Stainless Steel 316/316L – Grade

GENERAL PROPERTIES:  

Alloy 316/316L is a stainless steel containing Chromium-Nickel-Molybdenum. Before it is, welded it retains its original non-magnetic properties. It has a density of 0.285 lb/in3 and heat capacity of 0.12 BTU/lb-°F. 

Its machinability involves it being resistant to chip breaking. The Modulus of Elasticity of the alloy is 29 x 106.  It demonstrates excellent solidity at cryogenic temperatures; this alloy has an ultimate tensile strength of 85 psi and an electrical resistance of 29.5 x 106 Ω-inch. 

The thermal conductivity of this alloy lies at 8.7 Btu/ft hr°F. The alloy also scores 81 on the Rockwell B scale. Its melting Range is in between 2450–2630°F and 1390–1440°C and it shows the property of ductility.

CHEMICAL FORMULA AND CHEMICAL COMPOSITION:

The chemical formula of this compound is as follows: Fe, <0.03% C, 16-18.5% Cr, 10-14% Ni, 2-3% Mo, <2% Mn, <1% Si, <0.045% P, <0.03% S. The alloy consists of the following elements: Chromium, Molybdenum, Nickel, Carbon, Manganese, Phosphorous, Sulfur, Silicon, Nitrogen and Iron. The higher Molybdenum content is responsible for its high solidity and resistance. 

KEY PROPERTIES

  1. WELDING CHARACTERISTICS: 

This alloy is suitable for welding. All the standard fusion methods can be used, for its welding, and there is no heat treatment required later. However, the oxyacetylene process does not apply to this alloy.

The welding can be done, with filler metals with molybdenum content higher than the base metal or even without any filler metals. 316 L does not require post-weld annealing. However, some of the heavy weld sections of Grade 316 require post-weld annealing. It is, usually done to maximise corrosion resistance. 

  1. HEAT TREATMENT:

The internal stresses in the alloy are removed, in the process of annealing. Type 316/316L should be heated, at a temperature of 1900°F. It is then cooled rapidly with the water being, quenched. However, type 316/316L cannot be hardened through heat treatment.

  1. PROCESSING – HOT FORMING: 

The hot working processes take place under the extreme temperatures of 1700- 2200°F. The forgings can be further, annealed at the required temperature of 1900°F. With this, the alloy can be, physically deformed, allowing it to recrystallise.

  1. PROCESSING- COLD FORMING: 

In the cold working processes, the alloy can be completely fabricated and formed conveniently. The method includes various steps like squeezing, bending, shearing, drawing, upsetting and heading. All these steps ensure that the material has increased strength and hardness. However, in this process, the material can gain some magnetic properties, although originally it is non-magnetic.

  1. MACHINABILITY: 

This alloy is put, under work hardening during the deformation, for efficient operation, slow speed, outstanding lubrication, heavier feeds, acute tooling and robust and firm equipment. 

  1. CORROSION RESISTANCE: 

The alloy shows resistance to corrosion in many corrosive media and atmospheric environments. For mediums containing halides and chlorides, the constituent molybdenum ensures resistance to corrosion. The addition of molybdenum provides improved resistance to pitting and crevice corrosion in environments containing chlorides and other halides. 

However, it sometimes shows surface corrosion. It can be seen in the faint brown stains and is usually, caused because of cracks and rough surface finishing. At ambient temperatures, it is also resistant to drinking water with up to about 1000 mg/L chlorides. 

It is commonly used by many process industries to handle many chemicals. Even though it is referred, to as “marine grade stainless steel”, it is not resistant to warm seawater. In the as-welded condition, it also shows resistance to intergranular corrosion. 

  1. HEAT RESISTANCE: 

Grade 316/316L has good creep resistance and has high strength at increased temperatures which makes it suitable for using it for structural and pressure-containing applications. The creation of an oxide layer usually provides the scaling resistance.

The other two features that provide the alloy with good heat resistance are its stable microstructure and its high mechanical load. If the alloy is subjugated to 870°C intermittently and 925 °C continuously, the alloy will show good oxidation resistance. For water corrosion resistance, it is, advised that the continuous application of the temperature range 425-860 °C is avoided. It also shows resistance to carbide precipitation. 

  1. DUAL CERTIFICATION: 

The Grade 316/316 L is classified under the “Dual Certified type” as it is stocked and found mainly in the form of plate and pipe. The items under this certification have specifications that consist of the mechanical and chemical properties of both 316 and 316L types. 

With this certification, both the lower carbon limit of 316L and the upper limit of 316 are, met. However, due to discrepancy within the high-temperature application, the certification is not extended to type 31. It also meets all the AMS, ASTM, ASME, QQS, and MIL-S specifications.

APPLICATIONS:

  • Benches and equipment for the laboratories: Being very easy to clean and multipurpose, this alloy is very suitable for the laboratory equipment and benches.
  • Food and Beverage industry: The intrinsic property of Grade 316/316L to be resistant to corrosion makes its way to the food and beverage industry. From storage to transportation and from easy cleaning to sterilisation, this type is very beneficial to the industry.
  • Heat exchangers: Being resistant to corrosion and having high durability, Grade 316/316L is a highly reliable choice for being used in heat exchangers.
  • Textile industry: This type of stainless steel endures deterioration with its inherent properties of strength and high-resistance, making it the most suitable for the textile industry.
  • Petrol industry: Grade 316/316L is known for the formation of oxide layers that inhibit the process of oxidation. This property is useful for the petrol industry. Moreover, the high heat resistance of the alloy makes it very suitable for the petrol industry.
  • Nuclear reactors: Grade 316/316 L is known to be of big use to the nuclear industry. The nuclear reactors have to be made out of the best material to ensure safe chemical reactions. 

This alloy is very resistant to corrosion, can handle extreme temperatures, is durable and holds immense strength, making it a safe choice for nuclear reactors. The high mechanical formability is very advantageous to nuclear power plants.

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