Austenitic Stainless Steel
Austenitic steels are the most popular grades of stainless steels because of their ductility, ease of working and good corrosion resistance and are very commonly used in manufacture of piping components. Austenitic steels are non-magnetic and non-hardenable by heat treatment, however they can be hardened by cold working. The most commonly used stainless steel grades are Type 304, Type 316 and Type 321.
Stainless steel grades with suffix L have low carbon content. The low carbon content provides good weldability and good corrosion resistance after welding, however they have lower strength than the grades with higher carbon content. The dual certified grades of stainless steel are commonly used in the industry such as SS 304/304L or SS 316/316L. For e.g. the SS 304/304L dual certified grade has lower carbon content similar to SS 304L grade but higher mechanical strength of SS 304 grade.
Type 304 grade contains approximately 18% Chromium and 8% Nickel.
Effect of carbon on corrosion resistance
The lower carbon variants (316L) were established as alternatives to the standards (316) carbon range grade to overcome the risk of intercrystalline corrosion (weld decay), which was identified as a problem in the early days of the application of these steels. This can result if the steel is held in a temperature range 450 to 850°C for periods of several minutes, depending on the temperature and subsequently exposed to aggressive corrosive environments. Corrosion then takes place next to grain boundaries.
If the carbon level is below 0.030% then this intercrystalline corrosion does not take place following exposure to these temperatures, especially for the sort of times normally experienced in the heat affected zone of welds in thick sections of steel.
Effect of carbon level on weldability
There is a view that the low carbon types are easier to weld than the standard carbon types.
There does not seem to be a clear reason for this and the differences are probably associated with the lower strength of the low carbon type. The low carbon type may be easier to shape and form, which in turn may also affect the levels of residual stress left the steel after is forming and fitting up for welding. This may result in the standard carbon types needing more force to hold them in position once fitted-up for welding, with more of a tendency to spring-back if not properly held in place.
The welding consumables for both types are based on a low carbon composition, to avoid intercrystalline corrosion risk in the solidified weld nugget or from the diffusion of carbon into the parent (surrounding) metal.
Dual-certification of low carbon composition steels
Commercially produced steels, using current steelmaking methods, are often produced as the low carbon type as a matter of course due to the improved control in modern steelmaking. Consequently finished steel products are often offered to the market dual certified to both grade designations as they can then be used for fabrications specifying either grade, within a particular standard.

A/SA182 F316 / 316L Technical Data
Summary
316 is an improved version of 304, with the addition of molybdenum and a slightly higher nickel content. The resultant composition of 316 gives the steel much increased corrosion resistance in many aggressive environments.  The molybdenum makes the steel more resistant to pitting and crevice corrosion in chloride-contaminated media, sea water and acetic acid vapours.   The lower rate of general corrosion in mildly corrosive environments gives the steel good atmospheric corrosion resistance in polluted marine atmospheres.
316 offers higher strength and better creep resistance at higher temperatures than 304.  316 also possesses excellent mechanical and corrosion properties at sub-zero temperatures.  When there is a danger of corrosion in the heat-affected zones of weldments, the low-carbon variety 316L should be used.  316 Ti, the titanium-stabilised version, is used for its resistance to sensitization during prolonged exposure in the 550^oC-800^oC temperature range.
Typical Applications
Because of its superior corrosion and oxidation resistance, good mechanical properties and fabricability, 316 has applications in many sectors of industry.  Some of these include:
Tanks and storage vessels for corrosive liquids.
Specialised process equipment in the chemical, food, paper, mining, pharmaceutical and petroleum industries.
Architectural applications in highly corrosive environments.
Chemical Composition (ASTM A/SA 182)
 

Typical properties in the annealed condition
The properties quoted in this publication are typical of mill products and unless indicated must not be regarded as guaranteed minimum values for specification purposes.
1. Mechanical properties at room temperature
  2. Properties at elevated temperatures
The values given refer to 316 and 316 Ti only as strength values for 316L fall rapidly above 425^oC.
Short Time Elevated Temperature Tensile Strength Creep data
Stress for a creep rate of 1% in 10 000 hRecommended Maximum Service Temperature
(Oxidising conditions)
Continuous Service            925^oC
Intermittent Service             870^oC
3. Properties at Sub-Zero Temperatures (316 )
  4. Corrosion Resistance
4.1    Aqueous
         For specific conditions, consult VRN technical staff.  As a rough guide, the following examples are given
         for pure acid-water mixtures.
   Key:         0 = resistant    -    corrosion rate less than 100 mm/year
                 1 = partly resistant    -    corrosion rate 100 m to 1000 mm/year
                2 = non resistant    - corrosion rate more than 1000 mm/year
 
4.2    Atmospheric
          The performance of 316 compared with other metals in various environments is shown in the
          following table.  Corrosion rate is based on a 5 year exposure.
 

Note:  For corrosion resistance of 316 relative to other types, see the section in Comparative Data.
4.3    Thermal Processing
4.3.1 Annealing. Heat from 1 010^oC to 1 120^oC and cool rapidly in air or water.  The best corrosion
          resistance is obtained when the final annealing temperature is above 1 070^oC.
4.3.2 Stress relieving.  Heat from 200 - 400^oC and air cool.
4.3.3 Hot working
          Initial forging and pressing:                                    1150  - 1200^oC
          Finishing temperature:                                            above 900^oC
          For upsetting operations, forgings
          should be finished between:                                   930 and 980^oC
          All hot working operations should be followed by annealing.
Note:  Soaking times to ensure uniformity of temperature are up to 12  times that required for the same thickness of mild steel.
Cold Working
316 / 316L, being extremely tough and ductile, can be readily fabricated by cold working. Typical operations include bending, forming, deep drawing and upsetting.

DN15-DN3000
Maximum weight 6tons
25,000tons production annual year

ANSI B16.5,ANSI B16.47 Series A&B,ANSI B16.48,ANSI B16.36
API 605,API 16D,API 17D
BS4504,BS3293
DIN
AS
EN1092-1
GOST
EEMUA145