Stainless Steel – Grade 420F (UNS S42020)

Topics Covered

Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
    Machinability
    Welding
    Hot Working
    Cold Working
    Annealing
    Tempering
    Hardening
Applications

Introduction

Stainless steels are high-alloy steels that have good corrosion resistance in comparison with other steels because they contain more chromium.

According to their crystalline structure, stainless steels are divided into martensitic, austenitic and ferritic steels. A combination of martensitic and ferritic steels forms a fourth group known as precipitation-hardened steels.

Grade 420F stainless steel is a general purpose free machining version of 420 stainless. It is a heat treatable chromium steel. The following datasheet provides more details of grade 420F stainless steel.

Chemical Composition

The chemical composition of grade 420F stainless steel is outlined in the following table.

Element Content (%)
Iron, Fe 84
Chromium, Cr 13
Manganese, Mn 1.0
Silicon, Si 1.0
Molybdenum, Mo 0.60
Carbon, C 0.15
Sulfur, S 0.15
Phosphorous, P 0.040

Physical Properties

The following table shows the physical properties of grade 420F stainless steel.

Properties Metric Imperial
Density 7.80 g/cm3 0.282 lb/in³

Mechanical Properties

The mechanical properties of grade 420F annealed stainless steel are displayed in the following table.

Properties Metric Imperial
Tensile strength 655 MPa 95000 psi
Yield strength (@strain 0.200%) 380 MPa 55100 psi
Elastic modulus 190-210 GPa 27557– 30458 ksi
Poisson's ratio 0.27-0.30 0.27-0.30
Elongation at break (in 50 mm) 22% 22%
Hardness, Brinell 220 220
Hardness, Rockwell C (converted from Brinell hardness, value below normal Rockwell C hardness range, for comparison only) 18 18

Thermal Properties

The thermal properties of grade 420F stainless steel are given in the following table.

Properties Metric Imperial
Thermal expansion co-efficient (@0-100°C/32-212°F) 10.3 µm/m°C 5.72 µin/in°F
Thermal conductivity (@27°C/80.6°F) 25.1W/mK 174 BTU in/hr.ft².°F

Other Designations

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Equivalent materials to grade 420F stainless steel are:

  • AISI 420F
  • AMS 5620
  • ASTM A895
  • SAE 51420F
  • SAE J405 (51420F)

Fabrication and Heat Treatment

Machinability

Grade 420F stainless steel has good machinability due to the presence of sulfur.

Welding

Grade 420F stainless steel is basically not welded as it has air hardening characteristics. However, welding can be performed after preheating to 149-204°C (300-400°F) with post-weld tempering for 2 h. The filler metal used has to be AWS E/ER420.

Hot Working

The hot working of grade 420F stainless steel is performed by gradually increasing temperature to 760°C (1400°F), then further to 1097-1204°C (2000-2200°F). Later it is cooled slowly in the furnace so as to prevent cracking. Reheating has to be performed often to maintain the working temperature above 871°C (1600°F).

Cold Working

Grade 420F stainless steel can withstand only minor cold working. Radical forming will cause cracking.

Annealing

Annealing of grade 420F stainless steel can be performed at 843-900°C (1550-1650°F), followed by slow furnace cooling.

Tempering

Tempering of grade 420F stainless steel can be performed at 149-204°C (300-400°F), and then air cooled for maximum hardness (Rc 52) and corrosion resistance.

Hardening

To harden grade 420F stainless steel, it has to be soaked at 1010-1066°C (1850-1950°F) and quenched in heated oil.

Applications

Grade 420F stainless steel can be used in the following products:

  • Cutlery
  • Pump shafts
  • Dental and surgical instruments
  • Gears
  • Pinions
  • Cams
  • Steel balls
  • Hand tools

However, it is not suitable for vessels containing high pressure gases/liquids or for plastic molds requiring high surface finishes.

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