Welding Inspection & Metallurgy API ICP Self Study Notes

The addition of carbon generally makes the metal more difficult to weld.
Carbon content has the greatest effect on mechanical properties, such as
tensile strength, ductility and toughness in the base metal heat affected zone
and weldment. Carbon content influences the susceptibility of the metal to
delayed cracking problems from hydrogen. The carbon content or carbon
equivalent of carbon steel that determines the necessity for pre-heat and
post-weld heat treatment. Alloying elements other than carbon are added to
alloy steels for various reasons and can have an influence on the weldability
of the metal. Some alloying elements, such as manganese, chromium, nickel
and molybdenum are added to provide beneficial effects on strength,
toughness, and corrosion resistance. Some of these elements are beneficial
in non-heat treated steel while others come into play during heat treatments
necessary to produce the desired mechanical properties. These alloying
elements can have a strong effect on hardenability, so they can also affect
the weldability of the metal being welded.