Tensile properties of high Cr-Fe alloys with small amounts of C and N were investigated after the heat-treatments in the temperature range from 800 to 1200°C followed by air cooling (A.C.) or water quenching (W.Q.). The yield strength, σ_y, and the tensile strength, σB, showed considerable scattering with heat treatments even when the same condition of annealing was used.
However, Δσ_y defined as the difference between σ_y of A.G. specimens and σ_y of W.Q. ones where those specimens were heated at a time in a furnace, was uniquely determined by the annealing temperature. Δσ_y was primarily explained by the difference between the K_y·d^-1/2 term of Hall-Petch eq. for A.C. specimens and that for W.Q. ones, but some part of Δσ_y explained by the difference in the friction term, was present. Small difference in contents of C and N significantly affected the responces of ductility and of grain size in these alloys to the change in annealing temperature.