STEEL - Materials for Civil and Construction Engineers - page 127

0.4

Zone II

0.3

Zone III

0.2

0.1

Zone I

0.2 0.3 0.4 0.5 0.7 0.8

FIGURE 3.26 Welding zone classifica-

Carbon equivalent (CE)

tion of steel.

The hardness and hydrogen control methods are means of determining
the level of energy used to preheat the weld area before the weld is per-
formed. Preheating of the metal and the use of low hydrogen electrodes are
the best means of avoiding hydrogen embrittlement. This occurs when steel
is melted during welding, which may allow hydrogen to dissolve in the molten
metal and diffuse into the base metal adjacent to the weld.
Whenever metal is welded, the base material adjacent to the weld is
heated to a temperature that may be sufficient to affect its metallurgy. The
material affected in this manner is termed the heat-affected zone, HAZ
(Figure 3.27). The material in the HAZ is a high-risk area for failure, espe-
cially if proper preheating and cooling procedures are not followed.

3.10

Steel Corrosion

Corrosion is defined as the destruction of a material by electrochemical
reaction to the environment. For simplicity, corrosion of steel can be defined
as the destruction that can be detected by rust formation. Corrosion of steel

Weld deposit

Heat affected zone

FIGURE 3.27 Heat
affected zone poduced
during welding.

Base metal