Hastelloy B-3 Solution Heat Treatment Precautions

The heat treatment of HASTELLOY® B-3® (UNS N10675) is a critical process because heating and cooling must quickly pass through the 475°C embrittlement zone and avoid the formation of high-temperature sigma phase and other intermediate phases. Therefore, rapid heating and cooling of the workpiece are essential. Typically, the furnace should be preheated to the specified temperature before placing the workpiece inside. The surface of the workpiece should be cleaned before loading it into the furnace. After holding at a certain temperature for a specified time, rapid water quenching should be performed.

Unless specifically requested by the customer, all B-3 alloy forgings are supplied in the solution-treated condition. The solution treatment temperature for B-3 alloy is 1065°C (with the solution treatment temperature controlled within the range of 1060-1080°C), followed by rapid quenching. Thin sheets or wires are bright annealed at a heating temperature of 1150°C and cooled in hydrogen to achieve optimal corrosion resistance.

Due to the relatively high solution treatment temperature and subsequent rapid cooling, deformation of the workpiece is inevitable. During the heat treatment of B-3 alloy, the following issues should also be noted: to prevent deformation of equipment components during heat treatment, stainless steel reinforcing rings can be used; strictly control the furnace loading temperature, heating, and cooling times; pre-treat parts undergoing heat treatment to prevent the occurrence of thermal cracks before placing them in the furnace; perform 100% penetration testing on parts after heat treatment; if thermal cracks occur during heat treatment, grind the affected areas and use specialized welding techniques for repair.