An analysis of occurrence and beginning of stable crack growth in the low-alloyed steel for pressure vessels

Abstract

Pressure vessels are often made of low-alloyed steel that should be characterized by proper values of strenght, toughness, formability and weldability. In this paper the crack initiation in low-alloyed ferritic steel (Rp0.2 ≈ 475 MPa, Rm ≈620 MPa) has been analyzed using micromechanical approach to ductile fracture, where the critical values for material failure are determined by combining both experimental and numerical procedure. The values of the model parameters determined on simple specimens for the material characterization have been successfully used for predicting the onset of stable crack growth on precracked geometry. In that way so-called "transferability" of the micromechanical parameters has been established and their geometry-independence has been confirmed, which is of practical significance for the analysis of integrity of structure with initial cracks.

U izradi posuda pod pritiskom u znatnoj meri se koriste niskolegirani čelici koji treba da imaju odgovarajuće vrednosti čvrstoće, žilavosti, sposobnosti oblikovanja i zavarljivosti. U radu je analiziran nastanak prsline u niskolegiranom feritnom čeliku (Rp0.2 ≈475 MPa, Rm ≈620 MPa) primenom mikromehaničkog pristupa za žilav lom, gde se kritične vrednosti parametara otkaza materijala određuju kombinovanim eksperimentalno-numeričkim postupkom. Vrednosti parametara modela koje su određene na jednostavnim uzorcima za karakterizaciju materijala, uspešno su korišćene u predviđanju početka stabilnog rasta prsline na geometriji sa početnom prslinom. Time je ostvarena tzv. "prenosivost" mikromehaničkih parametara modela i potvrđena njihova nezavisnost od geometrije, što ima praktičan značaj u analizi integriteta konstrukcija na kojima su otkrivene prsline.