Experimental and Numerical Study on Damage Mechanisms in a High‐Carbon Steel With Bimodal Cementite Under Uniaxial Tension

ABSTRACT This study investigates damage evolution in a high‐carbon steel containing ferrite, retained cementite (RC), and precipitated cementite (PC) after inter‐critical quenching and tempering at 540°C and 600°C. In situ tensile testing and fracture‐section analysis identify ferrite/cementite interfacial‐debonding voids (IDV F/C ) and ferrite‐cracking voids (FCVs) as the predominant damage mechanisms. Finite element simulations show that IDV F/C and FCV are driven by interfacial stress concentration and localized plastic strain in ferrite, respectively. Cohesive‐zone simulations reveal that the critical strain for interfacial damage decreases exponentially with cementite diameter, indicating a critical diameter below which void nucleation is suppressed. This critical diameter is approximately 200 nm in T600. The higher‐strength T540 steel is more susceptible to interfacial damage than T600. Fracture proceeds through hierarchical void coalescence. Nanoscale dimples dominate the fracture surface and form by coalescence of voids nucleated at nanoscale cementite and within ferrite, whereas microscale RC contributes little.