• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.330-332
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• 2004

1970년대 구조용강의 경량화를 위해 합금 원소를 많이 첨가해 미세조직을 강화시킨 고강도강(high- yield)을 많이 사용했다. 하지만 탄소량의 증가로 저수소계 용접봉을 사용하고 예열과 후열처리 때문에 강재의 용접성과 생산성이 떨어졌다. (중략)

• Journal of Welding and Joining
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• 제14권5호
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• pp.134-144
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• 1996

A study was performed to investigate the properties of base metal and weldment for two HSLA steels and one HY-100 steel. Tensile, yield strength and elongation of HSLA-A steel were superior to those of HY-100 steel and yield ratios in HSLA-A and HSLA-B steels were higher than HY-100 steel owing to the precipitation of $\varepsilon$-Cu phase. The impact energy of HSLA-A steel was greater at all aging temperatures than that of HY-100 steel. HSLA-A and HY-100 steels had low impact transition temperature of about -l$25^{\circ}C$ and high upper shelf energy, The peak hardness of weldment in HSLA-A, HSLA-B and HY-100 steels were Hv 299, Hv 275 and Hv 441, respectively. The hardenability of HY-100 steel was largest due to the higher amount of carbon. The y-groove test showed that HSLA steels had superior resistance to cold cracking. Toughness of weld joint at the F. L. and F. L. ＋1mm in HSLA-A was almost the same as HY-100, but those at F. L.＋3mm and F. L.＋5mm was greater in HSLA-A steel.

• Journal of Advanced Marine Engineering and Technology
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• 제11권3호
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• pp.45-52
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• 1987

Generally the factors affected largely by the cold cracking sensitivity of the weld are the quantity of the diffusible hydrogen, the brittleness and hardness of the bond area and the tensile restraint stress. These factors have relation each other, and if we can reduce one of these factors, it becomes instrumental to the root cracks prevention of weld. This study deals with the gravity type-underwater-welding of KR Grade A-3 marine steel plate using E4303 welding electrode in order to compare wet-underwater-welding with in-air- welding, resulting in obtaining the tensile restraint characteristics, the hardness distribution, the quantity of diffusible hydrogen and the macro- and micro-crack properties in both underwater and in-air welds. The main results obtained are as follows: 1) The quantity of diffusible hydrogen measured for 48 hours is about 18cc/100g-weld-metal for the in-air-weld of one pass and about 48cc/100g-weld-metal for the underwater-weld of one pass which is about 3 times penetration of diffusible hydrogen compairing with the case of the in-air-weld. However, it was experimentally confirmed that, by the multi-pass welding of 2 to 5 passes, the diffusible hydrogen in the underwater weld metal can be reduced as much as 27 to 49%. 2) The hardness of the weld metal indicates the highest value in the heat affected zones of underwater weld for more rapid cooling rate, resulting in the higher sensitivity of cold cracking. So, it is desirable to soften the higher hardness in the HAZ by tempering effect such as the multi-pass welding in the underwater welding. 3) At the bond vicinity of the underwater weld HAZ, micro cracks were found as resulted by both more rapid cooling rate and more diffusible hydrogen and also by the stress corrosion cracking under the tensile restraint stress in the underwater. But this could be prevented by the tempering effect of the following weld bead such as the multi-pass welding.

• 한국도로학회논문집
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• 제4권3호
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• pp.35-42
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• 2002

본 연구는 동절기에 많이 발생하는 포장의 저온균열에 대한 폴리머 개질 아스팔트 혼합물의 저항 특성을 알아보기 위하여 수행하였다. 저온에서의 간접인장강도를 측정 분석한 결과 혼합물들이 $-10^{\circ}C의 저온 대에서 최대 인장강도를 나타냈다. 최대 인장강도를 보이는 온도 이하에서는 시차열 응력이 인장강도 이상으로 발생하여 내부에 손상이 발생하기 때문에 나타나는 인장강도 저하현상을 ITS 시험으로 증명하여 보였다. 저온의 시험 결과는 폴리머 개질 아스팔트 혼합물이 일반 아스팔트 혼합물에 비하여 보다 낮은 온도에서까지도 강도가 높게 나타나 폴리머 개질에 따른 효과를 보였으며, 바인더가 저온균열에 대한 저항에 큰 영향을 미치는 것으로 나타났다. 따라서 추운 지역에서는 저온균열을 예방하기 위하여 폴리머 개질 아스팔트의 사용이 추천된다.

• 터널과지하공간
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• 제7권1호
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• pp.58-64
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• 1997

A pilot plant of underground cold storage for food has been excavated as a R&D program. For the stability assessment of underground cold storage opeinengs in shallow jointed rocks, three kinds of stability problems were analyzed by numerical methods. For the analysis of unstability by rock block movements, DEM was used considering the statistical distribution of rock joints. Concerning thermally induced cracking, FDM was used with thermomechanical stress analysis. Finally, in order to evaluate the joint failure during the thawing process, BE algorithm was applied. Numerical examples applied for the pilot plant show that the possibility of unstable failure of opeings exists but can be avoided with proper rock reinforcements provided.

• 소성∙가공
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• 제8권2호
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• pp.160-168
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• 1999

This paper is concerned with the process sequence design of longneck flange forming by using cold extrusion with thick hollow pipe. The conventional hot forming process to produce a longneck flange is investigated by thermo-viscoplastic finite element method to observe the metal flow in detail and evaluate design requirements. Based on the results of simulation of the current hot forming process, design strategy for improving the process sequence are developed using the thick hollow pipe. The main goal is to obtain an appropriate improved process sequence which can produce the required product most economically without tensile cracking, workpiece buckling, and overloading of tools. Newly process condition such as semi-die angle, reductio ratio of cross-sectional area of axisymmetrical extrusion process. The final designed process can provide very useful guidelines to other flange forming industries.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.841-843
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• 2006

In high-performance cold work applications, tool failure depends on the predominating loading conditions. Typical failure mechanisms are a combination of abrasive wear, adhesive wear, plastic deformation, cracking and edge crumbling. In this paper we demonstrate how the microstructure of tool steels can be positively influenced by modifying the alloying system and the production route to meet the demands of the different loading situations which occur during operation. The investigation was focused on ductility, fatigue strength and wear resistance. Theoretical considerations were confirmed by practical tests.

• International Journal of Railway
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• 제3권1호
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• pp.1-6
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• 2010

The steel plate-girder bridges with concrete gravity piers have possibilities of overturning by lateral inertial force which can be reproduced by sudden earthquake attack. This paper explores an overturning mechanism of existing concrete gravity pier onto the sandy soil in the event of lateral push-over load by in-situ experimental observation. The in-situ push-over experiment for pier with earth anchors between spread footing and rock beds exhibits a reasonable enhancement of ductility against overturning. In unanchored system, a flexural crack at cold joint of concrete pier is not developed because of the over-turning of the pier. This leads a global instability (rotation) of pier-footing system with relatively low stresses in pier itself. While a lateral load is persistently increased in anchored system, the successive flexural cracking failure at cold joint is observed even after the local shear failure of soil due to redistribution of stress equilibrium between soil and pier structure as long as a tensile action of anchor cable is active.

• Journal of Welding and Joining
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• 제16권4호
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• pp.55-62
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• 1998

While excellent joint quality has been obtained using dry chamber underwater welding methods, the size limitations imposed by this process restrict its use for underwater construction work. The wet underwater shielded metal-arc welding eliminates this restriction but suffers from poor weld properties by the 1-pass bead-on-plate welding due to the excessive diffusible hydrogen. On the other hand, in the wet underwater welding, it is well known that the quantity of diffusible hydrogen in multi-pass welded parts reduce to less than that in 1-pass welded parts. Therefore, in this paper, welding experiments are made the 3-pass bead-on-plate welds by using TMCP and normalized steel plates and E4301 and cellulose coated electrode. After that, The amounts of the hydrogen absorbed into the 3-pass welded area were measured according to the JIS Z 3118 specification. The microstructural changes as well as the microhardness distribution after the underwater 3-pass welding were also investigated using Vickers microhardness tester and S.E.M and O.M. The results indicated that the quantity of diffusible hydrogen in 3-pass welded areas was reduced little less than a half of one of that in 1-pass welded areas at the specific welding condition. As a result, the cold cracking of 3-pass welded areas decreased by reduced effect of diffusible hydrogen. In the underwater 3-pass welding, the micrography of cold cracking fracture surface showed mainly the cleavage of hydrogen embrittlement.

• 대한금속재료학회지
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• 제48권5호
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• pp.377-386
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• 2010

An investigation was conducted into the effects of $\kappa$-carbides on the cracking phenomenon, which often occurred in cold-rolled light-weight steel plates. Three kinds of steels were fabricated by varying the C content, and their microstructures and tensile properties were investigated. In the two steels that contained a high carbon content, the band structures of ferrites and $\kappa$-carbides that were severely elongated along the rolling direction were well developed, whereas continuous arrays of $\kappa$-carbides were formed in the steel that contained a low carbon content. Detailed microstructural analyses of the deformed region beneath the tensile fracture surface showed that the cracks initiated at arrays of $\kappa$-carbides or $\kappa$-carbides formed interfaces between the band structures, which initiated cleavage fractures in the ferrite bands, while the bands populated with a number of $\kappa$-carbides did not play an important role in propagating the cracks. Thus, the minimization of interfacial $\kappa$-carbides or $\kappa$-carbide arrays by increasing the carbon content was essential for preventing cracking from occurring during cold rolling.