Study On Layered Fracture Of Ship Plate With Nb During Tensile Test In Hangang

Steel is rich in abundant, low in price, easy to recovery utilization, so it is most extensive used. As the production technologies advanced rapidly, the output increase, all the steel enterprise adjust production structure, increase the service performance and reduce the cost. Ship plate steel with Nb is the main production of Hangang. And as the increase of output, variety and quality requirements, the quality issues get more and more attention. And during the testing, the lamination of the tensile samples caused most of the loss. It indicates that the plate is anisotropic, especially in the thickness direction, and lead to the decrease of the mechanical property, the impact-toughness and fatigue property. This may cause the hydrogen damage and lamellar tearing, etc.The amount and time the lamination occurrence were statistic in Hangang, and the sample was taken from the concentrate batch. The fracture samples were protected properly, and used to fracture surface examination, quantitative spectrochemical analysis, sulfur print test, pickling test. The tests were taken at Hangang and Xauat. The cause of the lamination are discussed, and author summarized that the co-action of three-dimensional tensile stress state, segregation band in the center, trapped Nb, rarefactions, shrinkage voids, microcracks and banded structure etc, cause the center of the plate become the weak spot. The crack initiation and growth here, and caused the lamination enventally.The article presents that, we can decrease the lamination by purging the molten steel, removing impurity elements(C, Mn, S, P, etc.) and non-metallic inclusion; overhauling continuous casting equipment in time; stacking the slab for slow-cooling; cross rolling for homogenization of the inclusion distribution; after the end rolling rapid cooling the plate from 850℃to 700℃, and then stacking the plate down the cooling bed for slow-cooling.