420 Stainless Steel
420 Stainless is a martensitic stainless that has the same corrosion resistance of 410 while also having higher strength and hardness. It also maintains its magnetism in both annealed and hardened conditions. Alloy 420 has higher carbon content than Alloy 410 which is designed to optimize strength and hardness characteristics. It has good ductility it the annealed condition but is capable of being hardened up to Rockwell hardness 50 HRC, the highest hardness of the 12% chromium grades.
Attributes of 420 Stainless
Annealing – Grade 420 stainless steels can be heated at temperatures from 840 to 900°C, followed by slow furnace cooling at 600°C and then air-cooling.
Process Anneal – Grade 420 can be annealed at 735 to 785°C and air-cooled.
Hardening – This process involves heating grade 420 steels at 980 to 1035°C, followed by air or oil quenching. Oil quenching is usually preferred for heavy metal sections. Tempering is performed at 150 to 370°C to achieve high hardness and good mechanical properties. Grade 420 should not be tempered between 425 and 600°C
420 provides full corrosion resistance only in the hardened or hardened and stress relieved conditions. In these conditions, its corrosion resistance is similar to Type 410. Type 420 resists corrosion by the atmosphere, fresh water, mine water, steam, carbonic acid, crude oil, gasoline, perspiration, alcohol, ammonia, mercury, sterilizing solutions, soaps and other similar corrosive media.
Machinability is rated at 30% of B1112. Similar to machining High-carbon, high-chromium tools steels, but 420 creates tough stringy chip buildup.
420 stainless is not commonly welded due to its air hardening characteristics. Welding may be performed after preheating to 300°-400°F with post weld tempering at temperature for 2 hours.
420 can be hot worked by slowly bring the temperature to 1400° F, then on to 2000°-2200°F.Reheat often to keep the temperature above 1600°F. After working, cool in furnace slowly to avoid cracking. 420 will withstand only minor cold working. Radical forming operations will result in cracking.
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