| 摘要 |
<p>The surface of cast iron is decarbonised by immersing the casting in an aq. alkaline or neutral bath contg. a base and/or salts, and applying a potential from a counter electrode. The treatment is carried out at a bath temp. between 40 degrees C and the b.pt. of the bath, esp. 70-90 degrees C. A potential more positive than -0.2V (w.r.t. standard hydrogen electrode) is first applied for >20, esp. 20-50 hrs. then the electrode potential is made more negative than -1.0V (w.r.t. a standard hydrogen electrode) over a period of 0.5-5 hrs. esp. 1-2 hrs. Over the first period of treatment the graphite particles and carbon present in the Fe3C is oxidised to CO and CO2 and the Fe matrix is oxidised to iron oxide and is thus passivated. In the second phase, the iron oxide is reduced and the resulting evolution of hydrogen cleans the surface of the article. The process is easy to carry out and uses dil. treatment baths. The treated castings are corrosion-resistant. The process is useful e.g. for treating exhaust manifolds of internal combustion engines, coolers in contact with sea water, and other castings in contact with corrosive environments.</p> |
