The growth kinetics of borides formed on boronized AISI 4140 steel (original) (raw)
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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 .
Coatings
Boride layers are typically used to combat the wear and corrosion of metals. For this reason, to improve our knowledge of the boriding process, this research studied the effect of the size of the treated material on the kinetics of the growth of the boride layers obtained during a solid diffusion process. The purpose was to elucidate how the layers’ growth kinetics could be affected by the size of the samples since, as the amount of matter increases, the amount of energy necessary to make the process occur also increases. Furthermore, the level of activation energy seems to change as a function of the sample size, although it is considered an intrinsic parameter of each material. Six cylindrical samples with different diameters were exposed to the boriding process for three different exposure times (1.5, 3, and 5 h). The treatment temperatures used were 900, 950, and 1000 °C for each size and duration of treatment. The results show that the layer thickness increased not only as a fu...
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
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.
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.
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.
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.
Kinetics of borided AISI M2 high speed steel
The present study reports on kinetics of borided AISI M2 high speed steel. Boronizing thermochemical treatment was carried out in a solid medium consisting of EKabor powders at 850 C, 900 C and 950 C for 2, 4, 6 and 8 h, respectively. The presence of borides FeB and Fe 2 B of steel substrate was confirmed by optical microscopy and scanning electron microscopy (SEM). The results of this study indicated that the morphology of the boride layer has a smooth and compact morphology, and its hardness was found to be in the range of 1600e1900 HV. Depending on process time and temperature the thickness of boride layer measured by a digital instrument attached to an optical microscope ranged from 3 to 141 mm. Layergrowth kinetics were analyzed by measuring the extent of penetration of the FeB and Fe 2 B sublayers as a function of boronizing time and temperature. The fracture toughness of borides ranged from 4.80 to 5.21 MPa m 1/2 . Moreover, an attempt was made to investigate the possibility of predicting the isothickness of boride layer variation and to establish an empirical relationship between process parameters and boride layer thickness.
Investigation of Boronizing Kinetics of AISI 51100 Steel
Journal of Materials Engineering and Performance, 2012
In this study, some mechanical properties of borided AISI 51100 steel with high C concentration were investigated. Boronizing heat treatment was carried out in solid medium consisting of Ekabor-II at 850, 900, and 950°C for 2, 4, 6, and 8 h. Morphology and mechanical properties of boride layer, and the effect of chemical composition on properties and kinetics of borides were investigated. The results of this study indicated that the morphology of the boride layer has a saw-tooth nature, and its hardness is over 1500 HV. Depending on process time and temperature, the depth of boride layer ranged from 30 to 106 lm. Optical and SEM studies and XRD analysis revealed that borides formed on the surface of steel substrates have dominantly single Fe 2 B boride phase in addition to small amount of Cr 2 B.
Growth Kinetics of the Fe2B Coating on AISI H13 Steel
Transactions of the Indian Institute of Metals, 2014
A kinetic model was suggested to study the growth kinetics of Fe 2 B layers on AISI H13 steel via the pack-boriding method in the temperature range of 1,123-1,273 K. This model was based of the principle of mass conservation at the (Fe 2 B/substrate) interface where the boride incubation time was independent of the boriding temperature. The model was also validated experimentally by comparing the experimental Fe 2 B layers thicknesses with the predicted values at 1,173 K during 7 h, 1,223 K during 5 h, 1,253 K during 2 h and 1,273 K for 3 h. The Fe 2 B layers grown on AISI H13 steel were characterized by use of the following experimental techniques: optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. In addition, a contour diagram describing the evolution of Fe 2 B layers as a function of the boriding parameters (time and temperature) was proposed. Finally, the boron activation energy for AISI H13 steel was estimated as 233 kJ mol -1 on the basis of our experimental results. This value of energy was compared with the literature data.