低合金鋼在大氣環境下的腐蝕抗性與機械性質

Corrosion Resistance and Mechanical Properties of Low-Alloy Steels under Atmospheric Conditions

本研究利用實驗室的加速乾濕循環試驗，將四種新發展出來的低合金鋼與一碳鋼（SS400）及一耐候鋼（Acr-Ten A）在含氯鹽環境下（5wt.% NaC1）的腐蝕抗性與機械強度加以比較。這四種新的低合金鋼分別標號為1604A、1604B、1605A與1605B。結果發現：經過72通期的循環腐蝕測試後，六種鋼對腐蝕的敏感度由高至低依序為：SS400>Acr-Ten A>1604B≧1604A>1605B≧1605A。而因腐蝕造成機械特性的改變以SS400為最少，Acr-Ten A次之，其他四種鋼再次之且差異不大。最後，每一種鋼的銹層特性均以SEM觀察之，FTIR與EPMA作分析比較。結果顯示：在大多數鋼表面上所形成的銹層均由較松散的外銹層與一緻密的內銹層所組成。每一種鋼材的外銹層又是由α-FeOOH、γ-FeOOH、磁鐵礦（Fe3O4）、水、和非晶質的氫氧化鐵（FeOx（OH）3-2x所構成；另一方面，內銹層則主要由磁鐵礦與少量的α-FeOOH所組成。此外，本研究還發現合金添加物中的銅元素在銹層與基材的介面處富集；而鉻元素則在銹層中聚集。最後，綜合加速試驗與誘層分析的結果顯示：1605A與1605B低合金鋼在潮濕並含鹽分的環境下，其耐候性質較Acr-Ten A為佳。

The corrosion resistance and mechanical strength of four newly developed low-alloy steels (LAS) were compared with a carbon steel (SS400) and a weathering steel (Acr-Ten A) using a laboratory-accelerated test that involved cyclic wet/dry conditions in a chloride environment (5wt.% NaCl). The new LAS were designated 1605A, 1605B, 1604A, and 1604B. After 72 cycles of cyclic corrosion tests, the susceptibility of the steels to corrosion could be listed in the following order based on their weight loss (from high to low): SS400＞Acr-Ten A＞1604B≥1604A＞1605B≥1605A. The change in mechanical properties by corrosion was the least for SS400, Acr-Ten A was second, and effects of corrosion on the mechanical properties of the other four low alloy steels were similar. Finally, the characteristics of the rust layers on each LAS sample were observed by SEM, and analyzed by FTIR and EPMA. The results indicated that most of the rust layers on the test steels were composed of a loose outer rust layer and a dense inner rust layer. The outer rust layer of each steel was composed of α-FeOOH, γ-FeOOH, magnetite (Fe3O4), H2O, and amorphous ferric oxyhydroxide (FeO(subscript x)(OH)(subscript 3-2x), x=0-1), while the inner rust layer was composed mainly of Fe3O4 with a little α-FeOOH. In addition, it was apparent that the copper and chromium alloying additions were enriched, respectively, at the rust-layer/substrate interface and in the rust layers. Finally, combining the results of the accelerated tests and the rust layer analysis showed that low alloy steels, such as 1605A and 1605B, have better weathering steel properties than Acr-Ten A for use in the humid and salty weather.