Grade 420 hardness martensitic stainless steels

Grade 420 hardness martensitic stainless steels


Grade 420 stainless steel is a higher carbon version of 410; like most carbon and low alloy steels it can be hardened by heat treatment. It contains a minimum of 12 per cent chromium, just  sufficient  to  give  corrosion  resistant properties.  420  has  good  ductility  in  the annealed  condition  but  is  capable  of  being hardened up to Rockwell Hardness 50HRC, the highest hardness of the 12 per cent chromium grades.   Its   best   corrosion   resistance   is achieved when hardened and surface ground or polished.


Related grades to 420 are high carbon high hardness martensitic stainless steels such as the 440 series (see the Atlas Datasheet on this series of grades) and also variations to 420 containing molybdenum (for increased corrosion resistance and  mechanical properties),  sulphur (for increased machinability) or anadium (for higher hardness). A slightly higher carbon version of 420 is the non-standard grade 420C.

     
Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must allow for poor weldability and usually also include a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.  

Read more:
   
Austenitic stainless steel Grade 304, 304L and 304H

Utility stainless steel designation AtlasCR12Ti is a registered trade mark of Atlas Steels

Corrosion Resistance    

 
Grade 420 in the hardened condition has good resistance to the atmosphere, foods, fresh water and mild alkalies or acids. Corrosion resistance is lower in the annealed condition. Less corrosion resistant than the austenitic grades and also less than 17% chromium ferritic alloys such as Grade 430; 420 also has slightly lower resistance than grade 410. Performance is best with a smooth surface finish.    
     

This grade is commonly used for cutlery - particularly blades of table knives and for some carving knives and similar. The corrosion resistance is sufficient to resist food and normal washing methods, but prolonged contact with unwashed food residues can result in pitting. Consult Atlas Technical Assistance for specific environmental recommendations.

 Heat Resistance 


 Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties. The scaling temperature is approximately 650°C. 


 Heat Treatment Annealing 


 Full anneal - 840-900°C, slow furnace cool to 600°C and then air cool. Process Anneal - 735-785°C and air cool. 

 Hardening 


 Heat to 980-1035°C, followed by quenching in oil or air. Oil quenching is necessary for heavy sections. Temper at 150-370°C to obtain a wide variety of hardness values and mechanical properties as indicated in the accompanying table. 

The tempering range 425-600°C should be avoided. 

 Welding 


 Pre-heat to 150-320°C and post-heat at 610- 760°C. Grade 420 coated welding rods are recommended for high strength joints, where a post-weld hardening and tempering heat treatment is to be carried out. If parts are to be used in the "as welded" condition, a ductile joint can be achieved by using Grade 309 filler rod. AS 1554.6 pre- qualifies welding of 420 with Grade 309 rods or electrodes. 

 Machining


In the annealed condition this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult. Free machining grade 416 (refer Atlas Datasheet) is a very readily machined alternative. 


Typical Applications

Cutlery, knife blades, surgical instruments. Needle valves. Shear blades.         




Specified Properties

These properties are specified for bar product in ASTM A276. Bar is the most commonly available form of grade 420. Similar but not necessarily identical properties are specified for other products such as plate and forgings in their respective specifications.

Composition Specification (%)






COLLECTION OF COMMON STAINLESS STEEL GRADE



Source:

http://www.atlassteels.co.nz/