Experimental Study on Surface Erosion of Grade-A Marine Steel by Ultra-high Pressure Water Jet

With advantages such as zero pollution, high degree of automation and high efficiency, ultra-high pressure water jet rust removal technology is well in line with China’s advocacy for green and automated manufacturing and has stood out in the new wave of green vessel repair technologies, making it one of the most intensively studied topics. Grade-A marine steel, as an important material for marine quality steel plates, is highly resistant to corrosion and fatigue and accounts for one fifth of the total vessel building cost. Therefore, researching the interaction between water jet and marine quality steel plate, as well as the matrix damage process after rust removal, is of great significance for green vessel repairing. In order to study the interaction between ultra-high pressure water jet and the surface of Grade-A marine steel and the erosion mechanism of the former on the latter, a jet erosion test on Grade-A marine steel was carried out with 200 MPa ultra-high pressure water, and a comparative experiment was also conducted with 20 MPa water jet. The changes of microstructure, phase and surface morphology of Grade-A marine steel were analyzed under different pressures. The specific experimental process and parameters were as follows: Five groups of samples with specifications of 50 mm×50 mm×10 mm were made respectively for the 200 MPa and 20 MPa erosion tests. Using the jet medium of clean water, the experiment was conducted at room temperature with a jet impact distance of 30 mm and an impact angle of 90°. At times of water jet impacts, ASMC2-4 resistance strain gauge was used to collect the dynamic strain signal on the back of the vessel plate. Scanning electron microscope, transmission electron microscope and X-ray diffractometer were applied to observe and analyze the microstructure, phase and surface morphology and element distribution of Grade-A marine steel before impact. Under the pressure of 200 MPa, the average micro strain on the back of the impact center area of Grade-A marine steel was 180×10−6, micro strain amplitude was 35×10−6-50×10−6, and the impact force of water jet on Grade-A marine steel was cyclic pulsating alternating stress; The impact force of water jet at 20 MPa decreased radially from the center, while the pressure at the center and edge of the jet at 200 MPa was basically unchanged, and the difference in pressure could be ignored. Under the action of jet alternating stress, fatigue failure occurred to the material surface. After water jet erosion, the central area of Grade-A marine steel was dominated by long strip cementite hard phase, and there was also pearlite structure that had not been eroded; Under the action of 200 MPa ultra-high pressure jet, there were also typical fracture morphologies such as spalling pit, layer corrosion and cavitation corrosion on the material surface. Looking at the gradual peeling process of different hardness structures under the action of water jet cyclic alternating stress and water wedge, this paper establishes an erosion stripping model of Grade-A marine steel to discuss the erosion mechanism of water jet. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.