Stainless steel in an electronically excited state

Understanding the non-equilibrium behavior of stainless steel under extreme electronic excitation remains a critical challenge for laser processing and radiation science. We employ a hybrid framework integrating density-functional tight binding, transport Monte Carlo, and Boltzmann equations to model austenitic stainless steel (Fe$_{0.5875}$Cr$_{0.25}$Mn$_{0.09}$Ni$_{0.07}$C$_{0.0025}$) under ultrafast irradiation. The developed approach uniquely bridges atomic-scale electronic dynamics and mesoscale material responses, enabling the quantitative mapping of electron-temperature-dependent properties (electronic heat capacity, thermal conductivity, and electron-phonon coupling) up to the electronic temperatures Te~25,000 K. Two distinct lattice disordering mechanisms are identified: nonthermal melting at Te~10,000 K (the dose ~1.4 eV/atom), where the lattice collapses on sub-picosecond timescales without atomic heating driven by electronic excitation modifying the interatomic potential; and thermal melting (at ~0.45 eV/atom), induced by electron-phonon coupling on picosecond timescales. The derived parameters enable predictive modeling of stainless steel under extreme conditions, with implications for laser machining and radiation-resistant material design.