Fracture Toughness of 22K-Type Low-Carbon Steel After Extreme Thermal Exposure

A complex of comparative studies on static fracture toughness according to the three-point bending scheme was carried out for the 22K low-carbon steel (AISI 1022) after various heat treatment, namely after normalization, after prolonged heat treatment provoking temper brittleness (TO-1 regime included heating to 650 °C and slow stepwise cooling for 7 days), and after high-temperature heat treatment causing intensive grain growth (TO-2 regime included heating to 1200 °C with holding for 3.7 h). The criterion of non-linear fracture mechanics, namely the critical J-integral taking into account plastic deformation at the crack tip was used as a characteristic of fracture toughness. It is shown that, regardless of the type of structure formed by different heat treatment, the 22K steel is characterized by high fracture toughness. However, after heat treatment by the TO-1 and TO-2 regimes, the value of the critical J-integral decreases by 23 and 30%, respectively.