| In this paper, four point bend (4PB) tests of two kinds of HSLA material with coarse grain sizes and various level of prestrain are carried out at -196 ~C ,-125 C and -100 C. Macro and micro mechanical and fracture surface parameters are measured. Combining the FEM calculation results of the stress and strain distributions ahead of the notches of specimens with various prestrain, the effects of the prestrain on fracture behavior of specimen are analyzed. It is discovered that the specimen showed an appreciable decrease in notch toughness at -125 Cand -100C after putting 3% tensile prestrain of tensile at room temperature. The further prestrain up to 20% gave little effect. The notch toughness of specimens tested at -196 C is low and did not subject to the effect of prestrain. The mechanism of the effect of prestrain is analyzed. A detailed analysis of cleavage? controlling factors of course grains steel of higher purity with a low critical fracture stress and a high critical fracture strain are presented. |
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