Effect of aging before repeated cold treatment on the mechanical properties of steel N26T

1. After the complete heat-treatment cycle the strength characteristics of low-carbon steel N26T increase substantially (∼15–20%) after cold treatment due to two additional operations — intermediate aging at a temperature below Af and a second cold treatment. 2. The mechanical properties of the steel vary with the intermediate-aging temperature and improve as the temperature is raised from 500 to 625°. 3. Intermediate aging at temperatures below Af induces destabilization of austenite and increases (∼12%) the amount of α phase formed during the subsequent cold treatment. 4. The low strength characteristics after austenitizing at 720° are evidently due to the mutual effects of the two strengthening mechanisms — phase strain hardening and aging. The first mechanism is predominant at temperatures below 700°, and the second at higher temperatures.