Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

[EN] This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25-60°C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest iG values at 60°C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H3PO4 media from a corrosion point of view for all the temperatures analysedThe authors would like to express their gratitude to the Spanish MAEC (PCI Mediterráneo C/8196/07, C/018046/08, D/023608/09) and to Asuncion Jaime for her translation assistance.Sánchez Tovar, R.; Montañés Sanjuan, MT.; García Antón, J.; Guenbour, A.; Ben Bachir, A. (2011). Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures. Corrosion Science. 53(4):1237-1246. https://doi.org/10.1016/j.corsci.2010.12.017S1237124653

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 A degrees C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 A degrees C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of gamma aEuro(3) phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 A degrees C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the delta-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases

Hot corrosion of wrought and weld overlay alloy 625 in molten salts environments

KIVCET smelter is a modern direct smelting process which has been used to replace conventional sinter/blast furnace technology in pyrometallurgical process of lead and zinc. Although heavy metals including Cd, Pb, Zn, Fe as well as S, O and Cl, are the main elements playing a leading role in the formation of molten phase on the waterwall tubes of the KIVCET waste heat boiler, hot corrosion behavior and electrochemical properties of weld overlay and wrought alloy 625 have not been studied yet in the molten salt environments containing the above-mentioned elements. The present study was carried out to study hot corrosion behavior of the weld overlay and wrought alloy 625 as well as failure mechanism of the weld overlay alloy 625 under the corrosive conditions of the radiant boiler in the KIVCET smelter. It was found that the deposited salt mixtures on the waterwall tubes of the radiant boiler had a strong tendency to form a molten phase at the operating temperature range of the radiant boiler. Presence of the deposited salt mixtures and the formation of the molten phase led to the occurrence of the hot corrosion attack in the waterwall and the ultimate failure of the weld overlay. The dilution and, consequently, the presence of a significant amount of Fe in the weldment composition were the key issues in the alloy 625 weld overlay. High concentrations of sulfur and oxygen in the grain boundaries of the wrought alloy 625 are to blame for the occurrence of the intergranular corrosion together with the internal attack. An electrochemical model (a porous and non-protective barrier layer model) was used to explain the corrosion/electrochemical behavior of the wrought alloy which fit into the obtained EIS data well.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat

Microstructure development and mechanical properties of a C-Mn-Si-Al-Cr cold rolled steel subjected to quenching and partitioning treatment

The microstructural evolution and mechanical behavior of Fe-0.2C-2.7Mn-1.2Si-0.8Al-0.3Cr (wt.%) quenching and partitioning steel were studied. Partitioning was performed at 400, 440, and 480 °C for various durations from 30 to 300 s to obtain different fractions of retained austenite. Scanning electron microscopy, dilatometry, and X-ray diffraction analysis as well as uniaxial tensile testing were employed to characterize the microstructural evolutions and mechanical properties. The resulting microstructures were primarily composed of tempered lath martensite, bainitic ferrite, retained austenite, and blocky fresh martensite. The lower partitioning temperature of 400 °C was appropriate for efficient carbon partitioning and stabilization of retained austenite at room temperature. However, the retained austenite fraction decreased with increasing partitioning temperature, due to accelerated bainite formation and carbide precipitation at higher partitioning temperatures. The tensile results revealed that all specimens had tensile strength values of more than 1128 MPa and yield strength values of over 830 MPa. Additionally, prolonging the isothermal holding time had a negative effect on the yield strength due to bainite formation, while it enhanced the elongation. Fractography analysis showed that specimens treated at the partitioning temperature of 400 °C were fractured in a relatively ductile mode, but the fracture nature altered to an intergranular mode after partitioning at higher temperatures