• Journal of the Korean Ceramic Society
• /
• v.33 no.3
• /
• pp.251-258
• /
• 1996

The reactions between an active metal brazing alloy and interlayers together with the effects of interlayer type on the interfacial microstructure change were investiaged for silicon nitride/stainless steel joint. The bending strengths were measured for joints with Mo, Cu, Ni interlayer type of different thicknesses. It was found that the interlayer with a low yield strength value is effective to improve the bending strength of the Si3N4/stainless steel joint. The maximum joint strength obtained at room temperature for a laminated Cu/Mo interlayer was about 460 MPa. The combined use of Mo and thin Cu layer was found to be effective in enhancing the bending strength for the Si3N4/S.S.316 joint.

• Journal of the Korean Ceramic Society
• /
• v.39 no.10
• /
• pp.955-962
• /
• 2002

The microstructure change of brazed $Si_3N_4$/Stainless steel 316 joint with Cu buffer layer were examined to clarify the effects of brazing process conditions such as brazing time and temperature on the mechanical properties and reliability of brazed joints. For the brazed joint above 900${\circ}C$, the Cu buffer layer was completely dissolved into brazing alloy and the thickness of reaction product formed at $Si_3N_4$/brazing alloy joint interface was abruptly increased, which could increase the amounts of residual stress developed in the joint. The fracture strength of brazed $Si_3N_4$/Stainless steel 316 joint with Cu buffer layer at 950${\circ}C$ was much reduced comparing to those of joints brazed at the lower temperature. But, it was found that the effects of brazing time was not critical on the mechanical properties as well as the reliability of $Si_3N_4$/Stainless steel 316 joint with Cu buffer layer brazed at the temperature below 900${\circ}C$.

• Journal of Welding and Joining
• /
• v.29 no.4
• /
• pp.85-92
• /
• 2011

Microstructures and tensile properties in arc brazed joints of ferritic stainless steel, 429EM using Cu-8.6%Al insert metal was investigated as function of brazing current. The brazing speed was fixed at 800mm/min and brazing current varied in the range of 80A to 120A. The initial phase of filler metal was Cu single phase. However, the insert metal structures of brazed joints was composed of Cu matrix and intermetallic compound such as ${\gamma}_1(Al_4Cu_9)$, and flower-shape Fe-Cr. The fraction of ${\gamma}_1(Al_4Cu_9)$ phase was similar with 80A and 100A brazing currents while that of brazed with 120A was decreased. On the other hand, the fraction of Fe-Cr phase increased with increasing of the brazing current. A reaction layer at the base metal/insert metal interface was observed and this reaction layer was thickened with increasing of the brazing current. In the brazed joints with the current lower than 100A, crack was grew up along the interface which was perpendicular to the tensile stress, and then, passed through the insert metal in the final stage of fracture. As the brazing current increased to 120A, fracture occurred at the base metal.

• Korean Journal of Materials Research
• /
• v.17 no.3
• /
• pp.142-146
• /
• 2007

Vacuum brazing method has been coming to an important process as one of the new fabricating techniques of metals and alloys. In this study, a vacuum brazing of SUS304 stainless steel with BNi-2 filler metal was carried out in $1{\times}10^{4}$ Torr of vacuum atmosphere. The formation of brittle intermetallic compounds in brazed joints between SUS304 stainless steel and BNi-2 filler metal is a major concern, since they considerably degrade the mechanical properties of joints. To obtain enough stable joining strength, it is necessary to understand the unique properties of brazing process with Ni-based filler metals containing boron. So, in this research we investigated the performance of SUS304/BNi-2 brazed system and the brazed joint properties were evaluated at room temperature by using tensile test. Metallurgical and fractographic analysis were used to characterize the microstructure, the mechanisms of brazing, and joint failure modes.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.100-100
• /
• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1679-1683
• /
• 2007

Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. For fatigue design of gas welded joints such as fillet and plug and ring type joint, it is important to obtain optimum design parameter information on gas welded joints. In this paper, analysis approach for fatigue test using experimental design are evaluated optimum factor in gas welded joint type and geometrical parameters of materials. Using these results, that factors applied to fundamental information for fatigue design.

• Journal of Welding and Joining
• /
• v.28 no.4
• /
• pp.49-54
• /
• 2010

Stainless steel sheets are widely used as the structural material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the GMAW (gas metal arc welding). For fatigue design of GMA welded joints such as fillet and plug, ring type joint, it is important to obtain optimum design factor information on GMA welded joints. in this paper, analysis approach for fatigue test using design of experiment are evaluated optimum factor in GMA welded joint type and geometrical parameters of materials. Using these results, that factors applied to fundamental information for fatigue design.

• Journal of Welding and Joining
• /
• v.1 no.2
• /
• pp.45-52
• /
• 1983

Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

• Proceedings of the KWS Conference
• /
• v.43
• /
• pp.112-114
• /
• 2004

• Proceedings of the KWS Conference
• /
• 1990.04a
• /
• pp.76-80
• /
• 1990