• Title/Summary/Keyword: HAZ Microstructure

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Rotary Bending Fatigue Characteristics According to Optimal Friction Welding of SF45 to SM45C Steel Bars (SF45와 SM45C의 마찰용접 최적화에 따른 회전굽힘피로 특성)

  • Kong, Yu Sik;Park, Young Whan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.3
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    • pp.219-224
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    • 2017
  • A study on dissimilar friction-welded joints was performed for cam shaft applications using solid bar samples, 20mm in diameter, of forging steel(SF45) and carbon steel(SM45C). The main parameters of friction welding such as tensile tests, Vickers hardness surveys of the bond of area, the heat affected zone (HAZ), and the observation of microstructure were investigated to ensure a good quality of friction welding through visual observations. The specimens were tested as-welded and post weld heat treatment(PWHT). This paper deals with optimizing the welding conditions and analyzing various rotary bending fatigue test(RBFT) properties about heat-treated base metal(BM), as-welded and PWHT. Consequently, two materials for friction welding are strongly mixed with a well-combined structure of micro-particles without any molten material, particle growth, or any defect. Moreover, the fatigue limit of BM(SF45) and PWHT for the RBFT were observed as 180MPa and 250MPa, respectively. It was confirmed that the PWHT causes approximately 40% improvement in the fatigue limit when compared to the BM(SF45).

Joining Ability and Mechanical Properties of Friction Stir Lap Welded A5052-H112 Alloy (A5052-H112 합금의 겹치기 마찰교반접합 건전성)

  • Ko, Young-Bong;Choi, Jun-Woong;Park, Kyeung-Chae
    • Journal of Welding and Joining
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    • v.28 no.1
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    • pp.34-40
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    • 2010
  • In Friction Stir Lap Welding(FSLW), the movement of material within the weld was more important than the microstructure, due to the interface present between the sheets. Thus, The soundness of free defect, Effective Sheet Thickness(EST) and width of joint were most important factor of mechanical properties. Specimens by lap joint types that were 'A-type' and 'R-type' were made in this study. A-type tensile specimen was loaded at advancing side and R-type tensile specimen was loaded at retreating side. Macro-, micro-structural observation and mechanical properties of FSLW A5052-H112 alloy ware investigated under varying rotating and welding speed. The results were as follows: Material hook formed decreasing after sharply increasing was appeared at the end interface of joint area in advanced side, and material hook formed decreasing after smoothly increasing was observed at that in retreated side. Tensile load had no relation with defects. As rotating speed was higher, tensile strength was increasing and EST was decreasing regardless of joint types. joint efficiency was over 70%. In a result of fractography, fracture in A-type was partially occurred by dimple in SZ, and fracture in R-type was generally occurred by dimple in HAZ.

Tensile and impact toughness properties of various regions of dissimilar joints of nuclear grade steels

  • Karthick, K.;Malarvizhi, S.;Balasubramanian, V.;Krishnan, S.A.;Sasikala, G.;Albert, Shaju K.
    • Nuclear Engineering and Technology
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    • v.50 no.1
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    • pp.116-125
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    • 2018
  • Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

A Study to Improve Weld Strength of Al 6k21-T4 Alloy by using Laser Weaving Method (레이저 위빙을 이용한 Al 6k21-T4 합금의 용접 강도 향상)

  • Kim, Byung-Hun;Kang, Nam-Hyun;Park, Yong-Ho;Ahn, Young-Nam;Kim, Cheol-Hee;Kim, Jung-Han
    • Journal of Welding and Joining
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    • v.27 no.4
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    • pp.49-53
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    • 2009
  • For Al 6k21-T4 alloy, linear laser welding produced the lower shear-tensile strength than the base metal. This study improved the shear-tensile strength by using the weaving laser at the optimized welding condition, i.e., 2mm weaving width and 25Hz frequency. The large weaving width increased the weld width, therefore improving the joint strength. For the specimen of low strength, the porosity was distributed continuously along the intersection between the plates and fusion line. However, for the optimized welding condition, large oval-shaped porosities were located only in the advancing track of the concave part. Regardless of the welding condition, solidification cracking was initiated at the intersection and propagated through small porosities in the weld part. furthermore, the concave part had more significant porosity in the weld and HAZ, respectively than the convex part. The continuity of porosities played a key role to determine the strength. And, the weaving width was an important parameter to control the strength.

A Study on the Mechanical Properties as a Result of Friction Welding With SKH55 and SM45C (고속도강(SKH55)과 기계구조용 탄소강(SM45C)의 마찰용접특성에 관한 연구)

  • Choi, Su-Hyun;Min, Byung-Hoon;Kim, Noh-Kyung;Lim, Hyung-Taek;Min, Taeg-Ki
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.17 no.2
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    • pp.65-70
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    • 2008
  • This study deals with the friction welding of SKH55 and SM45C; The friction time was variable conditions under the conditions of spindle revolution 2,000rpm, friction pressure of 190MPa, upset pressure of 270MPa and upset time of 2.0 seconds. Under these conditions, the microstructure of weld interface, tensile fracture surface and mechanical tests were studied, and so the results were as follows. 1. When the friction time is 1.0 seconds, the tensile strength of friction welds was 926MPa, which is around as much as 84% of the tensile strength of base metal(SKH55), the bending strength of friction welds was 1,542MPa, which is around as much as 80% of the bending strength of base metal(SKH55), the shear strength of friction welds was 519MPa, which is around as much as 70% of the shear strength of base metal(SKH55). 2 According to the hardness test, the hardness distribution of the weld interface was formed from 964Hv to 254Hv. HAZ(Heat Affected Zone) was formed from the weld interface to 1.5mm of SKH55 and 2mm of SM45C.

Characteristics of Friction Stir Lap Weldment according to Joining Parameter in 5052 Aluminium Alloy (5052 알루미늄 합금에서 접합변수에 따른 겹치기 마찰교반접합부의 특성)

  • Ko, Young-Bong;Park, Kyeung-Chae
    • Journal of the Korean institute of surface engineering
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    • v.45 no.5
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    • pp.181-187
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    • 2012
  • The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, microstructures and mechanical properties of FSLW in A5052 alloy were investigated under varying rotating speed and probe length. Investigating the characteristics as FSLWed conditions were as below ; Failure Maximum load by shear fracture was increased proportional to the width of joint area, which was increased by input heat, stirring intensity in the case of 2.3 mm probe length. Tensile fracture occurred, and maximum load was determined due to side worm hole of joint area and softening of microstructure in the case of 3.0 mm probe length. In the case of 3.7 mm probe length, material hook and bottom worm hole were appeared at the end interface of joint area. The most sound FSLW condition with no defects was 3.0 mm probe length and 1500 rpm-100 mm/min. No defects were showed in 1500 rpm-100 mm/min and 1800 rpm-100 mm/min, but Vickers microhardness distribution in TMAZ/HAZ which was fracture zone was lower in 1800 rpm-100 mm/min than in 1500 rpm-100 mm/min. In this condition highest tensile strength, 215 MPa (allowable rate 78% of joint efficient) was obtained.

Effect of Paint Baking on the Strength and Failure of Spot Welds for 780 TRIP Steels (780 MPa급 TRIP강의 저항 점용접부 강도 및 파단에 미치는 Paint Baking의 영향)

  • Son, Jong-Woo;Nam, Dae-Geun;Kim, Dong-Cheol;Park, Yeong-Do
    • Journal of Welding and Joining
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    • v.28 no.2
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    • pp.66-73
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    • 2010
  • Conventional fracture test of resistance spot weld had been performed without consideration of paint baking process in automobile manufacturing line. This study was aim to investigate the effect of paint baking on fracture mode and load carrying capacity in fracture test for resistance spot welded 780TRIP steels. With paint baking cycle after resistance spot welds, peel tests and microhardness were conducted on the as-welded and baked samples. Resistance spot welds in AHSS (Advanced High Strength Steels) are prone to display partial interfacial fractures during fracture test or vehicle crash. Baking cycle increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial to full button fracture for the L-type peel tests. Specially, the differences in fracture appearance are apparent when the nugget size of spot welds is small enough to produce the partial interfacial fracture. The comparison of macrohardness and microstructure between as-welded and baked samples showed that there are no large difference in change the fracture mode. However, the results of the instrumented indentation test suggested that fusion zone and HAZ of baked sample have less tensile and yield strength and proves that the tempering effects are applied and enhanced the resistance to fracture on welds with application of baking cycle.

Evaluation of Repair Welding Method and PWHT Properties for Degraded CrMoV Casting Steel (열화된 CrMoV 주조강에 대한 보수 용접 방법 및 후열처리 특성 평가)

  • Hong, Jaehun;Jun, Moonchang;Jung, Kwonsuk;Lee, Young-Kook
    • Journal of the Korean Society for Heat Treatment
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    • v.35 no.3
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    • pp.121-129
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    • 2022
  • Recently the growth of the renewable energy production has caused the flexible operation in LNG combined cycle power plant. Due to the rapid start and stop operations, large CrMoV castings used for turbine casings and valve bodies could be distorted and lead to replacement or welding repair. This study was performed to find out the characteristics of the repair welding for a damaged CrMoV casting steel. A typical field repair method (arc & TIG welding) was applied to making specimens. The degraded N2 packing head sample from the steam turbine was used. The evaluations of weldments were carried out in terms of microstructural characterization, microhardness measurements, tensile, creep-rupture and fatigue tests. Color etching was also applied for better understanding of welding microstructures. As the boundary between HAZ and base material was deteriorated by welding, it caused microstructural changes formed during PWHT and the shortening of the remaining residual life. By comparing the properties according to repair welding method, it was possible to derive what important welding factors were. As a result, arc welding method is more suitable for repair welding on CrMoV castings.

A study on the Application Effect of Friction Stir Processing for Enhanced Pitting Corrosion Resistance of Stainless Steel Welds in Chloride Environment (염화물 환경에서 스테인리스강 용접부의 공식저항성 향상을 위한 마찰교반공정 적용효과에 관한 연구)

  • Jong Moon Ha;Deog Nam Shim;Seung Hyun Kim
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.19 no.2
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    • pp.84-92
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    • 2023
  • As temporary storage facilities for spent nuclear fuels in domestic nuclear power plants are expected to be saturated, external intermediate storage facilities would be required in the future. Spent nuclear fuels are stored in metal canisters and then placed in a dry environment within concrete or metal casing for operation. In the United States, the dry storage method for spent nuclear fuels has been operated for an extended period. Based on the corrosion experiences of dry storage canisters in chloride environments, numerous studies have been conducted to reduce corrosion in welds. With the construction of intermediate storage facilities in Korea for spent nuclear fuels expected near coastal areas adjacent to nuclear power plants, there is a need for research on the corrosion occurrence of welds and mitigation methods for canisters in chloride environments. In this paper, we measured and compared the residual stresses in the Heat-Affected Zones (HAZ) after electron beam welding (EBW) and gas tungsten arc welding (GTAW) processes for candidate materials such as 304L, 316L, and duplex stainless steel(DSS). We investigated the possibility of microstructure control through the application of surface modification processes using friction stir processing (FSP). Corrosion tests on each welded specimen revealed a higher corrosion rate in EBW welds compared to GTAW. Furthermore, it was confirmed that corrosion resistance improved due to phase refinement and redistribution of precipitates when FSP was applied.

A Feasibility Study on the Application of Self-Shielded Flux Cored Arc Welding Process for the On-Site Steel Bridge Box Fabrication (교량용 강재 박스의 현장 제조시 셀프실드 플럭스코어드 아크용접의 적용 타당성에 대한 연구)

  • Hwang, Yong-Hwa;Koh, Jin-Hyun;Oh, Se-Yong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.6 no.2
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    • pp.122-128
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    • 2005
  • A feasibility study on the application of self?shielded flux cored arc welding to the on-site SM520 steel bridge box fabrication for express trains and high way construction instead of gas-shield flux cored arc welding was conducted in terms of weld soundness, mechanical properties, toughness and microstructures. All welded specimens made with the self?shielded FCAW process were tested by magnetic particle and ultrasonic techniques and they were found to be sound. All multipass weld specimens made with both self-shielded and gas-shielded FCAW processes showed yield and tensile strengths of $462{\sim}549\;MPa$ and $548{\sim}640\;MPa$, respectively. The impact values of Charpy V-Notch weld specimens also met with the required value of 40J at $-20^{\circ}C$. The hardness values of the top area of weldments were higher than those of the bottom area because of higher residual stresses in the near surface. It was found that welding characteristics of SM520 steel by the on-site welding conditions with self-shielded FCAW showed almost equivalent to those by gas-shielded FCAW in terms of sound welds, mechanical properties and microstructure.

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