AISI 347, also known as UNS S34700, is a type of austenitic stainless steel that contains a higher percentage of chromium and nickel than standard austenitic stainless steels. It also contains a small amount of columbium and tantalum, which provides the steel with improved intergranular corrosion resistance compared to other stainless steels.
AISI 347 is often used in applications that require high temperature resistance, such as in the aerospace, chemical processing, and power generation industries. The alloy has a maximum operating temperature of 1600°F (870°C) and can withstand thermal cycling without losing its strength and corrosion resistance.
The alloy also exhibits excellent welding properties, making it a preferred choice for welded components in high-temperature applications. Its low carbon content ensures that it does not undergo intergranular corrosion during welding, which is a common issue with other high-temperature alloys.
In addition to its high-temperature properties, AISI 347 also has good resistance to corrosion in acidic and alkaline environments. Its improved intergranular corrosion resistance is due to the presence of columbium and tantalum, which form carbide precipitates at the grain boundaries to prevent chromium depletion.
AISI 347 is available in a range of forms, including sheet, plate, bar, and pipe. It is also commonly used in the manufacture of fittings, valves, and flanges for high-temperature applications. The alloy can be readily machined and formed using conventional techniques, although its increased hardness compared to standard austenitic stainless steels may require special tooling.
In summary, AISI 347 is a high-temperature austenitic stainless steel with improved corrosion resistance and good welding properties. Its elevated chromium and nickel content, coupled with the addition of columbium and tantalum, make it an ideal choice for applications that require high-temperature resistance and corrosion resistance in acidic environments.