ISSN:
1662-8985
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Surface graphitization is a well known defect that occurs when low carbon steel strip isbatch annealed. A small addition of chromium (about 0.04 wt %) can be used to minimize thesurface graphitization. However chromium and some other alloy elements, such as manganese usedin this class of steel, have higher affinities for oxygen than iron. Therefore it is possible for them tobe oxidized during batch annealing in a reducing environment to iron. Selective oxidation of thesetwo elements gives rise to a risk of forming different surface defects that may affect the quality ofthe tinned surface. The edge defect is characterized as a region of low reflectivity on the tin plateproduct caused by grain boundary precipitates. A porous tin coating with a dull appearance isproduced in the affected areas. Not only are the aesthetical values of the finished tin plate productaffected but the corrosion resistance is also reduced.In this investigation surface oxides formed at grain boundary of low carbon steels annealed at700°C in 5% hydrogen 95% nitrogen atmosphere were characterized using scanning electronmicroscopy and transmission electron microscopy. Two different oxide particles (Fe,Mn)O andMnCr2O4 were observed at the grain boundaries with the former five-fold coarser than the latter. Itwas found at the annealing temperature of 700°C, that the mean particle size of the (Fe,Mn)Odepends on the manganese content, while the mean particle size, and distribution of the MnCr2O4was dependent on chromium, but independent of manganese. The coarse (Fe,Mn)O precipitatespose no potential risks to electrolytic tinning as they will be removed by the pickling operation priorto tinning. Controlling the chromium content of the steel can minimize the potential risks posed bythe MnCr2O4 to the quality of electrolytic tinning
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/39/transtech_doi~10.4028%252Fwww.scientific.net%252FAMR.15-17.762.pdf
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