Increased Crack Resistance to Enhance Toughness in 20Si2MnCrNi Steel via Isothermal Bainite Formation

This work investigates the influence of microstructure of isothermal bainite and as‐tempered martensite in 20Si2MnCrNi steel on the toughness and crack propagation behavior. The results show that the impact absorption energy of the steel with isothermal bainite microstructure (211 J) is nearly double that of as‐tempered martensite (116.3 J), while the crack propagation rate is reduced by ≈15%. The superior toughness of isothermal bainite is largely attributed to the presence of high‐angle grain boundaries, which account for 82.3% of the total, compared to 62.6% in tempered martensite. These boundaries effectively deflect and branch cracks, thereby enhancing crack resistance and material durability.