• Journal of Welding and Joining
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• v.32 no.1
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• pp.22-27
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• 2014

In the past, cold crack was commonly observed in the HAZ(heat affected zone) of high-strength steels. Applying to TMCP(thermo-mechanical controlled process) and HSLA(high strength low alloy) steels, cold crack tends to increase the occurrence in the weld metal. It is generally understood that cold crack occurs when the following factors are present simultaneously : diffusible hydrogen in the weld metal, a susceptible microstructure and residual stress. In particular, many studies investigated the microstructural effect on the cold crack in HAZ and the cold crack in weld metals starts to receive the special attendance in modern times. The purpose of the study is to review the effect of weld microstructures (grain boundary ferrite, Widm$\ddot{a}$nstatten ferrite, acicular ferrite, bainite and martensite) on cold crack in the weld metals. Among various microstructures of weld metals, acicular ferrite produced the greatest resistance to the cold crack due to the fine interlocking nature and high-angle grain boundary of the microstructure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.59-60
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• 2022

When a metal sprayed film of several hundred ㎛ on the concrete surface is possible to 80 dB of shielding effect electromagnetic waves (ElectroMagnetic Pulse, EMP). Therefore, in this study, as a way to secure EMP shielding performance by applying a metal spray coating showing excellent EMP shielding performance to a concrete structure, the metal spray welding efficiency and thin film adhesion performance according to the concrete spray direction and surface treatment method were evaluated. Metal sprayed efficieny according to the metal spraying direction and method was confirmed that the difference was insignificant by applying the roughening agent. However, the method of strengthening the concrete surface and applying the sealing agent show maximum adhesion strength of 3.98 MPa compared to other methods, and it is judged that this method can be utilized for the metal spraying method for concrete EMP shielding.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5405-5411
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• 2011

The effects of heat input (1.5~3.6 kJ/mm) and post weld heat treatment (PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strengths and hardness of as-welded specimens were decreased as heat input increased, but CVN (Charpy V-Notch) impact energy did not show any differences. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high heat inputs. Meanwhile, tensile strength and hardness of PWHT weldments were decreased due to the coarsening and globular of microstructure as well as reduction of residual stresses.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.953-962
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• 1987

Domestic dissimilar structural steels, SM 45 C and SUS304 were friction welded under optimal welding condition and the micro-artificial holes were drilled at SM 45 C base metal, SM 45 C HAZ, welded zone, SUS 304 HAZ, and SUS 304 base metal for fatigue behavior tests. In this study, the fatigue limit and the behavior of micro-crack propagation, crack propagation rate, and its dependency on stress intensity factor under the low stress level and high stress level of bending stress have been investigated. The results obtained are as follows. (1) The fatgiue strength of the portion of SM45C B.M., SM45C HAZ, welded zune, SUS304 HAZ and SUS304 B.M. on notched friction welded specimens are 20 kgf/mm$^{2}$, 32 kgf/mm$^{2}$, 27kgf/mm$^{2}$, 29kgf/mm$^{2}$, and 29kgf/mm$^{2}$, respectively. (2) The fatigue strength of welded zone of unnotched and notched specimens are 32.5kgf/mm$^{2}$, and 27kgf/mm$^{2}$, respectively. (3) Micro-crack initiation in the welded zone, HAZ, and each base metals occurrs simultaneously in front and rear of micro-hole tips in the view of the rotational directions. (4) Fatigue crack propagates more slowly in the welded zone than in another protions of specimen, regardless of the magnitude of the stress level. (5) Fatigue crack propagation rates were plotted as a function of stress intensity range. The value of m in the equation da/dN=C(.DELTA.K)$^{m}$ was found to range from 2.09-2.55 in this study.

• Journal of Korean Society of Steel Construction
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• v.28 no.5
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• pp.303-312
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• 2016

Many researches on the application of stainless steels as structural steels have been performed thanks to their material properties such as superior ductility and corrosion resistance. Ferritic stainless steels(STS430) with little or no nickel have been used increasingly in building structure because it is inexpensive compared to austenitic stainless steels(STS304) with nickel, but provide performances similar to the austenitic stainless steel. This paper deals with block shear fracture behavior of base metal in stainless steel welded connection. Although the block shear fracture behavior for welded connection due to stress triaxiality is different from that of bolted connection, the block shear strength of welded connection in current design specifications has been predicted based on that of bolted connection. The main parameters are weld length and welding process(Arc and TIG welds). The ultimate strengths of TIG welded specimens were higher than those of arc welded specimens and current design predictions by AISC, EC3 etc. were compared with test strengths.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.6
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• pp.569-575
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• 1984

The characteristics of the stress corrosion cracking of SUS 304 stainless steel weldments were studied with the speciments of the constant displacement type under the environment of 42% MgC $l_{2}$ boiled solution (143.+.-.2.deg.C). The susceptibility of initiation and propagation of the stress corrosion crack was quantitatively inspected in the weld metal, heat affected zone and heat affected zone with including the reinforcement shape, respectively. Also, those susceptibility were discussed in connection with the change of mechanical and microstructural characteristics caused by heating cycle of welding. Main results obtained are as follows: (1)Stress corrosion cracking is easiest to initiate and propagate in the heat affected zone of weldment. (2)The susceptibility of stress corrosion cracking of the weldment is largely improved by eliminating the reinforcement part of the weld bead. (3)The dominant factor of the cracking susceptibility of the heat affected zone appeared to be the phenomenon of softening and sensitizing caused by welding heat cycle. (4)Under the low loading conditions, the behavior of stress corrosion cracking of the SUS 304 steel weldment is largely influenced by the pitting phenomenon in the front region of the main crack.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.519-525
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• 2008

For this study, SM45C steel rods using generally for power transmission shafts and machine components was selected and welded by butt-GMAW method. And then it was studied about estimation of fatigue strength and the region of infinite life by Haigh diagram using Goodman's equation. Fatigue strength in weld zone presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. This result agrees with distribution of hardness in weld zone. Fatigue strength in base metal zone presents highly compared with weld zone in low cycles between $10^4$ cycles and $10^6$cycles, but it presents the lowest fatigue strength on the order of heat affected zone in the vicinity of $10^6$cycles. It is the result that the first high compressive residual stress distributed by drawing process of the steel rods is released and the base metal is softened by alternating stresses. The region of infinite life by Haigh diagram presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. From this results, it is demanded that the stress for safety design of machine components using SM45C butt-welded steel rods must be selected in the region of the lowest infinite life of heat affected zone.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.158-165
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• 2002

This study was to evaluate mechanical properties and toughness of the Al5083-O aluminum alloy welding zone according to the mixing shield gas ratio and heat input change. The GMA(Gas Metal Arc) welding of the base metal was carried out with four different mixing shield gas ratios(Ar100%+He0%, Ar67%+He33%, Ar50%+He50%, and Ar33%+He67%) and three different heat inputs(low, medium, and high). To investigate the Charpy absorbed energy of the weld zone, the specimens were divided base metal, weld metal, fusion line, and HAZ notched specimen according to the worked notch position. The different gas ratio and heat input had little effect upon the tensile strength. But Ar33%+He67% mixture had the greatest mechanical properties considering that the more He gas ratio concentrations, the higher yield strength and elongation. The maximum load and displacement of the weld metal notche specimen was so much low more than that of the base metal, but fusion line and HAZ notched specimens showed almost same regardless of the mixing shield gas ratio and heat input. The Charpy absorbed energy was lowest in weld metal notched specimen, and increased in the fusion line, and HAZ notche specimen in order. Ar33%+He67% mixture had the greatest toughness considering that the more He gas ratio, the higher absorption energy.

• Journal of the Korean Institute of Rural Architecture
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• v.16 no.4
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• pp.75-81
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• 2014

In this study, we have intended to provide the related construction manuals with technical materials and to reduce the defects in the on-site construction, with reviewing the adhesive properties of joint parts according to change of temperature and speed of hot-air sealer for the products that have been made of polyvinyl chloride(PVC) materials in the single waterproof sheet. The result from the experiment is shown as following. 1) Bond strength was shown as high as the welding speed became slower. For the hot-air welding velocity with 3~6m/min, a stable bond strength has been shown in the range of the hot-air welding temperature with $175{\sim}210^{\circ}C$, while it has been shown in the range of the hot-air welding temperature with $210^{\circ}C$, when the hot-air welding velocity is between 9~12m/min. 2) If the hot-air welding temperature is lower, the adhesive strength has been shown as higher in the section where the hot-air welding velocity is low, while the adhesive strength has been also shown as higher in the section where the velocity is fast as the hot-air welding temperature becomes higher. The highest bond strength has been shown in the velocity with 3m/min for the hot-air welding temperature with $140{\pm}10^{\circ}C$, which is rather low. At $175{\pm}10^{\circ}C$, a high bond strength has been shown in the velocity with 3~6m/min, while the high bond strength has been shown in the velocity with 6~9m/min at $210{\pm}10^{\circ}C$.

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