MODELING THE STRESS-CORROSION CRACKING OF LOW-ALLOY STEELS

Based on a precise characterization of the stress-corrosion cracking b ehaviour of 41xx steels after various heat treatments, a model of the micromechanisms, on a microstructural scale, present in the cracking p rocesses during stress corrosion, has been defined. The model establis hes that stress-corrosion cracking occurs by a series of isolated and unstable local fractures inside the plastic zone, controlled by local embrittlement due to absorbed hydrogen. These local fractures occur wh en a critical strain is reached at an appropriate microstructural feat ure, and are controlled by the strain field and by the hydrogen concen tration and distribution in the plastic zone. The model explains the i ntergranular fracture behaviour of dislocated and lightly tempered mar tensites, associated with the plastic-zone fitting within the grain fa cets under critical conditions, also the intergranular-transgranular t ransition at a critical temperature of tempering and the transgranular fracture behaviour, either by microvoid coalescence for tempered mart ensites or by cleavage for bainites.