Kinetics of the Boride Layers Obtained on AISI 1018 Steel by Considering the Amount of Matter Involved (original) (raw)
Related papers
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
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 .
Simulating the Growth of Dual-Phase Boride Layer on AISI M2 Steel by Two Kinetic Approaches
Coatings
Two kinetic approaches (integral method and Dybkov method) have been applied for simulating the boriding kinetics of AISI M2 steel in the range of 1173 to 1323 K, by including the effect of incubation periods. For the integral method, a peculiar solution of the resulting system of differential algebraic equations (DAE) has been employed for assessing the diffusivities of boron in FeB and Fe2B. The boron activation energies in FeB and Fe2B have been deduced from both approaches and compared with the data taken from the literature. Furthermore, to experimentally extend the validity of both approaches, four additional boriding conditions obtained on the boronized samples at 1173, 1223, 1273 and 1323 K for 10 h were then used. The predicted boride layers’ thicknesses were confronted to the experimental values. Consequently, a satisfactory concordance was obtained when comparing the simulated layers’ thicknesses to the experimental values derived from the literature.
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...
Kinetics of Growth of Iron Boride Layers on a Low-Carbon Steel Surface
Laboratory Unit Operations and Experimental Methods in Chemical Engineering
This chapter describes the boriding process and the parameters that govern it. It also describes the features of the obtained layers and the main applications of materials treated with this hardening process. The kinetics of growth of the Fe 2 B face is described using a mathematical model, in which the evolution of the growth of the boride layers is assumed to be controlled by the boron diffusion by means of a dimensional analysis of Fick's second law. The evolution of the growth of the Fe 2 B face on a low-carbon steel surface is illustrated by contour diagrams that involve the main variables of the process (time and exposure temperature). This type of diagrams allows the optimization of the process as a function of the treatment parameters.
Diffusion kinetics and characterization of borided AISI D6 steel
Protection of Metals and Physical Chemistry of Surfaces, 2015
In this study, the case properties and diffusion kinetics of AISI D6 steel borided in Ekabor II pow der were investigated by conducting a series of experiments at temperatures of 1123, 1223 and 1323 K for 2, 4 and 8 h. The boride layer was characterized by optical microscopy, X ray diffraction technique and micro Vickers hardness tester. X ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe 2 B, CrB and Cr 2 B compounds. Depending on the chemical composition of substrates and boriding time, the boride layer thickness on the surface of the steel ranged from 13.54 µm and 164.42 µm. The hardness of the boride compounds formed on the surface of the steels ranged from 1672 to 2118 HV 0.05 , whereas Vickers hardness values of the untreated the steels was 584 HV 0.05. The activation energies (Q) of the borided steel were 180.359 kJ/mol. The growth kinetics of the boride layers forming on the AISI D6 steel and the thickness of boride layers were also investigated.
Applied Surface Science, 2006
Through this work we study the influence of the thickness of boron paste in the growth of Fe 2 B 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 Fe 2 B 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. #
The growth kinetics of borides formed on boronized AISI 4140 steel
Vacuum, 2005
The growth kinetics of boride layer on boronized AISI 4140 steel is reported. Steel samples were boronized in molten borax, boric acid and ferro-silicon bath at 1123, 1173 and 1223 K for 2, 4, 6 and 8 h, respectively. The morphology and types of borides formed on the surface of AISI 4140 steel substrate were analyzed by means of optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis (XRD). The boride layer thickness ranged from 38.4 to 225 mm. Iso-thickness diagrams for pre-determined thickness according to treatment time and temperature, were graphed by MATLAB 6.0 software. The hardness of borides formed on the samples changed between 1446 and 1739 HV 0.1 , according to treatment time and temperature. Layer growth kinetics way analyzed by measuring the extent of penetration of FeB and Fe 2 B sublayers as a function of treatment time and temperature in the range of 1123-1223 K. For practical use, an iso hardness diagram was established as a function of treatment time, temperature and boride layer thickness. The depth of the tips of the most deeply penetrated FeB and Fe 2 B needles were taken as measures for diffusion in the growth directions. The kinetics of the reaction, K ¼ K o expðÀQ=RTÞ were also determined by varying the treatment temperature and time. The results show that K increased with boronizing temperature. The activation energy (Q) was formed to be 215 kJ mol À1 . The growth rate constant (K) ranged from 3  10 À9 to 2  10 À8 cm 2 s À1 .
Kinetics of borided 31CrMoV9 and 34CrAlNi7 steels
Materials Characterization, 2008
In this study, kinetics of borides formed on the surface of 31CrMoV9 and 34CrAlNi7 steels borided in solid medium consisting of Ekabor II at 850-900-950°C for 2, 4, 6 and 8 h were investigated. Scanning electron microscopy and optical microscopy examinations showed that borides formed on the surface of borided steels have columnar morphology. The borides formed in the coating layer confirmed by X-ray diffraction analysis are FeB, Fe 2 B, CrB, and Cr 2 B. The hardnesses of boride layers are much higher than that of matrix. It was found that depending on process temperature and time the fracture toughness of boride layers ranged from 3.93 to 4.48 MPa m 1/2 for 31CrMoV9 and from 3.87 to 4.40 MPa m 1/2 for 34CrAlNi7 steel. Activation energy, growth rate and growth acceleration of boride layer calculated according to these kinetic studies revealed that lower activation energy results in the fast growth rate and high growth acceleration.
Boride Layer Growth Kinetics of Aisi H13 Steel Borided with Nano-Sized Powders
2018
Growth kinetics of boride layers in AISI H13 steel was investigated using the pack boriding method at temperatures of 1073, 1173 and 1273 K (800°C, 900°C and 1000°C) for periods of 2, 4 and 6 h with nano-sized boron (NB) and micron-sized Ekabor II powders as boriding agents. The total thickness of the boride layer (including both FeB and Fe2B) after boriding at 1273 K (1000°C) for 6 h was 103.8 μm and 96.5 μm for the NB and Ekabor II specimens, respectively. X-ray diffraction analysis of the boride layers on the surfaces borided with NB and Ekabor II revealed the presence of FeB and Fe2B phases with sawtooth morphology. The FeB/Fe2B volume ratio was higher in the specimens borided with NB. The thickness of the boride layer (FeB + Fe2B) increased with the increasing boriding temperature and time. The FeB layer in the NB specimen displayed a (002) preferred orientation.