What is alloy 20
Alloy 20Cb3 is a nickel-iron-chromium based, austenitic alloy with excellent corrosion resistance in chemical environments containing sulfuric acid and many other aggressive media. This alloy is stabilized with niobium to resist intergranular corrosion. Alloy 020 has excellent resistance to general corrosion, pitting and crevice corrosion and is commonly used for chemical, pharmaceutical and food processing, tanks, piping, heat exchangers, pumps, Kevlar production and much more.
Alloy 020 or cb3 (UNS N08020, W. Nr 2.4660)
|Alloy 20 Bar||ASTM B 473|
|Alloy 20 Plate||ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464|
|Alloy 20 Sheet||ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464|
|Alloy 20 Strip||ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464|
|Alloy 20 Wire||ASME SB-473 ASME SB-366, ASTM B 473, ASTM B 366|
|Alloy 20 Weld Wire||AWS ER320LR, ASTM Weld Tube B468|
|Alloy 20 Weld Pipe||ASTM B464|
|Alloy 20 Other||UNS N08020, Werkstoff Nr. 2.4660, Covered Electrodes AWS E320LR, Fordings ASTM B462|
Chemical composition of Alloy 20 cb3 (UNS N08020, W. Nr 2.4660
|Chemical Composition Limits|
|Alloy 20||32.0 – 38.0||19 – 21||3 – 4||2 – 3||bal||0.07 max||8 x C-1||2 max||0.045 max||0.035 max||1.0 max|
Mechanical properties of Alloy 20 cb3 (UNS N08020, W. Nr 2.4660
Physical properties of Alloy 20 cb3
|Density||8.08 g/cm³||0.292 lb/in³|
|Coefficient of Expansion||14.69 μm/m °C (20 – 100°C)||8.16 x 10-6 in/in °F (70 – 212°F)|
|Modulus of Rigidity||73.6 kN/mm²||10675 ksi|
|Modulus of Elasticity||193 kN/mm²||27993 ksi|
SMAW Welding rod & TIG/MIG filler wire Alloy 20 Welding
Oxyacetylene welding is not recommended as carbon pickup in the weld may occur. The alloy may be used in the as-welded condition, but for high-temperature service a stabilizing post-weld anneal is recommended.
Alloy 20 cb3 is commonly welded by TIG, MIG as well as shielded metal arc welding (SMAW) using either the matching filler metal, ER320LR for TIG and MIG and E320LR for SMAW. When welding to dissimilar alloys such as 316 or higher alloys such as C276 and Alloy 22, AWS ERNiCrMo-3 (Inco 625) can be used for TIG and MIG while using ENiCrMo-3 for SMAW.
Properties of ER320LR TIG wire
ER320LR ( where LR means Low Residuals) is a matching TIG/ MIG filler wire for the welding of Alloy 20 cb3. This classification has the same basic composition as ER320; however, the elements C, Si, P, and S are specified at lower maximum levels and the Nb and Mn are controlled at narrower ranges. These changes reduce the weld metal hot cracking and fissuring (while maintaining the corrosion resistance) frequently encountered in fully austenitic stainless steel weld metals. Consequently, welding practices typically used for austenitic stainless steel weld metals containing ferrite can be used in bare filler metal welding processes such as gas tungsten arc and gas metal arc. ER320LR filler metal has been used successfully in submerged arc overlay welding, but it may be prone to cracking when used for joining base metal by the submerged arc process. ER320LR weld metal has a lower minimum tensile strength than ER320 weld metal.
Welding amperage for SMAW & TIG welding of Alloy 20 cb3
In SMAW welding of Alloy 20 cb3, welding current selection is dependent on electrode diameter. Generally, used 1/8” electrode require 70 to 90 ampere current. For TIG welding, a current of 100- 140 ampere suits well for different TIG wire diameters.
Heat treatment of Alloy 20 cb3
Alloy 20Cb-3 cannot be hardened by heat treatment. Annealing is carried out at 1725/1850ºF (940/1010ºC) for 30 minutes per inch of section thickness followed by water quenching. This treatment will ensure optimum stabilization. If maximum softness is required, say for improved formability, the annealing temperature may be increased up to 2100ºF (1150ºC) but only if the part will not be welded or used in service above 1000ºF (540ºC).
Stress relieving may be used – up to 1000ºF (540ºC) – on welded structures of intricate design.