Showing papers on "Charpy impact test published in 2013"

Cleavage initiation in steel: Competition between large grains and large particles

Abstract: TiN particles in steel can limit austenite grain growth during reheating or welding. However, cuboidal TiN particles of large size (>1 μm) can act as cleavage fracture initiation sites and affect the low temperature toughness. Based on the assumption that the local principle stress acts uniformly everywhere within a grain, for a fixed particle size, a critical value of ferrite grain size can be obtained below which the grain boundary effectively retards the propagation of micro-cracks, which can be nucleated from TiN particles. In the present study, the relative effect of ferrite grain size and TiN particles on cleavage crack propagation has been assessed. Ti-containing high strength low alloy (HSLA) steels were processed using different thermo-mechanical schedules and their microstructures and Charpy impact properties were investigated. It has been found that in spite of the presence of large TiN particles, refinement in ‘effective ferrite grain size’ can significantly improve the impact toughness, provided the matrix strength and meso-texture (i.e. the intensity of low-angle boundaries) are restricted to low values.

Effect of reverted austenite on mechanical properties of precipitation hardenable 17-4 stainlesssteel

Abstract: Precipitation hardenable 17-4 stainless steel has been subjected to a solution annealing treatment followed by ageing treatment at 580 °C for durations upto 6 h Microstructural characterization of the solution annealed and the aged specimens has been done using optical microscopy, X-ray diffraction and electron backscattered diffraction Mechanical characterization was done using tensile testing and charpy impact toughness testing at room temperature Microstructural characterization indicated that the reverted austenite formation started in the initial stages of the ageing treatment itself and it continuously increased with duration of ageing Results of mechanical testing indicated that the austenite content did not correlate with the strength of the material therefore, nature of the copper precipitates, which form along with the reverted austenite, is the dominant factor controlling the strength and the impact properties

Influence of ferrite and pearlite content on mechanical properties of ductile cast irons

Abstract: The present work is to study the influence of ferrite and pearlite content on mechanical properties of ductile cast irons. Three casts with different microstructures were produced. The chemical composition of the casts was also considered. The pearlite content is varied from 0 to about 70 percent without using heat treatments. This paper also shows that is possible to obtain different microstructures with good mechanical properties through an adequate balance of alloying elements. The study of the tensile properties indicated that yield and tensile strengths are increased with increasing pearlite content. This analysis also shows that graphite shapes and the second phase particles found to have influence on these parameters. With this purpose an extensive study was also done on mechanical properties to achieve good results. Specimens were under different mechanical tests such as fracture toughness and tensile strength tests. The Charpy impact tests were done at different temperatures.

Application of ultrasonic methods for early detection of thermal damage in 2205 duplex stainless steel

Abstract: Early thermal damage in 2205 duplex stainless steel which is caused by the precipitation of second phases during a short term exposure to high temperature (700 °C) is investigated. Nonlinear ultrasonic measurements are performed and their results are compared with those from ultrasonic velocity and attenuation measurements. Experimental results show that the measured acoustic nonlinearity parameter is more sensitive than the ultrasonic longitudinal velocity and attenuation to the precipitation of chi and sigma phases early in the aging treatments. The results from the nonlinear ultrasonic measurements are also supported with those from the scanning electron microscopy (SEM), Rockwell C hardness and Charpy impact test. Especially notable is the close correlation between the hardness and the nonlinearity parameter. This research therefore proposes the nonlinear ultrasonic method as a nondestructive assessment means for early detection of thermal degradation of mechanical properties in 2205 duplex stainless steel.

Strengthening and Toughening of a Heavy Plate Steel for Shipbuilding with Yield Strength of Approximately 690 MPa

Abstract: HSLA-100 steel with high content of alloying elements (nominally in wt pct, 3.5 Ni, 1.6 Cu, and 0.6Mo) is now used to produce heavy plates for constructing a hull and drilling platform. We proposed here a substantially leaner steel composition (containing 1.7 Ni, 1.1 Cu, and 0.5Mo) to produce a heavy plate to 80 mm thickness with mechanical properties comparable with those of the HSLA-100 grade. A continuous cooling transformation (CCT) diagram of the steel was constructed. Key parameters of thermal treatment and revealing mechanisms of strengthening and toughening were derived based on industrial production trials. The microstructures of the 80-mm-thick plate were lath-like bainite (LB) at near surface of the quarter thickness (t/4), and granular bainite (GB)+LB at center thickness (t/2) after solutionizing and water quenching (Q). The effect of tempering (T) on the microstructures and properties of the plate was investigated. Excellent combination of room temperature strength and low-temperature Charpy V-notch (CVN) toughness approximately equivalent to that of the HSLA 100 grade (YS > 690 MPa, CVN energy >100 J even at 193 K [−80 °C]) was achieved in the plate treated by the QT process with tempering temperature of 898 K (625 °C). The combination of strength and toughness at t/4 is superior to that at t/2 of the plate under both as-quenched and QT conditions. This result is attributed to that the fraction of high-angle grain boundaries (HAGBs) at t/4 is higher than that at t/2.

Microstructures and impact toughness behavior of Al 5083 alloy processed by cryorolling and afterwards annealing

Abstract: The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from −190°C to 100°C. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample (14 μm) after annealing at 350°C for 1 h is found to be finer than that of the 30% cryorolled sample (25 μm). The scanning electron microscopy (SEM) analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.

Effect of microstructure on the impact toughness of Nb-microalloyed steel: Generalisation of existing relations from ferrite–pearlite to high strength microstructures

Abstract: The present work relies on the production of selected microstructures through the application of thermal and thermomechanical laboratory tests, followed by mechanical testing and microstructural characterisation. The relations that link the microstructure parameters and the tensile properties have already been discussed and extended from ferrite–pearlite to high strength microstructures in a previous work. Using these results as a starting point, the present work goes a step forward and develops a methodology to consistently incorporate the effect of mesotexture (EBSD) into the existing relations that link the Charpy impact toughness to the microstructure. The result is an extension of the existing equation for the FATT from ferrite–pearlite to high strength microstructures (bainite, tempered martensite). The upper shelf energy for the Nb-microalloyed steel under consideration correlates linearly with the sum of the different terms of the FATT equation (solutes, grain boundary carbides, pearlite and precipitation/dislocations strengthening) excepting the grain size.

Tensile and impact behavior of swaged tungsten heavy alloys processed by liquid phase sintering

Abstract: The microstructural influence on fracture behavior of tensile and Charpy impact toughness properties were investigated for 90W 6Ni 2Fe 2Co and 90W 6Ni 2Fe 1.5Mo 0.5Co tungsten heavy alloys, which are in use of kinetic energy penetrators. The alloys were sintered, heat treated and swaged with 40% reduction in area. Both microstructure and mechanical properties were sensitively dependent on the alloy composition. The W Ni Fe Co alloy exhibited increased tensile strength, ductility and impact toughness compared to the W Ni Mo alloy. Fractographic study revealed that the mode of tensile failure changes from flat to sheared tungsten grains for low to high strength tungsten heavy alloys, whereas the fracture behavior changes from flaws/cracks to transgranular cleavage of tungsten grains for low to high Charpy impact toughness alloys. The results indicate that a strong relationship between microstructure, fracture behavior, tensile and impact properties as a function of alloy composition.

Enhancing mechanical properties of a low-carbon microalloyed cast steel by controlled heat treatment

Abstract: In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200 °C for 2 h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100 °C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150 °C. Further growth in austenite grains at 1200 °C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100 °C for 2 h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties.

Mechanical behaviour of 6082-T6 aluminium alloy welds

Abstract: In the utilisation of aluminium alloys for structural applications, one difficulty to be overcome is the reduction of mechanical properties of welded joints as compared to the parent material, consequent upon the weaker strength of the Weld Metal (WM) and the deterioration in the Heat Affected Zone (HAZ) due to welding thermal cycles. In this paper the microstructure and mechanical characteristics of joints welded with Gas Metal Arc Welding (GMAW) procedure, made of plates of 6082-T6 alloy, are investigated. Experimental work included Vickers microhardness test, tensile test, fatigue rotating bending test, Charpy V impact test and Scanning Electron Microscopy (SEM) fractography. Diagrams of fatigue stress - cycles for parent and welded material were compared. Static tensile tests showed minimum strength in the HAZ, while fatigue strength and fracture toughness have minimum value in the WM. Fracture toughness in terms of KIC, estimated by empirical relations, showed the lowest value in the melted zone.

Effect of microstructure on mechanical properties of dual phase steels in the presence of stress concentrators

Abstract: The study investigated the effect of intercritical heat treatment on mechanical properties of three hot rolled steels with carbon contents ranging from 0.06 to 0.18 wt%. The steels were heat-treated at temperatures ranging from 740 to 820 °C, followed by water quenching (in some cases air cooling). The primary objective of this study was to investigate the relationship between microstructure and the effect of stress concentrator on deformation and fracture behavior of ferrite–martensite dual-phase (DP) steels. Besides the tensile tests with smooth specimens, notched tensile specimens with two notch geometries (flat rectangular specimens with a central hole and circumferentially notched cylindrical specimens) were used in order to modify the stress triaxiality. Moreover, Charpy impact test was carried out on sub-size specimens (10 mm×2.5 mm×55 mm) with notch root radius of 0.25 mm and on pre-cracked specimens. It was found that with increasing martensite volume fraction (MVF) the capacity of the steels to absorb energy (expressed as the product of the ultimate tensile strength and uniform elongation) remains roughly stable or decreases in case of smooth tensile specimens while it always increases in case of specimens with stress concentrator. The experimental results presented in this study clearly showed that DP steels with an excellent combination of strength and uniform or total elongation may have poor energy absorption capacity in the presence of stress concentrators.

Artificial neural networks application to predict the ultimate tensile strength of X70 pipeline steels

Abstract: The paper presents some results of the research connected with the development of new approach based on the artificial neural network (ANN) of predicting the ultimate tensile strength of the API X70 steels after thermomechanical treatment. The independent variables in the model are chemical compositions (carbon equivalent), based upon the International Institute of Welding equation (CEIIW), the carbon equivalent, based upon the chemical portion of the Ito-Bessyo carbon equivalent equation (CEPcm), the sum of the niobium, vanadium and titanium concentrations (VTiNb), the sum of the niobium and vanadium concentrations (NbV), the sum of the chromium, molybdenum, nickel and copper concentrations (CrMoNiCu), Charpy impact energy at −10 °C (CVN) and yield strength at 0.005 offset (YS). For purpose of constructing these models, 104 different data were gathered from the experimental results. The data used in the ANN model is arranged in a format of seven input parameters that cover the chemical compositions, yield stress and Charpy impact energy, and output parameter which is ultimate tensile strength. In this model, the training, validation and testing results in the ANN have shown strong potential for prediction of relations between chemical compositions and mechanical properties of API X70 steels.

Influence of Warm Tempforming on Microstructure and Mechanical Properties in an Ultrahigh-Strength Medium-Carbon Low-Alloy Steel

Abstract: A 0.4 pct C-2 pct Si-1 pct Cr-1 pct Mo steel was quenched and tempered at 773 K (500 °C) and deformed by multi-pass caliber rolling (i.e., warm tempforming). The microstructures and the mechanical properties of the warm tempformed steels were investigated as a function of the rolling reduction. At rolling reductions of more than 28 pct, not only extension of the martensite blocks and/or the packets in the rolling direction (RD) but also a grain subdivision became more significant, and an ultrafine elongated grain (UFEG) structure with a strong 〈110〉//RD fiber deformation texture was formed after 78 pct rolling. The tensile deformation behavior became significantly anisotropic in response to the evolution of UFEG structure. The longitudinal yield strength (σy) of the quenched and tempered sample increased from 1480 to 1860 MPa through the 78 pct rolling, while the transverse σy leveled off at around 1600 MPa up to 28 pct rolling. The transverse true fracture stress was also markedly degraded in contrast to the longitudinal one. Charpy impact properties were enhanced at a rolling reduction of 52 pct or more. The 52 pct-rolled sample underwent a ductile-to-brittle transition in the temperature range from 333 K to 213 K (60 °C to −60 °C), while the 78 pct-rolled sample showed an inverse temperature dependence of the impact toughness because of brittle delamination. The tensile and Charpy impact properties are discussed in association with the microstructural evolution.

Study on Mechanical Properties of Epoxy Polymer Reinforced with NanoSiC particles

Abstract: In this paper we study the effect of NanoSiC particles on the mechanical properties for the polymer composite material. We using the epoxy resin (EPOBOND Epoxy) supplied from epobond for chemicals and electrical components in Egypt as matrix reinforced with silicon carbide nanoparticles with different weight percentage (5, 10, 15 and 20). The tensile tests were made by using LLOYD" Universal Tensile Testing Machine System at room temperature, the wear tests were made by Pin-on-Disc machine and A Charpy impact test machine was used for measuring the impact toughness during impact testing . It is found that the addition of NanoSiC particles on epoxy resin can improve the wear resistance however the strength decrease with further increase in weight percentage of reinforcement.

Nanoscale Analyses of High-Nickel Concentration Martensitic High-Strength Steels

Abstract: Austenite reversion in martensitic steels is known to improve fracture toughness. This research focuses on characterizing mechanical properties and the microstructure of low-carbon, high-nickel steels containing 4.5 and 10 wt pct Ni after a QLT-type austenite reversion heat treatment: first, martensite is formed by quenching (Q) from a temperature in the single-phase austenite field, then austenite is precipitated by annealing in the upper part of the intercritical region in a lamellarization step (L), followed by a tempering (T) step at lower temperatures. For the 10 wt pct Ni steel, the tensile strength after the QLT heat treatment is 910 MPa (132 ksi) at 293 K (20 °C), and the Charpy V-notch impact toughness is 144 J (106 ft-lb) at 188.8 K (−84.4 °C, −120 °F). For the 4.5 wt pct Ni steel, the tensile strength is 731 MPa (106 ksi) at 293 K (20 °C) and the impact toughness is 209 J (154 ft-lb) at 188.8 K (−84.4 °C, −120 °F). Light optical microscopy, scanning electron and transmission electron microscopies, synchrotron X-ray diffraction, and local-electrode atom-probe tomography (APT) are utilized to determine the morphologies, volume fractions, and local chemical compositions of the precipitated phases with sub-nanometer spatial resolution. The austenite lamellae are up to 200 nm in thickness, and up to several micrometers in length. In addition to the expected partitioning of Ni to austenite, APT reveals a substantial segregation of Ni at the austenite/martensite interface with concentration maxima of 10 and 23 wt pct Ni for the austenite lamellae in the 4.5 and 10 wt pct Ni steels, respectively. Copper-rich and M2C-type metal carbide precipitates were detected both at the austenite/martensite interface and within the bulk of the austenite lamellae. Thermodynamic phase stability, equilibrium compositions, and volume fractions are discussed in the context of Thermo-Calc calculations.