Effect of Tempering Temperature on the Strength-Impact Toughness Combination of Naval Grade Steels with Varied Al and Si Contents
摘要
This study explores how tempering temperature influences the strength—impact toughness balance in three Cu-bearing naval-grade steels with varying Al and Si additions. At lower tempering temperature (Ae1 – 40 °C (Ae1 – 40 K)), shearing of fine Cu-rich precipitates significantly enhances strength and hardness but reduces impact toughness. Conversely, at higher tempering temperatures, the bypassing of coarser Cu-rich precipitates reverses this trend, enhancing toughness at reduced strength. The presence of retained austenite and finer Bain width at elevated temperatures further supports toughness improvements. In Al-alloyed steel, although the Bain width is coarser, strength is enhanced by the formation of ordered NiAl shell around Cu-rich precipitates. The base steel tempered above Ae1 demonstrates an excellent strength–toughness combination (yield strength > 750 MPa and impact toughness > 100 J at − 40 °C (~233 K), attributed to retained austenite, refined Bain structure, and sparse distribution of slightly coarser Cu-rich precipitates. The addition of Al enhanced strength remarkably at the expense of toughness, whereas Si addition caused a negligible change in properties compared to the base steel. This comprehensive exploration sheds light on the intricate interplay of microstructural features and alloying elements, providing valuable insights into optimizing the mechanical properties of naval grade steels for superior performance.