This review focuses on the mechanical properties of cementite as a single phase. The mechanical properties of interest are 1) sound velocity, 2) elastic constants, 3) hardness, 4) plastic deformation mechanism, 5) wear, 6) fracture toughness, and 7) crystal orientation anisotropy. The effect of temperature, magnetic transition and alloying element on sound velocity, elastic constants and hardness were reviewed. Experimental values of the above mechanical properties were collected together with the specimen shape, the amount of alloying elements, the measurement method, etc. A large variation was found in the reported experimental values. The main reason for this is that cementite is metastable and it is difficult to prepare large single-phase samples. Other factors such as sample shape, measurement method, alloying element, magnetic transformation, and crystal orientation anisotropy also influenced the measured values. The studies using the first-principles calculation on cementite were also reviewed. The crystal orientation anisotropy of the elastic constant of single crystal cementite based on the first-principles calculation was summarized and its comparison with experiment was discussed. Comparing the elastic constants obtained by the first-principles calculation with the measured values, the former values are several % to several tens of % larger than the latter values. The cause of this is thought to be the difference in temperature between 0 K (first-principles calculation) and room temperature (measured value), and theoretical and experimental researches in which the temperature is changed are expected.

As an innovative route to mitigating CO₂ emissions in ironmaking, increasing the hydrogen reduction in a blast furnace is promising. One possible method is the shaft injection or blast tuyere injection of coke oven gas (COG) with its hydrogen concentration enhanced by steam-reforming methane and tar. Therefore, the reduction behavior of sintered ores in a blast furnace by injecting reformed COG was investigated using a softening-melting tester and counter-current reaction simulator (BIS). The shaft injection of reformed COG promoted the reduction and improved the permeability of the ore layer, particularly in the wall area of the blast furnace. An injection rate larger than 200 Nm³/t-HM was required for reformed COG for a limiting intermediate distribution ratio of injection gas lower than 20% in a large blast furnace. Unchanged shaft temperature and increased hydrogen reduction were observed during the shaft injection of hot reformed COG in the BIS test. The water-gas shift reaction below the temperature of the thermal reserve zone was insignificant even for the shaft injection of reformed COG. As for tuyere injection, direct reduction was decreased by increasing the injection rate of reformed COG from tuyere. The injection of COG with or without reforming from tuyere reduced the carbon consumption of the blast furnace by 10 kg/t-HM. The influence of the composition of COG on carbon consumption was insignificant. Direct observation of hydrogen reduction revealed a decrease in flooding molten slag in the upper coke layer during reduction, thus explaining the improved permeability of the ore layers.

A computer model is constructed to simulate the dissolution of V carbide and carbonitride particles with size distribution in steels. Assuming local equilibrium of carbon, nitrogen, and V at the particle/matrix interface, the dissolution rate is calculated using the mean-field and invariant field approximations. The fraction of particles and size distribution (PSD) of V carbide are in good agreement with those in Fe-C-V austenite reported in the literature. The V mass fraction and PSD of carbonitride, measured by extraction replica in this study, were also reproduced well by simulation in an Fe-C-V-N alloy (N~20 ppm). Moreover, simulation using an equilibrium tie-line passing through the bulk alloy composition, as often done in the calculation of precipitate dissolution rate, is shown to yield a large error.

The development of cube texture in Fe-Mn-Si-Cr shape memory alloy by the preferential dynamic grain growth mechanism is experimentally examined. The plane strain compression deformation at 1173 K with strain rates of 2.0 × 10⁻³ s⁻¹, 1.0 × 10⁻³ s⁻¹, and 5.0 × 10⁻⁴ s⁻¹ results in the development of cube texture. The maximum volume fraction of cube orientated grains is about 25% which is ten times as high as that before the deformation. It is experimentally confirmed that the specimen with {001}(surface of the tensile specimens) <110>(tensile direction) shows higher shape memory efficiency than those prepared by the so called training treatment. The texture evaluation by neutron diffraction method elucidates that control of the texture in the γ single phase state is effective to specify the active shear system contributing to the shape memory effect.

Compact tension tests for fatigue crack growth were carried out on transformation-induced plasticity (TRIP) maraging steel with two different annealing times (1 h and 8 h). Interestingly, resistance to the long crack growth increased with increasing annealing time at a ΔK ranging from 33 to 50 MPa∙m^1/2, while short crack growth resistance, e.g., crack growth in a smooth specimen, was reported to show an inverse trend. It is also noteworthy that increasing annealing time in TRIP-maraging steel decreases both yield and tensile strengths. Namely, the resistance to the long crack growth showed totally inverse trend to the tensile properties, in terms of annealing time. The major microstructural change by increasing annealing time was retained austenite fraction. Specifically, increasing annealing time increases austenite fraction, which may have assisted TRIP-related phenomena and associated resistance to the long crack growth, e.g. transformation-induced crack closure.