Operational High-Temperature Strength of Controlled Austenite-Transformed and Dispersion-Hardenable Die Steel

The mechanical characteristics of chosen alloying levels (low, medium, and high) of new 4Kh3N3G7M7F die steel, recommended for operation at temperatures above 700°C, were investigated. The steel belongs to the group with in-service controlled austenite transformation (CAT), which combines the resistance to high-temperature softening of austenitic steels with the satisfactory cutting performance of those with the ferrite base. New steel features the ability to dispersion hardening with its maximum level after quenching from 1150°C and aging at 725°C. The sensitivity of its chemical composition, as CAT steel, to the retention of structure and necessary high-temperature strength requires determining a permissible maximum content of its components. It was established that all alloying levels as to the critical point values were consistent with those of CAT steel. After quenching, it retained a basic austenite structure necessary for dispersion hardening steels of this grade. In the high-temperature (750–850°C) strength characteristics, all alloying levels are 1.5–3 times higher than those of standard high-temperature 5Kh3V3MFS (DI23) martensitic die steels. Especially important features are offered at a test temperature of 850°C: σ_0.2 values are within 367–413 MPa, and σ_u are 399–461 MPa compared to 135 MPa and 179 MPa for standard steel, respectively. The advantages of new steel are also retained after cyclic cooling to room temperature from the high ones. It is vital to note that even at room temperature, it is not inferior to standard steel in terms of σ_0.2, σ_u, and hardness, which is not achieved even for the most high-alloy heat-resistant steels and dispersion-hardenable alloys. Based on the investigation results, a maximum content of components was determined to retain the advantages compared to standard heat-resistant die steels.