• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.264-266
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• 2004

for the kぉ mechanics analysis of a crack in a weld of dissimilar steels, residual stress analysis and fracture analysis must be performed simultaneously. The standard definition of the J-integral leads to a path dependent value in the presence of a residual stress field. And unlike cracks in homogeneous materials, a bimaterial interface crack always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, it is necessary to develope a path independent J-integral definition for a crack in a residual stress field generated by welding of dissimilar steels. This paper addresses the modification of the Rice-J-integral to produce a path independent J-integral when residual stresses due to welding of dissimilar steels and external forces are present. The residual stress problem is heated as an initial stain problem and the J-integral proposed for this class of problems is used And a program which can evaluate the 1-integral for a crack in a weld of dissimialr steels is developed using proposed J-integral definition.

• 한국강구조학회 논문집
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• 제15권3호
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• pp.241-250
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• 2003

본 연구는 동종강재 및 이종강재 용접시 발생하는 잔류응력 특징을 파악하기 위해서 유한 요소법을 이용한 3차원 탄소성해석을 수행하였다. 결과에 의하면, 동종강재 맞대기용접시 용접부의 잔류응력은 고강도강재의 인장강도가 클수록(POSTEN60

• 한국재료학회지
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• 제19권7호
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• pp.369-375
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• 2009

The spot weldability of dissimilar metal joints between stainless steels (AISI316) and interstitial free (IF) steels were investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensileshear strength, hardness, and microstructure. The fracture surface was investigated by using a Scanning Electron Microscopy (SEM). The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the STS316 sheet was larger due to the higher bulk-resistance. The microstructure of the fusion zone was fully martensite. In order to evaluate the microstructure further, dilution of stainless steels were calculated and imposed onto the Schaeffler diagram. The predicted microstructure from the Schaeffler diagram was martensite. In order to confirm the predicted microstructure, XRD measurements were carried out. The results showed that that initial weld nugget was composed of austenite and martensite.

• 한국전산구조공학회논문집
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• 제17권4호
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• pp.423-431
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• 2004

용접접합부 균열의 파괴역학적 해석을 위해서는 용접중에 발생하는 잔류응력해석과 파괴해석이 병행되어야 한다. 잔류응력이 존재하면 J-적분은 더 이상 적분경고에 관계없이 인정한 값을 갖는 특성을 잃어버리게 된다. 또한 균질한 재료와는 달리 이종재료 계면균열에서는 균열선난에서 Mode I과 Mode II의 파괴거동이 동시에 발생한다. 그러므로 이종강재 용접접합부 균열의 J-적분 해석을 위해서는 이종강재 용접시 발생하는 잔류응력이 존재하는 경우에도 적분경로에 관계없이 일정한 값을 갖는 새로운 J-적분식이 도입되어야 한다. 따라서 본 연구에서는 기존의 J-적분을 수정하여, 이종강재 용접시 발생하는 잔류응력이 존재하는 경우에 경로 독립성을 유지하는 J-적분을 고찰하고, 이를 이용하여 잔류응력과 외력이 동시에 작용하는 균열선단에서의 J-적분을 해석할 수 있는 프로그램을 개발하였다. 자체개발한 탄소성 해석프로그램을 이용하여 이종강재 용접시 잔류응력과 외력에 대한 응력분포를 계산하였으며, 이를 이용하여 잔류응력과 외력의 복합하중에 대한 J-적분을 계산하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.769-775
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• 2002

The results gained as part of the study on weldability of compositions from steels, aluminium, titanium alloys in various combinations including similar and dissimilar metal bonding variants with reference to solution of specific practical problems are presented in this work. It has been shown that in the case of HIP/DB carried out with direct interaction of bonding surfaces of the most dissimilar material combinations under study, formation of high-quality joints is not assured due to various reasons. That is why development of special bonding techniques was required. The bonding techniques developed and used for HIP/DB of dissimilar steels, "Steel-bronze", "Titanium-niobium"; "Titanium-steel" and other compositions under study ensured vacuum-tight microvoid-free joints strength of a which was equal to the milder parent metal, including those obtained at reduced welding pressures. Examples of new products manufactured by HIP/DB using the technologies developed are presented.

• 대한금속재료학회지
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• 제49권1호
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• pp.64-72
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• 2011

The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.

• 한국기계가공학회지
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• 제18권1호
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• pp.31-37
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• 2019

This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

• 한국해양공학회지
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• 제13권4호통권35호
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• pp.98-104
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• 1999

The crank shafts need anti-corrosion materials. So STS 304 is the essential material to manufacture this shaft. However, it costs more to manufacture the shafts by using only STS 304 than welding of STS 304 to other carbon steels. And it has been difficult to weld this sort of dissimilar materials. They could be unstable in the quality by the conventional arc welding. And also they have a lot of technical problems in manufacturing. But by the friction welding technique, it will be able to be made without such problems. Then, this study aimed not only to develop the optimization of dissimilar friction welding of crank shafts steels of STS 304, SM35C, but also to develop the application technique of the acoustic emission to accomplish in-process real-time quality(such as tensile) evaluation during friction welding of the shafts by the AE technique.

• Journal of Welding and Joining
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• 제4권3호
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• pp.32-42
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• 1986

In this study, the influence of carbon equivalents on friction welds of dissimilar steels was investigated. Four types of carbon steels with 10mm diameter were welded to a high-speed tool steel SKH 9. Main experimental results could be summarized as follows (1) Under constant friction pressure, the friction time increased almost linearly with the increasing burn-off length, while the forge length decreased almost linearly. (2) The maximum hardness in carbon steels increased almost linearly with the increasing carbon equivalent, but was much lower than that in the high speed steel. (3) After quenching and tempering of dissimilar steel friction welds, the hardness in carbon steel weldments became similar as that in the base metal, while the hardness in SKH 9 weld was still higher that of the base metal. (4) Relative movement in the friction phae occurred not at the interface of the weldments, but in the high speed steed steel near the interface. (5) For considered material combinations and welding parameters, most of fractures in tension and twisting tests occurred in the base metal. And welds with so high strength could produced in a wide range of welding parameters.

• Journal of Welding and Joining
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• 제33권3호
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• pp.75-80
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• 2015

Self-piercing riveting is an joining method of advanced high strength steels (AHSS) and other dissimilar materials. It has attracted considerable interest from the automotive industry. The SPR has become an interesting alternative joining technique for difficult to weld materials such as steels and aluminium alloys. In this paper, self-piercing rivet and anvil for SPR were designed for the joining conditions with AHSS and aluminium alloy. Various conditions of SPR were simulated for the design of rivets and anvils. The simulated results were in good agreement with experimental ones. As a result, over HV500 rivet is desirable to joint SPFC780 AHSS and aluminum alloy.