5.7 How Does Hardness Effect Welding?
Hardness is a measure of the resistance of the
material to plastic deformation. Hardness is a
comparative measurement that uses a
standardized indenter to create an indentation in
the surface of the material. The size of the
indentation created is measured against a
standardized scale. Softer materials will exhibit a
larger indentation. A hardness test is described in
Figure 5.18.
A weld contracts as it cools. Hot weld metal is
much weaker than the surrounding parent
material. As the temperature of the weld area
drops its volume must decrease. Since it is
prevented from uniformly shrinking in three
dimensions, it must compensate in those
directions which are free to contract (Figure 5.19).
The atoms of the material must move in order for
the contraction to occur in a manner without
cracking.