Papers by Keyword: Internal Crack

Abstract: An online slab quality diagnosis & analysis system named CISDI_SQDS ONLINE R2011 has been presented in this paper. The system is based on mechanism of defects, which mainly refer to surface crack & internal crack, heat-transfer & solidification simulation, stress & strain calculation and metallurgical process analysis about continuous casting. Combining with BP neural network, several kinds of quality loss factors are used to describe the possibility of inducement. Meanwhile, the respective crack formation indexes are introduced to be the theoretical reference data for slab quality level evaluation and guiding production. The CISDI_SQDS ONLINE R2011 system was firstly applied on the No.1 Slab Continuous Caster of Bayi Steel in China. It is preliminary proved that the model is reliable and reasonable. It can be widely used as an important theoretical tool for prediction & control for slab quality in continuous casting process.

Abstract: This paper deals with the causes of a transversal crack in a steel slab with an l300×l45 mm cross-section by means of results from two models. Samples were taken from and around the crack in order to analyze the concentration (chemical heterogeneity) of the selected elements. Simultaneously, the concentration of elements at the surface of the crack was measured after the crack was opened. The chemical heterogeneity of elements was analyzed by means of the JEOL JXA 8600/KEVEX analytical equipment. The measurement results were processed using mathematical statistics procedures. The results proved that there was an internal crack initiating immediately below the curve of the solid-state temperature and consecutively propagating.

Abstract: The elongation and the strength of rolled steel are severely affected by cracks in production. Reduction of cracks is important for the improvement of slab quality. In this paper, a series of experiments on internal crack healing in slab during rolling was carried out on the experimental rolling mill. The crack shape and the fracture morphology of the crack healing zones were observed by using the scanning electron microscope, and the shear strength of crack healing zone was tested through the tensile testing machine. With increase of the reduction ratio during rolling, the crack healing degree increases.

Abstract: Fatigue cracks in polycrystalline copper may originate from PSBs or grain boundaries. They usually form at the specimen surfaces, but also internal small stage I (shear) cracks have been observed with the ECC/SEM technique. They are formed together with a strongly elongated dislocation cell structure, which is reflecting in many cases localized deformation in “slip lamellae” with eventual ladder-like features, being typical of PSBs. Both, PSBs and small non-propagating cracks are initiated at cyclic stress/plastic strain amplitudes below the conventionally reported PSB threshold values, if the number of cycles exceeds a minimum, e.g. approximately 5x108 in the VHCF range. The internal small cracks are formed not only in polycrystalline electrolytic copper of 99.98% purity but also in high purity (99.999%) material.

Abstract: This paper deals with an analysis of the possible causes of a transversal crack in a steel slab with a l300×l45 mm cross-section using results from two models. Samples were taken from and around the crack in order to analyze the concentration (i.e. chemical heterogeneity) of the relevant elements. Simultaneously, the concentration of elements at the surface of the crack was measured after the crack was opened. The chemical heterogeneity of elements was analyzed with the aid of the JEOL JXA 8600/KEVEX analytical equipment. The measurement results were processed using mathematical statistics procedures. The results proved that there was an internal crack initiating immediately below the curve of the solid-state temperature and consecutively propagating.

Abstract: The fatigue testing of the specimen with a central open hole was carried out to investigate the influence of the surface roughness on the fatigue lifetime. Fracture morphology investigations were used by scanning electron microscope. The reliability analysis of the specimen was carried out by detail fatigue rating. The results revealed that the less the roughness is, the longer the fatigue life of open hole and the higher the value of DFR (Detail Fatigue Rating) is. Under the same technological conditions, the effect of corner crack on fatigue life of open holes is greater than the effect of internal crack. So, the effect of a decrease of roughness on the fatigue life of an open hole is similar to a change of crack type from a corner crack to an internal crack.