©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
V 5.6 SPECIAL
FERRITE
REQUIREMENT
IN
STAINLESS
STEEL
ELECTRODE
In order to meet the AWS classification
of a stainless steel electrode, a specific chemical range
must be followed by the electrode manufacturers. Since ferrite content is
mainly con- trolled
by chemical composition, the ferrite content will also fall into certain ranges
depending on the
particular electrode in question. However, some users of stainless steel
require the ferrite
content be above or below the normal ranges as found in typical chemical analyses.
An example
of this is the SMAW 316 electrode. Normally, a 316 stick electrode has a
FN in the 0- 2
range, but a specially formulated 316 stick electrode could have a minimum of
5 FN, if needed.
Since these electrodes require special chemical formulations, they must
be ordered on
a special request basis from most manufacturers. 5.7 MARTENSITIC
STAINLESS
STEEL
Martensitic stainless steels fall into
the 400 number series according to the American Iron and
Steel Institute. They are magnetic
and contain from 11.5% to 18% chromium. As previously
noted, they get the name martensite
because of the crystalline structure of the steel at room
temperature. With a lower alloy
content than the austenitic steels, they are lower in cost than
the austenitic types. They have
adequate corrosion resistance in many environments because
they form the characteristic chromium
oxide surface film. They also have a high hardenability
characteristic.
5.7.0.1 Other
chromium bearing heat resistant steels that have only 4% to 10% chromium
(not a true stainless steel by the
11.5% minimum chrome requirement) have similar hardenability
characteristics. These steels are designated by the 500 series numbers accord-
ing to the American Iron and Steel
Institute and from a welding standpoint, may be considered
in the same grouping as the martensitic
stainless steels. Nominal compositions of these types
are shown in Figure 11.
5.7.0.2 These
steels are frequently in a hard- ened
state meaning they have low ductility. If heat
is applied suddenly, as in arc welding, to a localized
area and it then is allowed to cool suddenly,
cracking may occur. The heated area contracts
on cooling and the lack of ductility in the
parent metal prevents it from following along. This
type of cracking can be prevented by pre- heating
the steel, since preheating lowers the thermal difference between the weld area
and AISI No.
Carbon
403 0.15
11.5
- 13 410
0.15 11.5
- 13.5 501
0.10 min 4
- 6 0.40 - 0.65
502 0.10
4 - 6 0.40
- 0.65 * Maximum
unless otherwise noted. NOMINAL
COMPOSITION-MARTENSITIC STAINLESS STEELS
AND CHROMIUM HEAT RESISTANT STEELS FIGURE
11
%*
%*
%*
Molybdenum
Chromium
