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Sulphuric Acid on the WebTM Technical Manual DKL Engineering, Inc.

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Materials of Construction - Metals - Alloy 20
December 12, 2001

Introduction
Chemical Composition
Corrosion Resistance
Designations
Specifications
Physical Properties
Mechanical Properties

Fabrication
Associated Links

Introduction

Alloy 20 is a highly alloyed iron-base nickel-chromium-molybdenum stainless steel developed primarily for use in the sulphuric acid related processes. Besides sulphuric acid related processes, some typical corrosion resistant applications for the alloy include chemical, pharmaceutical, food, plastics, synthetic fibres, pickling and FGD systems plus many others.

 

The high nickel content combined with chromium, molybdenum, and copper gives the alloy good resistance to pitting and chloride-ion stress-corrosion cracking. The copper content combined with other elements gives the alloy excellent resistance to sulphuric acid corrosion under a wide variety of conditions. The addition of columbium stabilizes the heat affected zone carbides so the alloy can be used in the as-welded condition. Alloy 20 has good mechanical properties and is easily fabricated.

 

Chemical Composition (wt% typical)

Nickel Ni 32.5 - 35.0
Chromium Cr 19.0 - 21.0
Molybdenum Mo 2.0 - 3.0
Iron Fe Balance
Carbon C 0.06 Max
Columbium + Tantalum Cb + Ta 8 x C or 1.00 Max
Copper Cu 3.0 - 4.0

Corrosion Resistance

Chart18.BMP (182906 bytes)

Designations

UNS N08020

Alternate Names: Carpenter 20Cb3

Specifications

AISI 664
ASTM B366, B462 (Forging - Open Die), B463, B464, B468, B471, B473, B474, B475, B729
DIN 2.4660

Physical Properties

Density 8083 kg/m³ (504.6 lb/ft³)
Specific Heat 32-212°F 0.12 Btu/lb/Deg°F
Electrical Resistivity 68°F 651 microhm-cm
Poissons Ratio 0.31
Magnetic Permeability 1.002
Modulus of Elasticity Tension 28

Mechanical Properties

Ultimate Tensile Strength 683 MPa (99,000 psi)
Elongation in 50.8 mm (2 in.) 35%
Yield Strength (0.2% offset)  414 MPa (60,000 psi)
Hardness  148 HV

Fabrication

To follow