Dynamic strain ageing in C-Mn steels and associated welds. 2. 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 to 300 deg C. After a literature review, the results of J-R tearing resistance tests, characterized by crack initiation resistance J0,2 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 J0,2 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 J0,2 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 deg C as a function of ageing sensitivity of the product. (authors)