| Blocker | (english) Preform die or impression, used when part cannot be made in a single operation. |
| Blow Down | (english) Process that rids boiler feed water of solids and maintains the proper chemical balance of the feed water. Blow down can also be used to rid drum(s) of excess water. |
| Blowhole | (english) A defect in a casting caused by trapped steam or gas. |
| Blowhole 2 | (english) A cavity which was produced during the solidification of metal by evolved gas, which in failing to escape is held in pockets. |
| Blue Annealing | (english) Heating hot rolled ferrous sheet in an open furnace to a temperature within the transformation range and then cooling in air, in order to soften the metal. The formation of a bluish oxide on the surface is incidental. |
| Blue Brittleness | (english) Brittleness exhibited by some steels after being heated to some temperature within the range of 300 (degrees) to 650 (degrees) F, and more especially if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness. |
| Blue Brittleness 2 | (english) Reduced ductility occurring as a result of strain aging, when certain ferrous alloys are worked between 300 and 700 (degrees) F. This phenomenon may be observed at the working temperature or subsequently at lower temperatures. |
| Blue Print | (english) A pen or ink line drawing reproduced (printed) on sensitized paper by direct exposure. |
| Blue Vitriol Copper sulfate | (english) A layout solution which turns a copper color when applied to a clean,polished metal surface. |
| Blush | (english) A coating defect consisting of the whitening of a cured film which results in a translucent or opaque appearance with accompanying loss of gloss. Blushing usually occurs during the pasteurization or steam processing of films which are undercured or water sensitive. |