G-TECH 657

Specifically designed to adapt to the IN-657 alloy, this subfamily is also suitable for welding the machined version containing titanium of the IN-671 alloy. The IN-657 alloy, characterized by a high chromium content, offers exceptional resistance to hot corrosion in the temperature range between 800 and 950 °C. This resistance is crucial to counteract the corrosive attack of combustion ashes containing vanadium pentoxide and alkali metal sulfates, often resulting from the combustion of lower-grade heavy fuel oils. Castings made from IN-657 alloy are widely used in various components of oil furnaces and boilers, such as tube sheets, pipe supports, and spacers, used in ships, power plants, refineries, and petrochemical plants. At lower concentrations of chromium and niobium, primary dendrites belonging to the gamma phase form during solidification, which may increase the tendency for crack formation. A higher content of chromium and niobium promotes the formation of the primary dendritic alpha phase, which, although less ductile, is more prone to cold cracking during cooling. The presence of carbon and nitrogen reduces ductility and therefore their content is kept to a minimum. It is essential to maintain a short arc length to avoid nitrogen absorption. Preheating is generally required: 150-200 °C for 10 mm thicknesses, 200-250 °C for most applications, and up to 450 °C for thicker sections. It is crucial to maintain interpass temperatures and allow slow cooling.