Ugur Sen

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 .

The fracture toughness of borides formed on boronized cold work tool steels

Abstract In this study, the fracture toughness of boride layers of two borided cold work tool steels have been investigated. Boriding was carried out in a salt bath consisting of borax, boric acid, ferro-silicon and aluminum. Boriding was performed at 850 and 950 °C for 2 to 7 h. The presence of boride phases were determined by X-ray diffraction (XRD) analysis. Hardness and fracture toughness of borides were measured via Vickers indenter. Increasing of boriding time and temperature leads to reduction of fracture toughness of borides. Metallographic examination showed that boride layer formed on cold work tool steels was compact and smooth.

Structural characterization of boride layer on boronized ductile irons

Abstract In this work, some surface properties of ductile irons were improved by a thermo-chemical boronizing process. Boronizing was performed in a slurry salt bath consisting of borax, boric acid and ferro-silicon at 850 and 950 °C for 2–8 h. Three different ductile irons namely GGG 50, GGG 60 and GGG 80 were used to investigate the surface properties and performance. Structural characterization of boride layer formed on the surface of ductile irons was carried out by using optical microscopy, scanning electron microscopy back scattered electron image, electron microprobe and X-ray diffraction (XRD) analysis. The hardness measurements of boride layers were conducted under 100 g loads by using Vickers microhardness indenter. Structural analysis studies showed that carbon and silicon were concentrated between boride layers and substrate. When copper concentration of ductile irons increases, the carbon and silicon enriched region between boride layer and substrate decreases. XRD analysis showed that borided GGG 50 and GGG 60 ductile irons have FeB and Fe2B phases. However, borided GGG 80 ductile iron at 850 °C has only Fe2B phase at the experimented range of time. Therefore, the hardness of boride layer formed on the surface of GGG 80 ductile iron is lower than that of GGG 50 and GGG 60 ductile irons.

The effect of boronizing and boro‐chromizing on tribological performance of AISI 52100 bearing steels

Purpose – The purpose of this paper is to study the tribological behavior of hardened, boronized and boro‐chromized AISI 52100 steel balls against boro‐chromized AISI 1040 steel disk under 2, 5 and 10 N loads at 0.1 and 0.3 m/s sliding speeds.Design/methodology/approach – Boronizing treatment was realized at 1,000°C for 2 h in a slurry salt bath consisting of borax, boric acid and ferro‐silicon. Some of the boronized steels were chromized at 1,000°C for 2 h by pack method in the powder mixture consisting of ferro‐chromium, ammonium chloride and alumina. Similarly, AISI 1040 steel disk was boronized at 900°C for 4 h in the same bath and then chromized by pack method. Friction and wear tests were carried out using a ball‐on‐disk machine.Findings – The results showed that the specific wear rate of hardened and boronized AISI 52100 steel balls decreased with increasing load and decreasing sliding speed. Untreated AISI 52100 steel balls showed much greater specific wear rate than the boronized and boro‐chromiz...

Thermo-Reactive Diffusion Vanadium Nitride Coatings on AISI 1020 Steel

Thermo-reactive diffusion (N and V) on AISI 1020 steel has been obtained by an initial gas nitriding followed by vanadizing. Vanadizing was performed by pack method in the powder mixture consisting of ferro-vanadium, ammonium chloride and alumina at the temperatures of 800, 900 and 1000 o C for 1-4 hours. The properties of the diffusion layers, namely microstructure and phase composition, have been studied. The influence of temperature and treatment time on thickness of vanadized layer and its phase composition has been determined. By increasing the temperature and treatment time with V on the steel substrate, the depth of vanadium nitride formed on steel samples changed between 5.16 μm to 16.77 μm. The micro-hardness value of vanadium nitride layers is 1855.8±74.24 HV0.025. X-ray diffraction analysis showed that the presence phases formed in the vanadium nitride layers on the steel samples are VN and V2N. Introduction Metal nitrides possess very high thermal, mechanical, and chemical stability. Several nitrides, characterized by low densities, are therefore of great technological interest for light weight applications [1]. The use of transition metal nitride coatings has been successfully explored in the last few decades, due to properties such as high hardness, biocompatibility, wear and corrosion resistance, and thermal stability [2-6]. However, there are a few studies on V-N system. The vanadium-nitrogen phase diagram shows that two stable phases exist: the hexagonal β-V2N and the cubic δ-VN phase [6,7]. Titanium nitride is certainly the most thoroughly studied among the transition metal nitrides. However, zirconium, niobium and vanadium nitrides also exhibit similar protection properties [2]. Because of their outstanding mechanical, optical, electrical and magnetic properties, thin films of nitrides have been widely utilized in many industrial applications. Protective coatings of nitrides enhance corrosion and wear resistance, optical and electrical properties and serve as diffusion barrier. Deposition techniques of thin films of nitrides comprise mainly chemical vapor deposition (CVD) [8,9], plasma assisted deposition [8], and sputter processes [10]. Pack or slurry vanadizing method of steel samples has become a key technology in industrial applications, due to attractive features of nitro-vanadizing such as cheap equipment, not needing atmospheric control, compatibility with nitriding and vanadizing. In this paper, we report on the formation of vanadium nitride (VN and V2N) by vanadization of nitrided steel in nitro-vanadizing process. The film was characterized by X-ray diffraction (XRD) analysis, optical microscopy with optical micrometer and Vickers microhardness tester. Experimental Details The chemical composition of the as-received AISI 1020 plain carbon steel (as in normalized condition) used in this study was Fe-0.198%C-0.579%Mn-0.326%Si-0.017%P-0.048%S, as analyzed using a Labtest Trabel spectroscopy. We used cylindrical samples of 5 mm in length and 10 mm in diameter. Samples polished progressively by hand finishing with 1200 grid emery paper to obtain the same surface conditions. Nitriding was performed in ammonia atmosphere at 575°C Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 577-580 doi:10.4028/www.scientific.net/KEM.264-268.577

Effect of process time on the tribological properties of boronized GGG‐80 ductile cast iron

Purpose – Wear behavior of boronized GGG‐80 ductile cast iron were studied against WC‐Co ball for determining the effect of boronizing time and temperature.Design/methodology/approach – Ball on disk arrangement was used for determination of tribological properties of boronized ductile cast iron depending on process time and temperature. Boronizing treatment was performed on GGG‐80 ductile cast iron using salt bath immersion boronizing technique at 850 and 950°C for 2‐8 h. Friction and wear tests were carried out at dry test conditions under 2, 5 and 10 N loads with 2.5 m/min sliding speed.Findings – The result showed that the friction coefficient values ranged from 0.12 to 0.2 depending on the process parameters. The higher the treatment temperature and the longer the treatment time, the thicker the boride layer, the more the FeB phase and the higher the specific wear rate became. The specific wear rate of boronized ductile cast irons depending on process time, temperature and applied load against WC‐Co b...

Oxidation Kinetics of Chromium Carbide Coating Produced on AISI 1040 Steel by Thermo-Reactive Deposition Method during High Temperature in Air

Oxidation of chromium carbide coating formed on AISI 1040 steel deposited by thermo-reactive deposition method (TRD) has been realized by two stepped reactions. In the initial part of the reactions in the oxidation process, carbon atoms combined with chromium on the outer part of the coating layer react with the oxygen in air, effectively up to 120 min. After that, the chromium atoms react with oxygen in the air and produce Cr2O3 phase on the coating layer. The higher the temperature and the longer the treatment time, the more the Cr2O3 phases became. The kinetic study was realized for the reactions of carbon and chromium with oxygen, individually. The kinetic study of oxidation was calculated by weight changing of the coated samples at the temperatures of 973 K, 1073 K and 1273 K up to 720 min. We established that the chromium carbide coated steel are characterized by an insignificant increase in the mass in the oxidation period up to 3.5 h, after which the degree of oxidation increases somewhat. The nature of oxidation kinetics for chromium carbide coated steel varies from some mass degrease in the initial period ( 2 h) in connection with the formation of CO and CO2 to later mass increase with in connection with the formation of Cr2O3 layer. The oxidation resistance of chromium carbide coated steel decrease with an increase in oxidation temperature. The growth rate constant of oxidation of chromium carbide coated steel ranged from 5.13x10-13 to-9.617x10-11 g4.cm-2s-1 in the initial period of oxidation (up to 120 min), while it ranged from 3,163x10-13 to 2.188 x10-10 g4.cm-2s-1 in the second period of oxidation test (over 120 min). The activation energies of oxidation of the chromium carbide coated steel are 185 kJ/mol for the initial period and 215 kJ/mol for the second period.

Improving the Surface Properties of Ductile Irons by Boronizing

In this work, some surface properties of ductile cast irons were improved by boronizing thermo-chemical process. Boronizing was performed in a slurry salt bath consisting of borax, boric acid and ferro-silicon at 850°C and 950°C for 2-8 hours. Three different ductile cast irons were performed to investigate the surface properties and performance of GGG 50, GGG 60 and GGG 80 ductile irons. Structural characterization of boride layer formed on the surface of ductile cast irons were carried out by using optical microscope, SEM-BEI, electron microprobe analysis and XRD analysis. The higher the boronizing temperature, the longer the treatment time and the lower the copper concentration of ductile cast irons, the higher the hardness and the lower the fracture toughness of boride layer became.

Characterization of Niobium Carbonitride Coating on AISI D2 Steel

Thermo-diffusion coatings containing Nitrogen, Carbon and Niobium (N+C+Nb) on AISI D2 steel have been carried out by an initial tufftriding process followed by saturation with Niobium. The properties of the diffusion layer, namely microstructure, phase composition and micro-hardness of the Niobium carbonitride layer, have been studied. The influence of treatment time of Niobizing on the thickness of the metallized layer and its phase composition has been studied. Nitriding treatment was performed at 575°C for 2 h. Then, the Niobizing treatment was performed by pack method in the powder mixture consisting of ferro-Niobium, ammonium chloride and alumina at 1000°C for 1–4 h. The phases formed on the Niobium carbonitride coated steel were NbN and NbC, confirmed by X-ray diffraction (XRD) analysis. The longer the treatment times, the thicker the Niobium carbonitride layer became. The thickness of Niobium carbonitride layer was changing between 6.53 3m and 17.45 3m, depending on treatment time and temperature. The microhardness of Niobium carbonitride layer formed on the AISI D2 steel was changing between 2132±203 and 2814±245 HV0.01 from surface to interior.

Microstructural Examinations of Fe-W-B Base Hard-Faced Steel

It is now well established that considerable improvement in the mechanical/chemical properties of near surface regions of materials can be achieved by the process of surface alloying. In the present study, surface alloying treatment with Tungsten and Boron on the surface of AISI 1020 steel was realized by the technique of TIG welding. Ferrous boron alloy and ferrous-tungsten were used for surface alloying treatment. Before the treatment, ferrous alloy was ground and sieved to be smaller than 45 \(\upmu \)m. The powders were mixed to be composed of Fe\(_{5}\)WB\(_{4}\). Prepared powder was pressed on the steel substrate and melted by TIG welding for surface alloying. Coated layers formed on the steel substrate were investigated using by optical and scanning electron microscopy, X-ray diffraction analysis and Vickers micro-hardness tester. It was shown that surface alloyed layer has composite structure including eutectic matrix and blocky boride phase which is white color and well distributed. Borides formed in the coated layers have a sharp corner structure and distributed in the matrix. X-ray diffraction analyses showed that coated layers include Fe\(_{2}\)B, FeB and FeW\(_{2}\)B\(_{2}\) phases. The hardness of blocky boride phases is 2095 HV\(_{0.01}\).