Study The Causes And Control Measures Of Surface Crack Defects On Shipbuilding Plate In Jigang

The shipbuilding plate is widely used in the fields like shipbuilding, militaryindustry, offshore oil drilling platform, and so on. Guerantee and control the quality ofshipbuilding plate is very important for the safety reason. Surface crack is one of themain defects of shipbuilding. It is very significant to sudy the causes and controllingmeasures of the surface crack for the high quality shipbuilding plate production.In this paper, the classification, the cause, the influence factors and the controllingmeasures of the surface defects of the shipbuilding plate are studied systematiclyaccording to the equipment, processing, technology, and the operation in real productionof the45t-2500mm steelmaking and rolling line in Jigang.According to the appearance of surface cracks and the relationship between thecrack direction and the rolling direction, the cracks on the shipbuilding plate can bedivided into three categories: surface longitudinal crack, surface transvers crack andsurface net crack.The cracks on the45t-2500mm steelmaking and rolling line in Jigang were tracedand analyzed. According to the production process, the high temperature properties andthe segregation behavior of carbonitride were investigated. Results indicated that thetemperature control, cooling control, liquid surface stability control in the mold,vibration parameters control and straightening control in continuous casting processinginfluence the cracks of the slab largely. Both the micro alloying elements and theharmful elements content in the steel influence the surface crack defects obviously onthe slab or on the plate, respectively. The reasonable control of the rolling process cangreatly reduced the influence of residual elements or micro alloying elements on thesurface cracks of shipbuilding plate.The surface cracks on the slab and the plate, and the corresponding relationshipbetween them were studied. Results showed that the surface and subsurface defects ofthe slab are the main influencing factors of the surface cracks on the shipbuilding plate,especialy the transvers cracks. The surface defects of the slab can be past down to theplate. Meanwhile, the reasonable rolling process also can mitigate or removel this kindof defects.In allusion to the various affecting factors, the control measures like controlling theharmful elements content of raw material in blast furnace or seelmaking process, reasonable use of micro alloying alloy, effectively controlling of the gas content in themolten steel, reducing the slab crack defects, taking cold deliver process, the reasonablecontrolling of heating process and so on were applied in the production of45t-2500mmsteelmaking and rolling line of Jigang. Practical production indicated that the surfacecrack defects can be effectively controlled by applying the above measures.