Statistical aspects of cleavage resistance of high strength microalloyed structural steels

Abstract

The statistical distribution of the cleavage fracture stress σ_cf was determinedfor two modern high strength microalloyed structural steels through a series of 30, four point bending tests at a temperature of 77 K. A parallel investigation of the distribution of the largest ferrite grain diameter d_max observable by optical microscopy in regions of approximately the same size as the cleavage process zone, was carried out using 120 datafor each steel. A calculated distribution of σ_max was then constructed by means of a theoretical formula developed in a previous work, which gives σ_cf as a power function of d_max. The comparison with the experimental distribution of σ_cf demonstrates that the statistical scatter of the cleavage fracture stress for the investigated steels can be explained as entirely due to the statistical scatter of d_max. Thus more evidence for the validity of the theoretical equation was obtained and, in addition, it was shown that the exponent of d_max was the same for both steels in spite of their different chemical composition.