Abstract
The base pressure and outgassing rate of a mild steel chamber were measured and compared to those of a stainless steel chamber. A combined sputter-ion and non-evaporable getter pump with a nominal pumping speed of 490 l/s generated the base pressure of $2.7{\times}10^{-11}$ mbar in the mild steel chamber and $1.2{\times}10^{-10}$ mbar in the stainless steel chamber. The rate-of-rise measurements show that the mild steel has an extremely low outgassing rate of $2.6{\times}10^{-13}$ mbar $ls^{-1}cm^{-2}$, which is about one-order of magnitude smaller than the outgassing rate of the stainless steels. Vacuum annealing of the mild steel at $850^{\circ}C$ reduced the outgassing rate further to $8.8{\times}10^{-14}$ mbar $ls^{-1}cm^{-2}$, which was comparable to the outgassing rate of a heat treated stainless steel for extreme-high vacuum use.