Multi-component boron coatings on low carbon steel AISI 1018

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the columnar growth of FeB phase likely follows into the [0021-crystallographic direction
and the saw-tooth structure of FeB phase is underneath that of Fe2B phase.
This dissertation will address several types of <strong>boron</strong>izing processes that are
generally deployed and developed in commercial industries and academic institutions.
2.3.1 Pack Boronizing
The pack or solid state <strong>boron</strong>izing process is the most widely favored process due to its
simplicity and cost-effectiveness. The process involves the embedding of the
metals/alloys into the powder mixture that consists of three substance groups [4]:
• Boron source: Boron carbide (B4C), ferro<strong>boron</strong>, and amorphous <strong>boron</strong>
• Activator: NaBF4, KBF4, (NH4)3BF4, NH4CI, Na2CO 3, BaF2, and Na2B4O 7
• Diluent: SiC, Al203
The well-cleaned and smooth metals/alloys are packed with the <strong>boron</strong>izing powder
mixture in the heat-resistant container sealed with a lid. The heat treatment is processed
in the furnace by heating the furnace to the preset <strong>boron</strong>izing temperature and being
preserved that temperature for a certain period of time. Boronizing temperature and time
vary depending on the type of substrate. Thereafter, the temperature in the furnace is
allowed cooling down to the ambient temperature, and the container is then removed
from the furnace. To avoid the adverse effect of oxygen on <strong>boron</strong>izing, the <strong>boron</strong>izing
process should be performed under the protective gas atmosphere, such as Ar, N2, H2, or
a mixture of Ar-N2-H2. The protective gas atmosphere must be maintained immediately
after <strong>boron</strong>izing until temperature is cooled down to 300 °C or equivalently 570 °F [1].
Using the above procedure, the powder mixture can be reused for about 5-6 times by
blending in 20-50% with the new powder mixture [7].