• Journal of Welding and Joining
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• 제11권4호
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• pp.79-90
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• 1993

Shielded metal arc welding, one-ploe and two-pole submerged arc welding were accomplished to investigate microstructure changes on phase transformation behavior in $60kg/mm^2$ quenched and tempered high strength steel. Microstructures were examined by optical micrograph and TEM. In shielded metal arc welding (oxygen 250ppm), the inclusions were small size (0.3-0.5$\mu\textrm{m}$)and small in number. In submerged arc welding (oxygen 430-529ppm), the inclusions were larger(0.7-2$\mu\textrm{m}$) than that of shielded metal arc welding and large in number. Microstructure mainly depends on number and distribution of inclusions in fusion zone of weld metal. It was noticed that a limited number of inclusions favors the formation of acicular ferrite.

• Journal of Welding and Joining
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• 제19권3호
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• pp.267-273
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• 2001

In this study, welding phenomena involved in formation of penetrators during high frequency electric resistance welding were investigated. High speed cinematography of the process revealer that a molten bridge between neighboring skelp edges forms at apex point and travels along narrow gap toward to welding point at a speed ranging from 100 to 400 m/min. The bridge while moving along the narrow gap swept away oxide containing molten metal from the gap, providing oxide-free surface for a forge-welding at upsetting stand frequency of the budge formation, travel distance and speed of the bridge were affected by the heat input rate into strip. The travel distance and its standard deviation were found to have a strong relationship with the weld defect density. Based on the observation, a new mechanism of the penetrator formation during HF ERW process is proposed.

• Journal of Welding and Joining
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• 제18권6호
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Journal of Welding and Joining
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• 제31권5호
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• pp.7-14
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• 2013

The legitimacy of dominating factor in the high accuracy prediction of welding distortion was investigated for butt welding and fillet welding. When out-of-plane distortion was measured by the experiment objecting to butt welding, if tack welding was easily performed, the position of a neutral axis was variously changed by the irregularity. Then, there have been a case that out-of-plane distortion was generated in the unexpected direction. This case should be especially noted. New model for the experiment was proposed so as to solve this problem. As it was elucidated by the case of fillet welding, it was verified that the analysis should be carried out with satisfying the yield condition (especially at high temperature above 700 degree Celsius) and with closely simulating the penetration shape (heat input in weld metal) in order to solve the proposition that is the high accuracy prediction of welding distortion. It was confirmed that residual stress is highly predicted because welding distortion is highly predicted, too.

• Journal of Advanced Marine Engineering and Technology
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• 제36권8호
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• pp.1069-1075
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• 2012

레이저는 고밀도 열원으로써, 입열을 최소화하면서 고속용접이 가능한 장비이다. 특히 최근 상업화된 고출력 파이버 레이저는 특유의 발진원리 때문에 높은 빔품질과 소형화된 시스템이 가능하다. 이러한 장점들로 인해 파이버 레이저는 LNG 카고탱크에 대해 선박 내부에서 용접이 가능한 가장 적합한 열원이라고 판단된다. 따라서 본 연구에서는 선박산업에 레이저 용접기술을 적용하기 위해 파이버 레이저를 이용하여 LNG 선용 스테인리스강의 용접을 진행하였다. 연구에서 사용한 재료는 카고탱크에 사용되고 있는 오스테나이트계 스테인리스강인 두께 1.2mm의 STS304L였다. 레이저 출력 및 용접속도를 변화시켜가면서 겹치기 및 맞대기 용접을 실시한 후 용입특성을 분석하여 최적의 접합조건을 도출하였다. 그 결과 용접부에서 모재보다 우수한 기계적 성질을 얻을 수 있었다.

• Journal of Welding and Joining
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• 제33권5호
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• pp.31-34
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• 2015

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of $1200^{\circ}C$ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

• 대한기계학회논문집
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• 제10권5호
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• pp.661-669
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• 1986

In this study, the resistance spot welding process of an aluminum alloy was analyzed through the numerical simulation including the electric contact resistance and the heat generation in the electrode. The finite element model was used to solve the electro-thermal responses in weld cycles. The resistance of the contact area was represented as the contact element modeling, but the thermal resistance between the contact surfaces was neglected. Welding tests of Alclad 2024-T3 aluminum alloy were made not only to get the input data for the numerical simulation, but also to compare the numerical results. The contact resistance was determined initially by the contact resistance tests and assumed to decay exponentially up to the solidus temperature. The temperature distributions and dynamic resistance obtained numerically were in good agreement with the experimental results. Numerical results revealed that nugget growth depends mainly on the heat generated in the workpiece and its contact area. The heat generated in the electrode has, however, only a little effect on the nugget growth, and the heat generation in the electrode-workpiece interface is initially high but decrease repidly.

• 한국전산유체공학회지
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• 제18권4호
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• pp.61-68
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• 2013

Laser welding is widely used in the industry for the advantage of small heat affected zone and short weld process time. Conduction limit welding can be used to modify the surface characteristic and it is important to identify the heat affecting area correctly for the improvement of manufacturing accuracy. Since time and length scale associated with laser welding process are extremely small, numerical study can be a useful tool. In this study, two-dimensional axi-symmetric version of energy equation with enthalpy method has been used to analyze the effect of laser input conditions on final shape by the laser welding process. The proposed numerical procedure has been benchmarked with several experimental results and compared well. The modified Marangoni and Peclet number have been introduced using controllable input variables. Simple parametric researches have been performed for high Pr number material. The results show that higher Marangoni number increase fluid mixing, thus generating convex type weld pool. On the other hand, the width of the weld pool is proportional to Peclet number.

• 한국정밀공학회지
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• 제12권9호
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• pp.86-94
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• 1995

Bead shape in high frequency electric resistance (HER) pipe welding gives useful information on judging current welding conditon. In most welding process, heat input is controlled by skilled operators observing color and shape of bead. In this paper, a visual monitoring system is designed to observe bead shape in HERW pipe welding process by using structured light beam and a C.I.D(Charge injection device) camera. To avoid some difficul- ties arising in extracting stable features of stripe pattern and classifying the extracted features, Kohonen neural network is used to classify such bead shapes. The experimental results show accurate classification performance of the proposed method.

• 한국레이저가공학회지
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• 제10권4호
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• pp.7-12
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• 2007

The aluminized steel sheet exhibits excellent resistance to oxidation and corrosion, and can substitute for stainless steel or heat-resisting steel in some situations. Furthermore it has wide applications, owing to its low cost and excellent performance, in the petrochemical industry, electric power, other energy conversion system, etc. and has attracted the attention of many investigators. Laser welding is a remarkably advantageous method for welding of thin sheets and surface-treated steel sheets since the method requires less heat input, and it is suitable for high-speed welding. In this study, thus, the laser weldability of aluminized steel sheet was investigated. As the result from the study, there is an Al-rich zone in a welded part which has decreased the welding strength due to the intermetallic compounds in the Al-rich zone.