Hastelloy B-2 alloy is a ni-MO138-2118-5638 cycle alloy with very low carbon and silicon content. It reduces the precipitation of carbides and other phases in the weld and heat affected zone, thus ensuring good corrosion resistance even in the welded state. As is known to all, Hastelloy B-2 alloy has excellent corrosion resistance in various reducing media, and can withstand the corrosion of hydrochloric acid at any temperature and concentration under atmospheric pressure. It has excellent corrosion resistance in non-aerated medium concentration of non-oxidizing sulfuric acid, various concentrations of phosphoric acid, high temperature acetic acid, formic acid and other organic acids, bromic acid and hydrogen chloride gas. At the same time, it is also resistant to halogen catalyst corrosion. Therefore, Hastelloy B-2 alloy is usually used in a variety of harsh petroleum and chemical processes, such as the distillation of hydrochloric acid, concentration, alkylation of ethylbenzene and low pressure carbonyl synthesis of acetic acid.
The medium temperature thermal stability of Hastelloy B-2 alloy is poor. When the iron content in Hastelloy B-2 alloy drops below 2%, the alloy is sensitive to the transformation of phase 3 (i.e. Ni4Mo phase, an ordered intermetallic compound). When the alloy stays in the temperature range of 650~750℃ for a long time, the phase 3 is generated instantly. The presence of phase 3 reduces the toughness of Hastelloy B-2 alloy, makes it sensitive to stress corrosion, and even causes the cracking of Hastelloy B-2 alloy in raw material production (such as hot rolling process), equipment manufacturing process (such as integral heat treatment after welding of Hastelloy B-2 alloy equipment) and service environment. At present, the standard test method for intergranular corrosion resistance of Hastelloy B-2 alloy is normal pressure boiling hydrochloric acid method and weight loss method. As hastelloy B-2 alloy is resistant to hydrochloric acid corrosion, it is not sensitive to test the intergranular corrosion tendency of hastelloy B-2 alloy by boiling hydrochloric acid at atmospheric pressure. It is found that the corrosion resistance of Hastelloy B-2 alloy depends not only on its chemical composition, but also on the control process of hot working. When the hot working process is not controlled properly, not only the grains of Hastelloy B-2 alloy grow up, but also the high Mo σ phase appears in the intergranular phase. Under this condition, the intergranular corrosion resistance of Hastelloy B-2 alloy decreases obviously. In the HCL test, the grain boundary erosion depth of coarse-grained plate and normal plate differs about twice.