RA 253 MA

RA 253 MA

RA 253 MA® is a lean austenitic heat resistant alloy with high strength and outstanding oxidation resistance. It offers an excellent combination of creep strength along with excellent resistance to oxidation, sulfidation, and erosion at high temperatures in an alloy containing just 11% nickel. Because of its lean chemistry, RA 253 MA is very economical compared to most heat resistant alloys.

RA 253 MA obtains its heat resistant properties by tight control of micro alloy additions. The use of cerium in combination with silicon results in superior oxidation resistance to 2000°F (1093°C). Nitrogen, carbon, and cerium combine to provide creep rupture strength that is double that of type 310 and 309 stainless at 1600°F (871°C).

Applications

• Boiler Nozzles
• Corrugated Boxes
• Cyclones
• Bar Baskets
• Radiant Tubes

Oxidation

RA 253 MA has exceptional oxidation resistance up to about 2000°F (1093°C). Above this temperature, its oxidation resistance drops off. A combination of rare earths and silicon is responsible for the excellent oxidation resistance of this 21% Cr alloy. The rare earths increase diffusion rate of the silicon to the scale-metal interface. This promotes the development of a continuous SiO2 subscale, which in turn slows further oxide growth. Rare earth metals also improve adhesion and elasticity of the oxide scale, even under cyclic conditions. These rare earths, primarily cerium, increase the number of nucleation sites for the oxide. This results in a fine grained chromia and silica scale.

Specifications

• ASME SA 182, ASME SA 213
• ASTM A 240, ASTM A 276, ASTM A 312, ASTM A 479
• UNS S30815
• Werkstoff 1.4835