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 to a minimum Rockwell hardness of 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.
APPLICATIONS:
Alloy 420 is used for a variety of applications where good corrosion and outstanding hardness is necessary. It is not usually used at temperatures exceeding 800oF (427oC) due to quick hardening and loss of corrosion resistance. Examples of applications that use alloy 420 include:
- Cuttery
- Knife blades
- Surgical instruments
- Needle valves
- Shear blades
- Scissors
- Hand tools
Composition
The compositional ranges of grade 420 stainless steels are given in following table:
Table 1 – Compositional ranges of grade 420 stainless steels
Grade | C | Mn | Si | P | S | Cr | |
420 | min. max. | 0.15 – | – 1 | – 1 | – 0.040 | – 0.03 | 12.0 14.0 |
Mechanical Properties
The key mechanical properties of grade 420 stainless steels are tabulated below:
Table 2 – Mechanical properties of grade 420 stainless steels
Tempering Temperature (°C) | Tensile Strength (MPa) | Yield Strength | Elongation (% in 50mm) | Hardness Brinell (HB) | Impact Charpy V (J) |
Annealed * | 655 | 345 | 25 | 241 max | – |
204 | 1600 | 1360 | 12 | 444 | 20 |
316 | 1580 | 1365 | 14 | 444 | 19 |
427 | 1620 | 1420 | 10 | 461 | # |
538 | 1305 | 1095 | 15 | 375 | # |
593 | 1035 | 810 | 18 | 302 | 22 |
650 | 895 | 680 | 20 | 262 | 42 |
* Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness is the specified maximum. | |||||
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