Modification of Superficial Microstructure and Strength–Ductility Trade‐Off in A100 Ultrahigh Strength Steel via Multiple Laser Shock Peening

Seeking further breakthrough in mechanical performance of A100 ultrahigh strength steel is crucial for broadening its applications in harsh service conditions. This study utilizes laser shock peening (LSP) to modify A100 steel, characterizing microstructure evolution and tensile properties as functions of coverage layers. Results indicate that substantial grain refinement of large‐scale martensite lath is achieved through deformation twins and shear bands. After a single LSP coverage layer, yield strength increases from 1600 to 1700 MPa and ultimate tensile strength from 1821 to 1882 MPa, while total elongation decreases from 12.5% to 11.0%. With three coverage layers, strength saturates whereas elongation further declines to 9.6%. The fracture mode transitions from ductile to mixed ductile/cleavage fracture. Grain refinement, martensitic phase transformation, and refinement and redistribution of pre‐existing tempered M ₂ C carbides synergistically enhance mechanical properties. This work provides insights into optimizing strength–ductility trade‐off in ultrahigh strength steels via LSP.