A method of manufacturing a valve body having one or more corrosion-resistant internal surfaces. The method involves performing a casting process, which includes pouring a first material into a mold box, to produce a valve body casting made of the first material. During the casting process, a layer of a second material is formed on one or more internal surfaces of the valve body casting, the second material having a higher corrosion resistance than the first material, by: (1) applying, with an additive manufacturing technique, the second material to one or more external surfaces of a core, and (2) inserting the core into the mold box. A portion of the first material binds to the second material on the one or more external surfaces of the core while the first material is poured into the mold box.