• Journal of the Korean Society of Safety
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• v.11 no.3
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• pp.59-65
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• 1996

This study is to evaluate dynamic fracture characteristics of alloy tool steel, STD-11, according to various tempering conditions (heat treatment). The dynamic fracture initiation toughness and some of the dynamic fracturing characteristics were evaluated by using the instrumented Charpy impact testing procedures. The distributions of Victors hardness and dynamic fracture initiation toughness with respect to varying tempering temperatures are found to be symmetric type with the help of experimental results for the STD-11. It is also found that the dynamic fracture initiation toughness is a inverse proportion to Vickers hardness. In this experimental study, it is found that the best heat treatment condition is 55$0^{\circ}C$ tempering in alloy tool steel, STD-11, because the results show high values of Vickers hardness and dynamic fracture initiation toughness.

• Nuclear Engineering and Technology
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• v.30 no.6
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• pp.609-616
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• 1998

Cast duplex stainless steels are extensively used for primary pressure boundary components. These components are, however, embrittled due to the precipitation of $\alpha$' phase by spinodal decomposition and other processes when exposed to reactor operating temperature for a design lifetime or life extension conditions. This report presents a procedure for estimating the current condition and the residual life of safety-related stainless steel components by using ANL database and correlations. The database of Charpy impact energy suggests that CF-8M grade is the most susceptible to thermal aging and CF-3 grade is the least. Thus, the integrity of CF-8M alleys may be degraded seriously and the degree of deterioration may exceed acceptance limit after several years of service in the nuclear reactors.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

• Journal of Welding and Joining
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• v.7 no.3
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• pp.19-27
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• 1989

Both the SS41 steel and the M.E.F(martensite encapsulated islands of frrite) dual phase steel made of SS41 steel by heat treatment were welded by friction welding, and then manufactured machinemade Vnotch standard Charpy impact specimens and precracked with a fatigue system at BM(base metal), HAZ(heat affected zone) and WZ(weld interface Zone). The impact test of them was performed with an instrumented impact test machine at a number of temperatures in constant loading velocity and the dynamic fracture characteristics were studied on bases of the absorbed energy, dynamic fracture toughness and fractography from the test. The results obtained are as follows; At the room temperature, the absorbed energy is HAZ.geq.WZ.geq.BM in case of the M.E.F. dual phase steel: BM.geq.HAZ.geq.WZ in case of the SS41 steel, HAZ.geq.BM.geq.WZ at the low temperature. The absorbed energy is decreased markedly with the temperature lowering; it is highly dependent on the temperature. The dynamic fracture toughness of the M.E.F. dual phase steel is HAZ.geq.WZ.geq.BM at the room temperature; BM.geq.WZ.geq.HAZ below-60.deg. C. Therefore the reliability of friction welding is uncertain at the low temperature(below-60.deg. C). The dynamic fracture toughness of the SS41 steel; HZA.geq.WZ.geq.BM at overall temperature region. The flaw formed by rotational upsetting pressure was shown y SEM; in this region. The absorbed energy per unit area and dynamic fracture toughness were low relative to other region.

• Korean Journal of Metals and Materials
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• v.48 no.11
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• pp.1021-1027
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• 2010

The charpy impact property was lower at the surface and middle regions than that at the root region in metal welded by Tandem EGW of 82 mm thick EH40-TM steel plates. Temperature distribution in the weld sample and the heating/cooling temperature throughout the various regions in the weld metal were estimated by the commercial weld simulation program SYSWELD. The microstructure of the weld metal consisted of acicular ferrite and grain boundary ferrite. Grain boundary ferrite in the acicular ferrite matrix was found more in the surface and middle regions than in the root region, and the acicular ferrite was also coarser in the surface and middle regions where the impact toughness was lower and the input temperature was higher. Our results indicated that the impact toughness property was related to the microstructure morphology, the distribution of grain boundary ferrite, and the acicular ferrite.

• Korean Journal of Materials Research
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• v.1 no.3
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• pp.115-124
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• 1991

In this study, the relationship between mechanical properties and the effects of second phase in tri-phase steel which was composed of ferrite-martensite-bainite was investigated. In order to obtain different microstructure of ferrite+martensite(DP), ferrite+bainite(F+B), and ferrite+martensite+bainite(TP, different heat treatment has been accomplished. The effects of volume fraction and microstructure of each specimen were studied on tensile property, Charpy impact energy and stretch-flangeability. As the bainite content in triphase steels increased, the tensile strength, and yield strength decreased as well as the reduction of area and strength-uniform elongation increased. However, ferrite-bainite steel had high yield ratio and yield point elongation. The Charpy impact energy of TP and F+B steel was higher than that of DP steel. In addition, the characteristics of hole expanding limit($\lambda$) of TP steel and F+B steel were higher than that of DP steel. These mechanical properties of tri-phase steel have been improved, because bainite could be deformed easily within ferrite matrix. The effect of bainite on ductility in tri-phase steel has been found to be favorable. In this experiment, tri-phase steel contained within 27% bainite volume fraction had good nechanical properties and superior stretch-flangeability.

• Korean Journal of Materials Research
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• v.10 no.11
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• pp.760-769
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• 2000

Mechanical properties of HSLA cast steels alloyed with 0.15% Nb, Ti or V were tested as variations of austenizing temperatures and tempering times. The test results are as follows. The hardness of HSLA cast steels austenized for 2hrs at 115$0^{\circ}C$ was shown the highest value regardless of alloying elements and then decreased as the temperature decreased below 110$0^{\circ}C$. The hardness of HSLA cast steels with 0.15% Ti austenized for 2 hrs at $1150^{\circ}C$ was higher than that of any other HSLA cast steels, and chich was mainly attributed to the relatively high amount of bainite, and solid solution hardening. Charpy impact energy of HSLA cast steels was comparable to the C-Mn cast steel except HSLA cast steels with 0.15% Ti austenized at 115$0^{\circ}C$. The hardness of HSLA cast steels austenized for 2 hrs at $1150^{\circ}C$ increased at a ten-minute tempering, and after that, the hardness kept almost sililar level except HSLA cast steels with 0.15% V.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.305-311
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• 2000

Applicability of crack arrest load measured from the Charpy V-notch impact test has been investigated to predict the fracture toughness of nuclear reactor pressure vessel (RPV) steels (ASME SA508 Cl.3). The temperature dependence of the crack arrest load was well described by the type of exponential function characterized by an index temperature at which the crack arrest load is 2kN. The specific index temperature, which also well correlated with $T_{NDT}\;and\;T_{41J}$ is expected to be representative index temperature characterizing the crack arrest fracture toughness of RPV steels. Also, the crack arrest load correlated well with the stable crack length measured from the fracture surface. From the measurements of the crack arrest load and the stable crack length, the lower bound fracture toughness, $K_{Ia}$ of RPV steels could be predicted with sufficient accuracy.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.4
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• pp.300-306
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• 2002

In this paper the failure mechanisms and Charpy impact tests of carbon fiber polypropylene composites have been studied in the temperature range -5$0^{\circ}C$ to 6$0^{\circ}C$ and 3 different supported length of specimen (span length). There are significant effects of temperature and span length on impact fracture toughness, which shows a peak at ambient temperature and decrease as temperature is reduced. Fracture toughness shows a maximum at span length s=20mm. Failure mechanisms are characterized based on SEM examination, which is correlated the measured fracture toughness. Mafor mechansms of this composites can be classified as fiber matrix debonding, delamination, fiber pull-out and matrix deformation.

• Geotechnical Engineering
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• v.13 no.1
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• pp.169-182
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• 1997

It is known that some amount of loss in impact energy takes place due to some limitations and problems during the performance of the field SPT. Actual energy level tractsferred to the rod should be measured to correct the SPT-N values tested in the field In this paper, the ratio of energy transferred to the rod through the anvil to impact energy is measured by using sharpy impact test equipment and also analysed by using GRL-WEAP This result is certified and compared with that of field SPT As the results of this study, the average rod energy ratio of the R-P hammer and the Trip hammer is calculated at 0.726 and 0.728 respectively, but it is suggested that 0.72 should be used. By using the hammer energy ratio 64.2% and 75.0% obtained from field measurement, the average energy ratio of the SPT for the R-P hammer is calculated at 46.7% and 54.5% for the Trip hammer.