低合金钢在3.5％NaCl中恒电位阳极极化能模拟在海水中腐蚀时各微区部位的电化学过程。用这种加速方法可以增加发生在各微区上的中间产物的相对含量。作者应用穆斯堡尔效应探测到这些微量中间产物,从而掌握目前还不能直接测定的,在海水中试样上阻挡层铁锈的相组成。研究结果表明,不同低合金钢具有不同的阻挡层铁锈相组成,它们除了都具有海水腐蚀后试样所持有的β-,γ-FeOOH终态相外,还分别具有不同组份的,呈微晶或无定形的一类似于绿锈Ⅰ,Fe_2(OH)_3Cl等的中间态铁锈。这些中间态铁锈在空气中极易氧化、脱水、时效,并根据不同条件,分别逐步转变成终态相FeOOH和Fe_3O_4等。合金中含有Ni,Cr可以抑制早期中间态相的形成,但Ni,Cr却会促使后期于局部地区形成另一些中间态相。因此含Ni,Cr低合金钢虽早期在一般腐蚀方面具有较好的抗蚀性,但在后期在局部腐蚀方面则会导致耐蚀性大大降低。根据穆斯堡尔谱学和腐蚀电化学,作者阐明了合金元素的作用,澄清了某些看法并初步提出发展和评定耐海水腐蚀低合金钢的途径。
Potentiostatic anodic polarization of low alloy steels in 3.5%NaCl solution can be used to imitate the electrochemical process of local micropits formed on these steels while corroding in sea water. The relative amount of the intermediate phase occuring in micropits may be increased by this accelerated test method. This micro intermediate product has been detected by the use of Mossbauer effect, so that we can determine the true composition of the barrier layer rust formed on low alloy steels in sea water, which could not be determined directly in sea water previously. Experimental results show that different low alloy steels possess different phase composition of the barrier layer rust. In addition to the final state phases, β-,γ-FeOOH, which were found in all the samples after corroding in sea water, there are also microcrystalline or amorphous intermediate, state iron rusts of different composition—similar to green Rust I, Fe_2(OH)_3Cl etc. These intermediate state rusts tend very easily to oxidize, dehydrate and age in the atmosphere. They will transform step by step to the final state phases such as FeOOH or Fe_3O_4 or both depending on conditions. While these intermediate phases were growing locally in the barrier layer rust, corrosion resistance of the alloy may be decreased. In Ni-or Cr-containing low alloy steels, the formation of some intermediate, phases in the early stage is inhibited, but the formation of other intermediate phases in the later stage can be promoted. Therefore, Ni-,Cr-containing low alloy steels show good corrosion resistance in the early stage, but bad corrosion resistance in the later stage. According to Mossbauer spectroscopy and corrosion electrochemistry,suggestions for developing and evaluating corrosion resistant low alloy steels in sea water are made.
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