• Korean Journal of Materials Research
• /
• v.19 no.7
• /
• pp.369-375
• /
• 2009

The spot weldability of dissimilar metal joints between stainless steels (AISI316) and interstitial free (IF) steels were investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensileshear strength, hardness, and microstructure. The fracture surface was investigated by using a Scanning Electron Microscopy (SEM). The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the STS316 sheet was larger due to the higher bulk-resistance. The microstructure of the fusion zone was fully martensite. In order to evaluate the microstructure further, dilution of stainless steels were calculated and imposed onto the Schaeffler diagram. The predicted microstructure from the Schaeffler diagram was martensite. In order to confirm the predicted microstructure, XRD measurements were carried out. The results showed that that initial weld nugget was composed of austenite and martensite.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.3
• /
• pp.220-226
• /
• 2003

This paper presents the result of an investigation on the application of the acoustic emission method to the monitoring of fatigue crack initiation, growth and track location in welded joints. Fatigue test was carried out for a typical fillet welded joint of ship structure. AE parameter such as ring down count was analyzed in time domain and crack locations were examined by source location and cluster option which is one of the functions of AE signal processor The usability of AE mettled was confirmed for the detection of the initiation and location of through crack.

• Korean Journal of Metals and Materials
• /
• v.48 no.12
• /
• pp.1090-1096
• /
• 2010

This pitting corrosion study of welded joints of austenitic stainless steels (AISI 304L and 316L) has addressed the differentiating solidification mode using three newly introduced filler wires with a flux-cored arc welding process (FCAW). The delta ferrite (${\delta}$-ferrite) content in the welded metals increased with an increasing equivalent weight ratio of chromium/nickel ($Cr_{eq}/Ni_{eq}$). Ductility dip cracking (DDC) was observed in the welded metal containing ferrite with none of AISI 304L and 0.1% of AISI 316L. The potentiodynamic anodic polarization results revealed that the $Cr_{eq}/Ni_{eq}$ ratio in a 3.5% NaCl solution didn't much affect the pitting potential ($E_{pit}$). The AISI 316L welded metals with ${\ddot{a}}$-ferrite content of over 10% had a superior $E_{pit}$ value. Though the AISI 316L welded metal with 0.1% ferrite had larger molybdenum contents than AISI 304L specimens, it showed a similar $E_{pit}$ value because the concentration of chloride ions and the corrosion product induced severe damage near the DDC.

• Steel and Composite Structures
• /
• v.31 no.3
• /
• pp.319-327
• /
• 2019

This paper describes an experimental study of steel beam-column connections with or without expanded beam flanges with different geometries. The objectives of this study are to elucidate the cyclic behavior of these connections, identify the location of the plastic hinge zone, and provide useful test data for future numerical simulations. Five connection specimens are designed and tested under cyclic load. The test setup consists of a beam and a column connected together by a connection with or without expanded beam flanges. A constant axial force is applied to the column and a time varying point load is applied to the free end of the beam, inducing shear and moment in the connection. Because the only effect to be studied in the present work is the expanded beam flange, the sizes of the beam and column as well as the magnitude of the axial force in the column are kept constant. However, the length, width and shape of the expanded beam flanges are varied. The responses of these connections in terms of their hysteretic behavior, failure modes, stiffness degradation and strain variations are experimentally obtained and discussed. The test results show that while the influence of the expanded beam flanges on hysteretic behavior, stiffness degradation and energy dissipation capacity of the connection is relatively minor, the size of the expanded beam flanges does affect the location of the plastic hinge zone and strain variations in these beam-column joints. Furthermore, in terms of ductility, moment and rotational capacities, all five connections behave well. No weld fracture or premature failure occurs before the formation of a plastic hinge in the beam.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.24 no.1
• /
• pp.28-36
• /
• 2020

In shipbuilding industry, there is conducting most of works by welding at the shipyard, and the volume of welding is increasing with international trends of green ships. Welding joint is guaranteed quality through non-destructive testing (NDT). The manual welding inspection report is produced by identifying the drawings designed, which results in losses the many workforce and occurs human errors. To solve these problems, this paper covers a system that reports on inspection information is automatically generation by input data based on shipbuilding-specific CAD. The developed system analyzes the shape data from drawings of modeling. Also, the system determines welding joints through expansion of the part boundary and generates tag numbers. In addition, it provides the function to automatically extract the information needed for inspection such as weld length, thickness and etc. We conducted test to verify the usefulness of the developed system and confirmed that the welding inspection information extracted through system matches the information shown in drawings of modeling.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.6 no.3
• /
• pp.53-62
• /
• 1986

For the research on the fatigue fracture behavior in the welded joints of steel structures, base metal specimens and welded ones were selected, and the direct fatigue tests were carried out. Thereafter, fatigue-life (S-N) curves, plastic strain-number of cycles (${\varepsilon}_p$-N) curve, the extrapolated fatigue-life (${\varepsilon}_p$-$N_c$) curve, and da/dN-${\Delta}K$ curves were plotted. By these results the followings were obtained. It was shown that the ratio of fatigue strength at $2{\times}10^6$ cycles of the welded specimen to that of the base metal one was 0.6, and that 0.72 for the base metal and 0.65 for the welded one were the ratio of fatigue strength at $2{\times}10^6$ cycles to yielding stress. The S-N curve for the welded specimen was separated into two sections, the low gradient section and the steep section. As this result, it was shown that the more stress became to reduce, the more the reduction of fatigue strength became to be great. It was shown that fatigue strength at $2{\times}10^6$ cycles from this case was about 83 % of that from the S-N curve plotted with one section. It was thought that the reason was that weld flaw acted greatly on the fatigue strength within the low stress range. It was shown that at the instart of crack initiation plastic strain increased abrupt1y in the case of the welded specimen more than the case of the base metal specimen, and increased abruptly in the upper stress range in both cases. It was shown that the experimental constant ${\alpha}$, 0.42, in the base metal nearly accorded with Manson-Coffin's result, but this made a great difference with the case in the welded specimen. It was thought that it was due to the abrupt change of plastic strain and the influence of weld flaw.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.5
• /
• pp.345-354
• /
• 2016

In the present study, hybrid moment connections of welding and bar reinforcement for composite beam-column connections were proposed. Concrete-filled octagonal tube and U-section were used for the column and beam, respectively. In the beam-column connection, the top flange and web of the beam U-section were connected to the column plate by welding. However, to reduce stress concentration at the weld joints, the bottom flange of the beam was not welded to the column plate. Instead, to transfer the tension force of the beam flange, reinforcing bars passing through the column plate were used. Four exterior connections with conventional welded and hybrid moment connections were tested under cyclic loading and their cyclic behaviors were investigated. The test results showed that the hybrid moment connections successfully transferred the beam moment to the column. The strength and ductility of the hybrid moment connections were comparable to the conventional welded moment connection with exterior diaphragm; however, the connection performance was significantly affected by the details of the hybrid moment connection.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1179-1185
• /
• 2011

Cold and hot-rolled carbon steel sheets are commonly used in railroad cars or commercial vehicles such as the automobile. The sheets used in these applications are mainly fabricated by spot welding, which is a type of electric resistance welding. However, the fatigue strength of a spot-welded joint is lower than that of the base metal because of high stress concentration at the nugget edge of the spot-welded part. In particular, the fatigue strength of the joint is influenced by not only geometrical and mechanical factors but also the welding conditions for the spot-welded joint. Therefore, there is a need for establishing a reasonable criterion for a long-life design for spot-welded structures. In this thesis, ${\Delta}P-N_f$ relation curves have been used to determine a long-life fatigue-design criterion for thin-sheet structures. However, as these curves vary under the influence of welding conditions, mechanical conditions, geometrical factors, etc. It is very difficult to systematically determine a fatigue-design criterion on the basis of these curves. Therefore, in order to eliminate such problems, the welding residual stresses generated during welding and the stress distributions around the weld generated by external forces were numerically and experimentally analyzed on the basis of the results, reassessed fatigue strength of gas welded joints.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.14 no.2
• /
• pp.79-87
• /
• 1978

This is an experimental study on friction welding and heat treatment of engine exhaust valve materials whose welding combination is SCr4 as stem to 21-4N as head and SUH3 to 21-4N. In this study, not only the experiments of friction welding under the selected optimum welding condition and the examination of the mechanical properties were carried out, but also the heat treatment of friction welded specimens under the two selected conditions was taken to obtain the better welding character, eliminating the latent stress and the hardness peak which appeared at the welded zones of heat resisting steel(21-4N, SUH3) and low alloyed steel ($SCr_4$) friction weldments. The results obtained by the experiments and consideration in this study are as follows: I) It was experimentally proved quite reasonable that 'speed=3,OOO rpm, heating pressure Pl=8 kg/ mm2, upsetting pressure p, = 20 kg/mm', heating time $t_1$ = 3 see, upsetting time TEX>$t_2$ = 2.5 sec' was selected as the optimum welding condition for friction-welding the engine exhaust valve materials $SCr_4$ to 21-4 Nand SUH 3 to 21-4 N. 2) The results of the previous study and this one on friction welding of such dissimilar materials as SUH 3-SUH 31, SCr 4-SUH 31, SCr 4-SUH 3, SUH 3-CRK 22, SCr4-21-4 Nand SUH3-21-4 N agreed with each other substantially in the friction welding characteristics at welded interface zones. 3) It was also certified quite satisfactory that '600\ulcornerCX30 min. Xroom air cooling' as an optimum heat treatment condition of the friction welded materials SCr 4-21-4 Nand SUH 3-21-4 N was experimentally determined to eliminate the latent stress and the hardness peak at welded zones. 4) About 20% of the tensile strength before heat treatment of friction welded specimens was decreased after heat treatment 600\ulcornerCX30 min. Xair cooling, but the location of fracture was moved from heat affected zone to parent $SCr_4$ & SUH3. 5) Microscopic examination of the weld joints friction-welded and heat-treated under the above mentioned conditions revealed that the weld zone is very narrow and has a fine grained intermixed structure without any welding defects. 6) The above mentioned conditions can be also utilized as friction welding parameters of the other dissimiar materials for engine valve production.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.20 no.1
• /
• pp.49-59
• /
• 1984

Optimizing investigation of characteristics of underwater welding by a gravity type arc welding process was experimentally carried out by using six types of domestic coated welding electrodes for welding of domestic marine structural steel plates (KR Grade A-1, SWS41A, SWS41B,) in order to develop the underwater welding techniques in practical use. Main results obtained are summarized as follows: 1. The absorption speed of the coating of domestic coated lime titania type welding-electrode became constant at about 60 minutes in water and it was about 0.18%/min during initial 8 minutes of absorption time. 2. Thus, the immediate welding electrode could be used in underwater welding for such a short time in comparison with the joint strength of in-atmosphere-and on-water-welding by dry-, wet-or immediate-welding-electrode. 3. By bead appearance and X-ray inspection, ilmenite, limetitania and high titanium oxide types of electrodes were found better for underwater-welding of 10 mm KR Grade A-1 steel plates, while proper welding angle, current and electrode diameter were 6$0^{\circ}C$, above 160A and 4mm respectively under 28cm/min of welding speed. 4. The weld metal tensile strength or proof stress of underwater-welded-joints has a quadratic relationship with the heat input, and the optimal heat input zone is about 13 to 15KJ/cm for 10mm SWS41A steel plates, resulting from consideration upon both joint efficiency of above-100% and recovery of impact strength and strain. Meanwhile, the optimal heat input zone resulting from tension-tension fatigue limit above the base metal's of SWS41A plates is 16 to 19KJ/cm. Reliability of all the empirical equations reveals 95% confidence level. 6. The microstructure of the underwater welds of SES41A welded in such a zone has no weld defects such as hydrogen brittleness with supreme high hardness, since the HAZ-bond boundary area adjacent to both surface and base metal has only Hv400 max with the microstructure of fine martensite, bainite, pearlite and small amount of ferrite.