What Does Alloy B2 Mean?
Alloy B2 is a solid solution strengthened, nickel-molybdenum alloy with excellent resistance to reducing environments. The nickel-base wrought alloy withstands hydrochloric acid at all concentrations and temperatures, and has excellent resistance to stress-corrosion cracking, pitting corrosion and heat-affected zone attack.
Alloy B2 is suitable for various chemical process applications in its welded form, and in extreme reducing conditions such as pure sulfuric acid, phosphoric acid and hydrogen chloride gas environment.
Other aliases for alloy B2 are Hastelloy B2, AL B2, Nickelvac H-B-2 or Nicrofer 6928.
Corrosionpedia Explains Alloy B2
The B2 nickel-based alloy contains between 26 and 30% molybdenum, 2% iron, 1% chromium, 1% manganese, 0.1% silicon, 0.02 carbon and about 68% nickel. The molybdenum alloying element contributes to the high resistance to reducing environments and hence corrosion. Solid solution strengthening process allows impurity atoms to impose lattice strains on the surrounding host metal atoms. This strain restricts the dislocation movement, leading to higher strength of the alloy.
Like other corrosion, temperature and wear-resistant alloys, B2 alloy is classified as being moderate to difficult in machining. However, it can be machined using conventional methods to provide satisfactory results. When machining, it work hardens rapidly, welds to the cutting surface, offers high resistance to metal removal, and generates heat during cutting.
In welding, the alloy resists the formation of grain boundary carbide precipitates in the heat-affected zones. The reduced precipitation of carbides and other phases in the heat-affected weld zones provides a uniform resistance to corrosion across all sections of the material.
Alloy B2 has excellent resistance to the reducing conditions such as the sulfuric, phosphoric and acetic acids, aluminum chloride catalysts, hydrogen chloride gas environment, and a number of non-oxidizing acids. However, it has very low corrosion resistance in oxidizing media or in a reducing media with oxidizing contaminants. It also suffers from premature corrosion failure if used in a hydrochloric acid environment where copper or iron is present. In addition, it is not used at temperatures in the range 870–1600°F due to the formation of secondary phases, which decreases the ductility.
Available forms include seamless pipe, seamless tube, welded pipe, welded tube, sheet plate, bar, forgings, wire, pipe fittings and flanges.
Applications of B2 alloy include mechanical components for use in reducing environments, heat exchangers, vacuum furnaces and chemical processing.