grade 91 steel welds created with cold metal transfer and flux-cored arc welding processes. Ultrasonic immersion testing in the through-transmission configuration was employed to generate shear waves, which helped identify the weld metal, heat-affected zone, and base metal regions. These weld microstructures were also correlated to their ultrasonic images using metallography, ultrasonic amplitude, hardness measurements, and grain size. The findings from this study can assist practitioners in developing new nondestructive evaluation technologies, improving the inspection reliability of creep strength–enhanced ferritic steel welds by potentially identifying weld microstructure regions susceptible to creep-type failures.

Grade 91 steel↗
DOE OSTI2020

Transient Microstructure Evolutions and Local Properties of Dual-Phase 980 MPa Grade Steel Via Friction Stir Spot Processing

Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400 °C), whereas higher peak temperatures (>Ac 1 ) led to a change in grain size with different microstructures (fine-grained DP or martensite). Electron back-scattered diffraction characterizations revealed a large deformation in the as-received microstructures (mixture of ferrite and tempered martensite) induced by friction stir spot processing, leading to recrystallization and grain refinement around the stirred zone. Also, nano-indentation measurements showed a higher hardness than the hardness of the as-received DP980. Friction stir processing with different process conditions effectively changed microstructures and local mechanical properties.

36 MATERIALS SCIENCE↗