S420海工钢在不同海洋区带环境下的腐蚀行为研究

Corrosion Behavior of S420 Steel in Different Marine Zones

通过1 a的青岛海域实海暴露实验,结合失重法、宏观和微观形貌、三维形貌和腐蚀产物分析,开展了S420钢在大气、飞溅、潮差和全浸4个不同海洋区带下的腐蚀行为研究。结果表明:S420钢在潮差环境中腐蚀速率最高,大气环境下腐蚀速率最低。一方面,这主要归因于锈层具有持水能力,为阴极反应提供充足的水介质,另一方面,潮差环境的干湿循环使得表面薄液膜中Cl^(-)浓度增加,同时加速了氧的传质过程,促进了腐蚀阴阳极反应速率。腐蚀产物主要由γ-Fe_(2)O_(3)、Fe_(3)O_(4)以及α/γ-FeOOH组成。电解液层的持续存在有利于γ-FeOOH的形成,使其在潮差和全浸环境中占主导地位。充足的氧气和干湿循环促进了Fe_(3)O_(4)的生成,导致其在飞溅环境中以主要形式存在。S420钢在潮差环境下表现出最大点蚀深度和高点蚀体积的局部腐蚀特性。

The effect of diverse marine zones on the corrosion behavior of low alloy steels exhibits unique environmental characteristics,leading to significant differences in the corrosion rate of steels,as well as the composition and structure of rust scales.In this paper,the corrosion behavior of S420 steel,exposed in four different marine zones,i.e.atmospheric,splash,tidal,and immersion zones in the sea area of Qingdao by 36°06'N and 120°25'E for one year,was assessed by means of mass loss measurement,macroscopic and microscopic morphology observation,three-dimensional morphology detection,and corrosion product analysis.The results show that S420 steel exhibits the highest corrosion rate in the tidal zone and the lowest corrosion rate in marine atmosphere.Which may be attributed to the water-holding ability of the rust scale,thus providing sufficient electrolyte for the cathodic reaction.On the other hand,in the tidal zone,the wet-dry cycle results in the increase of the Cl^(-)concentration,accelerating the anodic reaction.The formed corrosion products are mainly composed ofγ-Fe_(2)O_(3),Fe_(3)O_(4)andα/γ-FeOOH.The persistent presence of the electrolyte film may facilitate the formation ofγ-FeOOH,making it dominant in the rust scales formed in tidal zone and full immersion zone.In the splash zone,the production of Fe_(3)O_(4)may be promoted due to the synergist of adequate oxygen supply and wet-dry cycle,thus Fe_(3)O_(4)is dominant in the formed rust scale.In the marine atmosphere,the thickness of the formed rust scale is the smallest,and the value ofα/γ*is the largest,which has protective effect against further corrosion of the steel substrate to certain extent.In the tidal zone,the thickness of the formed rust scale is the highest and the value ofα/γ*is the lowest,which is loose and porous,and the number and width of cracks within the rust scale are larger and wider,resulting in worst protective effect for the substrate.In other words,the S420 steel exhibits obvious l℃alized corrosion characteristics with the maximum depth and high volume of pits in the tidal zone.