QT400-18铸态高韧性球墨铸铁拉伸断口特征与断裂机理

通过对QT400-18铸态高韧性拉伸断口特征及断裂机理的分析,发现伸长率超过20%时,试样断口具有韧性断裂的微观特征,在断口上留下较大、较深的韧窝,甚至有撕裂带.而伸长率为15%～16%时,试样断口具有混合型断裂的微观特征,在尖角处易形成微裂纹源,受外力作用时,裂纹源迅速扩展,造成局部穿晶断裂;同时由于铁素体含量减少,珠光体含量增多,基体塑性变形相对较差,在试样断口上留下大量较浅的韧窝.

Fracture Character and Fracture Mechanism of the Tensile Sample of QT400-18 As-cast High Toughness Ductile Iron

A study on fracture character and fracture mechanism of the tensile sample of QT400-18 as-cast high toughness ductile iron was given in the paper. The experiment results showed as the following: when the elongation of tensile sample was over 20% ,the micro-character of the tensile sample was toughness rapture (its fracture mechanism was given), first graphite was divorced from the ferrite matrix, then sufficient plastic distortion occurred in the ferrite matrix ,finally the greater and deeper toughness nest with teared surface layer left behind in the fracture of test sample; when the elongation of tensile sample was between 15% and 16%, due to many abnormality ductile and white impurity , some tiny cracks were found at their tine corner. These cracks spread rapidly through the crystal if they suffered the outside force; at the same time it was rather difficult that the plastic distortion took place in the matrix thanks to the ferrite content decreasing and the pearlite content raising , at last the flat toughness nest left behind in the fracture of test sample.