Abstract: In the light of analysis of the features of cleavage fractographs of low carbon steel,the stress criterion for cleavage crack propagation across ferrite grain boundary was established on the supposition that resistance to the propagation results from an arbitrary mutual orientation of the cleavage plans in the neighbouring grains.On the basis of concept of statistical distribu- tion of cleavage plane in space,the probabilistic characteristic of cleavage process was ex- pounded,and the fracture stress of the cracked specimen over temperature range in which fracture is initiated by cleavage mechanism was calculated by means of finite element analysis program and the calculated result was found to be in agreement with that measured.

Key words: cleavage, fracture mechanism, finite element analysis, criterion