• Title/Summary/Keyword: Post-bond Heat Treatment

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Mechanical Properties of the Flash Butt Welded Joint of 590MPa High Strength Steel (590MPa급 고강도강 플래시버트 용접이음부의 기계적특성)

  • Jeong, Bo-Young;Woo, In-Su;Kim, Jeong-Kil;Lee, Jong-Bong
    • Journal of Welding and Joining
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    • v.25 no.2
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    • pp.55-61
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    • 2007
  • Flash butt weldability of 590MPa dual phase steel is carried out under micro metallographical examination and macro mechanical property tests. The objective of present study is to investigate the cause that brings on bond line fracture, and is to improve mechanical properties of the flash butt welded joint. The joint of flash butt welding has a superior tensile property, but has bad formability due to oxide formed at bond interface. The HAZ softening in the weld joint does not show. It was found that mechanical properties were increased with optimizing welding parameters and making application of oil dripping and post-weld heat treatment.

Optimization of Friction Welding Conditions for Production of Hose Nipple for Marine Transport (해양 수송용 호스니플 제작을 위한 마찰용접 조건의 최적화)

  • Kim, Dong-Gyu;Kim, Yeuk-Ran;Kong, Yu-Sik
    • Journal of Ocean Engineering and Technology
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    • v.30 no.1
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    • pp.51-56
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    • 2016
  • In this study, for the tube-to-tube friction welding of hose nipple materials, the main parameters of friction welding were investigated using tensile tests, Vickers hardness surveys of the bond area (HAZ), and observations of the microstructure to increase the quality of friction welding based on visual examination. As-welded and post weld heat treated (PWHT) specimens were tested. The optimal welding conditions were found to be n = 1000 rpm, HP = 10 MPa, UP = 15 MPa, HT = 9 s, and UT = 5 s when the metal loss (Mo) was 7.5 mm. Furthermore, the peak of the hardness distribution of the friction welded joints could be eliminated by PWHT. Moreover, the two materials of the friction weld were thoroughly mixed with a well-combined structure of micro-particles, without any molten material, particle growth, or defects.

Optimization of Friction Welding for Motor Vehicle Safety Belts: Part 1-Mechanical Properties and Microstructure (수송차량 안전벨트용 모터축재의 마찰용접 최적화(1) - 기계적 특성 및 조직)

  • Kong, Yu-Sik;Ahn, Seok-Hwn
    • Journal of Ocean Engineering and Technology
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    • v.26 no.1
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    • pp.64-69
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    • 2012
  • Dissimilar friction welds were produced using 15-mm diameter solid bars of chrome molybdenum steel (KS SCM440) and carbon steel (KS SM20C) to investigate their mechanical properties. The main friction welding parameters were selected to ensure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond area and HAZ, and macro-structure investigations. The specimens were tested as-welded and post-weld heat treated (PWHT). The tensile strength of the friction welded steel bars was increased to 100% of the SM20C base metal under the condition of a heating time of more than four seconds. Optimal welding conditions were n = 2,000 (rpm), HP = 60 (MPa), UP = 100 (MPa), HT = 5 (s),and UT = 5 (s), when the total upset length was 7.8 (mm). The hardness distribution peak of the friction welded joints could be eliminated using PWHT. The two different kinds of materials were strongly mixed to show a well-combined structure of macro-particles, with no molten material, particle growth, or defects.

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).

Study on the Disbonding of Stainless Steel Overlay Welded Metal(Report 2) - A Metallurgical Study on PWHT of Overlaid Austenitic Stainless Steel Weld Metals - (스테인레스강 Overlay 용접부의 Disbonding 에 관한 연구(2) - 오스테나이트계 스테인레스강 오버레이 용접금속의 PWHT에 관한 야금학적 고찰 -)

  • 이영호;윤의박
    • Journal of Welding and Joining
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    • v.2 no.1
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    • pp.4-17
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    • 1984
  • Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

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Investigating the Cause of Hindrance to the Interfacial Bonding of INCONEL 718 Layer Deposited by Kinetic Spray Process (저온 분사 공정을 이용해 적층된 INCONEL 718의 계면접합 저해요인 분석)

  • Kim, Jaeick;Lee, Seungtae;Lee, Changhee
    • Journal of the Korean institute of surface engineering
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    • v.48 no.6
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    • pp.275-282
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    • 2015
  • The cost for maintenance (replacement cost) of Ni-superalloy components in plant industry is very expensive because of high unit price of INCONEL 718. A development of repairing technology using kinetic spray process can be very helpful for reducing the maintenance cost. However, it is very difficult to produce well-deposited INCONEL 718 layer showing high interfacial bond strength via kinetic spraying. Thus, INCONEL 718 was deposited on SCM 440 substrate and the interfacial properties were investigated, in order to elucidate the cause of hindrance to the bonding between INCONEL 718 layer and SCM 440 substrate. As a result, it was revealed that the dominant obstacle to the interfacial bonding was excessive compressive residual stress accumulated in the coating layer, resulting from low plastic-deformation susceptibility of INCONEL 718. Nevertheless, the bonding state was enhanced by the post heat-treatment through relieving the residual stress and generating a diffusion/metallurgical bonding between the INCONEL 718 deposit and SCM 440 substrate.

Mechanical Properties of Friction Welded SM 45C-SF 45 Joints for Automobile Reverse Idle Gear Shaft Applications (자동차 후진기어용 축재(SM 45C-SF 45)의 이종마찰용접 특성)

  • Kong, Yu-Sik;Yun, Seong-Pil;Kim, Seon-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.1
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    • pp.85-90
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    • 2010
  • Friction welding is a common practice to join axially symmetrical parts for automobile industry applications. The shaft for automobile reverse idle gear is generally produced by forging steel, SF 45. This method is not so good because of high cost of material and production. In this study, in order to investigate the possibility of application of SM 45C to SF 45 dissimilar friction welding, the dissimilar friction welded joints were performed using 20 mm diameter solid bar in forging steel(SF 45) to carbon steel(SM 45C). The optimal friction welding parameters were selected to ensure reliable quality welds on the basis of visual examination, tensile test, micro-Virkers hardness surveys of the bond of area and optical microstructure investigations for welded joint parts. Finally, post weld heat treatment(PWHT) of the high-frequency induction hardening was performed for the friction welded specimens under the optimal welding conditions. And then, the mechanical properties were compared for as-welded and PWHT in SM 45C to SF 45.