Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel

Abstract

The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of "crystallographic" bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the "Master-curve" (MC) approach, the Beremin model, and a "double-barrier" (DB) model) are applied to account for the ductileto-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.

3D Observation of Micro-cracks as Cleavage Fracture Initiation Site in Ferrite-pearlite Steel

“…20,21) The predictions of all the models were however limited to a unique steel, so that the applicability to the steels having different distributions of microstructures was not covered.…”

Crossing grain boundaries in metals by slip bands, cleavage and fatigue cracks

“…Influence of grain boundaries in cleavage fracture (a) Introduction: material GBs in ferritic steels offer an important resistance to the propagation of cleavage cracks, particularly in the DBT regime (e.g. the pioneering work by Hahn et al [41] who showed cleavage cracks arrested at GBs and, more recently, the work by Lambert-Perlade et al [42] who showed using acoustic emission that cracks could be arrested at GBs or packet boundaries). Based on further observations in hydrogen-charged Fe-3% Si alloy, Gell & Smith [43] demonstrated that the resistance of GBs to the transmission of cleavage cracks across them was governed more significantly by the twist misorientation than the tilt misorientation.…”

Structure–Property–Fracture Mechanism Correlation in Heat-Affected Zone of X100 Ferrite−Bainite Pipeline Steel

“…Recently, a few studies on the characterization of brittle cracks using EBSD have been reported. [14,[16][17][18][19][20] However, initiation and propagation of cleavage cracks in the HAZ of high strength (e.g. X100) have not been explored to the best of our understanding.…”