The main purpose of this article is to determine the optimal level of alumi
num content in plain steels to have the optimal mechanical properties by me
ans of surface heat treatments. Various plain steels with different alumini
um content have been studied. The importance of treatment temperature is an
alyzed. The influence of other factors, like nitrogen content or the homoge
neous distribution of particles, is evaluated. It is concluded that the alu
minum composition of plain steels that are subjected to heat treatments sho
uld not exceed 0.02 %.