Experiments were conducted to determine the effect of longer treatment at high temperature on the hardening characteristics of high-Cr steels. Solution treatments of 2, 4, and 8 hr were employed at each of the 3 austenitizing temperatures for 15 steels representing Cr levels of 18, 21, and 24 Ni levels of minimum, 2, and 3 N contents of minimum and .01 x Cr and C ranging from 0.23 to 0.56. Response of hardness levels to length os solution treatment was negligible. Six-hr tempering treatments were superior to 1 hr. Studies were made of structures produced by variations in Ni and N additions to a 0.35C, 21.0 Cr base alloy. Marked changes in primary ferrite were observed for 4 combinations of 0.12 and 2.17 Ni with 0.06 and 0.23 N the low-Ni, low-N alloy was more than 75 -structure at 1900 deg F. The high-Ni, high N alloy was austentic at all solution temperatures. Within certain ranges, Ni and N appeared to be nearly equivalent to C in its stability to change phase relationships. Excess carbides were present in nearly all instances. Tensile tests were made on 3 alloys of the 21 Cr group the low N grades displayed inadequate yield strenght at 2 hardness levels, and unsatisfactory ductility at the higher level. A 2 Ni, low-N alloy resisted softening by tempering treatments at 1100 and 1200 deg F, and showed high yield strength but little ductility.