In this study, the effect of composition and heat treatment (aging) on the corrosion resistance of high alloy steels containing 0.4% C, 29% Cr and 4-20% Ni has been investigated. Aging heat treatment was composed of quenching after holding at 1200 degrees C for 6 h and aging at 750 degrees C for 18 h. Corrosion tests were performed by suspending the samples of certain sizes into the 10% HCl solutions measuring the weight loss, and also by potentiodynamic polarization measurements in the same solution. The results of the corrosion tests revealed that, corrosion resistance of the aged alloys was increased with increasing Ni content. On the other hand, corrosion resistance of the austenitic matrix alloys was increased upon aging heat treatment while that of ferritic matrix alloy decreased with aging. (c) 2010 Elsevier B.V. All rights reserved.