BRIGHT ANNEALING

Bright annealing is the heat treatment of non-alloyed or low-alloyed steels and non-ferrous metals under a nitrogen-hydrogen atmosphere. The proportion of hydrogen varies here depending on the material and process temperature and ultimately naturally also due to the desired process results.

If the atmosphere consists predominantly of nitrogen (i.e. <= 5 % hydrogen) then no noteworthy reactions occur in the atmosphere of the annealing product. The protective gas (here for example forming gas 95/5) serves principally to eliminate oxidizing gases from the process chamber, for example oxygen (air) or water vapour. With an increasing hydrogen content in the furnace atmosphere the effect of the reduction in surface oxidation increases in significance. At the same time the conductivity of the protective gas rises with an increase in the proportion of hydrogen. This also has a positive effect on the heating and cooling speeds of the annealing product.

With certain material groups the treatment must be carried out with noble gases, e.g. with a hydrogen-argon mixture.

Heat treatments under a pure hydrogen atmosphere take place in specially equipped vacuum furnace systems.
 

Bright annealing consists of:

  • heating the steel from ambient temperature to a high temperature (above the re-crystallization temperature), and then cooling it down

To prevent oxide formation during the annealing process, the furnace atmosphere is generally a mixture of nitrogen and hydrogen.