Relation between size and density of nonmetallic inclusions and the [formula omitted] at crack initiation

Abstract

Two quantitative relations for the calculation of the fracture toughness of ductile materials available in the literature in mathematically closed form — the relation of Stroppe relating the critical value J c of the J- integral to microstructural data as well as data of tensile tests and the relation of Hahn and Rosenfield relating fracture toughness and data of tensile tests — are applied to three conditions of different toughness of the 12% Cr-steel X 20 CrMoV 12 1. The microstructural parameters necessary for the calculation of the J- integral at crack initiation such as type, size, density and arrangement of nonmetallic inclusions as well as precipitates were determined for the three material conditions, X 20 CrMoV 12 1 optimized (low sulphur content), X 20 CrMoV 12 1 conventional (higher sulphur content) and the aged similar weld metal. The tensile tests and J—R-tests were performed at 150°C, where the energy absorbed corresponds to the upper shelf. Comparing the J i-values calculated according to the equation of Stroppe with the J i-values experimentally determined it is shown that the calculated values fall into the scatterband of the experimentally determined ones, showing a good agreement of calculated with the measured values for the three material conditions. In the case of the optimized X 20 CrMoV 12 1 the value of J i , calculated according to the relation of Hahn and Rosenfield, corresponds to the measured one. However in the case of the conventional X 20 CrMoV 12 1 and the similar weld metal no more correspondence is found.