Effects of Flux Composition on the Element Transfer and Mechanical Properties of Weld Metal in Submerged Arc Welding

방국수,박찬,정홍철,이종봉 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.3

Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., △ quantity. Both carbon and manganese show negative △ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative △C and △Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. △Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal. Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., △ quantity. Both carbon and manganese show negative △ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative △C and △Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. △Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

피스톤 크라운용 단강에 인코넬 718 용접재료로 용접된 용접부의 특성 평가

이성열(Sung-Yul Lee),문경만(Kyung-Man Moon),정재현(Jae-Hyun Jeong),이명훈(Myeong-Hoon Lee),백태실(Tae-Sil Baek) 한국해양공학회 2016 韓國海洋工學會誌 Vol.30 No.4

The combustion chamber of a diesel engine is often exposed to a more serious wear and corrosion environment than other parts of the engine because its temperature increases as a result of using heavy oil of low quality. Therefore, repair and built-up welding methods must be performed on worn or corroded parts of the piston crown, exhaust valve, etc. from an economical point of view. In this study, Inconel 718 filler metal was used in repair welding on the groove of a forged steel specimen for a piston crown, along with built-up welding on the surface of another forged steel specimen. Then, the corrosion characteristics of the weld metal zone for the repair welding and the deposited metal zone for the built-up welding were investigated using electrochemical methods in a 35% H<SUB>2</SUB>SO<SUB>4</SUB> solution. The deposited metal zone indicated better corrosion resistance than the weld metal zone, showing a nobler corrosion potential, higher impedance, and smaller corrosion current density. It is considered that metal elements with good corrosion resistance were generally included in the filler metal, and these elements were also greatly involved in the deposited meta by built-up welding, whereas the weld metal consisted of metal elements mixed with both the filler metal and base metal elements because of the molten pool produced by the repair welding. Finally, it is considered that the hardness of the weld metal was increased by the repair welding, whereas the built-up welding improved the corrosion resistance of the deposited metal.

Microstructure and High Temperature Properties of the Dissimilar Weld between Ferritic Stainless Steel and Carbon Steel

김정길,강정윤,홍승갑,강기봉 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.5

Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400. Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400.

Corrosion Characteristics of Welding Zone by Types of Repair Welding Filler Metals and Post Weld Heat Treatment

Lee, Sung-Yul,Moon, Kyung-Man,Lee, Yeon-Chang,Kim, Yun-Hae,Jeong, Jae-Hyun Korean Society of Ocean Engineers 2012 International journal of ocean system engineering Vol.2 No.4

Recently, the fuel using in the diesel engines of marine ships has been changed to a low quality of heavy oil because of the steady increase in the price of oil. Therefore, the wear and corrosion in all parts of the engine such as the cylinder liner, piston crown, and spindle and seat ring of exhaust valves has correspondingly increased. The repair welding of a piston crown is a unique method for prolonging its lifetime from an economic point of view. In this case, filler metals with a high corrosion and wear resistance are mainly being used for repair welding. However, often at a job site on a ship, a piston crown is actually welded with mild filler metals. Therefore, in this study, mild filler metals such as CSF350H, E8000B2, and 435 were welded to SS401 steel as the base metal, and the corrosion properties of the weld metals with and without post weld heat treatment were investigated using some electrochemical methods in a 0.1% $H_2SO_4$ solution. The weld metal welded with CSF350H filler metal exhibited the best corrosion resistance among these filler metals, irrespective of the heat treatment. However, the weld metal zones of the E8000B2 and 435 filler metals exhibited better and worse corrosion resistance with the heat treatment, respectively. As a result, it is suggested that in the case of repair welding with CSF350H and 435 filler metals, no heat treatment is advisable, while heat treatment is desirable if E8000B2filler metal is used with repair welding.

용접 자세에 따른 해양구조물용 항복강도 420MPa급 고강도강 FCA 용접부 파괴인성에 대한 연구

김인찬(In-Chan Kim),정상훈(Sang-Hoon Jeong),최한글(Han-Geul Choi),김명현(Myung-Hyun Kim) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.2

The fracture toughness of flux cored arc weld metal with the yield strength 420MPa grade high strength steels for offshore structures depending on the welding position was investigated. Charpy V-notch impact test and the CTOD test of the weld metal in the horizontal and the vertical-up welding positions were carried out, and the microstructure and M-A constituents of the weld metals were observed. The recovery rate of alloying elements in horizontal position weld metal were higher than vertical-up position weld metal and the fraction of low temperature transformation phases having high dislocation density in the horizontal position weld metal was high. As a result, the yield strength, tensile strength and impact toughness of horizontal weld metal were higher than those of vertical-up position weld metal. On the other hand, the CTOD value of vertical-up position weld metal was much higher than horizontal position weld metal. This is because the M-A constituents transformation is promoted by the post-welding on the low temperature transformation region having a high local C concentration in the horizontal position welding, and therefore, the breakdown starts easily by the high M-A constituents.

430 스테인리스강 스트립재를 이용한 일렉트로슬래그 클래딩 용착금속의 화학성분 및 미세조직 변화

정재영(Jae-Young Jung),하태권(Tae-Kwon Ha) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.5

In this study, the weld metals were obtained by electroslag strip cladding process using 430 stainless steel strip according to welding process parameters such as welding current, welding voltage, welding speed and polarity. We measured carefully the micro-Vickers hardness, microstructure, and chemical composition in the crosssectional area of the electroslag strip cladding overaly using the AISI 430 stainless steel strip. The hardness of the cross section between the weld metal and the base metal was measured to be higher than those of the base metal and the weld metal around the boundary, which was related to the microstructure and chemical composition of the boundary. Particularly, the intermediate region of the boundary was observed, and the chemical composition of the constituent elements continuously changed in this part. The microstructural changes of the weld metal and the base metal were shown that the coarse pearlite structure, the fine perlite structure, the bainite structure, the martensite structure and the dual structure of the d-ferrite / martensite were observed from the base metal to the weld metal. The change of the constituent elements of the deposited metal after welding were analyzed by comparing with measured and calculated values. The variation in the deposited metal composition was mainly due to the interaction with the flux.

유한요소법을 이용한 용접공정 모사 시 입열 방법에 따른 용접잔류응력의 영향

양준석(Jun-Seog Yang),박치용(Chi-Yong Park),이경수(Kyoung-Soo Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

This paper is to discuss distribution of welding residual stresses of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two dimensional (2D) thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed and fabrication data. On performing the welding analysis generally, the characteristics on the heat input and heat transfer of weld are affected on the weld residual stress analyses. Thermal analyses in the welding heat cycle process is very important process in weld residual stress analyses. Therefore, heat is rapidly input to the weld pass material, using internal volumetric heat generation, at a rate which raises the peak weld metal temperature to 2200 ℃ and the base metal adjacent to the weld to about 1400 ℃. These are approximately the temperature that the weld metal and surrounding base materials reach during welding. Also, According to the various ways of appling the weld heat source, the predicted residual stress results are compared with measured axial, hoop and radial through-wall profiles in the heat affected zone of test component. Also, those results are compared with those of full 3-dimensional simulation.

플라스마 아크 용접에 의한 STS317L 용접부의 기계적 특성에 관한 연구

이일준(Il-Jun Lee) 산업기술교육훈련학회 2012 산업기술연구논문지 (JITR) Vol.17 No.3

Austenitic stainless steel(STS317L) were selected as base metal. The base metal were jointed by plasma arc welding(PAW) under proper welding conditions. Specimens were cut out from transverse line of welded respectively. Tensile, micro vickers hardness, bending test and microstructure inspection were preformed and the mechanical properties and microstructures investigated. The results of analyses are as follows: Tensile strength was the high in weld metal(565MPa) and elongation was the low(41.0%) then base metal. Hardness was the highest in bond(HV252) and decreased to the base metal gradually and the average hardness in heat affected zone was HV207. In bending test deformation was the largest in heat affected zone and smaller in weld metal zone. The microstructure of weld metal zone showed dual phase of austenite-ferrite contains σ phase and δ-Ferrite, and grain size was largest in heat affected zone then in base metal.

GMA용접에서 콘택트 팁 재질에 따른 용접특성 평가

김동윤,황인성,김동철,강문진,Kim, Dong Yoon,Hwang, In Sung,Kim, Dong Cheol,Kang, Moon Jin 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.6

The contact tip for gas metal arc welding has important functions to transmit the welding current to the wire and to guide the wire to molten pool. If the contact tip is damaged, it is a cause of lowering the welding productivity due to removal of welding defects and replacement of contact tip. In case of the use of a contact tip for a long time the arc is unstable because the processed hole in the contact tip center is larger, and the variation of aiming position of the welding wire causes a seam tracking error. In this study, gas metal arc welding experiments using contact tip of three different materials were performed. The contact tips with Cu-P, Cu-Cr, and Cu-ODS were used at the experiments, and the welding characteristics by each contact tip were evaluated. After welding contact tip appearance, welding spatter adhesion amount of the nozzle, and weld bead appearance were evaluated. The welding current and welding voltage were measured to verify arc stability during arc welding.

FEM을 이용한 초음파 용착부의 온도분포 해석

강은지(Eun-Ji Kang),민경탁(Kyung-Tak Min) 한국생산제조학회 2016 한국생산제조학회지 Vol.25 No.2

Ultrasonic metal welding, unlike the conventional welding techniques, does not require an external heat source, welding rod, or filler metal. Therefore, ultrasonic metal welding is not only economical but also environment-friendly, and hence, it has been receiving much attention. In ultrasonic welding, heat is generated because of the plastic deformation and the friction between both surfaces of the welded materials. It is important to identify the heat-affected zone by measuring the temperature generated at the weld. In this study, the effects of the welding pressure, welding time, and vibration amplitude on the temperature distribution in the weld were evaluated by performing a transient thermal analysis of the heat generated during ultrasonic metal welding. The experimental results indicated that the temperature of the weld tends to increase with the welding time and vibration amplitude. However, an increase in the pressure does not affect the temperature of the weld largely.