Quantitative Statistical Model for Cleavage Fracture Initiation in Carbide Strengthened Steels

摘要

A micromechanism based statistical cleavage fracture initiation model for carbide strengthened steels is presented. The model assumes that cleavage fracture initiates when a critical combination of tensile stress and carbide size is achieved in the plastic enclave ahead of the crack tip. Because the stress distribution in front of a crack varies strongly on a relevant microstructural distance, the probability of finding a carbide of critical size within the highly stressed region governs the macroscopic fracture toughness. The critical carbide size is dictated by the magnitude of the maximum principal tensile stress and thus by the yield properties of the matrix. The higher the yield stress and the strain hardening capacity, the stronger is the stress intensification at the crack tip, and thus the lower is the critical carbide size. The model correlates the macroscopic brittle fracture toughness parameter with microstructural variables and tensile properties of the material.