Pin-on-disc type wear tests have been conducted on steel under dry friction and the influence of Cr-content on its transition behavior from severe to mild-wear are discussed. In order to achieve mild-wear, the formation of a sufficient amount of oxide as well as that of work-hardened hard surface layer to hold the oxide layer is indispensable. The addition of Cr to steel produces two opposite effects on mild-wear: one to promote hardening and the other to inhibit oxidation. The range of severe-wear is enlarged by oxidation inhibition, and thus the Cr addition is harmful to T1-transitional load. On the other hand, the range of mild-wear is enlarged by hardening promotion and thermal softening inhibition, and the Cr addition is desirable to T2-transitional load. The increase of hardness by heat treatment contributes to the maintenance of oxide films and enlarges the range of mild-wear.
