• Journal of Welding and Joining
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• 제25권4호
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• pp.65-71
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• 2007

Laser weldability of the aluminized steel for the full penetration welding will be described in this paper. We focused on the effect of Al coating conditions on weld strength. For these objectives, aluminized steel sheets that have various thickness and coating weight were prepared for laser welding. And then, tensile-shear and hardness test were carried out. At the same time, Al contents in weld after laser welding were analyzed and their correlations with mechanical properties were investigated. Besides, as removing partially coating layer, weldability has been investigated according to the position of coating layer. As a result of this study, tensile-shear strength was decreased with increasing Al contents in weld, and Al of coating layer caused grain growth.

• 한국주조공학회지
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• 제30권2호
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• pp.66-75
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• 2010

The effects of alloying elements on the mechanical properties of normalized and quenched 3.60wt%C-2.60wt%C ductile cast iron poured into shell stack mold were investigated. The strength and hardness of as-cast specimen were increased and the elongation of it was decreased with the additions of Mn, Cu and Sn. The strength and hardness were increased with the addition of 0.40wt%Mo and then rather decreased with the increased addition of 0.80wt%. The strength and hardness were increased with normalizing treatment and the strengths of normalized specimens were increased slightly with the addition of alloying elements except Mo. Meanwhile the yield strength of the normalized specimen was increased slightly with the addition of Mo, the tensile strength was not changed much. Meanwhile the hardness and strength of the quenched specimen were slightly increased with the addition of Mn, those were almost not changed with the amount added. The tensile strength of the quenched specimen with larger diameter, when the Cu had been added, and the tensile and yield strengths of them, when Mo had been added, were increased with the addition of alloying element. On the other hand, those were not changed with the amount added. For the case of specimen with smaller diameter, there were no effects of these two elements. When Sn had been added, the strength of hardened specimen with larger diameter was slightly increased with the amount added. However, that with smaller diameter was rather decreased with it. The effect of specimen diameter on the strength of quenched specimen with the addition of Cu, Mo and Sn was reduced.

• 한국공작기계학회논문집
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• 제15권1호
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• pp.63-69
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• 2006

This study deals with the friction welding of A2024- T6 to A6061- T6; The friction time was variable conditions under the conditions of spindle revolution of 2000rpm, friction pressure of 50MPa, upset pressure of 100MPa, and upset time of 5.0seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests were studied, of friction weld, and so the results were as follows. 1. When the friction time was 1.5seconds under the conditions, the maximum tensile strength of the friction weld happened to be 292MPa, which is $94.2\%$ of the base material's tensile strength(310MPa). At the same condition, the maximum shear strength was 2l2MPa, which is equivalent to $103\%$ of the base material's shear strength (205MPa). 2. At the same condition, the maximum vickers hardness was Hv 146 at A2024- T6 nearby weld interface, which is higher Hv3 than condition of the friction time 0.5seconds, and the maximum vickers hardness was Hvl20 from weld interface of A6061-T6, which is higher Hv28 then base material's. 3. The results of microstructure analysis show that the structures of two base materials have fractionized and rearranged along a column due to heating and axial force during friction, which has affected in raising hardness and tensile strength.

• 한국레이저가공학회지
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• 제10권3호
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• pp.25-32
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• 2007

The effect of welding speed on the weldability, microstructures, hardness, tensile property of Nd:YAG laser welding joint in 600MPa grade precipitation hardening high strength steel was investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5kW. Porosity in the joints occurred at 1.8m/min, but were not observed over the welding speed of 2.1m/min. However, spatter occurred over the welding speed of 6.6m/min. The hardness was the highest at heat affected zone(HAZ) near fusion zone(FZ), and was decreased on approaching to the base metal. The maximum hardness increased with increasing welding speed. The microstructure of FZ was composed of coarse grain boundary ferrite and bainite(upper) but the HAZ near the FZ contained bainite(Lower) and fine ferrite at a low welding speed. With increasing welding speed, ferrite at the FZ and the HAZ became finely and upper binite changed to lower bainite. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal, and the tensile strength and the yield strength of joints was equal to those of raw material. Elongation was found to be lower than that of the raw material.

• Nuclear Engineering and Technology
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• 제31권6호
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• pp.561-571
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• 1999

Microstructure and mechanical properties of five Cr-Mo steels for nuclear industry applications have been investigated. Transmission electron microscopy, energy dispersive spectrometer, differential scanning calorimeter, hardness, tensile, and impact test were used to evaluate the Cr and W effect on the microstructure and mechanical properties. Microstructures of Cr-Mo steels after tempering are classified into three types : bainitic 2.25Cr-lMo steel, martensitic Mod.9Cr-lMo, HT9M, and HT9W steels, and dual phase HT9 steel. The majority of the precipitates were found to be M$_{23}$C$_{6}$ carbides. As minor phases, fine needle-like V(C,N), spherical NbC, fine needle-like Cr-rich Cr$_2$N, and Cr-rich M$_{7}$C$_3$were also found. Addition of 2wt.% W in Cr-Mo steels retarded the formation of subgrain and dissolution of Cr$_2$N precipitates. Hardness and ultimate tensile strength increased with increasing Cr content. Though Cr content of HT9W steel was lower than that of HT9 steel, the hardness of HT9W was higher due to the higher W content. W added HT9W steel had the highest ultimate tensile strength above $600^{\circ}C$. But impact toughness of W added steel (HT9W) and high Cr steel (HT9) was low.w.w.

• 소성∙가공
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• 제8권3호
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• pp.233-233
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• 1999

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

• 열처리공학회지
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• 제21권4호
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• pp.205-212
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• 2008

Characteristics of microstructures, mechanical properties and formability of two Al-20Si-5Fe-2Ni alloys produced by gas atomizing (P/M) and spray forming (S/F) respectively were compared at temperatures up to $560^{\circ}C$. Room temperature hardness values and tensile strengths of both alloys were increased in accordance with temperature after heat treatment above $300^{\circ}C$. The highest values of hardness and tensile strength of both alloys were obtained at $490^{\circ}C$. It was interpreted that increase in hardness and tensile strength according to heating temperature between $300{\sim}490^{\circ}C$ was mainly related to increase in internal stress between Al matrix and reprecipitated particles. S/F alloys showed better formability and wear property than P/M alloys due to the homogenity of microstructures above $300^{\circ}C$.

• 한국재료학회지
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• 제25권9호
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• pp.468-474
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• 2015

Evaluations of the microstructure and mechanical properties of age hardenable Cu-2.0wt%Be alloy are performed in order to determine whether it can be used as a welding electrode for projection welding. The microstructure examinations, hardness measurements, and tensile tests of selective aging conditions are conducted. The results indicate that the aging treatment with the fine-grained microstructure exhibits better hardness and high tensile properties than those of the coarse-grained microstructure. The highest hardness value and high tensile strength are obtained from the aged condition of $300^{\circ}C$ for 360 min due to the presence of the metastable ${\dot{\gamma}}$ precipitates on the grain boundaries. The values of the highest hardness and tensile strength are measured as 374 Hv and 1236.2 MPa, respectively. The metastable ${\dot{\gamma}}$ precipitates are transferred to the equilibrium ${\gamma}$ precipitates due to the over-aged treatment. The presence of the ${\gamma}$ precipitates appears as nodule-like precipitates decorated around the grain boundaries. The welding electrode with the best aging treated condition exhibits better welding performance for electrodes than those of electrodes used previously.

• 한국재료학회지
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• 제27권9호
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• pp.477-483
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• 2017

This present study deals with the microstructure and tensile properties of 600 MPa-grade high strength and seismic resistant reinforcing steels. The high strength reinforcing steel (SD 600) was fabricated by Tempcore processing, while the seismic resistant reinforcing steel (SD 600S) was air-cooled after hot-rolling treatment. The microstructure analysis results showed that the SD 600 steel specimen consisted of a tempered martensite and ferrite-pearlite structure after Tempcore processing, while the SD 600S steel specimen had a fully ferrite-pearlite structure. The room-temperature tensile test results indicate that, because of the enhanced solid solution and precipitation strengthening caused by relatively higher contents of C, Mn, Si and V in the SD 600S steel specimen, this specimen, with fully ferrite-pearlite structure, had yield and tensile strengths higher than those of the SD 600 specimen. On the other hand, the hardness of the SD 600 and SD 600S steel specimens changed in different ways according to location, dependent on the microstructure, ferrite grain size, and volume fraction.

• 한국강구조학회 논문집
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• 제26권6호
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• pp.617-626
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• 2014

본 연구에서는 드릴천공 대비 산소토치로 볼트홀을 천공한 강재의 인장강도 평가와 지압이음강도 평가를 위한 실험 연구를 수행하였다. 강재의 인장강도 평가를 위해 앵글과 H-형강으로부터 각각 두께 10mm와 20mm의 드릴 및 산소천공 시험편을 제작하였다. 지압이음강도의 평가를 위해서는 모재와 첨접판을 드릴천공한 강재와 산소천공한 강재를 조합하여 시험체들을 제작하고 볼트이음강도 평가 실험을 수행하였다. 한편, 산소천공 시 열영향으로 인한 볼트홀 주위의 강재 성질의 변화를 평가하기 위해 비커스 경도를 측정하고 그 결과를 제시하였다. 또한, 산소천공 시 볼트홀 주위의 경도 증가에 따른 볼트이음강도의 평가를 위해 수치해석을 수행하였다.