AISI 420 Stainless Steel (SS420), UNS S42000
AISI 420 stainless steel (SS420) is a straight chromium martensitic stainless steel grade with certain wear resistance, corrosion resistance and high hardness.
SS420 Datasheet
The tables below give 420 stainless steel (SS420) datasheet and specification including chemical composition, properties, heat treatment, etc.
Chemical Composition
Datasheet 1, The table below shows ASTM AISI 420 stainless steel composition.
| | Chemical Composition, % |
| ASTM | AISI (UNS) | C, ≥ | Si, ≤ | Mn, ≤ | P, ≤ | S, ≤ | Cr | Ni, ≤ | Mo, ≤ | Product form |
| ASTM A240/A240M | SS 420 (UNS S42000) | 0.15 | 1.00 | 1.00 | 0.040 | 0.030 | 12.0-14.0 | 0.75 | 0.50 | Plate, Sheet, and Strip |
| ASTM A276A/A276M | 0.15 | 1.00 | 1.00 | 0.040 | 0.030 | 12.0-14.0 | – | – | Bars and Shapes |
AISI 420 Stainless Steel Properties
The datasheets below list type 420 stainless steel (SS420) properties including physical properties and mechanical properties.
Physical Properties
SS 420 stainless steel physical properties are listed in the table below such as density, melting point, specific heat, electrical resistivity, elastic modulus, thermal conductivity, and coefficient of thermal expansion (CTE).
Datasheet 2, 420 stainless steel properties – 1.
| SS 420 Physical Properties |
| Density, g/cm3 (lb/in.3) | 7.8 (0.28) |
| Melting point, °C (°F) | 1450-1510 (2650-2750) |
| Specific heat capacity, J/kg·K (Btu/lb·°F) | 460 (0.11) at 0-100 °C (32 to 212 °F) |
| Electrical resistivity, μΩ·m | 0.55 at 20 °C |
| Elastic modulus (Modulus of elasticity), GPa (106 psi) | 200 (29) |
| Thermal conductivity, W/m·K (Btu/ft·h·°F) | 24.9 (14.4), at 100 °C (212 °F) |
| Coefficient of thermal expansion, μm/m·°C (μin./in. ·°F) | 10.3 (5.7), at 0-100 °C (32-212 °F) |
| 10.8 (6.0), at 0-315 °C (32-600 °F) |
| 11.7 (6.5), at 0-538 °C (32-1000 °F) |
Mechanical Properties
AISI 420 stainless steel mechanical properties are given in the datasheet below including tensile strength, yield strength, elongation, reduction in area, Brinell and Rockwell hardness, Charpy impact test, etc.
Datasheet 3, Type 420 stainless steel properties – 2.
| | SS420 mechanical properties in various heat-treated or cold-worked conditions. |
| Type (UNS) | Condition | Tensile strength, MPa (ksi), ≤ | Yield strength, MPa (ksi), ≤ | Elongation in 50.8 mm (2 in.), %, ≥ | Reduction in area, %, ≥ | Hardness | Charpy V-notch impact
strength, J (ft·lbf) |
| AISI 420 (UNS S42000) | Oil quenched from 1038 °C (1900 °F) and tempered at 316 °C (600 °F) | 1724 (250) | 1482 (215) | 8 | 25 | 52 HRC, Rockwell, ≥ | 20 (15), ≥ |
| Annealed bar | 655 (95) | 345 (50) | 25 | 55 | 195 HBW, Brinell, ≤ | – |
| Annealed and cold drawn | 760 (110) | 690 (100) | 14 | 40 | 228 HBW, Brinell, ≤ | – |
Type 420 Stainless Steel Heat Treatment
Type 420 stainless steel heat treatment includes annealing, hardening, tempering and stress relief. Preparation for heat treatment includes precleaning, preheating, atmosphere protection, salt bath, and hydrogen embrittlement.
- Precleaning: All workpieces of SS420 and fixtures must be thoroughly cleaned, such as oil, sweat and other stains on the surface of the workpiece.
- Preheating: The thermal conductivity of type 420 stainless steel is usually lower than that of carbon steel. When heating rapidly, the workpiece is easily deformed and cracked. Therefore, preheating is recommended. The preheating temperature is generally 760-790 °C (1400-1450 °F). Heavy-duty parts can be preheated in two stages: Preheat at 540 °C (1000 °F) firstly, and then heat to 790 °C (1450 °F).
- Atmosphere protection: Austenitizing temperature 1010 °C (1850 °F), dew-point temperature: 10-12 °C (50-54 °F) for AISI 420 wrought martensitic stainless steel.
- Salt bath: Bath salts give 420 grade stainless steel (SS 420) parts a better result.
- Hydrogen embrittlement: Hydrogen embrittlement is a serious problem with 420 steel.
Annealing
Annealing for ASTM AISI 420 wrought stainless steel.
- Subcritical annealing (Recommended) temperature for AISI 420 stainless steel: from 675-760 °C (1245-1400 °F); Air cool from the temperature range, use the upper heating temperature range to minimize hardness. The corresponding Rockwell hardness is 94-97 HRB.
- Full annealing temperature for type 420 steel: 830-885 °C (1525-1625 °F), and then soak thoroughly, furnace cool to 790 °C (1455 °F), continue cooling at 15-25 °C/h (27-45 °F/h) to 595 °C (1100 °F); Air cool to room temperature. The corresponding Rockwell hardness is 86-95 HRB.
- Isothermal annealing temperature for AISI 420 grade stainless steel: Heat to 830-885 °C (1525-1625 °F); keep 2h at 705 °C (1300 °F), the corresponding Rockwell hardness is 95 HRB. (Preheat at subcritical annealing temperature range is very important.)
