[en] The precipitation and sensitization characteristics in AISI436 weld metal were investigated in different chemical composition ranges of Ti and Nb content. We manufactured four welding wires made of 0-0.2 wt% of Ti and 0-1.0 wt% of Nb and did flux cored arc welding. After heat treatment at 900 °C for 20 hours, we made a Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) test, Electron Backscattering Diffraction and SEM. The DL-EPR test revealed that as the amount of addition of Ti and Nb rose, the degree of sensitization fell. The microstructure became more refined, and Cr carbide formed at the grain boundary that had no addition of Ti and Nb. Furthermore, in the specimen with the addition of Ti, Nb, the Ti, Nb carbide and nitride were precipitated in the intergranular boundary, and the laves phase was precipitated at the grain boundary.

[en] To investigate the effect of tungsten substitution of molybdenum on the formation of the second phase in Super Duplex Stainless Steel Weldments, welding wires with a composition of 3 wt% Mo, 2.2 wt% Mo-2.2 wt% W were designed for the flux cored arc welding process. As a result, the precipitation of the χ phase and σ phase increased in proportion to the decrease in the amount of δ ferrite content because the reaction, δ ferrite → σ + γ2, proceeded as the temperature rose. Under the same experimental conditions, the precipitation of the second phase, which degrades the properties of the material, was significantly reduced in the W substitution specimens compared to the Mo-only specimens. A polarization test conducted in a salt solution revealed that the pitting potential of the W substitution specimens was higher than that of the Mo-only specimens.

[en] The microstructure and mechanical properties characteristics in AISI 436 weld metal were investigated for different ranges of chemical composition of stabilization element Ti Three new filler wires were designed for flux cored arc welding (FCAW) process, and the Ti contents and solidification path of each of the weld metals was changed. Each specimen of AISI 436 transformed to fully ferrite or ferrite and martensite. Ti suppressed the formation of martensite and had a grain refinement effect. The tensile strength varied according to the content of additional Ti. The effects were negligible when 0.5 wt% Ti was added, but the tensile strength increased by 41 MPa with the addition of 0.8 wt% Ti. When the amount of added Ti was greater than 0.5%, some Ti dissolved. The increase in tensile strength is attributed to the remaining undissolved Ti. Cracking occurred in the specimens contained added Ti. Fracture monograph observed the Transgranular Cleavage Fracture that is a commonly occurring phenomenon in Mediumchromium Ferritic stainless steel. This crack may be influenced by stabilization elements and cooling speed.

[en] In this study, Precipitation behaviour and their corrosion properties about three types of weld metals adjusted the Ti content of AISI 436 stainless steel welding wire flux were evaluated by examining the microstructure of the welding metal and by conducting an anodic polarisation test after two hours of heat treatment at 850°C were produced. Microstructural examinations revealed that the sigma phase in the Ti-free specimen was formed by the segregation of Cr-Mo. However, in the Ti-added specimens, the sigma phase did not precipitate instead, TiN formed within the grain matrix. Ti expanded the ferrite region and delayed the formation of the sigma phase. EDS and mapping analyses revealed that the segregation of Cr-Mo occurred where the sigma phase precipitated. Anodic polarisation revealed that the potentials of passive film formation were nearly identical for all samples, but the pitting potential increased as Ti was added, improving the corrosion resistance. Examination of the starting point of pitting corrosion revealed that pitting in the Ti-free specimen began around the Cr-deficient area that surrounded the sigma phase, whereas in the Ti-added specimens, pitting began in the vicinity of the Ti precipitates that were formed within the grain matrix.

[en] The mechanical properties and corrosion behavior in welded EH36 TMCP steel were investigated with different Ni content and heat input. Weldments were produced by adjusting the heat input and Ni content of 0, 1.3 wt%. The acicular ferrite fraction increased as the Ni content increased. In contrast, the grain boundary ferrite and Widmanstaetten ferrite decreased. The impact energy absorption increased with the addition of the Ni content and decreased as the test temperature decreased. Both tensile and yield strengths increased with either the addition of Ni or reduced heat input. As a result of the polarisation test conducted in a salt solution, the corrosion potential of the 1.3 wt% Ni added specimens was higher than the free Ni specimens.

[en] This study investigated the effect of the aging time of weldment of 24Cr-3.5Mo duplex stainless steel on the microstructure and corrosion behavior. After performing FCAW, we carried out heat treatments at varying times at 850 ℃ and performed observation of microstructure, potentio dynamic test, SEM-EDS analysis, and X-ray diffraction analysis. As the aging time increased, the fraction of δ-ferrite decreased sharply, but the fraction of γ slightly increased. The σ phase was generated at a non-metallic inclusion along the grain boundaries of δ-ferrite and γ, while the χ phase was generated in the structure of δ-ferrite. As the intermetallic compounds increased, the critical pitting potential fell sharply, and PREN of the surrounding structure decreased by 5 due to precipitation of the σ phase in 3.5% NaCl at 60 ℃. Pitting occurred intensively under a multi-pass line which relatively had more intermetallic compounds, and the precipitation of the σ phase caused the formation of Cr carbide.

[en] This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses

[en] This study was performed to investigate the effects of the driving force for reduction and the surfactant (polyacrylic acid) on the size of Ag particles. As the driving force for reduction increases, the size of particles decreases due to a decrease of initial nuclei-size. Also, an increase of pH increases the amount of ionized surfactant, which leads to a decrease of particle size due to the prevention of particle growth. Both the driving force and the surfactant may affect the particle size, but the surfactant appeared to be a more dominant factor than reduction potential in terms of controlling the particle size. An increase of surfactant in the range of pH=3-4 decreases the size of Ag particles, although the reduction potential also decreases.

[en] The influence of High Temperature Gas Nitriding (HTGN) in STS347 and STS310S steels was experimentally investigated. The HTGN was carried out at 1,050 .deg. C∼1,150 .deg. C for 10 hrs in a gaseous atmosphere containing 1 kg/mm² of nitrogen. After HTGN, fine precipitates of Cr₂N and NbN appeared in austenite on the surface of STS 347, while nitrogen pearlite, which was layered of Cr₂N and austenite alternatively, appeared in austenite on the surface of STS 310S. The surface hardness of HTGN-treated, STS 347 and STS 310S specimens was 250∼360 Hv and 270∼400 Hv, respectively, depending on the temperature of HTGN. The nitrogen content was analyzed 1.4 wt% and 1.6 wt% at the surface layer of STS 347 and STS 310S steels, respectively. In addition, an improvement in the corrosion resistance of HTGN treated specimens was observed

[en] This paper identified the effects of Nb on microstructure. Also, it has studied on uniform and pitting corrosion resistance in a ferritic stainless steel weld metal of the automobile exhaust system. We fabricated 3 flux cored wires designed with 0-1.0 wt% Nb and performed Flux Cored Arc Welding. We observed the microstructure with the SEM/EDS and EBSD. To evaluate the uniform and pitting corrosion resistance, we performed a potentiodynamic polarization test in 0.2 M H_2SO_4 and 0.1, 0.3, 0.5 M NaCl. As a result of the tests, we found that as the amount of addition of Nb rose, the amount of Cr-carbide fell. The microstructure became more refined. The specimen with 1.0%Nb added had the highest uniform and pitting corrosion resistance. After the pitting corrosion test, a pit was formed at the grain boundary that has no addition of Nb. In addition, in the specimen with added Nb, pits were formed at the inclusions.