Sep 26 2012
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
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.