• Journal of Welding and Joining
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• v.33 no.5
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• pp.35-40
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• 2015

Characterization of microstructures and mechanical properties of 83mm thickness EH36-TM welds produced by the combined flux cored arc (FCA) and electro gas (EG) welding processes has been studied with the two different groove conditions, single-V (SV) and double-V (DV) bevels. The welding consumables used for FCA and EG welding processes were ASME/AWS A5.29 (E81T1-K2) and A5.26 (EG72T), respectively. Experimental results showed that all the mechanical properties of welds such as tensile property, CVN toughness and Vickers hardness met IACS requirements. The tensile strength of EG welded plates were reduced by approximately 4% (DV: 3.8%, SV: 4.2%) compared to the base metal. The hardness value of SV-beveled weld metal was slightly lower than that of DV-beveled one. There were no significant differences as per welding groove conditions except for the weld metal. In addition, at the fusion line, the toughness of SV condition was 20J lower and the weld metal was 40J lower than DV condition, respectively. On the basis of microstructural analysis, grain boundary ferrite (GBF) structures for SV condition were 2 times higher volume fraction than for DV condition and their packet sizes were coarsened to almost double. It was thus suggested that the GBF volume fractions and packet sizes in the weld metal of EH36-TM steel plates are the most important factors affecting the mechanical properties of the combined FCA and EG welded joint. Nevertheless, all the results of welds with both DV and SV conditions were found to be excellent.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.349-355
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• 2003

Material degradation due to corrosion fatigue was evaluated nondestructively using backward radiated Rayleigh surface wave. h corrosion fatigue test was carried out for the specimens made of thermo-mechanically controlled process steel in 3.5wt.% NaCl solution at $25^{\circ}C$. The backward radiation profile, which is the amplitude variation of backward radiated ultrasound according to the incident angle, of the specimens were measured in water at room temperature after the corrosion fatigue test. The velocity of Rayleigh surface wave, determined from the incident angle at which the profile of the backward radiated ultrasound became maximum, decreased for the specimen that had the large number of cycles to failure in the corrosion fatigue test. This fact implies that the corrosion degradation occurred at specimen surface in this specific test is dominantly dependant on the me exposed to corrosion environment. The result observed in the present work demonstrates the high potential of backward radiated Rayleigh surface wave as a tool for nondestructive evaluation of corrosion degradation of aged materials.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.7-20
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• 2016

A brief overview is given of the development of various structural steels and their welding application technology. Firstly, the general characteristics and welding performance of structural steels used in architecture and bridge are introduced. For safety against earthquakes or strong wind, and for highly efficient welding in high-rise building constructions, ultra high strength steel with tensile strength over 800 MPa or high HAZ toughness steel plates under high heat input welding have been developed. In particular, efficient welding technology ensuring high resistance to cold and hot cracking of ultra high strength steel is reviewed in the present paper. Secondly, various coated steels used mainly for outer part in construction are briefly discussed. Moreover, a major drawback of coated steel during welding operation, and several solutions to overcome such technical problem are proposed. It is hoped that this review paper can lead to significant academic contributions and provide readers interested in the structural steels with useful welding technology.

• Journal of Welding and Joining
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• v.8 no.4
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• pp.69-75
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• 1990

In this paper, ultimate compressive strength of TMCP 50HT steel plates (yield stress .sigma.$_{o}$=36kg/mm$^{2}$) with HAZ softening is studied. Finite element method formulated by the author is applied to analyze the elasto-plastic large deflection behaviour of the plates. The influence of HAZ softening breadth, welding direction and slenderness ratio on the ultimate compressive strength is investigated. The results obtained are summarized as 1) With the increasing of the HAZ softening breadth, early plasticity on the plates is formed and then the ultimate compressive strength is decreased, in which about 8% of the ultimate strength for the plate with h/t=4(h: HAZ softening breadth, t: plate thickness) was reduced comparing with no HAZ softening. 2) The large decrease of the ultimate strength for the case that the welding direction is normal to the loading direction is occurred than the case that the welding direction is parallel to the loading direction. 3) The influence of HAZ softening on the ultimate compressive strength is serious for thick plates, while it may be negligible for thin plates.s.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.67-73
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• 1987

The feasibility for a practical use of underwater wet arc welding process is experimentally investigated by using low hydrogen and high oxide type electrodes and TMCP steel plates. Main results are summarized as follows: 1)The absorption speed of the coated low hydrogen and high titanium oxide type eletrodes becomes constant after about 30 minutes in water, and more steeping time in water does not influnce welding arc behavior. 2) By bead appearance and X-ray inspection, the high titanium oxide type electrode is better than the low hydrogen type in underwater arc welding process. 3) The mechanical properties of underwater wet arc welds depend upon welding conditions more than those of in-air welds, and the optimum welding condition can be obtained. 4) Because of quenching effect by rapid cooling rate in underwater wet welding, the maximum hardness of HAZ is increased relatively higher in underwater wet welding, process.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.271-276
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• 1998

To apply the wear resistant steel plate for heavy duty vehicle, the wear characterisms of various kinds of commercial steel plates were invesigated by dry sand/rubber wheel tester which was tested under scratch abrasion mode. The wear tested pnaterials were boron steels which were manufactured by thereto machanical control process (TMCP) in order to achieve higher hardness. As the result of the test, wear resistance of steel plate increases with the hardness and carbon content. The wear loss of wear resistance steel plate (Hv440) is a half times than tinat of SWS490A (Hv160) steel plate in dry sand-rubber wheel test and the result in field test is similar to this dry sand/rubber wheel test result. Therefore, dry sand/rubber wheel tester can be used to predict the scratch abrasion life of the parts for heavy duty vehicle.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.299-309
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• 2014

HSA800 is a new high strength steel (HSS) plate for building structures developed by POSCO and RIST in 2011. It has upper and lower bounds for yield ($F_y$) and tensile ($F_u$) strength as of 650-770MPa and 800-950MPa, respectively, with yield ratio ($F_y/F_u$) limit as of 0.85 which make steel quality more reliable and enhance the seismic resistance of structures. As made by TMCP, it has a good weldability without increasing carbon percentage. The objective of this study is to provide alternative design of mega-structural members of the Lotte World Tower (555m, 123 story), a first super-tall building in Korea, using HSS considering structural safety, constructability, and cost-effectiveness. Steel outrigger trusses, belt-trusses and steel exterior columns were selected and analyzed to evaluate the structural performance between original and alternative designs using HSS. The results show that HSS can be applied to the members which do not affect lateral stiffness of a building and, in this study, approximately 1100tons of steel were saved. It implies that HSS can save overall construction costs - manufacturing, delivery, and erection costs - by reducing mega structural member size. HSA800 was very first applied to the Lotte World Tower based on the results of this study.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.409-412
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• 2003

Fatigue strength. especially crack initiation behavior of high strength steel under marine water environment was investigated. Marine structures were usually constructed by lot of weld joints and were designed by basis of the fatigue strength of weld joints. This study was carried out to mini. The fatigue initiation behavior is more important rather than crack propagation behavior under the design of marine structures, because it is very difficult to find out the crack propagation phenomena and repair the damaged part of welded joints in sea water Then, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the crack initiation tests with relatively low cycling loading and clearly find out a crack initiation fatigue life.

• Journal of Welding and Joining
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• v.32 no.1
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• pp.15-21
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• 2014

FCAW(Flux Cored Arc Welding), SAW(Submerged Arc Welding), EGW(Electro Gas Welding), and three-pole SAW are applicable in manufacturing the offshore wind tower. In this paper, mechanical properties of these welded-joints for TMCP steels were evaluated in all above welding processes. The tensile strength of welded-joints for all the welding methods satisfied the standard guideline (KS D 3515). No cracking on weldment was found after the bending test. Changes of weldedments hardness with welding processes were observed. In a weld HAZ (heat-affected zone), a softened HAZ-zone was formed with high heat input welding processes (SAW and EGW). However, the welded-joint fractures were found in the base metal for all cases and small decrease in welded-joint strength was caused by a softened zone. The multi-pole SAW welds exhibited similar mechanical properties comparing to the one with one-pole SAW process.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.565-572
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• 2009

This work intends to establish the reliability and fracture toughness $K_{IC}$ criterion of welded joints by EGW for high strength EH36-TMCP ultra thick plate. For this, firstly thermo elasto-plastic analysis has been carried out on two pass X-groove butt joint model to clarify the thermal and mechanical behaviour(residual stress, plastic strain, magnitude of stress and their distribution and production mechanism). Moreover, to establish fracture criterion, analysis of fracture toughness $K_{IC}$ has been performed under the notch machined and residual stress with the load condition on EGW welded joints. A quantitative fracture criterion for EGW welded joints is suggested by using $K_{IC}$.