Contents
440 Stainless Steel: Definition, Composition, Properties, Processing, Applications, and More
- John
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Overview of 440 Stainless Steel
440 stainless steel is a high-carbon-chromium 400 series martensitic stainless steel, which comes in four variants: 440A, 440B, 440C, and 440F. It is primarily composed of 0.60-1.20% carbon and 16-18% chromium. 440 conforms to standards like ASTM A276 and AISI 440, with equivalent grades such as SUS440. Its most notable feature is its excellent wear resistance and high hardness after heat treatment, which makes it widely used in knives, cutting tools, and bearings. 440 is primarily processed through heat treatment and grinding, and it may also undergo quenching and tempering to balance hardness and toughness in certain applications.
Typical Applications of 440 Stainless Steel
Check the table below for a quick view of where 440 stainless steel is commonly used:
| Industry | Application |
| Cutlery | Kitchen knives, hunting knives, scissors, surgical blades |
| Aerospace | Bearings, valve components, springs, fasteners |
| Automotive | Shafts, gears, bushings, wear-resistant components |
| Medical Equipment | Surgical instruments, dental tools, scalpels, medical implants |
| Industrial Machinery | Pump shafts, cutting tools, dies, bearings |
| Marine | Propeller shafts, marine fasteners, pump parts, cutting blades |
| Defense | Knife blades, firearm components, wear-resistant parts, tactical tools |
Advantages and Disadvantages of 440 Stainless Steel
Advantages and benefits of 440 stainless steel include:
- High hardness and wear resistance, especially after heat treatment.
- Excellent edge retention, making it ideal for knives and cutting tools.
- Strong corrosion resistance in mild environments.
- Durable under heavy use and stress.
- Good machinability in its annealed condition.
Disadvantages and limitations of 440 stainless steel are:
- Brittle in its hardened state; prone to cracking under high stress.
- Requires careful heat treatment to achieve the desired properties.
- Less corrosion resistance compared to austenitic grades like 304 or 316.
- Can be difficult to weld due to its high carbon content.
- More expensive than some other martensitic stainless steels.
Equivalent Grades of 440 Stainless Steel
Common equivalent grades of 440 stainless steel are as follows:
| Country | Standard/Specification | Equivalent Grade |
| USA | ASTM A276 | 440A, 440B, 440C |
| EU | EN 10088-1 | 1.4112 (440B), 1.4125 (440C) |
| China | GB/T 1220 | 9Cr18, 9Cr18Mo |
| Germany | DIN 17400 | X105CrMo17 |
| Russia | GOST 5632 | 95X18, 110X18 |
| Japan | JIS G4303 | SUS440A, SUS440B, SUS440C |
| UK | BS 970 | 440S29 |
Variants of 440 Stainless Steel
Common variants of 440 stainless steel include:
| Variant | What is it | Why might it be chosen instead of 440? |
| 440A | Lower carbon version of 440. | Better corrosion resistance, easier to machine |
| 440B | Mid-range carbon version of 440. | Balanced hardness and corrosion resistance |
| 440C | High carbon version of 440. | Maximum hardness and wear resistance |
| 440F | Free-machining version of 440. | Improved machinability due to added sulfur |
Heat & Corrosion Resistance of 440 Stainless Steel
Heat Resistance
440 stainless steel has good heat resistance. It can operate continuously at temperatures up to 425°C (797°F). For intermittent use, it can handle up to 600°C (1112°F). However, prolonged exposure to high temperatures can reduce its hardness, strength, and corrosion resistance.
Corrosion Resistance
440 stainless steel has moderate corrosion resistance. It performs better than standard carbon steel but falls short compared to other stainless steels like 304 or 316. It can handle fresh water, mild acids, and some alkaline environments. However, in chloride-rich or highly corrosive conditions, it is prone to pitting, crevice corrosion, and stress corrosion cracking (SCC).
Processing of 440 Stainless Steel
Welding
440 stainless steel is a high-carbon martensitic steel with poor weldability. Due to its high carbon content, it is prone to cracking and hardening during welding.
Preheating the material to around 120-200°C (250-400°F) helps reduce the risk of cracking. When choosing filler materials, austenitic stainless steel rods, like 308 or 309, are typically used to ensure corrosion resistance and reduce the chance of cracks. Post-weld heat treatment, usually at around 730-790°CF (1350-1450°), is needed to relieve stress and reduce brittleness.
Avoid rapid cooling during the process, as controlled cooling is essential to maintain material properties and prevent cracking.
Machining
440 stainless steel is difficult or even impossible to machine after hardening. It’s often easier to machine 440 in its annealed state (before hardening) and then heat-treated afterward to increase hardness.
If machining after hardening is necessary, specialized tools and slow cutting speeds are needed, and surface finish may require further grinding or polishing. Machining should also account for the risk of distortion during the hardening process, which can affect final part dimensions. Stress-relieving is sometimes performed after machining and before heat treatment to reduce distortion.
Heat Treatment
440 stainless steel can be hardened by heat treatment to achieve a hardness of up to 58-62 HRC, depending on the exact tempering temperature used.
- Annealing: Heat to 850-900°C, followed by slow cooling in the furnace to around 600°C, and then air-cooling. Sub-critical annealing can be done at 735-785°C with slow furnace cooling.
- Hardening: Heat to 1010-1065°C, then quench in air or oil (oil quenching is preferred for heavy sections). This hardens the material.
- Tempering: After hardening, temper at 150-370°C to achieve high hardness (up to 58-62 HRC) and better mechanical properties. Avoid tempering between 425-565°C, as this can reduce corrosion and impact resistance. If tempering at 590-675°C, it will increase impact resistance but reduce hardness.
Chemical Composition of 440 Stainless Steel
Check the table below for the chemical composition of 440 stainless steel:
| Element | Carbon, C | Chromium, Cr | Iron, Fe | Manganese, Mn | Molybdenum, Mo | Phosphorus, P | Silicon, Si | Sulfur, S |
| Content (%) | 0.60-0.75 | 16-18 | 78.4-83.4 (balance) | ≤ 1.0 | ≤ 0.75 | ≤ 0.040 | ≤ 1.0 | ≤ 0.030 |
Properties of 440 Stainless Steel
Here are three major reasons that make 440 stainless steel unique:
- Exceptional hardness and wear resistance, ideal for cutting tools and blades.
- High strength and edge retention under high stress.
- Good resistance to corrosion in mild environments.
Physical Properties
Check the table below for the core physical properties of 440 stainless steel:
| Property | Typical Value (Metric) | Performance |
| Density | 7.80 g/cc (0.282 lb/in³) | High density, typical for stainless steel |
| Melting Point | 1,480°C (2,696°F) | High melting point, suitable for high-temperature applications |
| CTE, Linear (0-100°C/32-212°F) | 10.2 µm/m-°C (5.67 µin/in-°F) | Moderate thermal expansion, stable under temperature changes |
| Specific Heat Capacity (0-100°C/32-212°F) | 0.460 J/g-°C (0.110 BTU/lb-°F) | Moderate, providing good heat retention |
| Thermal Conductivity (100°C/212°F) | 24.2 W/m-K (140 BTU-in/hr-ft²-°F) | Moderate thermal conductivity, less efficient than other metals |
| Electrical Conductivity | 1.55% IACS | Poor electrical conductor, typical of stainless steel |
| Magnetic Properties | Magnetic in the hardened state | Can be magnetized when hardened, unlike austenitic steels |
*CTE, Linear refers to the Coefficient of Thermal Expansion, Linear.
Mechanical Properties
Check the table below for the core mechanical properties of 440 stainless steel:
| Property | Value (Metric) | Performance |
| Tensile Strength, Ultimate | 1,750 MPa (254 ksi) | Very high, exceeds common stainless steels like 304 (515 MPa) |
| Tensile Strength, Yield | 1,280 MPa (186 ksi) | Higher than most stainless steels, suitable for high-strength applications |
| Rockwell Hardness | 58 HRC | Extremely hard, higher than common tool steels like 420 (50-55 HRC) |
| Elongation at Break | 4.00% | Low ductility, relatively brittle but suited for high-hardness applications |
| Young’s Modulus | 200 GPa (29 msi) | Standard elastic modulus, comparable to most steels |
Chemical Properties
Check the table below for the core chemical properties of 440 stainless steel:
| Chemical Property | Description | Performance |
| Corrosion Resistance | The ability to resist corrosion in various environments, especially in water or chemicals | Good, but inferior to more corrosion-resistant steels like 316 stainless steel |
| pH Sensitivity | How the material reacts to different pH levels, especially in acidic or basic environments | Sensitive to highly acidic environments; performs well in neutral to slightly alkaline conditions |
| Reactivity | The tendency of the material to chemically react with substances like acids or alkalis | Moderate; less reactive than carbon steels, but more reactive than higher-grade stainless steels like 316 |
| Oxidation Resistance | The ability to resist oxidation or rust when exposed to oxygen or air, especially at high temperatures | High, but slightly lower than austenitic steels such as 304 |
| Passivation | The ability to form a protective oxide layer on its surface to prevent further oxidation | Excellent, forms a protective chromium oxide layer but not as robust as 316 stainless steel |
| Combustibility | The ability of the material to catch fire or burn when exposed to a heat source | Non-combustible |
| Flammability | The likelihood of the material to sustain and propagate a flame | Non-flammable |
Difference Between 440, 304, and 316 Stainless Steel
Check the table below for a quick comparison between 440, 304, and 316 stainless steel:
| Property | 440 | 304 | 316 |
| Type | Martensitic | Austenitic | Austenitic |
| Crystal Structure | Body-Centered Cubic (BCC) | Face-Centered Cubic (FCC) | Face-Centered Cubic (FCC) |
| Chemical Composition | Cr: 16-18%, C: 0.60-0.75 % | Cr: 18-20%, Ni: 8-10.5% | Cr: ≤18%, Mo: ≤3%, Ni: ≤14% |
| Corrosion Resistance | Moderate | Good | Excellent, especially in marine environments |
| Tensile Strength | 1,750 MPa (254 ksi) | 505 MPa (73.2 ksi) | 580 MPa (84.1 ksi) |
| Yield Strength | 1,280 MPa (186 ksi) | 215 MPa (31.2 ksi) | 290 MPa (42.1 ksi) |
| Rockwell Hardness | 58 HRC (~101 HRB) | 70 HRB | 79 HRB |
| Weldability | Poor | Excellent | Excellent |
| Cost | Moderate | Low | Higher than 304 |
| Applications | Cutting tools, blades, bearings | Food equipment, architecture | Marine environments, chemical and medical equipment |
What You Might Also Concern
Is 440 stainless steel good quality?
Yes, 440 stainless steel is considered high-quality, known for its high strength, hardness, and good corrosion resistance, making it ideal for knives and tools.
What does 440 stainless mean on a knife?
“440 stainless” on a knife refers to a high-grade stainless steel known for its hardness, corrosion resistance, and ability to hold a sharp edge. It is often used in knife blades.
Is 440 stainless steel good for knife blades?
Yes, 440 stainless steel is good for knife blades, especially 440C, as it offers excellent corrosion resistance, hardness, and edge retention, though it can be a bit harder to sharpen compared to softer steel.
Can 440 stainless steel rust?
Yes, 440 stainless steel can rust if exposed to harsh conditions, such as prolonged moisture or saltwater, but it is highly resistant to corrosion compared to other steels due to its high chromium content. Proper care and maintenance can prevent rust.
Related Reading
Will Stainless Steel Rust and How Can You Solve It?
How to Clean and Polish Stainless Steel?
Is stainless steel 440 magnetic?
Yes, stainless steel 440 is magnetic in its hardened and annealed states.
Related Reading
Is Stainless Steel Magnetic?
Can 440 stainless steel be machined?
Yes, 440 stainless steel can be machined, but it is more challenging due to its high hardness, especially after heat treatment.
Is 440 stainless steel food safe?
Yes, 440 stainless steel is considered food-safe when properly treated, as it has good corrosion resistance.
How do you temper 440 stainless steel?
To temper 440 stainless steel, heat it to 400-750°F (200-400°C) after hardening, then hold it at that temperature for 1-2 hours, followed by air cooling. The exact tempering temperature depends on the desired balance between hardness and toughness.
Is 440 stainless steel sharp?
Yes, 440 stainless steel can be sharpened to a very fine edge and is known for its ability to hold a sharp edge due to its high hardness.
Summary & Furthermore
This article briefly explains the definition, composition, properties, processing, applications, and other important aspects of 440 stainless steel. To learn more about stainless steel or other steel types, check out our blog or contact our metal experts.
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