Our Location
Understanding 420 Stainless Steel: A Complete Guide
Stainless steel is a widely utilized and versatile material that offers a variety of alloys with unique properties and applications. Among these, 420 stainless steel is a popular choice due to its distinctive combination of properties, making it suitable for certain uses. From tableware and surgical instruments to industrial components, 420 stainless steel is used in various applications requiring wear, strength, corrosion, and ductility.
This article will discuss 420 stainless steel in detail, including its composition, fundamental properties, and the wide range of uses in which it excels.
Definition of 420 Stainless Steel
420 stainless steel is a hardenable martensitic stainless steel containing a minimum of 12% chromium. This high percentage of chromium provides the steel with good corrosion resistance properties. However, the steel must be hardened and surface ground or polished for optimum corrosion resistance. 420 SS has a higher carbon content, which enhances its strength and hardness characteristics. However, its corrosion resistance could be better than that of the common austenitic grades.
420 stainless steel possesses good ductility when annealed, but it can be hardened to a minimum Rockwell hardness of 50 HRC. This makes it the hardest among the 12% chromium grades and is often used for making knives. Additionally, due to its martensitic microstructure, it is magnetic.
Production Process of 420 Stainless Steel
420 stainless steel is produced by melting and refining raw materials in a furnace, followed by processing the ingots or continuous-cast billets into primary forms that manufacturers can use to create final products. The production process of 420 stainless steel involves several stages:
- The raw materials used to produce stainless steel, such as iron ore, chromium, and other alloying elements, are fused together using either an electric arc furnace or an induction furnace, where they are heated to temperatures exceeding 1,500 °C.
- During refining, impurities are removed, and composition is adjusted to achieve desired properties. This can involve degassing, desulfurization, and alloying additions.
- After refining the molten metal, it is transformed into solid shapes like ingots, billets, or slabs. The choice of the final product determines whether the metal is cast into discrete forms or continuously cast into long, solid strands. In continuous casting, the molten metal is poured into a water-cooled mold to create continuous solid strands. On the other hand, in ingot casting, molten metal is poured into molds to create solid blocks or ingots.
- After being cast, the stainless steel undergoes hot working processes, like forging, rolling, or extrusion.
- The steel is annealed by heating it to a certain temperature and cooling it tardily and controlled.
- The steel is heated to a high temperature, quenched to harden it, and tempered at a lower temperature to obtain the desired balance of hardness and toughness.
- After achieving the desired properties, the 420 stainless steel can undergo surface finishing processes like grinding, coating or polishing to improve its look or provide additional protection against corrosion.
Chemical Composition of 420 Stainless Steel
| Element | Percentage(%) |
| Sn* | 0.05% max |
| Al* | 0.15% max |
| Cu* | 0.50% max |
| S | 0.03% max |
| P | 0.04% max |
| Mo* | 0.50% max |
| Ni* | 0.50% max |
| Cr | 12.00-14% |
| Si | 1.00% max |
| Mn | 1.00% max |
| C | 0.15-0.40% |
| Fe | Balance |
The Properties of 420 Stainless Steel
Physical Properties of 420 Stainless Steel
| Property | Value |
| Density | 7.74 g/cm3 |
| Magnetism | Magnetic |
Mechanical Properties of 420 Stainless Steel
| Property (Annealed) | Value |
| Elastic Modulus | 200 GPa |
| Electrical Resistivity | 0.55 x 10-7 .m |
| Elongation (% in 50 mm) | 25 |
| Tensile Strength | 655 MPa |
| Yield strength (Temper: Annealed) Minimum 0.2% offset | 40,000 psi |
| Yield Strength (Temper: Hardened + 350°F) Typical 2% offset | 195,000 psi |
| Brinell Hardness (HB) | 241 max |
| Poissons Ratio | 0.24 |
| Shear Modulus | 80.7 GPa |
Thermal Properties of 420 Stainless Steel
| Property | Value |
| Melting Point | 1495 °C |
| CTE, linear（0- 100 °C ） | 10.3 µm/m-°C |
| CTE, linear（0- 650 °C ） | 12.2 µm/m-°C |
| Thermal Conductivity (@ 100 °C) | 24.9 W/m·K |
| Thermal Conductivity (@ 500 °C) | 28.7 W/m·K |
| Specific Heat 0-100°C | 460 J/Kg.K |
| Mean Coefficient of Thermal Expansion (0-100 °C) | 10.2 µm/m·K |
| Mean Coefficient of Thermal Expansion (0-649 °C) | 12.1 µm/m·K |
| Maximum Service Temperature, Air | 620 °C （Continuous Service） |
| 735 °（C Intermittent） |
Some other properties of 420 stainless steel
Corrosion Resistance
Grade 420 steels exhibit high resistance to fresh water, alkalis, air, mild acids, and foods under hardened conditions. The smooth surface finish of these steels results in excellent performance. However, under annealed conditions, the corrosion resistance properties of grade 420 can decline. Notably, the resistance to corrosion of grade 420 is inferior to that of grade 430 Ferritic alloys with 17% chromium, grade 410 steel, and other austenitic grades. Although grade 420 steels have good corrosion resistance against food, continuous exposure to unwashed food substances can lead to pitting corrosion.
Heat Resistance
Grade 420 stainless steel can resist scaling up to 650°C, but it is not suitable for use at temperatures above the standard tempering temperature.
Heat Treatment
Annealing: Grade 420 stainless steel may be heated between 840 and 900°C, then slowly cooled in a furnace at 600°C, followed by air cooling.
Process Anneal: Grade 420 steel can undergo annealing by being heated to 735 to 785°C and then allowed to cool in the air.
Hardening: Hardening grade 420 steels involves heating them at a temperature range of 980 to 1035°C, followed by quenching them in either air or oil. For heavy metal sections, oil quenching is usually preferred. After quenching, tempering is performed at 150 to 370°C to achieve high hardness and perfect mechanical properties. It’s important to note that 420 stainless steel should not be tempered between 425°C and 600°C.
Stress-relieving: Heat between 300 – 800°F (149 – 427°C) for 1-3 hours, then cool in the air.
Low-temperature tempering: Heat between 300-500°F (150-260°C) for 0.5-1 hour, then cool.
Welding
Grade 420 stainless steels are commonly welded using welding rods coated with grade 420 metals, which helps create high-strength joints. Before welding, the steels must be pre-heated at 150 to 320°C. After welding, the parts must be post-heated at 610 to 760°C.
In the condition of “as welded”, grade 309 filler rods are recommended to achieve ductile joints. However, grade 309 electrodes or rods are recommended when welding grade 420 steels, as per AS 1554.6.
Machining
Grade 420 steels can be easily machined in their annealed state, but they are difficult to machine if their hardness exceeds 30HRC. One of the most readily available machined alternatives is free-machining grade 416 steels.
The following are standard processing methods for 420 stainless steel:
- Cutting: Use a shear, cutter, or EDM cutter to cut 420 stainless steel. Ensure that the cutter has the proper cutting capacity and that the tool is sharp.
- Welding: When welding stainless steel, it is recommended to use appropriate methods such as TIG or MIG welding. Controlling the temperature during welding is essential to prevent the steel from annealing or oxidizing.
- Bending: Use a mechanical bending machine or hand-bending tools to shape 420 stainless steel plates or bars. Choose the appropriate bending radius to avoid cracks during the bending process.
- Milling: To mill 420 stainless steel, use a milling machine or gantry machining center. Select appropriate tools and cutting parameters to ensure a smooth cutting process and surface.
- Grinding: Use a sander, polisher, or sandpaper to grind 420 stainless steel to the desired finish. Use different grain sizes as needed.
- Drilling: Use a drill press or hand-held drill with cobalt or titanium drill bits for stable cutting and cooling lubrication.
- Turning: When turning 420 stainless steel, select the appropriate cutting tool, feed, and speed to achieve the desired accuracy and surface finish.
Characteristics of 420 Stainless Steel
420 SS is a type of high-carbon steel with a minimum of 12% chromium. This steel can be hardened using heat treatment, which is a common process for martensitic stainless steels. These steels are known for their high hardness and carbon content. They are typically fabricated using methods that involve hardening and tempering treatments. However, it’s essential to note that extreme temperatures can impact the strength and ductility of martensitic steels. AISI 420 steel is an excellent choice regarding corrosion and wear resistance.
High hardness: Stainless steel 420 is often utilized in the manufacture of knives, surgical tools, and industrial components due to its high level of hardness, which can be obtained through heat treatment.
Good corrosion resistance: 420 stainless steel has good corrosion resistance and can resist many chemicals, including some acids and salt solutions. However, its corrosion resistance is relatively low compared to other stainless steels.
Easy machining: 420 grade steel has good plasticity and machinability before heat treatment. It is easy to forge, draw, mill, and cut.
Excellent grinding properties: 420 is an ideal material for crafting knives and blades due to its exceptional grinding properties, which enable a sharp cutting edge.
Moderate strength and wear resistance: Type 420 is widely used in manufacturing parts that require wear resistance due to its moderate tensile strength and wear resistance.
It’s essential to keep in mind that 420 grade may suffer from corrosion issues in specific extreme environments. This is because of its high carbon content and low chromium content. Environments with high temperatures and high levels of corrosive substances can be particularly problematic. Therefore, evaluating and selecting the appropriate use based on the specific application is important.
Equivalent Forms of 420 Stainless Steel
| Grade | 420 |
| UNS No. | S42000 |
| Old British BS | 420S37 |
| Old British En | 56C |
| Euronorm No | 1.4021 |
| Euronorm Name | X20Cr13 |
| Swedish SS | 2303 |
| Japanese JIS | SUS 420J1 |
Common Forms of 420 Stainless Steel
AISI 420 stainless steel comes in various forms to accommodate different applications. The most common forms of 420 stainless steel include:
Sheet
420 stainless steel sheet is a thin, flat material typically between 0.5 mm and 3 mm thick. It is commonly used in applications requiring corrosion resistance, wear resistance, and strength and can be further processed or cut to specific dimensions.
Bar
Bars are solid cylindrical or rectangular pieces of material. Stainless steel bars can be further processed through machining, forging, or other fabrication methods.
Plate
420 stainless steel plates are large, thick pieces of material, sometimes up to 200 mm thick, commonly used in structural applications or as a base for machining components. Plates are utilized when the load-carrying capacity of 420 sheet steel is inadequate.
Hot Rolled
Hot-rolled 420 stainless steel is a type of steel heated higher than its recrystallization temperature and then rolled into the required shape or form. This process softens the material, creating diverse products like sheets, plates, and bars.
Annealed
Annealed 420 stainless steel is offered in its soft condition, along with a ferrite + carbide microstructure after being heated at 840-900°C. After achieving this temperature, the stainless steel should gradually cool down by placing it in a furnace and allowing it to cool tardily at approximately 600°C. It is then air-cooled to accomplish the heat treatment procedure. This process liberates internal stresses, enhances ductility, and
ameliorates the microstructure, making the material easier to machine or work with.
Cold Drawn
It refers to the process of pulling the material through a die at room temperature. This process improves the material’s dimensional accuracy, surface finish, and mechanical properties. However, 420 stainless steel has limited tolerance to cold working and needs to be better suited for extreme forming operations, as they can cause the material to crack.
Applications of 420 Stainless Steel
420 stainless steel is a high-quality material with excellent wear resistance and hardness, making it perfect for manufacturing knives, blades, surgical instruments, bearing components, assembly parts, and more. This material is also versatile, allowing it to be processed into various shapes and sizes without difficulty through cutting, forging, heat treatment, and other manufacturing techniques. However, it should not be used at temperatures above 800°F (427°C) as it can quickly lose its corrosion resistance and become too complicated.
- Knife manufacturing: 420 stainless steel is frequently used in producing blades, handles, scalpels, and other medical devices due to its exceptional cutting ability and hardness.
- Pressure vessels: 420 stainless steel is widely used in chemical, petroleum, and natural gas industries on account of its outstanding corrosion resistance and high strength, making it ideal for pressure vessels, tanks, and pipelines.
- Food processing equipment: 420 stainless steel is corrosion-resistant, easy to process, and meets hygiene standards. It is commonly used in food processing equipment, knives, and cutting instruments.
- Aerospace: Stainless steel 420 is a crucial material in the aerospace industry. Because of its strength and resistance to corrosion, it is used to manufacture a variety of aircraft components, such as shafts, propellers, and aircraft parts.
- Chemical equipment: Due to its resistance to various corrosive media, 420 stainless steel is widely utilized in the chemical industry to produce equipment, storage tanks, and pipelines.
- Medical equipment: 420 stainless steel is widely used in medical, surgical, and dental equipment due to its good corrosion resistance, high-temperature strength, and low-temperature toughness.
Advantages & Disadvantages
Advantages:
- 420 SS is magnetic.
- It has reasonable resistance to corrosion, alkalis, freshwater, mild acid, food, air, ammonia, carbonic acids, detergents, vinegar, steam, crude oil, and dilute nitric acids.
- Welding can be accomplished by using welding rods.
- When it is in its annealed state, machining becomes easier.
- Heat treatments can be easily carried out with the proper process.
- When annealed, it has excellent ductility but can also be hardened to a minimum Rockwell hardness of 50 HRC.
Disadvantages:
- When annealing the material, its resistance is reduced.
- Only when 420 stainless steel undergoes hardening it becomes more corrosion-resistant.
- The welding properties of this material are suboptimal.
Comparison
420 Stainless Steel & 304 Stainless Steel
420 is a type of martensitic stainless steel that contains high levels of chromium and carbon, along with small amounts of manganese, silicon, and sometimes molybdenum and nickel. On the other hand, 304 is an austenitic stainless steel alloy that contains a significant amount of nickel and more chromium than 420. However, the carbon content in 304 is much lower than that of 420.
There is a significant difference between 304 stainless steel and 420 grade steel. The primary difference lies in their corrosion resistance. While 304 stainless steel boasts good corrosion resistance, 420 grade steel offers only mild resistance in similar environments and is not as resistant as 304 stainless steel. In terms of strength and hardness, 420 steel excels, whereas 304 stainless steel provides better ductility and toughness. However, it is easier and stronger than 420 alloy.
420 Stainless Steel & 440 Stainless Steel
| Item | 420 | 440 |
| Chemical composition | 1. Contains copper in its makeup. 2. Has up to 14% chromium. | 1. No copper in its makeup. 2. Has up to 18% chromium. |
| Resists heat | 1. Low heat resistance. 2. Can deform when heat temperature is too high. | 1. Higher heat resistance. 2. Doesn’t deform easily at higher temperatures. |
| Hardness | 1. Soft 2. Easier to shape. | 1. Harder compared to 420. 2. Not so easy to shape. |
| Price or Cost | Cheaper due to the less chromium element in its makeup. | Expensive due to high chromium percentage. |
| Corrosion resistance | Resists corrosion. | Higher chromium levels makes it more corrosion resisting compared to 420. |
| Electrical properties | 1. 550 nano-ohm meters which is at 21°C. 2. Ideal for projects where low resistivity is required. | 1. 600 nano-ohm at 21°C. 2. Provides you with high resistivity. |
Summary
This article explains 420 stainless steel’s composition and properties. Invest in quality 420 alloys for successful applications. Contact us if you want to learn more.
