• Journal of Welding and Joining
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• v.18 no.6
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Bulletin of the Society of Naval Architects of Korea
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• v.18 no.4
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• pp.21-29
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• 1981

In this paper, plastic behavior and plastic strength of cruciform fillet welded joint under tension is investigated by finite element method. Attension is focussed, in particular, on the effect of geometry of fillet weld including its contour, size and penetration. And the approximate analysis of welded joint have been carried out from a simple model constructed by three zone, ie, base metal, heat affected zone, and weld metal.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.290-294
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• 1997

In this study, the welded residual stresses test was carried out with pure titanium and TIG welded material using in chemical plants an airplane frames etc.. The relationship between process parameters and residual stresses is complex since a number of factors are involved. Extensive studies have been carried out to determine the effects of various process parameters on residual stress. The result of micro-hardness about butt welded spacemen was measured of low hardness value in the melting metal zone. The residual stress of welded zone on the Titanium plate by the sectioning method and finite element method was high measured in the spacemen of high current and voltage. Also, compressive residual stress in the range of distance about 15∼20mm from the middle of the deposited metal area is very change. The result of impact test about butt welded spacemen of pure titanium plate was measured of very difference in the welded bead, heat affect zone and base metal, and be measured of high impact value in the heat affect zone. The measure result of welded residual stresses about pure titanium is high measured hen nominal steel plate. The V-Type butt welded spacemen, that of the measurement result on the welded residual stress is high measure then X-Type butt welded spacemen.

• Journal of Welding and Joining
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• v.20 no.5
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• pp.87-92
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• 2002

Weldability of Friction Stir Welded(FSW) AZ31B-H24 Mg alloy sheet with 4m thick was evaluated by changing welding speed. The sound welding conditions mainly depended on the suffiicient welding heat input during the process. The insufficient heat input resulted in the void like defect in the weld zone. Higher welding speed caused a larger inner void or lack of bonding. The defects were distributed at the stir zone or the transition region between stir zone and thermo-mechanical affected zone (UE). The size of defects slightly increased with increasing welding speed. These defects had a great effect on the joint strength of weld zone. The weld zone was composed of stir zone, TMAZ and heat affected zone. The stir zone was cosisted of fine recrystallized structure with $5-8\mu\textrm{m}$ in the mean grain size. The hardness of weld zone was near the 60HV, which was slightly lower than that of base metal. The maximum joint strength was about 219MPa that was 75% of that of base metal and the yield strength was also lower than that of base metal partly due to the existance of defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.1
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• pp.43-48
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• 2009

The fatigue crack growth behavior of high strength X80 pipeline steel was investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the rolling direction of the pipeline. Also, the fatigue crack growth rates for welded joint of X80 pipeline steel were investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the welding line. The experimental results indicated the fatigue crack growth behavior was markedly different in three zones, weld metal, heat affected zone and base metal of welded joints. There was a trend toward increment in the fatigue life of weld metal and heat affected zone as compared with the X80 pipeline steel.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.6
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• pp.113-118
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• 1999

In order to evaluate strength of spot welded joint, at first it is importent that we should know strain distribution near nugget zone. During loading, in HAZ, compressive strain increase with Increase of load, but in nugget zone tensile strain increase. During unloading, on the other hand, even through the decreases, the strain variation is not almost appeared in nugget zone and HAZ. In nugget boundary zone, the strain range increases continuously along with load increase on outer surface, but the strain increases continunously and decreases rapidly beyond yield strength on inner surface. In this paper, strain distribution are measured in inner and outer surface with variation of thickness and load under tensile-shear load. Tensile-shear strength increased as with increase of specimen thickness. As for thickness increase rates are 25%, 50%, 100%, and 150%, tensile-shear strength in crease rates are 40%, 81%, 130% and 228%.

• Journal of Welding and Joining
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• v.13 no.1
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• pp.138-144
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• 1995

Recently, as the industrial structure tends to become large, the thickness of structural plate becomes thicker. Therefore, the thicker the plate of welded structure is, the larger the shape of welded joint. The effect of large heat input makes large heat affected zone(HAZ). These bring to complict welding residual stress and to weaken material, which may cause extremely harm to the safety of structures. Nevertheless, welding is design is regulated by the KS, JIS or standard in the resister of shipping such as KR, ABS or LR. However, these rules are based on rather experimental than theoretical. In this study, the computer program of heat conduction, considering un-steady state and quasi-steady state, is developed for optimizing(minimizing) a shape of welded joint. The characteristics of heat on the welded joints with various shapes are clarified by the results of the analyses.

• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.455-465
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• 2017

To figure out the weldability and welded joint performance on the FCAW of SM490TMC 120mm, several specimens were manufactured and 10 kinds of experiments were implemented. The result of the weld zone chemical composition test, weld metal tensile test, weld zone tensile test, and weld zone impact test has satisfied the KS. Especially, the weld zone tensile test result shows the base metal fracture, which means the weld zone performs enough required performance. In addition, the results of the weld zone bending test, hardness test, macroscopic test, microscopic test, and the maximum hardness in HAZ were showing that the FCAW weld zone has fine quality.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.68-76
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• 1999

The welding residual stresses produced by the welding frequently caused a crack and promote stress corrosion etc. in HAZ(heat affected zone) contained with external load and weakness of material. Therefore, PWHT(post welding heat treatment) is widely used to reduce wekdubg residuss, to relax hardening of heat affected zone and to get rid of impurity. In this study, in order to define the effect on shappes of T-welded joint, during the post welding heat treatment, we have carried out numerical analyses on the several test pieces by using computer program which was based on thermal-elasto-plato-plasto-creep theories for the study. The main results obtained form this study is as follows: 1) The mechanical difference for change the thickness of plate and groove angle did not appear. 2) The distribution modes of welding residual stresses are same on the all test specimens during the post welding heat treatment. 3) In a mecharical point of view, minimum groove groove angle($40^{circ}$) is more suitable than maximum groove angle($60^{circ}$). 4) Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• Journal of Ocean Engineering and Technology
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• v.17 no.4
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• pp.31-36
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• 2003

In case of this thick rolling-steel for a multistory building, a large oil-drilling structure, a large vessel, a bridge and so on, Lamella Tearing around the welded joint zone is the most serious problems. In order to prevent Lamella Tearing, not only is choice of material important, but also the comprehensive investigation for the structural design and the construction. The Lamella Tearing that is a staircase-shape occurs due to the contraction stress to the thickness direction of the plate and has the character that the cracks progress along the elongated inclusion by rolling. In general, because cracks occur at the heat affected zone and around HAZ, it is necessary to establish the safety and the confidence of the welded structure to restrain the welding defect such as Lamella Tearing. The mechanical approaches are the easier and more economical than the approaches of the material and the construction method. In addition, the appropriate welding profile and the optimum welding condition contribute toward the improvement of the productivity and influence on the standardization of the manufacturing technology.