Defectology
Thermite welding of railways rails

Thermite welding has a number of weaknesses:

• disturbed internal cleanliness (blowholes, hercynites) due to inadequate settling times, combined with reactions that are sometimes too slow;

• As far as blowing is concerned, the maximum reaction temperature should be limited to 2,000°C by adding an adequate quantity of cooling scrap, since the Richardson diagram (figure 1) shows that, above this temperature, carbon becomes more reductive than aluminum and favors the appearance of carbon monoxide CO (blowing);

• of this metallographic set, fractures such as the one shown in figure 14 may result.

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