Ultrastrong and stress corrosion cracking-resistant martensitic steels

This study aims to reveal the atomic-scale effects of tempering on the complex substructures and stress corrosion cracking (SCC) resistance of high-strength martensitic steels. The SCC resistance and strength of boron-doped Fe-0.3C-0.3Si-1.0Mn-1.0Ni-0.5Cr (wt%) martensitic steel increase concurrently without low-temperature tempering. Notably, the degradation of SCC resistance caused by tempering is in contrast with the known effect. To explore this unexpected result, subboundaries inside the martensitic microstructure are investigated via atomic-nano-micro-scale analyses. The strongly segregated carbon at the lath boundaries during tempering is a precursor to the harmful cementite, which acts as severe SCC initiation sites. Eventually, intensive crack grew along the lath boundaries, deteriorating the SCC resistance of the material.