Showing 15 results for Hardness
Y. Najafi , F. Malekghaini, Y. Palizdar, S. Gholami,
Volume 2, Issue 1 (8-2016)
Abstract
Recent research suggests that extraordinary combinations of strength and ductility can be achieved in the so-called TRIP steels. With the development of these steels, welding with small weld nugget size and acceptable strength are needed. For these reasons present study was carried out to investigate the effect of heat input onweld size, microstructure and the hardness of the welded metal of 0.4%C- 4%Al δ-TRIP steel after continues fiber-laser welding process. To achieve this goal a bead on plate welding with three different values of heat input 28, 60 and 80 J/mm were used.The results of welding process revealed that by increasing the heat input, cooling rate decreased and the volume percent of the δ-ferrite in weld metal increased due to the availability of sufficient time for partitioning of Al in high heat input which leads to the stable δ-ferrite and as a result the difference between the hardness of the weld metal in comparison to the base metal decreased.
M. Vanaee, M. Ardestani, A. Abbasi,
Volume 4, Issue 2 (1-2019)
Abstract
In this research, the dissimilar welding of St52 plain carbon steel to W400 wear resistant steel and its effect on the microstructure and wear properties of the wear resistant steel was investigated. The wear resistant steel was produced via direct quenching with nominal hardness of 400 HB. Gas tungsten arc welding was used for joining process. The results showed that welding led to hardness reduction, wear rate increase and also significant changes in microstructure of the heat affected zone of the wear resistant steel. According to the results, by increasing the heat input for about 9%, the hardness and wear rate of the heat affected zone was decreased 8% and increased 250%, respectively. According to the scanning electron microscopy observations the main wear mechanisms of the base metal were adhesion and abrasion. However, the wear mechanisms of the heat affected zone were mainly adhesion and delamination. By increasing the heat input, the delamination was increased significantly.
R. Tamasgavabari, A. Ebrahimi, S. M. Abbasi, A. Yazdipour ,
Volume 5, Issue 1 (9-2019)
Abstract
In this research, the effect of vibration at the resonant range (75 Hz) on the hardness and tensile strength of AA-5083-H321 aluminum alloy, were welded by gas metal arc welding (GMAW) investigated. Vibration forces were ranged from 850 N to 2200 N, under identical welding parameters. Tensile strength and hardness testing of welded samples were performed. After mechanical tests, the fracture surfaces of welds were examined using scanning electron microscope (SEM) and discussed. The results showed that with increasing vibration force, the tensile strength and fracture strength of the specimens were welded during vibration, were increased by about 3 and 9 percent, respectively, compared to the non-vibrated weld sample. However, no significant change was observed in the hardness of the welded specimens. Mean grains size and heat affected zone of the sample was welded was welded with conventional GMAW, were about 200 μm and 1800 μm, but due to inducing vibration, as vibration force increased from 850 N to N 2200 N, Mean grains size was reduced to about 75 μm and HAZ was reduced from about 1000 μm to 700 μm, that is, about 44 to 61%.
N. Rahimi, T. Saed,
Volume 5, Issue 2 (1-2020)
Abstract
In this study the effect of activating fluxes on the penetration depth, microstructure and microhardness of AISI316L austenitic stainless steel were evaluated by three TIG process variations (TIG, A-TIG and FB-TIG) and the results were compared together.. After selecting the optimal flux in the second stage, the effect of that on the penetration depth, microstructure and weld microhardness of welded 316L austenitic stainless steel by A–TIG and FB-TIG methods, were evaluated and the results were compared by the sample which was welded by TIG process. At this stage, it was found that the depth and width to depth ratio in FB-TIG method is slightly greater than the other two methods. Also in FB-TIG method, eqiaxed dendritic zone in the center line of weld is slightly greater than in A-TIG method. Study of microhardness of weld in three methods shows that in A-TIG and FB-TIG methods hardness of center line is more than TIG method.
F. Pahnaneh , M. Aghakhani *, R. Eslami Farsani, M. Karamipour1,
Volume 6, Issue 1 (8-2020)
Abstract
This paper reports the applicability of fuzzy logig (FL) to predict the hardness of melt zone (HMZ) during the gas metal arc welding (GMAW) process, which is affected by the combined effect of ZrO2 nano-particles and welding input parameters. The arc voltage, welding current, welding speed, stick-out, and ZrO2 nano-particles were used as the input parameters and HMZ as the response to develop FL model. The predicted results from FL were compared with the experimental data. The most important input parameter affecting the HMZs was the addition of ZrO2 nanoparticle coatings with a thickness of 1 mm, which increased the hardness from 78 to 84 HRB. The correlation factor value obtained was 99.98% between the measured and predicted values of HMZ. The results showed that FL is an accurate and reliable technique for predicting HMZ because of its low error rate. Also, the presence of ZrO2 nano-particles in the weld pool has increased the penetration up to 2 times.
A. Ghandi, M. Shamanian, M. R. Salmani3,
Volume 6, Issue 1 (8-2020)
Abstract
The structural and hardness developed in advanced high-strength steel DP590 have been investigated with the help of optical microscopy and scanning electron microscopy on resistance spot welded specimens. The hardness diagram of the weld sections was prepared by microhardness test and the temperature peak and heat distribution were simulated by menas of the Abaqus software. The results show that according to the temperature generated in each region of the weld nugget, the HAZ and base metals have different microstructures, and these difference affects the hardness of the regions. The presence of tempered martensite islands with a fraction of 44% in ferrite matrix in base metal, mainly martensitic structure in the nugget, and martensitic structure along with scattered areas of ferrite in the HAZ was observed. The results of the microhardness tests showed difference in hardness values of the regions, and also it was observed that the hardness values increased in the HAZ and weld zone. The hardness values measured in the nugget, base metal, and HAZ were around 400, 200, and 450 HV which were in accordance with the observed structures
H. R. Alinaghian, S. A. Sadough Vanini, S. M. Monir Vaghefi,
Volume 6, Issue 1 (8-2020)
Abstract
The surface of continuous casting moulds with high number of castings may be worn or destructed. As result, an approach for increasing these moulds life is necessary. In this project, the goal is the restoration of the DHP copper sample. In this project, the destruction of the copper sample is done by creation of groove using a CNC machine. The restoration of the sample is done using OAW and filler to fill groove area. In this project, the effect of preheating temperature, filler type and heat treatment of welding area on hardness, microstructure, chemical analyses of welding area and thermal conductivity of the weld are investigated. The preheating temperature range of 300 to 450oC was selected. The Cu-P and Cu-Ag-P fillers were chosen to fill the groove of the weld area. The scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), micro hardness tester, optical microscope and thermal conductivity meter were employed for evaluation of the results in this project. The results showed that the increase of preheating temperature creates oxide layers and the decrease of preheating temperature causes the incomplete filling of the welding area. Finally, the preheating temperature of 400 oC was a proper choice considering the above mentioned factors. The stress relieving operation to decrease stress and preserve the mechanical properties in the temperature of 250 to 400 oC and duration two hours was carried out. The result demonstrated that the selected temperature causes no unwanted decrease on the hardness. It was also found that increasing the annealing duration, decreases the hardness of weld for Cu-P filler for Cu-Ag-P filler increasing the annealing duration, first decreases the weld hardness and then increases the weld hardness. The Cu-P filler was compared with Cu-Ag-P filler. The results showed that the Cu-Ag-P filler has less hardness (around 10 percent) than the filler without silver. On the other hand, the thermal conductivity of the Cu-Ag-P filler was around 10 percent more than the thermal conductivity of the Cu-P. It is obvious that the selection of the filler type depends on the type of base metal and its geometry. The results showed that the segregation in the Cu-P filler with 7.2 percent phosphorous, because of the proximity of the weld structure to the eutectic point, has slightly happened; while, the selection of the Cu-Ag-P filler with 6 percent silver caused severe segregation of silver to 90 percent silver at the center of weld at the non-dendrite area
Mojtaba Vakili-Azghandi, Ali Shirazi,
Volume 7, Issue 1 (8-2021)
Abstract
The results showed that the microhardness and tensile strength of the heat-affected zone as the weakest welding zone in some samples reduced up to 30% compared to the base metal. On the other hand, a decrease in rotational speed, an increase in tool movement speed, and the number of welding passes cause grain refinement and improve mechanical properties. However, the effect of decreasing the rotation speed and increasing the tool movement speed were shown to be more favorable due to less heat production. Accordingly, the hardness in the welded zone with a rotational speed of 600 rpm and a movement of 80 mm/min increased from 90 to 125 HV compared to the base metal, and the hardness reduction in the zones around the welded zone was only 5 Vickers. It was also found that reducing the grain size of the stir zone, while improving the mechanical properties leads to increasing the density of the surface pasive layer, preventing the attack of aggressive chlorine ions and thus reducing the corrosion intensity by 50 times in saline seawater.
H. Tazikeh, S. E. Mirsalehi, A. Shamsipoor,
Volume 7, Issue 1 (8-2021)
Abstract
In this research, the effect of bonding temperature on the microstructure and mechanical properties of Inconel 939 super alloy by transient liquid phase bonding method. For this purpose, the middle layer of MBF20 with a thickness of 50 microns and three temperatures of 1060 °C, 1120 °C, 1180 °C and a time of 45 minutes have been used. In order to evaluate the microstructure, a scanning electron microscope equipped with an elemental analysis system has been used. Vickers hardness test and shear strength test have been used to evaluate the mechanical properties. The research findings showed that with increasing temperature from 1060 °C to 1120 °C, the width of the athermal solidification zonedecreased from 38µm to 35µm and with increasing temperature at 1180 °C, the athermal solidification zone was completely removed and isothermal solidification zone was replaced. In addition, with increasing temperature, the hardness in the joint center decreases and the shear strength increases.
Hossein Tahmasebi Manesh, Alireza Nasresfahani, Alireza Nasresfahani,
Volume 7, Issue 1 (8-2021)
Abstract
One of the applications of P460NH micro-alloy steel is its use in pressure vessel tanks. Electrode E8018-G can be used for welding this steel. In this study, to obtain the optimal welding parameters, the arc process based on ASME IX standard was used. Then, by sampling from the weld section, Vickers hardness test was performed and hardness profiles were drawn in different areas. Then the microstructure of each area was examined and compared with the hardness test results. The corrosion behavior of the heat affected zone, weld zone and base metal was investigated separately using the TOEFL polarization test in a 3.5% solution of NaCl. The results showed that the weld zone had the highest percentage of perlite (62%) and the base metal had the highest percentage of ferrite (73%). Also, the heat affected zone has the highest hardness number (298) and the base metal has the lowest value (210) in the Vickers scale. Evaluation of corrosion behavior of different areas also showed that the heat affected zone has the highest corrosion potential (-.651v) and the lowest corrosion current density (1.75×10-5 A/cm2). This is while the base metal has the lowest corrosion potential (-.691v) and the highest corrosion current density (1.2×10-6 A/cm2) compared to the weld metal and the heat affected zone.
M.h. Zakeri, A.r. Nasresfahani, S.m. Barekat,
Volume 7, Issue 2 (1-2022)
Abstract
In this research, the microstructure of Inconel 625 cladded layer on ASTM A575 steel has been investigated. By examining different parameters, the optimal single-pass sample with the least amount of dilution, porosity and fusion and suitable wetting angle was determined. Then cladding process with the optimal parameter was performed. The microstructure of the cladding layer was evaluated from the base metal to the top. Due to different cooling rates, dendritic morphologies were observed at different distances. Also, the cladding layer was free of any cavities, porosity and cracks and its thickness was 0.9 mm (900 micrometers). The results of (XRD) and (EDS) analyzes indicate thatthe γphase is formed and there is a relatively uniform distribution of elements in the cladding layer. These results also indicate that no change in the chemical composition of the substrate surface was achieved near the interface.The hardness test results also show that the hardness starts from 450 VHN at the top surface and reaches to 135 VHN in the base metal with a gentle slope. This slope of hardness can be attributed to the cooling or heating rates of the substrate.
H. Gorji, Dr. S. M. Barakat, S. R. Shoja Razavi, S. S. Babaie Sangetabi, M. Erfanmanesh,
Volume 8, Issue 1 (8-2022)
Abstract
The aim of the present study is to investigate the mechanical and microstructural properties of 1.7225 steel in laser welding process using Nd:YAG pulsed laser device and then to determine the optimal focal length relative to the part in the welding area. After welding, microstructural characterization, microhardness and tensile tests were performed. Evaluations showed that the optimal focal length for welding of steel sheet 1.7225 with a thickness of 1 mm, it was about 9 mm and the focus was 1 mm below the surface of the part. Due to the high thermal concentration and cooling rate in laser welding, a completely martensitic microstructure has been observed in the molten and heat-affected regions of all specimens. In this alloy, the hardness of the base metal is 310±10 HV. After welding, the hardness of the sample with the optimal focal length has reached 625±10 HV in the heat affected zone and 730±10 HV in the melting zone. Also, the results of tensile test showed that the tensile properties of the sample with the optimal focal length were almost similar to the base steel and fracture was observed in the base steel region.
M. J. Bagban, M. Mosallaee Pour, H. Hajisafari, A. Babnejad, A. Saboori,
Volume 8, Issue 1 (8-2022)
Abstract
In the present study, the microstructure and mechanical properties of the dissimilar joint of Inconel 625 (IN-625) superalloy to austenitic stainless steel AISI316L (SS-316L) via AWS-BNi3 interface layer and transient liquid phase (TLP) bonding process were evaluated and necessary conditions for creating an efficient joint were determined. TLP bonding was performed in temperature and time range of 1050-1150ºC and 5-20min, respectively, under the protection of argon shielding gas with a purity of 99.9995%. Microstructural (OM and SEM) and phase (XRD) studies revealed that bonding at 1150 ° C for 20 min results in completion of isothermal solidification and develops a uniform gamma (γ) phase at the bonding zone. Cooling the samples before completion of isothermal solidification results in the formation of chromium and molybdenum-rich eutectic compounds at the bonding centerline. The continuous morphology of the eutectic compounds caused a sharp drop in the shear strength of the specimens (~50% reduction of shear strength). The inter-diffusion of alloying elements between the bonding area and the surrounding base metal results in the formation of chromium carbide in the IN-625 and chromium- boron compounds in the SS-316L, which increased the microhardness of these areas compared to the base metals and the bonding zone.
Gh. Khalaj, E. Asadian,
Volume 8, Issue 2 (1-2023)
Abstract
In this paper, the microstructure and mechanical properties of the plain carbon steel-bronze interface of explosive welding and rolling were investigated. Explosive connection was done at two stop distances and with two different thicknesses of explosive material. Rolling of the welded composite was done at both ambient and preheated temperatures of 300 °C and with a constant thickness reduction of 33.3%. The results showed that the wave interface of the steel-bronze connection includes different parts. By rolling, the connection interface was stretched and flattened and the vortex areas were compressed together and in some cases entered the steel field. The steel particles separated from the background along the wave crest and remained as isolated islands in the bronze background. On the other hand, in the areas near the vortex, a part of the bronze flying metal was caught under the wave and was observed as islands separated from the bronze background inside the steel. Porous areas were crushed and compressed as a result of rolling. The rolling force and temperature had partially removed the diffusion barriers and a metal bond had been formed between bronze and steel. During the connection, the voids and shrinkage pores were pressed together due to rolling and the separate borders were close to each other. Explosive joining and cold rolling had increased the hardness in the interface, and hot rolling has led to a decrease in the hardness in the interface. In the hardness test, the welding samples are arranged in the order of the highest impact energy. The effects of welding parameters remain after cold and hot rolling and the hardness rating does not change.
M.r. Borhani, S.r. Shoja Razavi, F. Kermani, M. Erfan Manesh, S.m. Barekat, H. Naderi Samani, M. Shahsavari,
Volume 8, Issue 2 (1-2023)
Abstract
The purpose of this research is to laser cladding of stellite6 and stainless steel 17-4PH powders on the substrate of stainless steel 17-4PH, and investigate its solidification microstructure. The results showed that the microstructure of the stellite6 cladding has a cobalt solid solution ground phase with an FCC structure and Cr7C3 and Cr23C6 carbides. Also, the values of the primary dendrite distance and the distance of the secondary dendrite arm have decreased by moving away from the interface; The reason for this is related to the difference in the cooling rate in different parts of the coating. The microstructure of 17-4PH stainless steel coating includes martensitic, ferritic, and austenitic phases; Due to the same chemical composition of the substrate and the cladding, the weight percentage of elements such as iron, nickel, chromium, and copper did not change from the cladding to the interface. It indicates the uniformity of the chemical composition of the cladding and the substrate. The calculated microhardness for the cladding of stellite6, the substrate and the cladding of stainless steel 7-4PH is about 480, 350, and 350 respectively. The reason for the higher microhardness of the cladding is the presence of chromium carbides (Cr7C3 and Cr23C6) formed in the cobalt field and the cobalt solid solution field of the cladding.
