• Journal of Welding and Joining
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• v.13 no.1
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• pp.89-102
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• 1995

The evaluation of reheat cracking susceptibility in CrMoV turbine rotor steel was performed using thermally simulated heat affected zones. The examinations were carried out in terms of microstructural characterization, microhardness measurement and a Charpy type notch opening three point bend test. It was found that reheat cracking susceptibility increased as the peak temperature increased. This effect was due to the combined effects of the carbide dissolution and unrestricted grain growth at 1350.deg. C peak temperature. Reheat cracking susceptibility was estimated based on microhardness measurement and prior austenite grain size. It was established that for this particular material, reheat cracking in coarse grained heat affected zone can be eliminated if the microhardness is below about 360DPH and the grain size is below about 30.mu.m. It is evident that reheat cracking susceptibility can be eliminated or reduced by carefully controlling the welding parameters such that a refined structure is produced in the coarse grained heat affected zone.

• Laser Solutions
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• v.4 no.1
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• pp.21-28
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• 2001

Simulation on the electron beam welding of Al 2219 alloy was carried out by using commercial FEM code MARC, which encounters moving heat sources. Due to axisymmetry of geometry, a half of the cylinder was simulated. A coupled thermo-mechanical analysis was carried out and subroutine for heat flux was substituted in the program. The material properties such as specific heat, heat transfer coefficient and thermal expansion coefficient were given as a function of temperature and the latent heat associated with a given temperature range is considered. As a result, the proper beam power is 60㎸${\times}$60㎃ and welding speed is 1∼1.5 m/min. The residual stress in the heat-affected zone as well as the fusion zone does not increase. It is necessary to use jigs for preventing distortion of cylinder and improving weld quality.

• Korean Journal of Materials Research
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• v.22 no.3
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• pp.123-129
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• 2012

The microstructures and mechanical properties of friction stir welded lap joints of Inconel 600 and SS 400 were evaluated; friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. Electron back-scattering diffraction and transmission electron microscopy were introduced to analyze the grain boundary characteristics and the precipitates, respectively. Application of friction stir welding was notably effective at reducing the grain size of the stir zone. As a result, the reduced average grain size of Inconel 600 ranged from $20{\mu}m$ in the base material to $8.5{\mu}m$ in the stir zone. The joint interface between Inconel 600 and SS 400 showed a sound weld without voids and cracks, and MC carbides with a size of around 50 nm were partially formed at the Inconel 600 area of lap joint interface. However, the intermetallic compounds that lead to mechanical property degradation of the welds were not formed at the joint interface. Also, a hook, along the Inconel 600 alloy from SS 400, was formed at the advancing side, which directly brought about an increase in the peel strength. In this study, we systematically discussed the evolution of microstructures and mechanical properties of the friction stir lap joint between Inconel 600 and SS 400.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.6
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• pp.40-47
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• 2004

The influence of heat input on fracture toughness was investigated in SAW weldments, which were prepared at two different welding conditions in API 2W Gr.50 and EN10225 5420. By examining the fracture initiation point, refined areas(ICHAZ and SCHAZ) in weld metal was identified as local brittle zone, in which M-A constituents and coarsed grain size were observed. Impact values showed the most significant difference at root portion, and CTOD transition temperature was related with impact values obtained at root portion. Hardness values in refined area were less than columnar microstructure about 20 HV5.

• Earthquakes and Structures
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• v.19 no.5
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• pp.315-329
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• 2020

Through bolt connections in Concrete Filled Steel Tubes (CFSTs) has been proved to be good in terms of seismic performance and constructability. Stiffened extended end plate connection with full through type bolt helps to avoid field weld altogether, and hence to improve the quality of joints. An experimental study was conducted on the hysteretic performance of square interior beam-column connections using flat extended end plates with through bolt. The study focuses on the effect of the bond between the tie rod and the core concrete on the cyclic performance of the joint. The study also quantifies how much the interior joint is getting strengthened due to the confinement effect induced by bi-directional bolting, which is widely used in 3D moment resisting frames. For a better understanding of the mechanism and for the prediction of shear capacity of the panel zone, a mathematical model was generated. The various parameters included in the model are the influence of axial load, amount of prestress induced by bolt tightening, anchorage, and the concrete strut action. The study investigates the strength, stiffness, ductility, and energy dissipation characteristics. The results indicate that the seismic resistance is at par with American Institute of Steel Construction (AISC) seismic recommendations. The bidirectional bolting and bond effect have got remarkable influence on the performance of joints.

• Steel and Composite Structures
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• v.26 no.1
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• pp.67-78
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• 2018

The application of rib stiffeners is common on steel connections, with regard to the stiffened angle connection, experimental results about the influence of stiffeners under monotonic and cyclic loading are very limited. Consequently, this paper presents the experimental investigation on four types angle connections with or without stiffener under static loading and another four type stiffened angle connections subjected to cyclic loading. The static experimental result showed that the rib stiffener weld in tension zone of the connection greatly enhanced its initial rotational stiffness and flexural strength. While a stiffener was applied to the compression zone of the connection, it had not obvious influences on the initial rotational stiffness, but increased its flexural strength. The moment-rotation curves, skeleton curves, ductility, energy dissipation and rigidity were evaluated under cyclic loading. Stiffened top-and-seat angle connections behaved as semi-rigid and partial strength, and rotation of all stiffened angle connections exceeded 0.04rad. The failure modes between monotonic and cyclic loading test were completely different and indicated certain robustness.

• Journal of Welding and Joining
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• v.2 no.1
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• pp.41-48
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• 1984

Recrystallization technique was applied to analyze plastic strain at the notch tip of coarse grain HAZ in mild steel (SB 41) and high strength steel (SA 588). The notch tip of specimen was deformed by three point bending. Accumulated displacement (Crack Opening Displacement ${delta}t$) by the monotonic and cyclic loading under room temperature and hot strain embrittlement temperature ($250^{\circ}C$) was 0~1.0mm. Recrystallization heat treatment conditions were $650^{circ}C{ imes}3hr$ for SB 41 and $700^{circ}C{ imes}3hr$ for SA 588. The experimental results obtained were as follows ; 1) Distribution of the effective plastic strain at plastic zone was appeared by the function of crack opening displacement, and plastic zone or the effective plastic strain increased with crack opening displacement. 2) Plastic strain at notch tip of HAZ due to accumulated hot strain calculated as follows. .epsilon. over bar $_{p}$ = .epsilon. over bar $_{cr}$ (x/ $R_{x}$ ) $^{m}$ (m=0.25) 3) Work hardending ratio of notch tip for hot strain was linearly increased with .epsilon. over bar $_{max}$ and dependent upon the material types.s.

• Journal of Welding and Joining
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• v.30 no.5
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• pp.40-45
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• 2012

Nowadays in Republic of Korea, whole amount of the thermite welding powder for rail joinning is dependent on import. However the demand of the thermite welding powder would be enlarge because some constructing high-speed train and city metro projects are currently in progress. In addition this is the main reason why we should develop the thermite welding powder, domestically. This study is focused on utilizing the recyclable materials like Al powders from cans and iron oxide scales from wire rods as the main components of the thermite welding powder. By minimizing Al content in weld zone by controlling the mixing ratio of the Al powder in the thermite welding powder, the excessive dissolution of the Si and Mn components came from the Al powders could be controled. The tensile strength of welding zone in welded rail was 740 MPa, with that the developed thermite welding powder.

• Laser Solutions
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• v.4 no.3
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• pp.30-39
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• 2001

This work was tamed out to apply a laser welding technique in joining between a Zn coated low carbon steel plate(SECC) and a free cutting carbon steel shaft(SUM24L) with or without W coating. Experiments were carried out and analysed by applying the FD(factorial design)method to obtain the optimum Laser welding condition. Optical microscopy, SEM, TEM and XRD analyses were performed in order to observe the microstructures in the fusion zone and the HAZ. Mechanical properties of the welded specimens were examined by microhardness test, tensile test and twist test. There was no flawed Zn in the fusion zone by EDS analysis. This means that during the welding process, Zn gas could be eliminated by appropriate shielding gas flow rate and butt welding gap. Ni coating itself did not influence on the tensile strength and hardness. However, twist bending strength and the weld depth of the Ni-coated free cutting carbon steel were lower as compared with those of the uncoated free cutting carbon steel. It was attributed to a lower absorbance of laser beam to the shin Ni surface. According to the results of the factorial design tests, the twist bending strength of welded specimens was primarily affected by pulse width, laser power, frequency and speed.

• Journal of Welding and Joining
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• v.14 no.4
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• pp.89-98
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• 1996

This study was performed to establish the characteristics of the heat affected zones from view point of the repair weldability for a damaged CrMoV steam turbine rotor steel. Characterization of the heat affected zones of the weldment was conducted with respect to various of postweld heat treatment temperatures, $566^{\circ}C$, $621^{\circ}C$ and $677^{\circ}C$. The evaluations of the heat affected zones were carried out in terms of microstructural characterization, microhardness measurements, Charpy v-notch impact, tensile and stress-rupture tests. The results indicated that the effect of the postweld heat treatment at $677^{\circ}C$ exhibited the favorable microstructure and mechanical properties for the stability of the heat affected zones. While the heat affected zone of the weldment, produced without postweld heat treatment, displayed the inferior toughness and microstructure indicating localized carbide precipitations on the grain boundary. It was also indicated that the stability of the heat affected zones were deteriorated by the formation of the cavitation on the grain boundaries.