CVN impact energy and fracture characteristics correlations with different oxide nanoparticles improving submerged arc welds
A. JiménezAna María Paniagua-MercadoArturo García‐BórquezA. TorreC. Mejía‐GarcíaVı́ctor M. López-HirataMaribel L. Saucedo‐MuñozE Miguel-Díaz
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Abstract The main aim of this research is to correlate the toughness improvement with fracture features of tested Charpy V-Notch impact specimens obtained from submerged arc welds enriched by different oxide nanoparticles (TiO 2 , SiO 2 , Al 2 O 3 and Mn 2 O 3 ). Through Scanning Electron Microscopy (SEM) fractography, fracture features were determined, which are the shear fracture percent, the loading angle, as well as the diameter of dimples and the width of cleavage sheets at ductile and brittle fracture regions, respectively. It was observed an increase of the Charpy V-Notch impact energy with the decrease of loading angle and the average diameter of dimples, as well as with the increase of its shear fractures percents. Moreover, it was correlated the increase of Acicular Ferrite surface density with the decrease of width of cleavage sheets. Thus, the toughness of the submerged arc welds can be improved by adding TiO 2 , SiO 2 , Al 2 O 3 or Mn 2 O 3 nanoparticles.Keywords:
Charpy impact test
Fractography
Acicular ferrite
Dimple
Brittleness
Cleavage (geology)
Charpy impact test
Compact tension specimen
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Dimple
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Equiaxed crystals
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The present study aimed at investigating the improvement of Charpy impact properties in heat affected zones (HAZs) of API X80 pipeline steels containing complex oxides. Three kinds of steels were fabricated by adding Ti, Al and Mg to form complex oxides and their microstructures, tensile properties and Charpy impact properties were investigated. The number of complex oxides increased as the excess amount of Ti, Al and Mg was included in the steels. After the HAZ simulation test, the steel having a number of oxides contained about 72 vol.-% of acicular ferrite in the simulated HAZ, together with bainitic ferrite and granular bainite, whereas the HAZ microstructures of the conventional steels consisted of bainitic ferrite and granular bainite with a small amount of acicular ferrite. The volume fraction of acicular ferrite increased as the amount of complex oxides increased and the heat input decreased, and thus, Charpy impact properties of the oxide containing steel HAZs were greatly improved over those of the conventional steel HAZs.
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Abstract In this paper, the mechanical properties and microstructures of AISI4140 low alloy steel under different tempering conditions are investigated. The samples are quenched, tempered to a martensite structure and loaded to fracture by means of Charpy machine according to standard test. Fractography analysis showed that the morphology fracture surface was changed by increasing tempering temperature. The variation of energy of Charpy impact fracture as a function of tempering temperature exhibits minimum values at 300 °C, which suggests the occurrence of temper embrittlement.
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Fractography is the essential method for failure analysis. Diameter, depth and direction of dimples observed on ductile fracture surface is related deeply to the ductility and the crack propagation direction. In this paper, we propose one of numerical methods for fractography to characterize dimple's diameter. Long Run Emphasis (LRE) which is the statistic value of texture analysis and relates directly to the diameter of dimple, is calculated. The method is applied to the fracture surfaces of Titanium alloy which were formed by the high-temperature tensile test. In the result, the relationship between the temperature and LRE was obtained. Therefore, we could estimate the temperature from the dimple by the method.
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The effects of P and S on the toughness and heat-checking resistance of the 5%Cr hot work die steel.
This study was carried out to investigate the effects of phosphorus and sulfur contents on the Charpy impact toughness and heat-checking resistance of 5% Cr hot working die steel. Segregation behavior and morphology of fracture surface were observed by means of AES, SEM and optical microscopy.Results are summarized as follows:(1) Charpy impact toughness at 20°C and 400°C are greatly improved by lowering of phosphorus and sulfur contents to very low level.(2) The decrease in directionality of Charpy impact toughness accompanying the lowering of these impurities is due to the increase in Charpy impact toughness transverse to the forging direction.(3) The total number and mean length of heat checks decrease with decreasing content of these impurities.Such improvements of Charpy impact toughness and heat-checking properties are considered to result from the decrease in the segregation and MnS content respectively.
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A 4 K Charpy test is defined as a Charpy test in which the initial temperature of a specimen is 4 K. Two methods, a glass Dewar method and a flow method, are compared in this study to demonstrate that both provide consistent results as long as initial specimen temperature is the same. An improved correlation between the Charpy absorbed energy and the fracture toughness at 4 K is also examined to clarify the limitation of Charpy test applications at cryogenic temperatures.
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Herein we present an experimental investigation on the toughness evaluation method for the samples of copper and aluminum, which are generally employed as electronic equipment parts, through the miniaturized version of the Charpy impact test. Overall, the resulting high reproducibility of the absorbed energy values informed by the miniaturized Charpy impact test can be witnessed; moreover, it is possible to compare the values given by the Japanese industrial standard (JIS) Charpy impact test to those given by the miniaturized Charpy impact test and correction factors were calculated accordingly.
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Microalloyed steel
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The effect of weld metal chemistry on the microstructures and mechanical properties of submerged arc welds has been studied. It was found that additions of Ti promote the formation of acicular ferrite to greater extent as compared with additions of other elements such as Mn and Mo, improve Charpy and COD properties of as-welded deposits and offer welds with quite homogeneous properties both in as-welded and reheated region.Correlations were found among 0.25 mm COD transition temperatures Ti0.25, Charpy transition temperatures vTrs and tensile strengths σB provided that these test specimens were sampled from the same area and are eiven as follows:[T0.25]as-weld=0.84vTrs+4.3σB-286, [T0.25]regeated=0.72vTrs+2.6σB-176It was also found that N deteriorates Charpy and COD properties significantly and the deposits contained Ti-B provide a good tolerance to it. Among the deposits bearing Ti, the consumable types likely to give the best combinations of tensile strengths in the range 50-60 kg/mm2, Charpy and COD properties were proved to be those containing Ti-B.
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