Study On Abnormal Defect For Fracture Of Tensile Test Samples In Plate

Abnormal defect of tensile fracture existed in the medium thick plate is a popular phenomena in the domestic and international medium thick plate. The plates in the plate mill of Chongqing Iron & Steel Co. Ltd is no exception.Abnormal defect of tensile fracture is a kind of defects in the course of normal tensile test , which have different appearance with that of tensile fracture in tensile experiment according to the standard GB228-2002..In the paper, by the analysis of abnormal fracture defect's physics and chemistry fracture characteristic, the formation mechanism of the defects was determined and the improvement measure of the processing were put forwarded. The fracture are divided into five fractures according to their fracture appearance, and it is determined that the flat fracture, crack fracture and transfixion fracture are regarded as the most fatal defects to tensile property. Thus, the criteria of abnormal defect and the grades evaluation standard for fracture of tensile test samples were established. The research end up situation mat there have been no criteria for these kinds of defects, which has benefits to the quality management and control in the company by reducing the sampling numbers, releasing the burden in the physics and chemistry labs, quickly promoting products circulation and increasing the company economical benefits.By various kinds of physics and chemistry inspection analysis such as the macroscopic sour solution wash test, macroscopic metallography analysis, the flat plane test, check of split open in the direction of "Z", TEM and EDX analysis, the experiments show: inclusion is situated at the boundary of columnar crystal and equiaxed crsytal, meanwhile, the gas is distributed at the site of alloy element enrichment. As the steel liquid is solidified and the plate is cooled after being rolled, Nitrogen and hydrogen gas diffuse to the sites of inclusion and alloy elements aggregation and form enrichment area which cause the steel brittle, so there appears white brittleness district with surface tension at the tensile fracture.Tensile fractures are divided into five fractures according to fracture appearance. The flat fracture, crack fracture and transfixion fracture are the most fatal defects to tensile performance. The abnormal defect description diagram for fracture of tensile test samples and the grades evaluation standard for fracture quality end the history that there is no standard for this kind of defects.