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.
The chemical composition of grade 420F stainless steel is outlined in the following table.
The following table shows the physical properties of grade 420F stainless steel.
|Density||7.80 g/cm3||0.282 lb/in3|
The mechanical properties of grade 420F annealed stainless steel are displayed in the following table.
|Tensile strength||655 MPa||95000 psi|
|Yield strength (@strain 0.200%)||380 MPa||55100 psi|
|Elastic modulus||190-210 GPa||27557� 30458 ksi|
|Elongation at break (in 50 mm)||22%||22%|
|Hardness, Rockwell C||18||18|
The thermal properties of grade 420F stainless steel are given in the following table.
|Thermal expansion co-efficient (@0-100�C/32-212�F)||10.3 �m/m�C||5.72 �in/in �F|
|Thermal conductivity (@27�C/80.6�F)||25.1W/mK||174 BTU in/hr.ft�.�F|
Equivalent materials to grade 420F stainless steel are:
SAE J405 (51420F)
Fabrication and Heat Treatment
Grade 420F stainless steel has good machinability due to the presence of sulphur.
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.
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).
Grade 420F stainless steel can withstand only minor cold working. Radical forming will cause cracking.
Annealing of grade 420F stainless steel can be performed at 843-900°C (1550-1650°F), followed by slow furnace cooling.
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.
To harden grade 420F stainless steel, it has to be soaked at 1010-1066°C (1850-1950°F) and quenched in heated oil.
Grade 420F stainless steel can be used in the following products:
Dental and surgical instruments
However, it is not suitable for vessels containing high pressure gases liquids or for plastic molds requiring high surface finishes.
Source - www.azom.com