Dynamic strain ageing in C -Mn steels and associated welds. II. Effect on fracture toughness behaviour

C-Mn steels and associated welds are susceptible to Dynamic Strain Ageing (DSA). In this case, fracture toughness shows a minimum when the temperature increases from 20°C to 300°C. After a literature review, the results of J - R tearing resistance tests, characterized by crack initiation resistance J$_{0,2}$and tearing modulus dJ/da relative to a base metal (A48 French standard steel) and Manual Metal Arc deposited metals are presented and discussed. The decrease of both crack initiation resistance J$_{0,2}$and tearing modulus dJ/da is related to the DSA sensitivity of the material. A simplified engineering method based on the evolution of the Ultimate Tensile Strength versus temperature and a method of J$_{0,2}$determination according to a local approach model of ductile fracture are proposed to predict the maximal drop in tearing resistance exhibited by the materials around 200°C as a function of ageing sensitivity of the product.