Stainless Steel - Grade **4L
Chemical Formula
Fe, <0.*2% C, ****3% Cr, ****8% Ni, **5% Mo, <2.0% Mn,
<1.0% Si, <0.**5% P, <0.**5% S, 1.**2.0%
Cu
The "L" in **4L stands for Low Carbon, specifically, that carbon
added to the alloy represents. *3 percent or less. This means that
**4L has very good welding properties. It is also an austenitic
alloy, which means that a nonmagnetic solid solution of ferric
carbide or carbon in iron is used to increase corrosion
resistance.
Properties and Uses of **4L Stainless Steel
**4L cannot be hardened by heat treatment. You can weld **4L
stainless using any standard method, but it is susceptible to hot
cracking. It can be machined but does not machine
well.
Common applications take advantage of **4L\'s corrosion resistance.
These include acid processing plants, pulp and paper operations,
equipment for cooling seawater, oil refining, and environmental
equipment.
The chemical processing industry makes extensive use of **4L
stainless steel due to its broad corrosion resistance. Among **4L
stainless steel suppliers, Tampa Bay Steel has the largest **4L
plate inventory in Florida.
Corrosion Resistance
Although originally developed for its resistance to sulphuric acid
it also has a very high resistance to a wide range of environments.
A PRE of *5 indicates that the material has good resistance to warm
sea water and other high chloride environments. High nickel content
results in a much better resistance to stress corrosion cracking
than the standard austenitic grades. Copper adds resistance to
sulphuric and other reducing acids, particularly in the very
aggressive "MID concentration" range.
In most environments **4L has a corrosion performance intermediate
between the standard austenitic grade **6L and the very highly
alloyed 6% molybdenum and similar "super austenitic"
grades.
In aggressive nitric acid **4L has less resistance than
molybdenum-free grades such as **4L and **0L.
For maximum stress corrosion cracking resistance in critical
environments the steel should be solution treated after cold
work.
Heat Resistance
Good resistance to oxidation, but like other highly alloyed grades
suffers from structural instability (precipitation of brittle
phases such as sigma) at elevated temperatures. **4L should not be
used above about **0° C.
Heat Treatment
Solution Treatment (Annealing) - heat to ********5° C and cool
rapidly. This grade cannot be hardened by thermal
treatment.
Welding
**4L can be successfully welded by all standard methods. Care needs
to be taken as this grade solidifies fully austenitic, so is
susceptible to hot cracking, particularly in constrained weldments.
No pre-heat should be used and in most cases post weld heat
treatment is also not required. AS ***4.6 pre-qualifies Grade **4L
rods and electrodes for welding of **4L.
Fabrication
**4L is a high purity, low sulphur grade, and as such will not
machine well. Despite this the grade can be machined using standard
techniques.
Bending to a small radius is readily carried out. In most cases
this is performed cold. Subsequent annealing is generally not
required, although it should be considered if the fabrication is to
be used in an environment where severe stress corrosion cracking
conditions are anticipated.
Applications
Typical applications include:
Processing plant for sulphuric, phosphoric and acetic
acids
Pulp and paper processing
Components in gas scrubbing plants
Seawater cooling equipment
Oil refinery components
Wires in electrostatic precipitators
