420 stainless steel is a martensitic stainless steel, renowned for its moderate corrosion resistance, excellent strength, and outstanding machinability and hardness. Its core features stem from a relatively high carbon content (minimum 0.15%) and at least 12% chromium content. Through appropriate heat treatment, it can achieve very high hardness and strength, but its corrosion resistance is usually lower than that of more common austenitic stainless steels such as 304.
| Element | Content(%) | Function |
| C | 0.15-0.40 | Key element,improve strength and hardness |
| Cr | 12.0-14.0 | Core element,provide corrosion and oxidation resistance |
| Mn | ≤1.00 | Improve strength and hardness |
| Si | ≤1.00 | Improve strength |
| P | ≤0.04 | Impurity element |
| S | ≤0.03 | Impurity element |
The balance of carbon and chromium determines the properties of 420 stainless steel. Sufficient chromium provides corrosion resistance, while a higher carbon content enables it to be strengthened through heat treatment.
Hardness and wear resistance:This is the most prominent advantage of 420 stainless steel. After proper heat treatment (quenching and tempering), its hardness can reach HRC 50-55 or even higher (depending on the specific carbon content).
Strength: After heat treatment, it has a high combination of strength and good toughness
Corrosion resistance: Medium level. It performs well in mild atmospheric environments, fresh water, and some weak acid, alkali and salt solutions.
Processability: Due to its high strength and toughness, work hardening occurs during processing.
Magnetic: As a martensitic steel, 420 stainless steel is magnetic.
Heat treatment is a key step to bring out the potential of 420 stainless steel:
Annealing: Heat to approximately 840-900°C and then cool slowly. The purpose is to soften the material to facilitate machining and cold forming.
Hardening (quenching) : Heat to approximately 980-1050°C and then rapidly cool (oil quenching or air cooling). This process hardens the steel, but it is also very brittle.
Tempering: Reheat the quenched steel to a lower temperature (150-370°C) and then cool it. The aim is to eliminate internal stress, reduce brittleness, while retaining most of the hardness, and achieve an ideal combination of strength and toughness.
Cutting tool field: It is very commonly used in high-quality table knives, kitchen knives, surgical and dental instruments, pocket knives and scissors. It can strike a good balance among sharpness, retention and corrosion resistance.
Shafts and mechanical components: It is used for manufacturing mechanical components such as pump shafts, valve parts, bearings, mold pins, nozzles, etc., which require wear resistance and certain corrosion resistance.
Mold industry: It is used for plastic molds (especially those requiring a high-gloss surface) because it has excellent polishing and wear resistance.
Consumer goods and hardware: It is used for making watch straps, decorative strips, furniture accessories, home appliance parts, etc. Its easy polishing to a mirror finish makes it look exquisite.
In conclusion, 420 stainless steel is a “function-oriented” type of steel. When your application’s primary requirements are hardness, strength and wear resistance, and the demand for corrosion resistance is not extremely strict, it is an excellent and highly cost-effective choice.