• Journal of the Microelectronics and Packaging Society
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• v.15 no.4
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• pp.51-57
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• 2008

In this paper, wetting and interfacial reaction properties for low Ag containing Sn-Ag-Cu Pb-free solder alloy, i.e., Sn-0.3Ag-0.7Cu were investigated and compared with those of Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu. Melting behavior and stress-strain curves of some Sn-xAg-xCu alloys were also measured using a differential scanning calorimeter(DSC) and a tensile test machine, respectively. In order to enhance insufficient wetting properties of Sn-0.3Ag-0.7Cu alloy, the improvement of wetting properties were analyzed by applying fluxes containing higher content of halide or indium adding of 0.2wt.% into the solder alloy. It was concluded that the small addition of indium is more effective for the improvement of wettability in low temperature range of $230{\sim}240^{\circ}C$ than applying flux containing higher content of halide.

• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.73-80
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• 2012

It is well known that a considerable amount of scatter is shown in experimental results relating to fatigue crack growth even under identical and constant amplitude cyclic loading conditions. Moreover, flux cored arc welding (FCAW) is a common method used to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the macro- and microscopic observations of the fatigue crack growth (FCG) behavior of the FCAWed API 2W Gr. 50 steel joints typically applied for offshore structures. In order to clearly understand the randomness of the fatigue crack growth behavior in the materials of three different zones, the weld metal (WM), heat affected zone (HAZ), and base metal (BM), experimental fatigue crack growth tests for each of five specimens were performed on ASTM standard compact tension (CT) specimens under constant amplitude cyclic loading. Special focus was placed on the fatigued fracture surfaces. As a result, a different behavior was observed at the macro-level, depending on the type of material property: BM, HAZ, or WM. The variability in the fatigue crack growth rate for WM was higher than that of BM and HAZ.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.61-68
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• 2016

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E91T1-B9C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, tempered martensite and lower bainite were formed in first layer of weld metal. The amount of tempered martensite was decreased and the amount of lower bainite was increased with increasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered Martensite and lower Bainite. Tensile strengths of dissimilar welds decreased with increasing heat inputs. Dissimilar welds seemed to have a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals showed that the corrosion rate increased with increasing heat inputs due to the increase of the amount of lower Bainite.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.65-73
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• 2011

Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.70-70
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• 2010

In the present study, to estimate the mechanical properties of 800 MPa grade weld metal, welding was carried out using 800 and 600 MPa grade flux cored arc welding (FCAW) consumable and characteristics of the weld metals were investigated. The chemical composition of weld metals was investigated by an optical emission spectroscopy (OES) method. The microstructure of weld metals was analyzed by optical microscopy (OM) and secondary electron microscopy (SEM). The compositions and sizes of inclusions which are the dominant factors for the nuclei of acicular ferrite were analyzed by an transmission electron microscopy (TEM). In addition, mechanical properties of the weld metals were evaluated through tensile tests and charpy impact tests. Mostly the acicular ferrite phase which has high strength and toughness was observed. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 73% acicular ferrite and 27% low temperature phase (bainite, martensite). Toughness was considerably decreased due to the increase of tensile strength (from 600 MPa to 800 MPa). The sizes of inclusions which were observed in both weld metal were $0.4{\sim}0.8\;{\mu}m$, it is effective size to form acicular ferrite.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.21-21
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• 2010

AISI 316L 용접금속의 크롬/니켈 당량비에 따른 시그마상의 영향을 알아보기 위하여 응고모드가 다른 3종류의 플럭스 코어드 와이어를 제작하였다. AISI 316L 시편에 FCAW 프로세스를 적용한 용접재를 $650^{\circ}C$, $750^{\circ}C$, $850^{\circ}C$, $950^{\circ}C$에서 각 각 1H, 5H, 24H, 72H동안 열처리하였다. 크롬/니켈 당량비가 높을수록 즉, 크롬의 함량이 높아질수록 $\delta$-페라이트 함량은 증가하였으며, $\delta$-페라이트는 고온에서 시그마상으로 변태되었다. $\delta$-페라이트는 $650^{\circ}C$에서 가장 느리게 분해되었으며 $850^{\circ}C$에서 가장 활발히 분해되었다. 용접부의 특성상 크롬과 니켈 등의 합금원소에 의하여 응고온도범위가 넓어져 $950^{\circ}C$에서도 시그마상이 석출되었으며, 5시간 이상 유지 시 구형으로 존재하였다. 충격시험 시 시그마상에 의해 취약해진 inter-dendrite 를 따라 파면이 형성되었으며, $-100^{\circ}C$이하의 극저온에서는 시그마상의 양과 무관하게 충격흡수에너지는 0에 가까워졌다. 하지만 3%미만의 $\delta$-페라이트를 함유하는 AF모드에서 발생한 DDC와 미량의 시그마상은 충격흡수에너지에 결정적인 영향을 미치지 않았다.

• Journal of Welding and Joining
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• v.28 no.3
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• pp.79-85
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• 2010

Hardfacing is one of the frequently applying method to increase surface hardness in hot forging die. Recently, hardfacing receives great attention due to it's repair availability and low cost. In hot forging die, crack resistance and thermal shock resistance have been considered as major properties, However there are few studies for the assessment of these properties. So, it is necessary to establish the assessment method for crack resistance and thermal shock resistance in hardfacing for hot forging die. In this study, flux cored arc welding was applied to make hardfacing welds. Three point bending test was carried out to assess hardfacing weld's crack resistance, and high temperature bending test using salt bath was developed for thermal shock resistance. Consequently, it was possible to assess crack resistance and thermal shock resistance of hardfacing welds for hot forging die quantitatively.

• Journal of Welding and Joining
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• v.35 no.3
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• pp.68-74
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• 2017

Characteristics of dissimilar metal welds between alloy steel ASTM A387 Gr. 91 and carbon steel ASTM A516 Gr.70 made with Flux cored arc welding(FCAW) have been evaluated in terms of microstructure, mechanical strength, chemical analysis by EDS as well as corrosion test. Three heat inputs of 15.0, 22.5, 30.0kJ/cm were employed to make joints of dissimilar metals with E71T-1C wire. Post-weld heat treatment was carried out at $750^{\circ}C$ for 2.5 h. Based on microstructural examination, Intragranular polygonal ferrite and grainboundary ferrite were formed only in first layer of weld metal. Another layers consisted of acicular ferrite and $Widmannst{\ddot{a}}tten$ ferrite. The amount of acicular ferrite was increased with decreasing heat input and layer. Heat affected zone of alloy steel showed the highest hardness due to the formation of tempered martensite and lower bainite. Lower and upper bainite were formed in heat affected zone of carbon steel. Tensile strengths of dissimilar metal welds decreased with increasing heat inputs. Dissimilar metal welds showed a good hot cracking resistance due to the low HCS index below 4. The salt spray test of dissimilar metals welds showed that the weight loss rate by corrosion below 170 hours was decreased with increasing heat inputs due to the increase of the amount of acicular ferrite.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.5933-5938
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• 2014

In this study, the effect of varying the mixture gas during FCA welding was studied for an Atos 60 test piece. To examine the characteristics of welding, the weldability of the material was checked before welding and online monitoring was performed to examine the mechanical properties after welding. The mixture Ar 80% + $CO_2$ 20% at low speed gave very elegant beads with very little spatter. 100% $CO_2$ gave rise to high spatter generation. For Ar 80% + $CO_2$ 20%, the low current region due to the normal short circuits created spatter, which was more than double for 100% $CO_2$. This peak distribution occurred due to the instability of the arc. The tensile test result for Ar 80% + $CO_2$ 20%, Ar 90%+ $CO_2$ 10% and $CO_2$ 100% at 511MPa, 507MPa, and 469MPa showed that the yield strength was improved by 8.1 and 8.9% for 80%+ $CO_2$ 20% and Ar 90%+ $CO_2$ 10%, respectively, compared to 100% $CO_2$. The tensile test result at 622MPa, 609MPa, and 581MPa showed that the yield strength was improved by 7.0% for both the mixture gas compared to 100% $CO_2$.

• Journal of Welding and Joining
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• v.10 no.4
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• pp.33-38
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• 1992

우리나라의 용접재료는 산업구조 및 그 발전 속도와 용접재료 제조업체의 기술 및 연구개발 수 준과 더불어 발전하여 왔다. 용접이 본격적으로 이용되기 시작하여 약 40년이 경과되고 용접재료 제조업체가 현대적인 제조설비를 도입하여 체계적으로 용접재료를 생산하고 개발하기 시작하여 30년이 경과되었다. 용접재료가 양 및 질에 있어서 비약적인 발전으로 이룩할 수 있는 계기가 마련된 것은 제1차 경제개발5개년 계획의 수립과 추진으로 다양한 종류의 수요창출과 높은 수 준의 품질이 요구되면서 부터다. 1970년대에 조선공업등 강구조물을 주류로 하는 양적 수요 증 가의 기반이 조성되고 화학 프랜트, 원자력 발전등의 건설이 주축이 되어 관련 주변 기술이 발 전하므로서 용접재료의 품질보증 SYSTEM확보등 기술 발전의 획기적인 전기를 맞이하게 되 었다. 용접재료용 고품질의 원재료 및 일부 부재료가 국산화되고 용접재료 제조업체의 연구소 설립과 기술 및 연구개발 인력 확보, 그리고 대학 및 관공 연구소에서의 용접재료 관련 연구의 활성화에 힘입어 용접재료 기술은 국내 자체 기술로서 정착하게 되었다. 1941년 용접봉의 FLUX를 수제로 피복한 피복아크 용접봉(일미나이트계와 고산화철계의 혼합계통) 년산 17톤을 생산하기 시작하여 현재 년 12만톤을 생산하는 장족의 발전을 하게 되었다. 특히 1985년부터 1991년까지 용접재료의 고도성장은 종례가 없었던 기간이지만 1992년부터는 수요가 진정되고 경제의 불황이 예고되면서 저성장 추세는 상당기간 지속될 전망이다.