The amount of solid solution hardening by some elements was investigated using Fe-25 massÿCr ferritic steel and Austenitic steels. It was revealed that the hardening amount
by Austenite-former elements was considerably larger than that by ferrite-former elements in Ferritic steel. Meanwhile the hardening amount by Ferrite-former elements showed higher
value in Austenitic steel, which was a reverse tendency to Ferritic steel. The mechanism was discussed from the point of solubility limit of elements. As a result, the good correlation
between the hard-ening amount and solubility limit was found and the predictive expression of the hardening amount from solubility limit was suggested.