Iman El-Mahallawi

Influence of heat input and post-weld heat treatment on boiler steel P91 (9Cr–1Mo–V–Nb) weld joints Part 2 – Mechanical properties

AbstractThree thick pipes of modified 9Cr–1Mo steel were welded using three different levels of heat inputs: low heat input 1·1 kJ mm−1, medium heat input 2·3 kJ mm−1 and high heat input 3·16 kJ mm−1. Two types of heat treatments were employed, namely subcritical post-weld heat treatment and normalising/tempering treatment. The influence of heat input and post-weld heat treatment on the microstructure of boiler steel P91weld joints has been investigated in the previous paper. In the present work hardness, tensile, impact toughness and stress rupture properties were evaluated. Our results show a great influence of heat input and heat treatment on mechanical properties. The best combination of properties was obtained in low to medium range of heat input, between 1 and 2·8 kJ mm−1 for both treatments and a 90% increase in time to rupture was observed for normalising/tempering treatment compared to subcritical post-weld treatment.

Influence of heat input and post-weld heat treatment on boiler steel P91 (9Cr–1Mo–V–Nb) weld joints Part 1 – Microstructure

AbstractSteel P91 is known for its excellent high temperature properties. The achievement of optimum weld metal properties for steel P91 within the course of its extensive applications in power plants has however often caused concern. In the present work, three thick pipes of P91 steel were welded using three different levels of heat inputs within the range of 1·15–3·5 kJ mm−1. A circumferentially multipass butt welded P91 steel pipe, typically used for high temperature applications in power plants was selected for this investigation. The achievements of optimum weld metal properties, which are closely linked to microstructure, are known to cause concern in such weldments. Two types of heat treatments were employed, subcritical post-weld heat treatment and normalising/tempering treatment. The microstructure was evaluated by optical, scanning electron microscope, X-ray diffraction and magnetic permeability. The results have shown a great influence of heat input and heat treatment on the microstructure. Mar...

The Effect of Process Parameters on the Mechanical Properties of A356 Al-Alloy/ZrO2 Nanocomposite

In this study the effect of zirconia (ZrO2) nanoparticles (40 nm) in reinforcing A356 aluminum alloys as a base metal matrix were investigated. Zirconia nanopowders were stirred in the A356 matrix with different fraction ratios ranging from (0, 1, 2, 3, 5%) by weight at variable stirring speeds ranging from (270, 800, 1500, 2150 r.p.m) at a mushy zone (600°C) and liquid state (700°C) using a constant stirring time for one minute. The microstructure revealed the change of grains from dendritic to spherical shape with increasing stirring speed. The Scanning Electron Microscopy of the fractured surface revealed the presence of nanoparticles at the interdendritic spacing of the fracture surface and was confirmed with EDX analysis of these particles.The results of the study showed that the mechanical properties (strength, elongation and hardness) using ZrO2 as reinforcements were increased at the following parameters: 1500 r.p.m stirring speed in semi-solid state (600oC) and adding 3 wt.% of ZrO2.

Effect Of Pouring Temperature And Water Cooling On The Thixotropic Semi-Solid Microstructure Of A319 Aluminium Cast Alloy

The cooling slope (CS) casting is the simplest and cheapest technique for producing feedstock materials with non-dendritic microstructure. Such materials are required for semi-solid metal (SSM) processing methods such as thixoforming. In the present investigation, the effect of the pouring temperature and the water cooling on the thixotropic microstructure of commercial A319 Al-Si cast alloy was studied. The results showed that increasing the pouring temperature slightly reduces the bulk porosity of the CS ingots. The ingots poured with water-cooling exhibited slightly lower porosity content than those poured with without water-cooling. Generally, the primary α-Al grains exhibited higher shape factor near the edge of ingot than the middle and center. Ingots poured with water-cooling exhibited lower grain size and shape factor than those poured without water-cooling. Increasing the pouring temperature increases the size α-Al grains.

Morphology and identification of carbides in aged W-alloyed austenitic stainless steel

Alloy X12CrNiWTi1613 is an alloy developed specifically for high temperature applications. The alloy is of an austenitic stainless steel type, containing the carbide formers, W, Ti and Mo, ordered according to their weight percent. However, the literature does not include much data regarding carbide morphology and identification for this type of steel. The aim of this work is to identify the type and morphology of the carbides that form in this alloy after aging heat-treatment. Three shapes of carbides; globular, rod-like, and small round, were found to be present of the types (TiWMo)C, Ti(C,N), and TiC or TiWC.

Options for Nanoreinforced Cast Al–Si Alloys with TiO 2 Nanoparticles

This study presents a new concept of refining and enhancing the properties of cast aluminium alloys by adding nanoparticles. In this work the effect of adding titanium dioxide (TiO2) nano-particles (40 nm) to the aluminum cast alloy A356 as a base metal matrix was investigated. Titanium dioxide nano-powders were stirred into the A356 matrix with different fraction ratios ranging from (0, 1, 2, 3, 4, 5 %) by weight at variable stirring speeds ranging from (270, 800, 1500, 2150 rpm) in both the semisolid (600 °C) and liquid state (700 °C) using a constant stirring time of one minute. The cast microstructure exhibited change of grains from dendritic to spherical shape when increasing stirring speed. The fracture surface showed the presence of nanoparticles at the interdendritic spacing of the fracture surface and was confirmed with EDXS analysis of these particles. The results of the study showed that the mechanical properties (strength, elongation and hardness) for the nanoreinforced castings using TiO2 were enhanced for the castings made in the semi-solid state (600 °C) with 3 % weight% of TiO2 at 1500 rpm stirring speed.

Effect of Tempcore Processing on Mitigating Problems of Tramp Elements in Low C Steel Produced from Recycled Material

The effect of tramp elements in the steel was intensively studied. It was found that the solubility of tramp elements decreased as the temperature decreased under normal cooling conditions. The tramp elements (Cu, Pb, and Sn) diffused toward the grain boundaries, and intermetallic compounds or rich phases which have low melting points were formed, causing reduction in ductility and failure during the bending test. Rebars with Cu content which were left to air cooling after the last step showed drop in elongation, up to 32%. On contrast, the samples with high percentage of tramp elements (Cu, Pb, and Sn) in the billet, which were rolled and subjected to Tempcore process, did not show drop in elongation or failure in bending test (especially for rebar with diameter less than 32 mm) ; however, copper must be less than 0.35 mass% to prevent the precipitation of Cu-rich zones of critical size in 32 mm. When quenching was applied, the tramp elements remained in the interstitial supersaturated solid solution positions inside the grains and would not have the chance to diffuse and form precipitates, hindering the copper precipitates from reaching the critical size necessary for impairing the properties. This would hinder the occurrence of the harmful effect of the tramp elements on the elongation or the hot shortness after rolling.

Improvement of Mechanical Properties and Structure Modifications of Low Carbon Steel by Inoculations with Nano-Size Silicon Nitride

AISI 1020 steel is considered to be one of the most applicable structural steels, in particular in the cold drawn form. Heating of this grade of steel prior to AC1 must have been applied to spheroidize the lamellar cementite, and consequently enhances the cold formability character of the steel. Si3N4 nanoinoculation of this grade of steel has been used in this study, where it is added to the molten steel, in order to avoid the high cost long term heat treatment process prior to cold deformation process. Optical microscopy and SEM have been used to evaluate the morphology of cementite after nanoinoculation process with Si3N4. Tensile properties of nanoinoculated steels have been investigated. Finally, wear adhesive resistance of investigated samples has been evaluated. The obtained results showed a great enhancement in the mechanical properties, strength, ductility and adhesive wear resistance, as a result of the nucleation of cementite into a new spheroidal phase and grain refinement by Si3N4 inoculation and allow usage of AISI 1020 steels inoculated by nanoinoculant Si3N4 in further technological applications.

Effect of Nano‐Reinforcement on Properties of Cast Mg‐Al Alloy AZ91

In this study, nanocomposites based on magnesium alloy system AZ91 were fabricated by Semi-Solid Rheocasting (SSR) technique. Al2O3 (alpha) nanoparticles were added to the AZ91 alloy with different weight fractions. The results showed that Al2O3 nanoparticles could be mixed with AZ91 semi-solid slurry using mechanical stirrer technique. However, large clusters of nanoparticles were observed. SEM images also detected significant refinement the microstructural features due to the Al2O3 additives. Hardness tests showed that an addition of 2 wt. % Al2O3 nanoparticles resulted in 17% increase in the hardness. Corrosion tests indicated an improvement of 50% in corrosion resistance due to the addition of 2wt. % Al2O3 nanoparticles. Finally, mechanical dry wear tests revealed a 5% improvement in wear resistance for 2wt. % Al2O3 nanoparticles.

Studying The effect Of Nano-dispersions (Al2O3) On The Properties Of A356 Hypo-eutectic Al-Si Cast Alloy

Improving the strength to weight ratio is a target aimed by many researchers. Metal Matrix Nano Composites (MMNC) have recently emerged as a new generation of composites, where the addition of nano-sized particles leads to an increase in the strength not according to conventional Metal Matrix Composites rules. Aluminium matrix composites reinforced with nano-sized Al2O3 particles are widely used for high performance applications such as automotive, aerospace and electricity industries. In this work a number of cast specimens made from hypoeutectic aluminium silicon alloy (A356) were cast with and without alumina (Al2O3) nanoparticles at different pouring temperatures with stirring during the addition of nano-reinforcement. The microstructure of the new castings was studied using optical microscopy and scanning electron microscopic techniques. Also, the tensile strength, hardness and ductility were evaluated. The significant factors for the tensile strength were analysed using L4 orthogonal array and Analysis of Variance (ANOVA) techniques then building a model by Response Surface Methodology (RSM). The results obtained in this work show that adding alumina nanoparticles and pouring at different temperatures lead to an increase in the tensile strength and the hardness with less change in ductility.