• Journal of Welding and Joining
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• v.7 no.3
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• pp.19-27
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• 1989

Both the SS41 steel and the M.E.F(martensite encapsulated islands of frrite) dual phase steel made of SS41 steel by heat treatment were welded by friction welding, and then manufactured machinemade Vnotch standard Charpy impact specimens and precracked with a fatigue system at BM(base metal), HAZ(heat affected zone) and WZ(weld interface Zone). The impact test of them was performed with an instrumented impact test machine at a number of temperatures in constant loading velocity and the dynamic fracture characteristics were studied on bases of the absorbed energy, dynamic fracture toughness and fractography from the test. The results obtained are as follows; At the room temperature, the absorbed energy is HAZ.geq.WZ.geq.BM in case of the M.E.F. dual phase steel: BM.geq.HAZ.geq.WZ in case of the SS41 steel, HAZ.geq.BM.geq.WZ at the low temperature. The absorbed energy is decreased markedly with the temperature lowering; it is highly dependent on the temperature. The dynamic fracture toughness of the M.E.F. dual phase steel is HAZ.geq.WZ.geq.BM at the room temperature; BM.geq.WZ.geq.HAZ below-60.deg. C. Therefore the reliability of friction welding is uncertain at the low temperature(below-60.deg. C). The dynamic fracture toughness of the SS41 steel; HZA.geq.WZ.geq.BM at overall temperature region. The flaw formed by rotational upsetting pressure was shown y SEM; in this region. The absorbed energy per unit area and dynamic fracture toughness were low relative to other region.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.69-76
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• 2000

Formation of the weld defect, such as a blowhole and a pit in lap-jointed fillet arc welds has been a serious problem in arc welding Zn-coated steel sheet. In this study, the relationship among welding conditions, welding materials and defect formation was investigated in order to minimize these defects in the CO₂welds. In addition, the arc stability of the commercial welding wires was evaluated for revealing their effects on defect formation. Main conclusions obtained are as follows: 1) There was no difference between shear tensile strength of the sound welds and that of the welds with blowholes whose diameters are less than 0.5mm. However, the welds with blowholes whose diameters are equal or large than 0.5mm and pits exhibited tensile strength 10∼ 20% and 30∼40% lower than that of the sound welds respectively. 2) The optimum welding condition to effectively prevent or reduce the weld defects formation are as follows: -The welding variables of 220A-23V-100cm/min and 120A-19V-30cm/min were recommended for minimizing the weld defects. -The gap between the two sheets at the lap-joint should be controlled to more than 0.2mm. -Solid wire was less susceptible to the formation of the weld defects than the flux-cored wire. -The low welding current condition produced less weld defects than the high welding current condition. 3) One of the reason why the amount of the defect was reduced at the low welding current was the gas discharging by the active agitation of the molten pool, due to an increasing in the number of the short circuit.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.56-62
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• 2009

With weld metal of X65 steel, hydrogen was charged by electro-chemical method and mechanical behavior such as strength was measured by the small punch test. The weld metal was more sensitive to hydrogen charging than the case of base metal. The small punch (SP) strength was decreased as the hydrogen contents increased. Magnitude of strength decrease was dependent on current density, temperature, charging time. Current density and charging time have significant effect on the mechanical properties but temperature of electrolyte has limited effect. Fractured surfaces of the tested specimens were observed by SEM (scanning electron microscope). In the hydrogen charged specimens cleavage fracture were observed, which is consistent with the SP test results. Since the testing procedure for studying hydrogen embrittlement proposed in this study has shown good reproducibility of test results, the proposed method can be assumed to be a reliable test procedure. Using the electrochemical charging and the small punch test, the change of SP strength for X65 weld metal due to hydrogen embritlement could be evaluated sensitively.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.42-42
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• 2009

마찰교반접합 (Friction Stir Welding)은 1991년 영국 TWI에서 개발된 접합 법으로서 회전하는 툴이 재료내부에 삽입되면 툴과 재료사이에서 발생하는 마찰열에 의하여 온도가 상승하게 되어 재료는 연화되고, 이러한 재료 내부에서 회전하는 툴이 이동하게 되면 재료 내부는 기계적 교반에 의해 소성변형이 일어남과 동시에 접합이 이루어진다. 마찰교반접합은 동적 재결정에 의한 접합부의 미세한 결정립 형성으로 인하여 기계적 특성이 향상되며 보호 가스가 필요 없어 친환경적임과 동시에 용융 용접 법에 비해 접합 시 에너지 소모가 적으며 또한 접합 후 접합부에서의 변형이 상대적으로 적다는 장점이 있다. 이러한 장점을 가진 마찰교반접합은 알루미늄 합금, 마그네슘 합금 그리고 동 합금과 같은 저 융점 비철재료에 많은 연구와 적용 사례들이 있어왔다. 하지만 최근에는 일반 탄소강, 연강, 오스테나이트계 스테인리스강, 니켈 합금, 티타늄 합금과 같은 고융점 재료에도 연구 및 적용이 진행되고 있는 추세이다. 페라이트계 스테인리스강은 가격이 비싼 Ni을 함유하지 않아 오스테나이트계 스테인리스강에 비하여 강재의 가격은 낮으면서도 고온특성 및 내식성이 우수하여 건축용, 자동차 배기계용으로 널리 사용되고 있다. 하지만 이런 장점을 가진 페라이트계 스테인리스강을 기존의 용융 용접 법으로 접합 시 용접부 및 열영향부에서의 결정립의 조대화로 인한 인성 및 연성이 저하되며, 특히 예민화된 열영향부 입계 내에 Cr 탄화물이 석출되어 입계주변에 Cr 결핍 층을 형성되어 입계부식이 발생되는 문제점이 발생된다. 본 연구에서는 마찰교반접합을 이용하여 두께 3mm의 409 스테인리스강에 대해 맞대기 접합을 실시하였다. 접합 변수를 툴의 재료 (WC-12wt%Co, $Si_3N_4$)로 하여 접합을 실시하였고 접합 후 외관상태 점검, 광학 현미경과 주사 전자 현미경을 통하여 미세조직을 관찰하였으며 황산-황산동 부식 시험을 실시하여 접합부의 부식 특성을 평가하였다.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.10a
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• pp.137-151
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• 2002

최근 급속한 첨단산업의 발전과 더불어 각 분야에서 신소재 개발 등의 연구가 활발히 진행되고 있어 비금속 자원은 그 수요가 점차 증가하는 추세에 있다. 여러 비금속 자원 중 장석은 세라믹, 법랑, 타일, 유약용 등의 요업원료와 유리, 용접봉, 플라스틱, 페인트, 카리비료등 무기 재료 공업원료로 다양하게 사용되고 있는 비금속자원 이다. 2001년도 우리나라 장석 생산량은 389,361톤 (2001년도 광산물 수급현황, 2002, 5, 산업자원부)이며 매장량은 41,470,000톤 (2001년도 광산물 수급현황, 2002, 5, 산업자원부)이며 전국적으로 등록된 장석 광구수는 811개에 개발광산은 69개 이른다. 이상의 예를 보면 막대한 양의 매장량과 장석 광산이 알려져 있지만 실제 연중 가행 광산은 10개 광산 미만이며 영세한 상태로 체계적인 개발이 이루어지지 못하고 있다. 이런 문제점을 해소하고 장석 자원의 확보 및 안정적 공급을 위하여 장석의 정의, 용도, 품질요건, 부존, 산출상태, 가행광산현황 및 장석자원현황등을 규명하여 장석광산의 향후. 개발대책 및 고부가가치화에 필요한 자료를 제공하고자 한다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.322-325
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• 2000

In the previous report1), the grinding characteristics of quartz were investigated. In this paper, the grinding mechanisms of brittle materials including ceramics and quartz are modeled and a new parameter SDR(Surface roughness Direction Ratio) is proposed to characterize the grinding mechanisms of such materials. A set of experiments were performed to verify the effectiveness of the suggested parameter. The experimental results indicate that the plastic deformation is the dominant material removal mode at the grinding conditions which show the higher value of SDR. In the case of quartz, the material was removed by brittle fracture in a lower value of SDR and by plastic deformation in a higher value of it. SDR is not affected by wheel mesh size when brittle fracture occured. But in the plastic deformation case, SDR value increases with wheel mesh size.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.676-684
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• 2000

In this study, behavior of $C_t$ which is a well-known fracture parameter characterizing creep crack growth rate, is investigated for weld interface cracks. Finite element analyses were per formed for a C(T) specimen under constant loading condition for elastic-plastic-creeping materials. In modeling C(T) geometry, an interface was employed along the crack plane which simulated the interface between weld and base metals. The $C_t$ versus time relations were obtained under various creep constant combinations and plastic constant combinations for weld and base metals, respectively. A unified $C_t$ versus time curve is obtained by normalizing $C_t$ with $C^*$ and t with $t_T$ for all the cases of material constant variations.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.274-279
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• 2001

Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of 1Cr-0.5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_t$-parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of $(da/dt)_{avg}$ vs. $(C_t)_{avg}$ for residual life assessment.

• Bulletin of the Society of Naval Architects of Korea
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• v.7 no.1
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• pp.45-56
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• 1970

The penetration of domestic high-titania potassium type arc welding rod has been investigated experimentally. The penetration of this type arc welding rod is influenced much more by changing welding current than welding speed and thickness of base metal in range of $6{\sim}9mm$. Values of penetrations were $1.00{\sim}1.75mm$ for $3.2mm{\phi}$ rod, and $1.10{\sim}1.86mm$ for $4mm{\phi}$ rod in adequate welding current range. The domestic rod's penetration is deeper than same type rod of the United State's product.

• Proceedings of the KSEEG Conference
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• 2002.10a
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• pp.137-151
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• 2002

최근 급속한 첨단산업의 발전과 더불어 각분야에서 신소재 개발등의 연구가 활발히 진행되고 있어 비금속 자원은 그 수요가 점차 증가하는 추세에 있다. 여러 비금속 자원중 장석은 세라믹, 법랑, 타일, 유약용 등의 요업원료와 유리, 용접봉, 플라스틱, 페인트, 카리비료등 무기 재료 공업원료로 다양하게 사용되고 있는 비금속자원 이다. 2001년도 우리나라 장석 생산량은 389,361톤 (2001년도 광산물 수급현황, 2002, 5, 산업자원부)이며 매장량은 41,470,000톤 (2001년도 광산물 수급현황, 2002,5,산업자원부)이며 전국적으로 등록된 장석 광구수는 811개에 개발광산은 69개 이른다. 이상의 예를 보면 각대한 양의 매장량과 장석 광산이 알려져 있지만 실제 연중 가행 광산은 10개 광산 미만이며 영세한 상태로 체계적인 개발이 이루어지지 못하고 있다. 이런 문제점을 해소하고 장석 자원의 확보 및 안정적 공급을 위하여 장석의 정의, 용도, 품질요건, 부존, 산출상태, 가행광산현황 및 장석자원현황등을 규명하여 장석광산의 향후 개발대책 및 고부가가치화에 필요한 자료를 제공하고자 한다.