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In this paper, a natural marine immersion zone seawater environment, material properties, two angles of the marine environment, the comprehensive utilization of weight loss method, the open circuit potential (OCP), AC impedance (EIS), metallurgical microscope, scanning electron microscopy (SEM) and energy spectroscopy (EDS) and other means of detection, focus on the steel substrate corrosion products interface perspective, consider the types of corrosion and corrosion-induced proliferation, as well as the impact of the product of two organizations Q235 steel seawater corrosion kinetics and mechanism; combined point The pitting potential measurements, microbial culture method to study the influence and control of the natural marine biofilm on Q235 steel and stainless steel 304,316 L corrosion behavior, discussed the phenomenon of seawater immersion zone steel corrosion inhibition. First time corrosion interface and electrochemical tests combined, the corrosion diffusion kinetics. The results show that, according to the influence factors, corrosion is divided into three stages, the cementite and ferrite galvanic role as corrosion process is the most important impetus, because of spurious distribution of spherical cementite and ferrite electrical coupling greater role, Q235 steel normalizing organizations corrosion resistance better than the annealing organization. Both the first phase of the driving force as well as the grain boundary, the third stage becomes a rust galvanic. Annealed structure, corrosion diffusion mainly along grain boundaries, especially small grains and elongated grains, the span between the corrosion interface small peaks in the 30-40μm, the size of the pits of the surface of 20-30μm is formed, corrosion along the small grain The grain boundary diffusion faster. Normalizing organizations corrosion along the grain boundary diffusion in addition to, and also along the pearlite proliferation, formed at the interface of about 60μm, 15-20μm deep small arc, consistent with the size of the pearlite colony produce more localized corrosion. Pearlite the corrosion regional oxygen content was significantly higher than other regions, up to 68%, the pearlite more easily corrosion. Through systematic observation and analysis of the formation and transformation of the two organizations rust found rust accelerate Q235 steel corrosion, especially within the rust layer. The complete rust surface ferritic increased substrate corrosion resistance increases. Q235 steel rust layer of the two organizations are separate nucleation, the annealing organization of six hours 1μm independent spherical body is not dense, dispersed cementite match, part of the spherical body 10 hours to grow up into a 10μm aggregates, 45 days into 10μm dense spherical body 90 within the rust layer also individually shaped core, the crack surrounded by a separate body of 40-50μm, 10-20μm of the nuclei on which, the transition is formed by the spherical body 45 days rust layer. Normalizing organized six hours rust layer two morphologies: the formation of the core is about 0.3μm, emitted approximately 1μm round and core about 0.5μm and fanned outward expansion 2μm the group flocculent pearlite distribution 45 days uniform inner rust layer, the outer rust layer becomes dense group floc. Full grain boundaries, inclusions, grain morphology of cementite galvanic electrochemical test, found that the initial oxygen is plentiful, the grain boundary cementite is the main driving force. Q235 steel silicate inclusions can cause significant pitting, initial size of 50-60μm 15-20μm size of the inclusions can cause pitting, significantly greater than the alumina of calcium formate inclusions caused 5μm size pits, composite inclusions greater impact. The first small grains and elongated grains corrosion, one month later, the oxygen content is reduced, the grain boundary weakened, the driving force for the corrosion inclusions, cementite and rust, especially inclusions. Corrosion tend to be large grain diffusion. Biofilms contain a variety of bacteria (SOB, SRB). Q235 steel the aerobic corrosion rate of Q235 steel surface of natural biofilm inhibition, to promote the generation of anaerobic corrosion than the test. Soak during natural seawater samples Rp (polarization resistance) 1-100 days remained at 1000-1100Ω · cm2, 100 days after the sharp decline to 600Ω · cm2, inner rust layer sulfur content of 9.63%, appears anaerobic corrosion; while The sterilized sample Rp basic maintained at 600-700Ω · cm2, sterilized environment Q235 steel corrosion rate was significantly higher than that of natural seawater, which is 1.4 times that of natural seawater A biofilm is an important marine immersion zone steel corrosion inhibition reasons. Qingdao marine natural seawater, 316L stainless steel pitting potential of 0.551V; 304 stainless steel is 0.249V, the difference between the two 0.3V. After soaking, 316L stainless steel corrosion resistance increased 304 stainless steel decline in the impedance of the high-frequency region, the Z value of the third day, 316L stainless steel is about 1.62 times 304, 35 days later expanded to 4.25 times. 304 stainless steel alumina inclusions induced the 5μm pitting. After 6 months of soaking, 316L stainless steel base body of chromium, nickel, molybdenum / iron than rise, and manganese elements disappear, which improves its corrosion resistance.
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