Features of structural changes due to the formation of the boride crystal structure in steels (original) (raw)
Related papers
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...
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
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.
Mechanical behavior of borides formed on borided cold work tool steel
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 1000ЊC 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.
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 .
Influence of Boron on the Hardenability of Unalloyed and Low Alloyed Steel
Boron exerts a large influence on mechanical properties of steel through microstructural control. It increases the hardenability of steel by retard ing the heterogeneous nucleation of ferrite at the austenite grain surfaces and the decomposition kinetics of austenite to ferrite t ransformat ion are governed by its location and chemical state. To understand the effect of boron (~ 25 pp m) on microstructural evolution and change in continuous cooling transformat ion (CCT) diagram , a systematic study has been carried out using Gleeble thermo-mechanical simulator in unalloyed (C: 0.05 wt%; Mn : 0.2 wt%) and low alloyed (C: 0.2 wt%; Mn : 1.2 wt%: Cr: 0.15 wt%) steels. CCT diagrams, plotted for the onset and end of pearlit ic, bainitic and martensitic reactions, consisted essentially of two C-curves and a remarkable d ifference was observed on comparing the results for both steels. It is interesting to note that bainite and martensite are co mpletely absent even at higher cooling rate o f 70°C/sec in the unalloyed steel with boron addition. In contrast, the addition of boron was observed to promote significant bainite format ion even at a slower cooling rate of only 20°C/sec in the low alloyed steel. These contradicting effects on hardenability can be explained by the effect of boron in shifting only the upper C curve to the right for reconstructive transformation.
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.
Evaluation of Boride Layers on C70W2 Steel Using a New Approach to Characterization of Boride Layers
Materials
In this study, boride layers on C70W2 steel, obtained by boronizing at temperatures ranging from 870 to 970 °C and durations from 4 to 8 h, were investigated. The characterization of the layers was carried out using a new approach based on the change in the volume fraction of the boride phase. Analysis of the change in volume fraction showed that an increase in temperature and duration resulted in thicker layers, with temperature having a greater influence. Based on the volume fraction of the boride phase, the layer is divided into compact and toothed parts. With increasing temperature, the thicknesses of both parts of the layer increased. The thickness of the toothed part was the highest after 6 h of boronizing and further prolongation of boronizing led to a decrease in the thickness. Regression equations were estimated for the prediction of the volume fraction of the boride phase, the thickness of the compact part, and that of the toothed part of the boride layer as a function of ...
A mechanical aspect of borides formed on the AISI 440C stainless-steel
Vacuum, 2004
In the present study, some properties of borides formed on AISI 440C stainless-steel have been investigated. Boronizing was carried out in a solid medium consisting of EKabors powder at a temperature of 950 C for 2-8 h. The presence of borides e.g. FeB, Fe 2 B, CrB, Cr 2 B, Mn 2 B and MnB were revealed by means of X-ray diffractometry, scanning electron microscopy, and optical microscopy. The hardness of borides which was over 1500 VHN and boride layer thickness were measured and it was observed that, the thicknesses of the boride layers were strongly dependent on the process time, and chemical composition of the substrate materials. It was also found that the longer boronizing time results in an increase in thickness layer; the thickness of boride layers ranged from 10 to 50 mm. Optical microscopy examinations of the borides formed on the surface of AISI 440C stainless-steel substrate revealed a smooth and compact morphology. To determine distribution of alloying elements from surface to the interior energy dispersive Xray spectroscopy was used.
Journal of Material Science & Engineering, 2019
The new thermal treatment of subcritical annealing and water quenching, applied to boron steels (30MnB5), which we propose in our research, achieve excellent variability in mechanical properties, as a result of obtaining a very versatile dual structure. In addition, there is a significant reduction in energy consumption and process time, which results in the Life Cycle Analysis (LCA) and process costs. The presence of boron favours the success of the thermal treatment. The explanation of the process has been investigated by means of a metallographic study, mechanical characterization and in this work the results obtained by means of the study of the treated and untreated samples by means of X-Ray diffraction are presented. The presence of very small FeB crystals in the structure are the cause of the dual structure and its good characteristics. They have only been detected by X-Ray Diffraction, although we have also tried Transmission Electron Microscopy with unclear results.