152
Gas Tungsten Arc Welding Handbook
Types of steel include carbon steels, low-alloy
steels, heat-treated steels, and tool steels. Carbon
steels are classifi ed as low-, medium-, and high-
carbon steels. Alloying elements in low-alloy steels
include chromium, molybdenum, nickel, vanadium,
and manganese. Heat treatments include quenching,
tempering, and annealing. Tool steels are steels with
a combination of high carbon and alloy content.
Common steel forms include hot-rolled steel,
cold-rolled steel, castings, and forgings. Steels are
manufactured to specifi cations developed by various
organizations, including ASTM International.
Filler metals must be selected to produce the
desired mechanical properties in the weldment
after any required welding or heat treatment. When
selecting a steel fi ller metal, the type of steel to be
welded and the possibility of excessive porosity
within the completed weld should be considered.
Joint preparation considerations include
removing oxide fi lm from edges prepared by thermal
cutting processes, providing weld backing where
needed, and preheating. Quenched and tempered
steel requires preheat and interpass temperature
control to retain the original mechanical properties of
the metal.
Two torch angles that affect how the weld bead
is placed into the weld joint are the work angle and
travel angle. Work angles usually split the weld pool
evenly between the two pieces of base metal. A good
travel angle allows the welder to see the weld pool.
Stringer beads, or stringer passes, are welds
made without oscillation of the torch. Weave beads
are welds made with torch oscillation.
Thoriated, lanthanated, ceriated, zirconiated,
and pure tungsten electrodes can be used for
welding steel. Lanthanated electrodes work well
for either ac or dc current and have good current-
carrying capacities. Higher welding amperages
require larger electrodes. An electrode that is
sharpened to a point with a slight fl attened tip is
recommended for welding steel.
Pure argon gas can be used when welding metal
up to 1/8″ (3.2 mm) thick. For increasing thicknesses,
helium should be added to the shielding gas.
Manual GTAW requires a great deal of skill to
perform correctly. The ability to read a weld pool
must be developed so that the welder can make the
appropriate adjustments to ensure a quality weld.
Write your answers on a separate sheet of paper. Do not
write in this book.
1. What are the three classifi cations of carbon steel?
2. Medium-carbon steel has a content of _____
carbon.
3. List three alloying elements commonly used to
make low-alloy steels.
4. What is heat treating?
5. The oxide fi lm on the surface of hot-rolled steel
is _____ in color.
6. What color is the surface of castings that have
been sandblasted?
7. Why should stainless steel fi ller metals not be
used for welds in service over 1000°F (538°C)?
8. List the three fi nishes available on steel fi ller
metals.
9. Why must the oxide scale be removed from the
edges of thermally cut joints before use?
10. What two types of backing are used when
welding 100% penetration steel welds?
11. Why is backing used for 100% penetration steel
welds?
12. When are carbon steels less than 1″ (25.4 mm)
thick and with less than .30% carbon preheated?
13. What causes low-alloy steels to have hard heat-
affected zones after welding?
14. What is the main reason for maintaining a good
travel angle?
15. The welding rod to be added to the molten pool
is held at what angle?
16. Tool steels should be welded with small _____
beads to reduce the amount of heat input and
expansion of the base material.
17. At what approximate temperature can postweld
stress relief of carbon steel weldments be done?
18. Welds made without any side-to-side movement
of the torch are called _____ beads.
19. Welds made with side-to-side movement of the
torch are called _____ beads.
20. When steel is being welded, a small white dot
may form on the top of the molten metal. What
is this material?
Summary Review Questions