Control of Impact-Abrasion Resistance by Changing the Austenitising Temperature of 25 % Cr Cast Irons

The austenitising temperature for 3 mass % C-25 mass % Cr cast iron was changed from 1120 K up to 1470 K to change the hardness as well as the amount of retained austenite after air hardening, and the relation to weight loss resulting from impact wear was investigated. To evaluate weight loss due to impact wear, a small impeller breaker type tester was used. When the austenitising temperature was changed, the amount of retained austenite changed about 5∼90 %. For the maximum hardness of the material, when the austenitising temperature was 1320-1350 K, 65 HRC was obtained, and the amount of retained austenite was between 20∼30 %. The weight loss due to impact wear was minimum when the austenitising temperature was between 1270 K and 1429 K. When the amount of retained austenite in the matrix was 10∼70 %, the austenite effectively acted to reduce impact wear, but when the amount exceed 70 %, the hardness of the material dropped to 55 HRC, and the resistance to impact wear decreased. Moreover, the austenite obtained in this composition system was absolutely not effective in improving the toughness and flexural strength of the material.