<P> Many alloy systems allow the aging temperature to be adjusted . For instance, some aluminium alloys used to make rivets for aircraft construction are kept in dry ice from their initial heat treatment until they are installed in the structure . After this type of rivet is deformed into its final shape, aging occurs at room temperature and increases its strength, locking the structure together . Higher aging temperatures would risk over-aging other parts of the structure, and require expensive post-assembly heat treatment because a high aging temperature promotes the precipitate to grow too readily . </P> <P> There are a number of ways by which a matrix can be hardened by precipitates . </P> <P> 1 . Coherency hardening </P> <P> 2 . Modulus hardening </P>

Hardness of stainless steel increases with increasing temperature