Speckle defect refers to the steel plate after shot blasting and sandblasting treatment, part of the surface of the oxide sheet falls off, and part of the adhesion is tight and remains on the surface of the steel plate, forming a bumpy spot defect, which is especially obvious when the one-way light source such as a strong flashlight is irradiated horizontally. Due to the large distribution area of the spot defects, they can only be used after grinding, which increases the labor cost and manufacturing cycle of the shipyard, and excessive local grinding may cause the entire wear-resistant steel plate to be scrapped, which needs to be controlled. Relevant measures are:
1, wear-resistant plate composition adjustment
The average silicon mass fraction control of low alloy wear-resistant plate is about 0.31%, and the content is high. Through experiments, the silicon mass fraction in the billet is reduced to less than 0.20%, and the heating temperature of the billet is controlled to less than 1170℃. The phenomenon of pressing into the furnace oxidizing iron sheet is obviously reduced, and the spot defects are effectively reduced.
2. Improvement of descaling system
Due to the large distance between the nozzle and the surface of the wear-resistant plate, the high pressure water descaling effect is poor. By reducing the distance of the upper high pressure water nozzle from 1400mm to 410mm, the impact effect of high pressure water on the upper surface of the steel plate is effectively improved. At the same time, a new water storage tank is added to increase the high pressure water volume, strengthen the high pressure water pipe, optimize the nozzle type and injection Angle, and increase the opening degree of the high pressure water valve from 50% to 75%.
3, optimize the rough rolling, finishing rolling descaling water
(1) The second-to-last pass of roughing is descaled to suppress or weaken the foaming on the surface of the steel plate when the steel is rolled before finishing rolling.
(2) Strictly control the number of swing steel blocks between rough and finishing rolling, and swing a piece of steel at most. By controlling the temperature of the heating and rough rolling area, ensure that the billet temperature before finishing rolling is lower than 950℃. After finishing rolling, direct rolling is no longer waiting for temperature. If the temperature is higher than the process regulations, the secondary pendulum steel is used to wait for temperature, and the steel is waiting for temperature for a short time to prevent a large number of secondary oxide sheet from bubbling and breaking.
(3) In order to avoid the first pass of finishing rolling, the first pass of empty pass is taken, that is, the mill does not give the amount of pressure when the steel plate is moved from the front to the back, so as to avoid the pressure of the iron sheet, and the back of the steel water to remove the scale.
(4) Improve the high pressure water descaling method at the background of the finishing mill, and use the method of water descaling when entering steel in the background, the first pass of finishing rolling is empty, the second pass of finishing rolling is descaling when returning from the background, the penultimate second pass of finishing rolling is descaling when returning from the background, reduce the temperature of the steel plate, make the steel plate quickly enter the low temperature oxidation zone, ensure that the steel plate is clean and avoid the oxide sheet being pressed into.
Through the above measures, the surface spot defects of high-strength Marine wear-resistant plate are basically eliminated, and the amount of wear-resistant plate correction is greatly reduced due to the spot.
