Iron boride

About: Iron boride is a research topic. Over the lifetime, 269 publications have been published within this topic receiving 3584 citations.

FeB/Fe2B phase transformation during SPS pack-boriding: Boride layer growth kinetics

Abstract: The iron boride layer growth kinetics in mild steel through the spark plasma sintering (SPS) pack-boriding technique is investigated at 850 °C with different boriding durations (maximum 240 min). Results show that both FeB and Fe 2 B layers form and grow on the mild steel surface with the FeB layer on the top of Fe 2 B sublayer in the samples with boriding duration less than 90 min. However, at longer boriding duration, the top FeB layer eventually ceases growing, starts to diminish, and, finally disappears completely by transforming into the Fe 2 B phase. Numerical simulation is implemented to explain this phenomenon. Subsequently, the diffusion coefficient of boron in FeB and Fe 2 B phase is obtained through fitting the experimental results into the model. The simulation results are found to be in good agreement with the experimental results, and the estimated diffusion coefficients of boron in FeB and Fe 2 B phases as 2.33 × 10 −9 and 4.67 × 10 −9 cm 2 /s, respectively. Both the simulation and experimental results reveal that the Fe 2 B mono-phase layer can be obtained through the transformation of FeB to Fe 2 B phase due to the depletion of boron concentration in the boriding medium, and is indifferent to the formation of FeB phase at the very onset of the boriding process. This provides a new approach to overcome the side effect of FeB formation in borided components.

Hard iron boride (Fe2B) on 99.97 wt% pure iron

Abstract: Some properties such as hardness and fracture toughness of boride formed on the 99.97 wt% pure iron were investigated. Boronizing was carried out in a solid medium, consisting of Ekabor powders of 5% B4C as donor, 5% KBF4 as an activator and 90% SiC as diluent at 800 °C for 2, 4 and 8 h. The dominant phase formed on the substrate was found to be Fe2B that had a finger-like shape morphology. The hardness of boride on the 99.97% pure iron was over 1700HVN, while the hardness of pure iron was about 130HVN. It was found that the fracture toughness of boride formed on surfaces of 99.97% pure iron, depending on the process time, ranged from 3.59 to 3.83 MPa m1/2. Depending on process time and temperature, the depth of the boride layer ranges from 22 to 43 μm, leading to a diffusion-controlled process.

Mechanical behavior of borides formed on borided cold work tool steel

Abstract: In this study, some mechanical properties of borided cold work low-alloy tool steels were investigated. Boronizing was performed in a solid medium consisting of Ekabor-I powders at 1000°C for 2, 4 and 6 h. The substrate used in this study was high-carbon, low-alloy tool steel essentially containing 1.18 wt.% C, 0.70 wt.% Cr, 0.30 wt.% Mn, 0.10 wt.% V and 0.25 wt.% Si. The presence of borides (FeB+Fe 2 B) formed on the surface of steel substrate was confirmed by optical microscope and X-ray diffraction (XRD) analysis. The hardness of the boride layer formed on the surface of the steel substrate and unborided steel substrate were 1854 and 290 kg/mm 2 , respectively. Experimental results revealed that longer boronizing time resulted in thicker boride layers. Optical microscope cross-sectional observation of the borided layers revealed denticular morphology. The fracture toughness of the boride layers measured by means of a Vickers indenter with a load of 3 N was in the range of 2.52–3.07 MPa m 1/2 .

Sulfur poisoning of cobalt and iron fischer-tropsch catalysts

Abstract: A cobalt/silica and four iron catalysts (unsupported, silica-supported, K-promoted and borided) were exposed to 0.5–8 ppm H 2 S either in situ in a 2/1 H 2 /CO reaction mixture or in pure hydrogen. Catalyst activity and selectivity were monitored as a function of sulfur coverage. Monolayer surface sulfides are formed on the iron catalysts at H 2 S concentrations below 2 ppm at 500 K, while bulk sulfides are formed at higher sulfur concentrations or lower temperatures. Loss of activity is greater during in situ poisoning compared to presulfiding for equivalent S/metal coverages. Iron boride is significantly more resistant to sulfur poisoning than unpromoted iron. At sufficiently low H 2 S concentrations the CO hydrogenation activity of iron boride increases with time. The average molecular weight of hydrocarbons produced by cobalt increases through a maximum with increasing in situ exposure to H 2 S. The product distribution of iron catalysts is essentially unaffected by su fur poisoning.

Effect of boron paste thickness on the growth kinetics of Fe2B boride layers during the boriding process

Abstract: Through this work we study the influence of the thickness of boron paste in the growth of Fe2B boride layer during the paste boriding thermochemical treatment applied on AISI 1045 steel. Different thickness of boron paste over the material surface with constant temperature and time show the variability of the diffusion coefficient of boron in Fe2B phase depending, basically, on the boron potential at the external surface of the substrate. The mobility of boron in the formed phase is determined by the balance mass equation that considers the concentration profiles in the corresponding interphases layer–substrate, the thermodynamic equilibrium in the growth of the iron boride layer and the experimental results obtained during the process.