Research On The Effect Of High-energy Shot Peening On Rust Layer Densification Of Low Alloy Marine Steel

In order to adapt the harsh marine environment, good mechanical property is necessary for marine steel. Apart from this, strong corrosion resistance is also important. Low alloy steel has been widely used for its lower cost and better corrosion resistance in the marine environment. However, it maybe takes a few years or even decades for low alloy steel to form a stable density protective rust layer in the wild, led to a unsatisfactory corrosion resistance in the bare environment use. Therefore, it is usually required external anti-corrosion technology.To shorten the time of formation about dense rust layer, scholars have proposed many technologies of accelerating the formation of rust layer at home and abroad, of which rust layer stabilization process and depolarization agent accelerated corrosion are often used. It is a complex chemical reaction process for the formation of rust layer on the surface of material. Based on high chemical activity about special structure of grain boundary of nano-crystalline, It is hopeful for improving the steel chemical activity to accelerate the formation of rust layer by nano-machining. Moreover, high-energy shot peening could realize surface nano-crystallization via the surface of large plastic deformation fine grains. Therefore, this topic adopted high-energy shot peening to treat three kinds of typical low alloy marine steel-Q235, Q345 and 15CrMo, selected three kinds of methods of artificial accelerated corrosion to accelerate formation of rust layer respectively before and after high-energy shot peening. On the basis of refining effect as high-energy shot peening surface organization, to research characteristics of rust layer before and after high-energy shot peening, to reveal the influence rule on rust layer formation and properties of three kinds of typical steel’s accelerated corrosion after high-energy shot peening, so as to provide powerful theoretical guidance and basis for improving the low alloy steel corrosion resistant performance of the ocean. The main research results are as follows:(1) A certain thickness of deformation layer could be obtained on surface of three kinds of common low alloy marine steel-Q235, Q345 and 15CrMo by high-energy shot peening, greatly refined of surface grain and microstructure. Q345 and 15CrMo steel obtain nano-crystalline on the surface, the average grain size is less than 100nm. But under the same shot peening parameters, the refining effect of Q235 steel not as good as Q345 steel and 15CrMo steel.(2) Under H2O2 immersion, PVB coating add splash test, PVB coating add salt spray test, high-energy shot peening is conductive to accelerate the formation of Q345 steel rust layer, rust layer density as well as the corrosion resistance are improved. Result show that the self-corrosion potential improved by 80mV, 100mV and 300mV respectively; the self-corrosion current density decreased by 34%,80% and 68% respectively of rust layer after high-energy shot peening under three kinds of accelerate corrosion methods. PVB coating add splash test is the best corrosion condition among three of them, which could get the most significant effect on the improvement of rust layer density as well as the corrosion resistance by high-energy shot peening.(3) Under PVB coating add splash test, high-energy shot peening is conductive to accelerate the formation of rust layer on Q235 steel and 15CrMo steel, rust layer density as well as the corrosion resistance are improved. It is find that the self-corrosion potential improved by 280mV and 500mV respectively; the self-corrosion current density decreased by 24% and 70% respectively of rust layer after high-energy shot peening under PVB coating add splash test. Result show that 15CrMo steel could get the better effect on the improvement of rust layer density as well as the corrosion resistance than Q235 steel by high-energy shot peening.