General Properties Alloy 420 is a hardenable, martensitic stainless steel that is a modification of Alloy 410. Similar to 410, it contains a minimum of 12% chromium, just sufficient enough to give corrosion resistant properties. 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. Due to its hardening properties, Alloy 420 is not often welded, although it is possible. Martensitic stainless steels are designed for high hardness and sometimes other properties are to some degree compromised. Corrosion resistance is lower than the common austenitic grades and their useful operating range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures. Its best corrosion resistance is achieved when the metal is hardened and surface ground or polished. STANDARDS INDUSTEEL TRADEMARKS UNS ASTM EURONORMS EN SUS A4 S42000 420 1.4021 SUS 420J1 Chemical Properties: C Mn Si P S Cr 420 0.15 max 1.00 max 1.00 max 0.04 max 0.03 max min: 12.0 max: 14.0 Mechanical Properties: Tempering Temperature (°C) Tensile Strength (MPa) Yield Strength 0.2% Proof (MPa) Elongation (% in 50mm) Hardness Brinell (HB) Annealed * 655 345 25 241 max 399°F (204°C) 1600 1360 12 444 600°F (316°C) 1580 1365 14 444 800°F (427°C) 1620 1420 10 461 1000°F (538°C) 1305 1095 15 375 1099°F (593°C) 1035 810 18 302 1202°F (650°C) 895 680 20 262 * Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum. Physical Properties: Density kg/m3 Thermal Conductivity W/mK Electrical Resistivity (Microhm/cm) Modulus of Elasticity Coefficient of Thermal Expansion µm/m/°C Specific Heat (J/kg.K) 7750 24.9 at 212°F 550 (nΩ.m) at 68°F 200 GPa 10.3 at 32 – 212°F 460 at 32°F to 212°F – at 932 °F 10.8 at 32 – 599°F 17.7 at 32-1000°F Corrosion Resistance: 1、Less resistant than the austenitic grades and the 17% chromium ferritic alloys 2、Good resistance in the hardened condition to the atmosphere, foods, fresh water, and mild acids 3、Resistance lowered in the annealed condition 4、Best with a smooth surface finish Heat Resistance: 1、Not recommended for use above the relevant tempering temperature because of reduction in mechanical properties 2、Scaling temperature is approximately 1202oF (650oC) Machinability 1、Tough, stringy chip build-up. 2、Similar to machining some of the high carbon tool steel Welding 1、Not commonly welded due to air hardening characteristics. 2、Welding may be performed after preheating to 300-400 F 3、Post weld tempering at temperature for 2 hours Hot Working 1、Recommended to bring temperatures slowly up to 1400, then on to 2000-2200 F 2、Furnace cool slowly to avoid cracking, after furnace working 3、Reheating is necessary to keep working temperature above 1600 F. Cold Working 1、Can withstand only minor cold work. 2、Radical forming operations will result in cracking. Annealing 1、Anneal at temperatures between 1550-1650 F (843-900 C) 2、Allow for slow furnace cooling. Tempering 1、Temper at temperatures of 300-400 F 2、Air cool for maximum hardness and corrosion resistance. Hardening Soak at 1850-1950 F to quench in heated oil.