Effects of process current density and temperature on electrochemical boriding of steel in molten salts (original) (raw)
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Kinetics of electrochemical boriding of low carbon steel
Applied Surface Science, 2011
In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm 2 in a borax based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5-120 min. After boriding, the presence of both FeB and Fe 2 B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 ± 200) HV), while the hardness of un-borided steel samples was approximately (200 ± 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 ± 8.6) kJ/mol.
Electrochemical boriding and characterization of AISI D2 tool steel
Thin Solid Films, 2011
D2 is an air-hardening tool steel and due to its high chromium content provides very good protection against wear and oxidation, especially at elevated temperatures. Boriding of D2 steel can further enhance its surface mechanical and tribological properties. Unfortunately, it has been very difficult to achieve a very dense and uniformly thick boride layers on D2 steel using traditional boriding processes. In an attempt to overcome such a deficiency, we explored the suitability and potential usefulness of electrochemical boriding for achieving thick and hard boride layers on this tool steel in a molten borax electrolyte at 850, 900, 950 and 1000°C for durations ranging from 15 min to 1 h. The microstructural characterization and phase analysis of the resultant boride layers were performed using optical, scanning electron microscopy and X-ray diffraction methods. Our studies have confirmed that a single phase Fe 2 B layer or a composite layer consisting of FeB + Fe 2 B is feasible on the surface of D2 steel depending on the length of boriding time. The boride layers formed after shorter durations (i.e., 15 min) mainly consisted of Fe 2 B phase and was about 30 μm thick. The thickness of the layer formed in 60 min was about 60 μm and composed mainly of FeB and Fe 2 B. The cross sectional micro-hardness values of the boride layers varied between 14 and 22 GPa, depending on the phase composition.
Corrosion and Materials Degradation
In this study, mechanical and electrochemical performance of borided additively manufactured (AM) and wrought 8620 low alloy steel were investigated and compared to their bare counterparts. The microstructure of borided 8620 exhibited the presence of FeB and Fe2B phases with a saw tooth morphology. Both AM and wrought samples with boride layers showed a similar performance in hardness, wear, potentiodynamic polarization (PD), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) experiments. However, borided steels exhibited about an 8-fold increase in Vickers hardness and about a 6-fold enhancement in wear resistance compared to bare ones. Electrochemical experiments of borided specimens (both AM and wrought) in 0.1 M Na2S2O3 + 1 M NH4Cl solution revealed a 3–6-fold lower corrosion current density, about a 6-fold higher charge transfer resistance, and about a 6-fold lower double-layer capacitance, demonstrating an improved corrosion resistance compa...
Production and characterization of boride layers on AISI D2 tool steel
Vacuum, 2010
a b s t r a c t AISI D2 is the most commonly used cold-work tool steel of its grade. It offers high hardenability, low distortion after quenching, high resistance to softening and good wear resistance. The use of appropriate hard coatings on this steel can further improve its wear resistance. Boronizing is a surface treatment of Boron diffusion into the substrate. In this work boride layers were formed on AISI D2 steel using borax baths containing iron-titanium and aluminium, at 800 C and 1000 C during 4 h. The borided treated steel was characterized by optical microscopy, Vickers microhardness, X-ray diffraction (XRD) and glow discharge optical spectroscopy (GDOS) to verify the effect of the bath compositions and treatment temperatures in the layer formation. Depending on the bath composition, Fe 2 B or FeB was the predominant phase in the boride layers. The layers exhibited ''saw-tooth'' morphology at the substrate interface; layer thicknesses varied from 60 to 120 mm, and hardness in the range of 1596-1744 HV were obtained.
Characterization of Boride Layers on Ryalloy Steel
Metal ..., 2022
Boronizing is a thermochemical process in which the boron atoms are introduced into the steel surfaces. During this process, the boride layers with high hardness, wear-and corrosion-resistance are formed. In this study, the Royalloy (0.05 wt.% C; 12.6 wt.% Cr; 0.4 wt.% Si and 1.2 wt.% Mn) steel was powder-boronized at 900, 950, 975, 1000 or 1050 °C, and for 1, 3, 5, 7 or 10 h. The boronized samples were analyzed by X-ray diffraction analysis (XRD) to analyze their phase composition, and by scanning electron microscope to analyze their thickness and morphology at the interface with the substrate. To investigate the chemical elements redistribution during the boronizing process, the EDS mapping and EDS point analysis were used. The treatments produced boride layers with a thickness from 8 to 168 µm, depending on the boronizing parameters. During the boronizing process, the chromium was redistributed between the boride layers, where creates the chromium borides, and the transient region underneath the boride layers, where creates the particles with the biggest amount of chromium. The silicon was focused at the layersubstrate interfaces. The concentration of manganese was slightly higher in substrate compared to the boride layers.
Characterizations and Kinetic Modelling of Boride Layers on Bohler K190 Steel
In this study, the Bohler K 190 steel was used. The steel was manufactured by the powder metallurgy (PM) process. The boronizing process was carried out in the range of 1173 to 1323 K, for 1-10 h. The samples were boronized in solid medium, called the Durborid powder mixture. For the microstructural observations, the scanning electron microscopy was utilized for determining the morphology of interfaces and measuring the layers’ thicknesses. The phase composition of boride layers was also determined with X-ray diffraction analysis. To investigate the redistribution of chemical elements redistribution during the boronizing process, the EDS mapping and EDS point analysis were used. The boride layers were constituted by FeB and Fe2B phases except for 1173 K for 1 h. The values of Vickers microhardness of Fe2B, FeB and transition zone were estimated. Finally, to assess the boron activation energies in FeB and Fe2B, the so-called integral method was applied and the results in terms of act...
Growth kinetics of the boride layers formed on SAE 1035 steel
Matériaux & Techniques, 2013
Growth kinetics of the boride layers formed on SAE 1035 steel has been investigated during the boriding treatment. This treatment was carried out in slurry salt bath consisting of borax, boric acid and ferrosilicon for temperatures ranging from 1073 to 1273 K and treatment times of 2, 4 and 8 h. The presence of both FeB and Fe2B phases formed on the surface of SAE 1035 steel was confirmed by X-ray diffraction. Scanning electron microscopy (SEM) and optical microscopy examinations showed that the boride layers have a saw-tooth morphology. The thickness of boride layers was found to be increased when the treatment time and the boriding temperature increase, its value ranged from 20 to 387 µm. The average hardness of the boride layer was about 1760 ± 200 HV0.1, while the hardness of un-borided steel was about 225 ± 20 HV0.1. The fracture toughness of boride layers (KC) was found to be ranged between 3.42 and 4.57 MPa m 1/2. The kinetic study showed a parabolic relationship between the boride layer thickness and the process time. The value of boron activation energy for the borided SAE 1035 steel was estimated as 227.51 kJ mol −1 .
Effect of Diffusion Annealing on Borides Layers Produced on XC38 Steel
Acta Physica Polonica A, 2017
In this work, we present a study of the effect of diffusion annealing at 700 • C for 1 h on the nature and properties of boride layers obtained on XC38 steel through a molten salt consisting of borax (Na2B4O7) and boron carbide (B4C). We evaluated the changes brought by the diffusion annealing on the morphology of the boride layer, the thickness of this layer, the distribution of elements in the steel, and the hardness. Comparing the results obtained allowed concluding that the diffusion annealing will completely transform the two-phase layer formed of FeB and Fe2B borides in a single-phase layer consisting of single boride Fe2B. The transformation of the two-phase boride into a single-phase boride is done with an increase in thickness of about 30% compared to the initial thickness of the sample. The values of Si concentration obtained in the underlying zone after the diffusion annealing treatment are more important than those obtained in the same underlying zone of samples borided directly by immersion in molten salt consisting of borax and silicon carbide (SiC).
An approach to kinetic study of borided steels
Surface & Coatings Technology, 2005
In present study, kinetic studies on borided AISI 5140, AISI 4340 and AISI D2 steels are reported. Steels were borided in a salt bath consisting of borax, boric acid and ferro-silicon between 1073 and 1273 K for 2, 4, 6 and 8 h. The morphology and types of borides formed on the surface of steel substrates were confirmed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Boride layer thickness formed on the borided steels ranged from 21 to 238 Am depending on process temperature, treatment time and alloying elements of the substrates. The hardness of borides formed on the samples changes between 1077 and 2140 HV 0.1 according to treatment time and temperature. Layer growth kinetics were analyzed by measuring the extent of penetration of FeB and Fe 2 B sublayers as a function of boronizing time and temperature in the range of 1123 -1273 K. The depth of the tips of the most deeply penetrated FeB and Fe 2 B needles are taken as measures for diffusion in the growth directions. The kinetics of the reaction, K = K o exp ( À Q/RT), have also been determined by varying the boriding temperature and time. The results showed that K increase with boriding temperature. Activation energies ( Q) of borided AISI 5140, AISI 4340 and AISI D2 steels at present study were determined as 223, 234 and 170 kJ/mol, respectively. Moreover, an attempt was made to investigate the possibility of predicting the contour diagrams of boride layers variation and to establish some empirical relationships between process parameters and boride layer thicknesses. D