• 한국레이저가공학회지
• /
• 제10권4호
• /
• pp.13-17
• /
• 2007

Electron beam weldability was investigated for 1mm thick cold rolled sheets of commercially pure grade titanium and Ti-6Al-4V alloy. Accelerating voltage of 40kV, beam current of 6mA, and weld speed of 0.8m/min was used and focal position of focused electron beam was just on the surface of workpiece. Microstructure of weld metal, the heat affected zone and base metal was observed using optical microscope. Vickers hardness was measured across the welds and the transverse tensile test was carried out. Hydroformability test was also carried out for the butt welded coupons of commercially pure grade titanium. For the electron beam welded C P Ti, the average grain size was equiaxed $\alpha(15{\sim}25{\mu}m)$ for base metal, coarse equiaxed $\alpha(80{\sim}200{\mu}m)$ for weld metal and annealed and enlarged grain($40{\sim}120{\mu}m$) for the HAZ. The vickers hardness of C P Ti was $180{\sim}200Hv$ for base metal, and $160{\sim}180Hv$ for the weld metal and the HAZ. For the electron beam welded Ti-6Al-4V alloy, the vickers hardness was 360Hv for the base metal, abd $400{\sim}425Hv$ for the weld metal and the HAZ. All the failure occurred at the base metal, when the transverse weld tensile test was carried out for both electron beam welded C P Ti and Ti-6Al-4V alloy. The formability of electron beam welded C P Ti was decreased compared with that of C P Ti base alloy.

• Journal of Welding and Joining
• /
• 제26권5호
• /
• pp.79-89
• /
• 2008

With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel ($R_{a}=1.70\;{\mu}m$) was higher than that for T-L steel ($R_{a}=1.33\;{\mu}m$), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.

• Journal of Welding and Joining
• /
• 제34권6호
• /
• pp.42-46
• /
• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 1997년도 특별강연 및 추계학술발표 개요집
• /
• pp.147-150
• /
• 1997

The characteristics of underwater welding of SWS490 steel were investigated. The bead-on-plate type welding with one or three pass using ilmenite and water-proofed type electrodes was performed by varying welding currents and the sizes of electrodes used. The amounts of hydrogen absorbed inter the weld metal were measured according to the JIS Z 3118 specification and the results were interpreted in terms of the cold cracking behaviours of the welded steel. The microstructural changes as well as the microhardness distribution after underwater welding were also investigated using Vickers microhardness tester and S.E.M (scanning electron microscopy) and O.M (optical microscopy). The results indicated that the cold cracking could be avoided by three pass welding under low current with an electrode with a small diameter.

• 한국전기전자재료학회논문지
• /
• 제26권5호
• /
• pp.415-420
• /
• 2013

The new recycling technology for aged Aluminum wires in overhead conductor have been carried out. We are attempting to develop remanufacturing method for them for more effective way of recycling in stead of its conventional remelting process. The weld of aged aluminum wires play a vital role in remanufacture process. The paper investigates the mechanical properties during cold welding process of aged Aluminum wire. The tensile tests and microscopic analysis results are discussed to underscore the hardening features of welded aluminum wire. Various graphs are presented accompanied by discussion about their relevance on the process.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
• /
• pp.273-275
• /
• 2005

Variation of hardness and corrosion potential of welding zone was investigated when cold arc welding of cast iron was carried out with a parameter of Ni electrode. Hardness of HAZ was the highest compared to other welding zone. And corrosion potential of HAZ was also more negative value than other welding zone. However there was not a proportional relation between hardness and corrosion potential. Local corrosion of HAZ was clearly appeared than other welding zone by small anode and large cathode in seal water solution.

• 수산해양기술연구
• /
• 제23권2호
• /
• pp.61-65
• /
• 1987

선박용 강판(KR Grad A-3)과 라임티타니아계 피복 아아크 용접봉(E4303)을 이용하여 대기중용접 및 습식 수중 용접하여 TRC 임계응력치, 열 사이클, 경도분포, 확산성 수소량, micro조직 등을 실험적으로 조사한 결과를 요약하면 다음과 같다. 1. TRC 시험에 의한 초기 임계응력치 $\sigma$ 하(cr) 은 대기중 용접 및 수중용접의 어느 쪽에서도 Y groove 형상의 경우가 각각 71kg/mm 상(2), 51kg/mm 상(2) 로서 가장 높고, 반대로 45$^{\circ}$r 형 groove의 경우가 각각 52kg/mm 상(2), 41kg/mm 상(2)로서 최저이며, 수중용접부의 냉파괴 감수성이 대기중용접보다 높다. 2. 용접부의 경도는 조립 열영향부에서 가장 높고 대기중용접에서 약 H 하(k) 365, 수중용접에서는 급격한 냉각속도 때문에 약 H 상(k) 670으로 높게 되어 후자의 경우 파괴 감수성의 증가에 의한 낮은 임계응력치를 갖게 된다. 3. 48시간 동안의 확산성 수소량은 대기중용접에서 약 18cc/100g-weld-metal, 수중용접의 경우 약 48cc/100g-weld-metal로서 수중용접의 경우가 약 3배 정도 더 침입하고 있으므로 이의 방지책이 필요하다.

• 수산해양기술연구
• /
• 제23권2호
• /
• pp.15-15
• /
• 1987

선박용 강판(KR Grad A-3)과 라임티타니아계 피복 아아크 용접봉(E4303)을 이용하여 대기중용접 및 습식 수중 용접하여 TRC 임계응력치, 열 사이클, 경도분포, 확산성 수소량, micro조직 등을 실험적으로 조사한 결과를 요약하면 다음과 같다. 1. TRC 시험에 의한 초기 임계응력치 σ 하(cr) 은 대기중 용접 및 수중용접의 어느 쪽에서도 Y groove 형상의 경우가 각각 71kg/mm 상(2), 51kg/mm 상(2) 로서 가장 높고, 반대로 45°r 형 groove의 경우가 각각 52kg/mm 상(2), 41kg/mm 상(2)로서 최저이며, 수중용접부의 냉파괴 감수성이 대기중용접보다 높다. 2. 용접부의 경도는 조립 열영향부에서 가장 높고 대기중용접에서 약 H 하(k) 365, 수중용접에서는 급격한 냉각속도 때문에 약 H 상(k) 670으로 높게 되어 후자의 경우 파괴 감수성의 증가에 의한 낮은 임계응력치를 갖게 된다. 3. 48시간 동안의 확산성 수소량은 대기중용접에서 약 18cc/100g-weld-metal, 수중용접의 경우 약 48cc/100g-weld-metal로서 수중용접의 경우가 약 3배 정도 더 침입하고 있으므로 이의 방지책이 필요하다.

• 한국강구조학회 논문집
• /
• 제16권3호통권70호
• /
• pp.315-324
• /
• 2004

본 논문은 지관에 압축력을 받는 냉간성형 각형강관 T형 용접접합부의항복선 해석에 관한 연구이다. 기존 연구 중 냉간성형 정방형 각형강관 T형 용접 접합부만을 포함하는 실험결과와 Kato, Packer, Zhao, CIDECT 및 본 연구진들의 제안식을 비교하였다. 제안된 항복선 모델의 적용한계치를 제안하기 위하여, 항복선 해석에 기초하여 이전 논문에서 제안된 항복선모델을 재검토하였다. 제안된 항복선 모델은 냉간성형 각형강관 곡률부와 용접크기를 고려한다. 마지막으로, 실험상의 실체 파괴모드와 해석상의 비교결과를 참조하여, 항복선 해석의 적용범위를 ${\beta}^{\prime}{\leq}0.8$로 제안하였다. 여기서, ${\beta}^{\prime}=0.8$, ${\beta}^{\prime}=b_1^{\prime}/b_0^{\prime}$, $b_1{^{\prime}}=b_1+t_0$, $b_0{^{\prime}}=b_0-t_0$.

• 대한건축학회논문집:구조계
• /
• 제35권4호
• /
• pp.157-165
• /
• 2019

Recently, lean duplex stainless steel, STS329FLD with less nickel (reduced to 0.5~1.5%) has been developed as a substitute of austenitic stainless steel (8%~10.5% nickel in STS304) and included in Korean standards (KS). This paper investigates the block shear behavior of cold-formed duplex stainless steel (STS329FLD, nominal plate thickness of 1.5mm) fillet-welded connection with base metal fracture. Main variables are weld lengths in the longitudinal and the transverse directions of applied force ranged from 20mm to 50mm. As a result, specimens failed by typical block shear facture (the combination of gross section tensile fracture and shear fracture or shear yielding) and ultimate strength of the specimens got higher with the increase of weld length. Block shear fracture strengths predicted by current design specifications (KBC2016/AISC2016 and EC3) and existing proposed equations for welded connections by Topkaya, Oosterhof & Driver and Lee et al. were compared with test strengths. KBC2016/AISC2016 and EC3 design specifications underestimated block shear strength of STS329FLD welded connections by on average 24%, 29%, respectively and Oosterhof & Driver, Topkaya and Lee et al's equations overestimated the ultimate strength of the welded connection by the range of 3% to 44%.