©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
V 5.1.0.8
That group of stainless steels that
contain both chromium and nickel (austenitic grade)
is more readily and satisfactorily welded than those that contain less than 5%
nickel (martensitic
and ferritic grades). Weld joints produced in austenitic stainless steels
are strong, ductile
and tough in their as-welded condition. They do not normally require preheat
or post weld heat
treatment. On the other hand, the martensitic and ferritic stainless steels
are charac- terized
by hardness or brittleness after welding, and preheat and post-heating is necessary
to improve their
properties. 5.1.0.9
Austenitic stainless is commonly referred
to as the "chrome-nickel" type
and the martensitic
and ferritic steels are commonly called the "straight chrome"
types. 5.2 DIFFERENCES
IN STAINLESS AND CARBON STEELS
The behavior of stainless steel in
the heat of the arc differs from that of mild steel. Figure 3
shows that the rate of expansion of
the chromium-nickel types is about 50% greater than that
of carbon steel. This means that
distortion from warping must be compensated for to a greater
extent. CARBON
STEEL CHROMIUM-
NICKEL TYPES
STRAIGHT CHROMIUM
TYPES .020
.040
.060 .080
.100
.120 INCHES
EXPANSION PER FOOT 1000°F
TEMPERATURE RISE RATE
OF EXPANSION FIGURE
3 5.2.0.1
When welding an austenitic stainless
steel to a carbon steel, the different rates of expansion
can cause cracking due to internal stresses unless the proper electrode and weld-
ing procedure is used. The expansion
of the straight chromium types is about the same as or slightly
less than that of carbon steels.
