STATISTICAL ASPECTS OF CLEAVAGE RESISTANCE OF HIGH-STRENGTH MICROALLOYED STRUCTURAL-STEELS

The statistical distribution of the cleavage fracture stress sigma(cf) was determined for two modern high strength microalloyed structural s teels through a series of 30, Soul point bending tests at a temperatur e of 77 K. A pai allel investigation of the the distribution of the la rgest ferrite grain diameter d(max) observable by optical microscopy i n regions of approximately the same size as the cleavage process zone, was carried out using 120 data for each steel. A calculated distribut ion of sigma(cf) was then constructed by means of a theoretical formul a developed in a previous work, which gives sigma(cf) as a power funct ion of d(max). The comparison with the experimental distribution of si gma(cf) demonstrates that the statistical scatter of the cleavage frac ture stress for the investigated steels can be explained as entirely d ue to the statistical scatter of d(max). Thus more evidence for the va lidity of the theoretical equation was obtained and, in addition, it w as shown that the exponent of d(max) was the same for both steels in s pite of their different chemical composition. (C) 1997 The Institute o f Materials.