420 Stainless Tool Steel is a martensitic stainless steel with 12% Chromium which is sufficient to give good corrosive resistance properties. It’s best corrosive resistance is when hardened and surface is ground or polished.It has good ductility in the annealed condition but can be hardened up to 500HB (highest of the chromium grades). Martensitic Grades are known for high hardness and allowances must be made for poor weldability and usually allowances for a final harden and temper treatment. Steel is magnetic and welding is not recommended.
Moulds for corrosive plastic materials such as PVC, recycled polymers etc., moulds for chemically aggressive plastics and plastics containing abrasive fillers, mould inserts, dies and gauges for PVC extrusions, screws and barrels for extruders, moulds for automotive, food, medical and optical industry such as spectacles, compact discs, lenses.
Mechanical Properties (Q+T)
Tensile Strength (Mpa)
Yield Strength (Mpa)
Annealing: For maximum softness, heat uniformly to 1500 – 1650°F (816 – 899°C) and cool slowly in the furnace.
Stress Relieving: Heat at 300 – 800°F (149 – 427°C) for 1 to 3 hours, cool in air or quench in oil or water.
Hardening: Preheat, then heat to 1800 -1950°F (982 – 1066°C), soak at temperature and air cool or quench in warm oil.
Welding: The martensitic class of stainless steels has limited weldability due to its hardenability. Special consideration is required to avoid cold cracking by preheating to 550°F (260°C). Post-weld heat treatment should be considered to achieve required properties. This particular alloy is generally considered to have poorer weldability than the most common alloy of this stainless class, Type 410. A major difference is higher carbon content for this alloy which requires both preheat and post-weld heat treatment. When a weld filler is needed, AWS E/ER 420, 410 NiMo and 309L are most often specified. Type 420 is well known in reference literature and more information can be obtained in this way.
Forming: If annealed for maximum softness, Type 420 can be moderately drawn and formed.