Hastelloy B-2 alloy, characteristic hardness and melting point, mechanical properties
Hastelloy B-2 alloy is a Ni-Mo alloy with extremely low carbon content and extremely low silicon content. The advantage of this alloy is that it reduces the precipitation of cementite and other phases in the weld seam and heat affected zone, thus ensuring good corrosion resistance even under welding conditions. Hastelloy alloys have always been known for their excellent corrosion resistance, and Hastelloy B-2 alloy is no exception. It exhibits good corrosion resistance in various oxidizing media, including inorganic and organic acids such as sulfuric acid, phosphoric acid, and acetic acid, as well as bromic acid and hydrogen chloride gas.
In many years of industrial application, Hastelloy B-2 alloy has been widely used in rigorous petroleum and chemical processes such as sulfuric acid distillation and concentration. It is also suitable for processes such as the alkylation of ethylbenzene and the production of acetic acid from low-pressure sulfuric acid. However, some problems have also been discovered in the practical application of Hastelloy B-2 alloy.
First of all, Hastelloy B-2 alloy has two sensitization zones: a high temperature zone of 1200~1300°C and a medium temperature zone of 550~900°C. These areas have considerable resistance to stress corrosion, but there is also some susceptibility. Due to dendrite shrinkage, intermetallic phases and cementite will precipitate along the grain boundaries in the weld metal and heat-affected zone of Hastelloy B-2 alloy, making it more sensitive to stress corrosion.
Secondly, Hastelloy B-2 alloy has poor thermal stability. If the stay time is slightly longer in the temperature range of 650~750℃, the β phase will be generated instantly. The existence of β phase will reduce the toughness of Hastelloy B-2 alloy, making it more sensitive to intergranular corrosion, and may even cause Hastelloy B-2 alloy to crack during raw material production, equipment production process or system operation.
At present, the normal pressure boiling sulfuric acid method is the standard test method for the stress corrosion resistance of Hastelloy B-2 alloy designated domestically and around the world, and its evaluation method is the weight loss method. However, this method is not very sensitive for detecting the stress corrosion tendency of Hastelloy B-2 alloy. In order to better evaluate the performance of Hastelloy B-2 alloy, domestic research institutions used the high-temperature sulfuric acid method to conduct research and found that the corrosion resistance of Hastelloy B-2 alloy not only depends on its chemical composition, but also depends on its heat treatment process. control. If the thermal processing process is not properly controlled, the grains of Hastelloy B-2 alloy will grow and a high Mo phase will precipitate between the grains. At this time, the stress corrosion resistance of Hastelloy B-2 alloy will be significantly reduced.
Overall, Hastelloy B-2 alloy is an excellent corrosion-resistant material widely used in chemical, petrochemical, energy production and pollution control fields. However, its application also needs to fully consider its existing sensitization area and hygrothermal stability issues. At the same time, more sensitive methods need to be used to evaluate its stress corrosion tendency. By fully understanding and mastering the performance characteristics and application fields of Hastelloy B-2 alloy, we can better leverage its advantages and provide more reliable solutions for industrial production.
