Systematic thermodynamics calculations based on density functional theory-calculated energies for crystalline solids have been a useful complement to experimental studies of hydrogen storage in metal hydrides. We report the most comprehensive set of thermodynamics calculations for mixtures of light metal hydrides to date by performing grand canonical linear programming screening on a database of 359 compounds, including 147 compounds not previously examined by us. This database is used to categorize the reaction thermodynamics of all mixtures containing any four non-H elements among Al, B, C, Ca, K, Li, Mg, N, Na, Sc, Si, Ti, and V. Reactions are categorized according to the amount of H2 that is released and the reaction's enthalpy. This approach identifies 74 distinct single step reactions having that a storage capacity >6 wt.% and zero temperature heats of reaction 15 ≤ ΔU0 ≤ 75 kJ mol−1 H2. Many of these reactions, however, are likely to be problematic experimentally because of the role of refractory compounds, B12H12-containing compounds, or carbon. The single most promising reaction identified in this way involves LiNH2/LiH/KBH4, storing 7.48 wt.% H2 and having ΔU0 = 43.6 kJ mol−1 H2. We also examined the complete range of reaction mixtures to identify multi-step reactions with useful properties; this yielded 23 multi-step reactions of potential interest.

Large-scale screening of metal hydrides for hydrogen storage from first-principles calculations based on equilibrium reaction thermodynamics.

The effects of the microstructural constituents, chemical composition, and retained austenite on high-strength weld metal were studied using preheat-free steels and GMAW solid wires with a low hydrogen content. The cold cracking susceptibility of these GMAW wires was evaluated using the y-groove Tekken test. The results showed that acicular ferrite produced the greatest resistance to cold cracking and that the microstructure of the deposit was more important than the hardness and diffusible hydrogen content in low-hydrogen weld metal. Crack blunting and branching occurred when a crack propagated through fine acicular ferrite because of the fine interlocking nature of the microstructure. Alloying elements for nucleating acicular ferrite, such as Ti, Al, and V, are required for proper austenite grain size, and sequence of inclusion formation was identified in the present paper. Furthermore, the retained austenite was not found to play the role of a hydrogen trapping site and so had no effect on the cold cracking susceptibility at a low preheating temperature (≤100°C) and low heat input (≤1.5 KJ/mm) to the weld metal.

/pdf/effect-of-microstructure-and-chemical-composition-on-cold-2wnxew01l0.pdf

Effect of microstructure and chemical composition on cold crack susceptibility of high-strength weld metal

This review paper concerns the development of the chemical compositions and controlled processes of rolling and cooling steels to increase their mechanical properties and reduce weight and production costs. The paper analyzes the basic differences among high-strength steel (HSS), advanced high-strength steel (AHSS) and ultra-high-strength steel (UHSS) depending on differences in their final microstructural components, chemical composition, alloying elements and strengthening contributions to determine strength and mechanical properties. HSS is characterized by a final single-phase structure with reduced perlite content, while AHSS has a final structure of two-phase to multiphase. UHSS is characterized by a single-phase or multiphase structure. The yield strength of the steels have the following value intervals: HSS, 180–550 MPa; AHSS, 260–900 MPa; UHSS, 600–960 MPa. In addition to strength properties, the ductility of these steel grades is also an important parameter. AHSS steel has the best ductility, followed by HSS and UHSS. Within the HSS steel group, high-strength low-alloy (HSLA) steel represents a special subgroup characterized by the use of microalloying elements for special strength and plastic properties. An important parameter determining the strength properties of these steels is the grain-size diameter of the final structure, which depends on the processing conditions of the previous austenitic structure. The influence of reheating temperatures (TReh) and the holding time at the reheating temperature (tReh) of C–Mn–Nb–V HSLA steel was investigated in detail. Mathematical equations describing changes in the diameter of austenite grain size (dγ), depending on reheating temperature and holding time, were derived by the authors. The coordinates of the point where normal grain growth turned abnormal was determined. These coordinates for testing steel are the reheating conditions TReh = 1060 °C, tReh = 1800 s at the diameter of austenite grain size dγ = 100 μm.

Overview of HSS Steel Grades Development and Study of Reheating Condition Effects on Austenite Grain Size Changes.

Reactivity of vanadium oxytrichloride with β-diketones and diesters as precursors for vanadium nitride and carbide

Martensitic stainless steel (MSS) coatings with different vanadium (V) contents (0-1.0 wt%) by microalloying have been successfully fabricated utilizing a unique laser cladding technique. The microstructure and properties of the resulting MSS coatings, with and without element V addition, have been carefully investigated by various advanced techniques, including XRD, SEM, TEM, microhardness tester, universal material testing machine, and electrochemical workstation. It was found that the V-free coating was mainly composed of martensite (M) and ferrite (F), trace M23C6 and M2N, while the V-bearing coatings consisted of M, F, M23C6, and VN nano-precipitates, and their number density increased with the increase of V content. The V microalloying can produce a significant impact on the mechanical properties of the resulting MSS laser-cladded specimens. As the V content increased, the elongation of the specimen increased, while the tensile strength and microhardness increased firstly and then decreased. Specifically, the striking comprehensive performance can be optimized by microalloying 0.5 wt% V in the MSS coating, with microhardness, tensile strength, yield strength, and elongation of 500.1 HV, 1756 MPa, 1375 MPa, and 11.9%, respectively. However, the corrosion resistance of the specimens decreased successively with increasing V content. The microstructure mechanisms accounting for the property changes have been discussed in detail.

https://www.mdpi.com/1996-1944/13/4/826/pdf

Influence of Vanadium Microalloying on Microstructure and Property of Laser-Cladded Martensitic Stainless Steel Coating

1.

Electron microscopic and phase analysis were used to determine the solubility of pure vanadium and niobium nitrides in iron. The solubility of these phases is less than 0.05 wt. % at low temperatures but increases sharply with the temperature above 700°, reaching ∼0.1% for niobium nitride and 0.2% for vanadium nitride at temperatures around 1350°.




2.

Electron microscopic analysis is a more sensitive method than phase analysis for determining the solubility of nitrides.

Solubility of vanadium and niobium nitrides in iron

Vanadium nitride in low-alloy low-carbon steels

To obtain the best combination of strength and toughness due to grain refining and controlled precipitation hardening with particles of carbonitride phase, controlled rolling is carried out in the lower range of the austenite region, followed by cooling at a certain rate. This treatment can be called high-temperature thermomechanical treatment for low-alloy steels. The effect of thermomechanical treatment (controlled rolling) increases as the initial and final rolling temperatures are lowered and the degree of deformation in the last passes is increased, and also with the addition of elements that inhibit the recrystallization of austenite (Nb, V, Ti).

Structure and properties of low-alloy steels after controlled rolling

The favorable effect of doping with carbonitride-forming elements-vanadium, niobium, and titanium — on the structure and properties of low-pearlite steels subjected to controlled rolling is due to the change of the structural state of hot-deformed austenite, of the temperature range and nature of the γ→α-transformation, of the phase composition of the steel, and of the state of the α-solid solution caused by the alloying with these elements.

Mechanisms of the effect of vanadium, niobium, and titanium doping on the structure and properties of low-pearlite steels

1.

The first additions of vanadium up to 0.04% in low-pearlite steel of the 09G2 type lead to larger amounts of dispersed phases due to the formation of V(CN), which promotes ferrite grain refining.




2.

With increasing amounts of vanadium over 0.04% the quantity of V(CN) increases due to the smaller quantity of nitrogen bound with A1N and carbon bound with iron (Fe3C).




3.

When the vanadium content is raised from 0.04 to 0.26% there is a constant change in the stoichiometric formula of vanadium carbonitride from V(Co.6No.4) to V(Co.9No.1).




4.

The first addition of 0.04% V favors a substantial reduction of the ductile-brittle transition temperature and higher fracture toughness of the steel. With increasing amounts of vanadium over 0.4% the fracture toughness decreases and the ductile-brittle transition temperature rises.

Yu. I. Matrosov

Papers

Solubility of vanadium and niobium nitrides in iron

Vanadium nitride in low-alloy low-carbon steels

Structure and properties of low-alloy steels after controlled rolling

Mechanisms of the effect of vanadium, niobium, and titanium doping on the structure and properties of low-pearlite steels

Effect of vanadium on the mechanical properties, phase composition, and structure of low-pearlite steel