Study on High‐Strength‐Plasticity Balance of Laser‐Deposited Bainitic Steel through Isothermal Heat Treatment

Traditional bainitic steel for railway switches suffers from strength and toughness reduction due to blocky retained austenite (RA, alongside lengthy, energy‐intensive production. Laser‐deposited bainitic steel offers high hardness, superior strength‐toughness, and short cycles. This study proposes a novel process combining laser deposition using 4340/Ni‐coated SiC/FeSi6.5/Al composite powders with short‐duration isothermal heat treatment. The Si‐Al synergy suppresses carbide precipitation. Microstructure and mechanical properties after isothermal treatment were investigated. Results show transformation completes within 180 min at 300 °C, yielding a composite microstructure of nanoscale lath bainite and high‐density thin‐film retained austenite. This achieves a maximum strength‐ductility product of 30.74 GPa%—1.5 times that of traditionally rolled bainitic steel—demonstrating excellent strength‐plasticity synergy. Prolonged isothermal time increases retained austenite content to a peak while its carbon content gradually rises. Blocky retained austenite decreases continuously, film‐like increases, and martensite content progressively declines. Tensile strength initially rises then slightly decreases with extended isothermal time, while both elongation and strength‐ductility product increase. This approach achieves short‐process preparation of high strength‐toughness bainitic steel.