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DP강의 전기저항점용접부 너깃직경에 미치는 Si 함량의 영향
공종판,강길모,한태교,진광근,강정윤,Kong, Jong-Pan,Kang, Gil-Mo,Han, Tae-Kyo,Chin, Kwang-Geun,Kang, Chung-Yun 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.5
In this study, effect of Si content on nugget diameter in electric resistance spot welded dual-phase(DP) steel was investigated. The cold rolled DP steels with different Si content (0.5, 1.0, 1.5, 2.0 wt.%) were used and thickness of those sheet was 1.2mm. With increasing Si content, nugget diameter was increased at the same welding current. This is attributed to increase of heat input result from high resistivity. Also, nugget diameter was increased with an increase in Si content for the same heat input. For this reason, the melting point of DP steel is lowered with an increase in the Si content. And solid DP steel can easily be transformed to a liquid phase because the low melting point. Finally, a prediction formula for the nugget diameter(N.D.) could be obtained in terms of heat input(Q) and melting point(M.P) as follows: N.D.(mm) = 0.11Q(J) - 0.0031 M.P.($^{\circ}C$) + 0.32.
409L페라이트계스테인리스강CO2레이저용접부의미세조직과경도
공종판 ( Jong Pan Kong ),박태준 ( Tae Jun Park ),나혜성 ( Hye Sung Na ),엄상호 ( Sang Ho Uhm ),김정길 ( Jeong Kim Kim ),우인수 ( In Su Woo ),이종섭 ( Jong Sub Lee ),강정윤 ( Chung Yun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.4
The microstructure and hardness of CO2 laser welds were investigated in the Ti-stabilized ferritic stainless steel 409L. The observed specimen was welded in a fully penetrated condition in which the power was 5 kW and the welding speed 5 m/min. The grain structure near the bond line of the laser welds was produced by epitaxial growth. The grain size was the largest in the fusion zone, and HAZ showed nearly the same grain size as that of the base metal. The HAZ microstructure consisted of subgrains and precipitates that were less than l00 nm in size and that were located along the subgrain boundaries. On the other hand, the hardness was the highest in the fusion zone due to the large amount of small precipitates present. These were composed of TiN, Ti(C,N) and TiO2+Ti(C,N). The hardness decreased continuously from the fusion zone of the base metal. The HAZ hardness was slightly greater than that of the base metal due to the existence of subgrains and precipitates in the subgrain boundary. (Received January 13, 2010)
CP강 전기저항점용접부의 기계적 성질에 미치는 Ti 함유량과 용접전류의 영향
공종판 ( Jong Pan Kong ),김대업 ( Dae Up Kim ),강정윤 ( Chung Yun Kang ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.4
When complex-phase (CP) steel with a tensile strength of more than 1 GPa grade is joined using resistance spot welding (RSW), the optimum Ti content should be chosen in order to satisfy the weldability and mechanical properties. Therefore, in this study, the effect of the Ti content (0~300 ppm) on the tensile- shear load of the RSW in CP steels is investigated. Because the resistivity of the base metal is independent of the Ti content, it does not affect the nugget diameter. Regardless of the Ti content, the specimens under 5t1/2 (t = sheet thickness) are fractured in the interfacial failure mode. In the low welding current condition (lower than 6.4 kA), the measured nugget diameters are smaller than the calculated critical nugget diameter regardless of the amount of Ti addition in order that the fracture mode is interfacial failure. Pull-out failure occurs at the softened zone, which is the boundary between the base metal and heat-affected zone. The tensile-shear load of the specimen failure in the pull-out mode increases as the fractured diameter and hardness of the softened zone increase. The shear load is only dependent on the fractured diameter.
첨단고강도강 전기저항점용접의 비산현상에 미치는 Cr과 Si 함유량의 영향
공종판 ( Jong-pan Kong ),강정윤 ( Chung-yun Kang ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.6
An expulsion phenomenon occurred during resistance spot welding of advanced high-strength steel sheets, and the effects of the Cr and Si contents on the expulsion limit current (CExp) were investigated. The correlation between CExp and the steel properties (e.g., resistivity, melting point, coefficient of thermal expansion, high-temperature yield-strength and viscosity), were evaluated, as were the qualities of the alloying elements. The CExp decreased with increasing Si contents. This resulted in a narrow range of acceptable welding current, as well as poor suitability for spot welding. On the other hand, the effects of Cr-contents on the CExp, and on the acceptable range of welding current were minimal (with content of 3 wt%). Thus, the suitability for spot welding was not affected by the Cr-Contents (at the experimental concentration). As Si-Contents increased, resistivity also increased and the melting point decreased. This resulted in easy melting of the base metal at a low welding current (low heat input) and in the rapid increase of the pressure due to the increased coefficient of expansion. However, the high-temperature yield-strength of the corona bond, which blocked the expulsion of the molten melt, also decreased. Consequently, the CExp of steel containing additional Si was lower than that containing Cr.
DV-Xα분자궤도법을 이용한 Zn alloy의 기계적 성질 예측
나혜성,공종판,김양수,강정윤,Na, H.S.,Kong, J.P.,Kim, Y.S.,Kang, C.Y. 한국재료학회 2007 한국재료학회지 Vol.17 No.5
The alloying effects on the electronic structures of Zinc are investigated using the relativistic $DV-X{\alpha}molecular$ orbital method in order to obtain useful information for alloy design. A new parameter which is the d obital energy level(Md) and the bonder order(Bo) of alloying elements in Zinc was introduced and used for prediction of the mechanical properties. The Md correlated with the atomic radius and the electronegativity of elements. The Bo is a measure of the strength of the covalent bond between M and X atoms. First-principles calculations of electronic structures were performed with a series of models composed of a MZn18 cluster and the electronic states were calculated by the discrete variational- $X{\alpha}method$ by using the program code SCAT. The central Zinc atom(M) in the cluster was replaced by various alloying elements. In this study energy level structures of pure Zinc and alloyed Zinc were calculated. From calculated results of energy level structures in MZn18 cluster, We found Md and Bo values for various elements of Zn. In this work, Md and Bo values correlated to the tensile strength for the Zn. These results will give some guide to design of zinc based alloys for high temperature applications and it is possible the excellent alloys design.
Al-Si 용융도금된 11%Cr 페라이트 스테인리스강, STS409L GTA 용접부의 미세조직과 경도
박태준,공종판,나혜성,강정윤,엄상호,김정길,우인수,이종섭,Park, Tae-Jun,Kong, Jong-Pan,Na, Hye-Sung,Kang, Chung-Yun,Uhm, Sang-Ho,Kim, Jeong-Kil,Woo, In-Su,Lee, Jong-Sub 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.3
Ferritic stainless steels, which have relatively small thermal expansion coefficient and excellent corrosion resistance, are increasingly being used in vehicle manufacturing, in order to increase the lifetime of exhaust manifold parts. But, there are limits on use because of the problem related to cosmetic resistance, corrosions of condensation and high temperature salt etc. So, Aluminum-coated stainless steel instead of ferritic stainless steel are utilized in these parts due to the improved properties. In this investigation, Al-8wt% Si alloy coated 409L ferritic stainless steel was used as the base metal during Gas Tungsten Arc(GTA) welding. The effects of coated layer on the microstructure and hardness were investigated. Full penetration was obtained, when the welding current was higher than 90A and the welding speed was lower than 0.52m/min. Grain size was the largest in fusion zone and decreased from near HAZ to base metal. As welding speed increased, grain size of fusion zone decreased, and there was no big change in HAZ. Hardness had a peak value in the fusion zone and decreased from the bond line to the base metal. The highest hardness in the fusion zone resulted from the fine re-precipitation of the coarse TiN and Ti(C, N) existed in the base metal during melting and solidification process and the presence of fine $Al_2O_3$ and $SiO_2$ formed by the migration of the elements, Al and Si, from the melted coating layer into the fusion zone.
Al-Si 용융 도금된 보론강의 Yb:YAG 디스크 레이저 용접부의 미세조직과 인장성질에 미치는 도금두께의 영향
조위업,공종판,안영남,김철희,강정윤,Cao, Wei-Ye,Kong, Jong-Pan,Ahn, Yong-Nam,Kim, Cheol-Hee,Kang, Chung-Yun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.3
In this study, the effect of coating thickness($20{\mu}m$ and $30{\mu}m$) on microstructure and tensile properties in Yb:YAG disk laser welds of Al-Si-coated boron steel (1.2mmt) was investigated. In the case of as welds, the quantity of ferrite was found to be higher in base metal than that in HAZ (Heat Affected Zone) and fusion zone, indicating, fracture occurrs in base metal, and the fracture position is unrelated to the coating thickness. Furthermore, yield strength, tensile strength of base metal and welded specimens showed similar behavior whereas elongation was decreased. On the other hand, base metal and HAZ showed existence of martensite after heat treatment, the fusion zone indicated the presence of full ferrite or austenite and ferrite during heat treatment ($900^{\circ}C$, 5min), After water cooling, austenite was transformed to martensite, and the quantity of ferrite in fusion zone was higher as compared with in base metal, resulting in sharply decrease of yield strength, tensile strength and elongation, which leads to fracture occured at fusion zone. In particular, results showed that because the concentration of Al was higher in 30um coating layer specimen than that of 20um coating specimen, after heat treatment, producing a higher quantity of ferrite was higher after heat treatment in the fusion zone; howevers, it leads to a lower tensile property.