hot working operation

Hi folks,
A metals recrystallization temperature is not quite as easy to determine as its melting point, because it is influenced by such factors as the level of internal stress that exists in the metal before heating, the alloys contained within the metal and its melting point .for many metals the recrystallization temperature is between 0.4 and 0.5 of the materials absolute melting point (k). Depending upon carbon content, for most steels it is generally in the region of 500 – 700 C. as can be seen from ambient, with aluminum being at just 150C. Thus, hot working does not necessarily imply that the temperature of the metal being worked is above ambient, although in most cases it is. And an important characteristic of hot working process is that the metal behaves in a perfectly plastic manner. Therefore the metal becomes neither internally stressed nor work hardened, so an unlimited amount of hot working can be performed on it without at a lower temperature. Hot working causes slag porosity and other inclusions inherent to some degree in most cast metal to be deformed and broken up into insignificantly small pieces. Also, the coarse granular structure typical of cast metals is realigned and a large number of smaller grains are formed. The effect of this is to impart a degree of toughness to the worked materials, although hardness and density are unchanged by hot working. Thank you.