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Austenitics Stainless Steel

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Austenitics Stainless Steel

Austenitic stainless steel is a type of stainless steel that primarily consists of the austenite phase in its microstructure. Austenite is a crystal structure that imparts specific properties to this type of stainless steel. Austenitic stainless steel is known for its excellent corrosion resistance, high ductility, and versatility, making it one of the most widely used categories of stainless steel.

A few examples of commonly used austenitic stainless steel grades:

AISI 321 (UNS S32100)

AISI 304 (UNS S30400)

AISI 304L (UNS S30403)

AISI 316 (UNS S31600)

AISI 316L (UNS S31603)

AISI 310S S31008

● AISI 321 (UNS S32100)

These titanium bearing stainless steels are stabilized against carbide precipitation and designed for operation within the damaging temperature range where carbide precipitation develops. In this type of steel, the carbon combines preferentially with titanium to form a harmless titanium carbide, leaving the chromium in solution to maintain full corrosion resistance.

Type 321 is basic type 304 modified by adding titanium in an amount at least 5 times the carbon plus nitrogen contents.

Chemical Composition

0.0817.0 – –*

Design Features

Immune to intergranular corrosion when heated within the carbide precipitation range.

Titanium addition eliminates the formation of chromium carbides at the grain boundaries by typing up the carbon and nitrogen as titanium carbides or nitrides.

Better high temperature properties than 304 or 304L. Generally used for parts which are intermittently heated up to 1500 ̊ F. For continuous service the alloy is good to 1650 ̊ F.

May be susceptible to chloride stress cracking.

Excellent weldability in field.

Type 321H has high carbon (.04-.10) for better high temperature creep properties.

Typical Applications

  • High temperature chemical process heat exchanger tubes
  • Refineries
  • High temperature steam service
  • Features: Contains titanium for stabilization against carbide precipitation during welding. Good corrosion resistance and high-temperature strength.
  • Applications: High-temperature applications, such as heat exchangers, furnace parts, and jet engine components.

● AISI 304 (UNS S30400):
  • Features: Excellent corrosion resistance, high ductility, and ease of fabrication. Non-magnetic in the annealed condition.
  • Applications: Food and beverage industry, architectural applications, kitchen equipment, and various structural components.

● AISI 304L (UNS S30403):

304 stainless is a low carbon (0.08% max) version of basic 18-8 also known as 302. Type 302 has 18% chromium and 8% nickel. Type 304 has slightly lower strength than 302 due to its lower carbon content. Type 304 finds extensive use in welding applications because the low carbon permits some exposure in the carbide precipitation rang of 800 ̊ F – 1500 ̊ F without the need for post-annealing operations. However, the severity of corrosive environments may necessitate annealing after welding or the use of 304L.

Type 304L has a carbon content of 0.03% or less. This alloy can be used in the as-welded condition without becoming susceptible to intergranular corrosion.

Chemical Composition

0.03518.0 – – 13.00.0400.0300.75

Design Features

  • Oxidation resistance up to 1650 ̊ F for continuous service and up to 1500 ̊ F where cyclic heating is involved.
  • General purpose corrosion resistance.
  • Non-hardenable except by cold working.
  • Non-magnetic except when cold worked.
  • May be susceptible to chloride stress corrosion cracking
  • Used where field working is employed.

Typical Applications

  • Sanitary
  • Dairy and Food Processing
  • Heat exchangers, evaporators
  • Feedwater heaters
  • Features: Low carbon version of AISI 304 for improved weldability and reduced susceptibility to sensitization and intergranular corrosion.
  • Applications: Similar to AISI 304, particularly in applications requiring welding.

● AISI 316 (UNS S31600):

Features: Improved corrosion resistance compared to AISI 304, particularly in chloride environments. Contains molybdenum for enhanced pitting resistance.

Applications: Chemical processing, marine environments, medical implants, pharmaceutical equipment, and coastal architectural applications.

● AISI 316L (UNS S31603):

Type 316 is a molybdenum steel possessing improved resistance to pitting by solutions con- taining chlorides and other halides. In addition, it provides excellent elevated temperature tensile, creep and stress – rupture strengths.

Chemical Composition

0.03516.0 – – 3.010.0 – 15.00.0400.0300.75

Design Features 

Type 316 is more resistant to atmospheric and other mild environments than Type 304. It is resistant to dilute solutions (i.e. 1-5%) of sulfuric acid up to 120 ̊ F. However, in certain oxidizing acids, Type 316 is less resistant than Type 304.

316 is susceptible to carbide precipitation when exposed in the temperature range of 800 ̊ – 1500 ̊ F and therefore is susceptible to intergranular corrosion in the as-welded condition. Annealing after welding will restore corrosion resistance.

Type 316L has the same composition as Type 316 except the carbon content is held below 0.03%. Not unexpectedly, its general corrosion resistance and other properties closely correspond to those of Type 316. However, it does provide immunity to intergranular attack in the as-welded condition or with short periods of exposure to the temperature range of 800 ̊ – 1500 ̊ F. The use of 316L is recommended when exposure in the carbide precipitation range is unavoidable and when annealing after welding is not practical. However, prolonged exposure in this range may embrittle the material and make it susceptible to intergranular attack.

The maximum temperature for scaling resistance in continuous service is about 1650 ̊ F, and 1500 ̊ F for intermittent service.

May be susceptible to chloride stress corrosion cracking.

Non-hardenable; non-magnetic in the annealed condition, and slightly magnetic when cold worked.

Improved corrosion resistance to chlorides

Typical Applications

  • Nuclear
  • Chemical processing
  • Rubber
  • Plastics
  • Pulp/paper
  • Pharmaceutical and textile industries
  • Heat exchangers, condensers and evaporators
  • Features: Low carbon version of AISI 316 for improved weldability and reduced susceptibility to sensitization and intergranular corrosion.
  • Applications: Similar to AISI 316, particularly in applications requiring welding.

● AISI 310S S31008

310S has excellent resistance to oxidation under constant temperatures to 2000 ̊ F. Cyclic conditions reduce its oxidation resistance, and a maximum operating temperature of 1900 ̊ F is generally recommended if cycling is involved. Having a lower coefficient of expansion than most 300 stainless steels, 310S may be used in operations involving moderately severe thermal cycling, such as rapid air cooling.

It is not usually recommended for liquid quenching. Although 310S has less resist- ance to absorption of carbon and nitrogen than the higher alloys such as 330 and 333, it is widely used in moderately carburizing atmospheres such as encountered in petro-chem plants. Because of its high chromium and medium nickel contents, 310S may be used in atmospheres containing moderate amounts of sulfur.

Chemical Composition

0.0824.0 – – 22.00.0450.030.75

Design Features

  • Austenitic stainless steel with excellent high temperature oxidation resistance.
  • Good for continuous exposure to 2100 ̊ F, intermittent service to 1900 ̊ F.
  • Better elevated temperature creep strength than the 18-8 grades.
  • Good resistance to both carburizing and reducing environments.
  • General corrosion resistance better than Type 304 and 309.
  • May be susceptible to chloride stress corrosion cracking.
  • Availability.
  • Ease of fabrication.

    Typical Applications

    • Heat exchanger and heat recuperator tubing
    • Molten salt applications
    • Sulfur bearing gas atmospheres

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