440 steel is a series of high-carbon martensitic stainless steels, including grades 440A, 440B, and 440C type, these grades have excellent hardness and wear resistance and are commonly used in the production of high-performance knives and cutting tools.
440C stainless steel is a high-carbon martensitic stainless steel, high carbon content in 440C provides high strength, moderate corrosion resistance, good hardness, and wear resistance. these characteristics make 440C particularly suited to such applications as ball bearings and valve parts, it has the highest hardness among stainless steel.
440A and 440B are the same composition as 440C except for slightly lower carbon contents (0.60 – 0.75% and 0.75 – 0.95% respectively); these have lower attainable hardnesses but slightly higher corrosion resistances. Although all three versions of this grade are standard, in practice 440C is more available than the A or B variants.
440 Stainless Steel Chemical Composition
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N |
|---|---|---|---|---|---|---|---|---|---|
| 440A | 0.65- 0.75 | – 1.00 | – 1.00 | – 0.040 | – 0.030 | 16.00- 18.00 | – 0.75 | – | – |
| 440B | 0.75- 0.95 | – 1.00 | – 1.00 | – 0.040 | – 0.030 | 16.00- 18.00 | – 0.75 | – | – |
| 440C | 0.95- 1.20 | – 1.00 | – 1.00 | – 0.040 | – 0.030 | 16.00- 18.00 | – 0.75 | – | – |
These properties are specified for bar products in ASTM A276. Similar but not necessarily identical properties are specified for other products such as wire and forgings in their respective specifications. These grades are not normally available in flat rolled or fluid products.
440C Stainless Steel Mechanical Properties
| Tempering Temperature (°C) | Tensile Strength (MPa) | Yield Strength 0.2% Proof (MPa) | Elongation (% In 50mm) | Hardness Rockwell (HR C) | Impact Charpy V (J) |
|---|---|---|---|---|---|
| Annealed * | 758 | 448 | 14 | 269HB Max # | – |
| 204 | 2030 | 1900 | 4 | 59 | 9 |
| 260 | 1960 | 1830 | 4 | 57 | 9 |
| 316 | 1860 | 1740 | 4 | 56 | 9 |
| 371 | 1790 | 1660 | 4 | 56 | 9 |
| * Annealed Properties Are Typical For Grade 440C ASTM A276 Annealed Condition. # Brinell Hardness Is ASTM A276 Specified Maximum For Annealed 440A, B And C, Hot Finished. | |||||
440C Stainless Steel Physical Properties
| Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (mm/m/°C) | Thermal Conductivity(W/m.K) | Specific Heat 0-100°C (J/kg.K) | Electrical Resistivity (nW.m) | |||
|---|---|---|---|---|---|---|---|---|---|
| 0-100°C | 0-200°C | 0-600°C | at 100°C | at 500°C | |||||
| 440 C | 7650 | 200 | 10.1 | 10.3 | 11.7 | 24.2 | – | 460 | 600 |
Grade Specification Comparison
| Grade | UNS No | Euronorm | Swedish SS | Japanese JIS | |
|---|---|---|---|---|---|
| Steel No. | Name | ||||
| 440A | S44002 | – | – | SUS 440A | |
| 440B | S44003 | 1.4112 | X90CrMoV18 | SUS 440B | |
| 440C | S44004 | 1.4125 | X105CrMo17 | – | SUS 440C |
| These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted. | |||||
440 Stainless Steel Properties and Types
The 440 family of stainless steels is most typically offered in long forms—bars, wires, billets, coils, and tubes are the most common, but there may be others. These raw forms are the most conducive to metalworking with 440 steel.
440 steel refers to four types of steel: 440A, 440B, 440C and 440F steel, which only differ based on the level of carbon in their composition. All types of 440 steel are popular choices, but 440C steel is the most popular of the four, as it has the highest hardness.
- 440A – With the least amount of carbon among the four types, this makes 440A stainless the most stain-resistant. It is the most ideal for diving and saltwater applications that require superior corrosion resistance.
- 440B. The 440B grade of stainless steel is ideal for crafting blades in areas when they need higher toughness than 440A and higher stain resistance than 440C, such as wet knives for cooking.
- 440C. With the greatest amount of carbon out of the 440 variants, this is considered to be the strongest and most desirable steel for knife making—especially over type 440A (except in aquatic conditions).
- 440F. When talking about the 440 stainless grades, 440F often remains unmentioned. 440F is a free-machining variant of 440C. The popularity of 440c led to the development of this variant that works better for machining but is nearly the same composition.
All 440 steels are hardenable, meaning they gain additional strength via heat treatment, and they are considered high-carbon alloy steel. When strengthened using this process, 440 steels are the hardest of all the stainless steels, making them both abrasion-resistant as well as corrosion-resistant. When in its soft “annealed” state, 440 steel is easily worked, machined, and manipulated into shape,
Corrosion Resistance
Good resistance to the atmosphere, freshwater, foods, alkalies and mild acids. Best resistance in the hardened and tempered and passivated condition. A smooth polished surface also assists. The corrosion resistance of Grade 440C is close to that of grade 304 in many environments. Consult Atlas Technical Assistance for specific environmental recommendations.
Heat Resistance
Not recommended for use in temperatures above the relevant tempering temperature,because of reduction in mechanical properties by over-tempering.
Heat Treatment
Annealing Full anneal – 840-870°C, slow furnace cool to about 600°C and then air cool. Sub-critical Annealing – 735-760°C and slow furnace cool.
Hardening
Heat to 1010-1065°C, followed by quenching in warm oil or air. Oil quenching is necessary for heavy sections. Immediately temper at 150- 370°C to obtain the hardness values and mechanical properties as indicated in the accompanying table. Best corrosion resistance is when tempered below 425°C. Tempering in the range 425- 565°C is to be avoided because of reduced impact resistance and corrosion resistance.
Tempering in the range 600-675°C results in lower hardness – the product becomes machinable.
Maximum achievable hardnesses are approximately HRC56 for Grade 440A, HRC58 for 440B and HRC60 for 440C.
Welding
Welding is seldom carried out because of the grades’ high hardenability. If welding is necessary pre-heat at 250°C and follow welding with a full anneal. Grade 420 filler will give a high hardness weld (although not as high as the 440C), but 309 or 310 will produce soft welds with higher ductility.
Machining
In the annealed condition this grade is relatively easily machined; approximately the same as for high-speed steel. Chips are tough and stringy so chip breakers are important. If these grades are hardened machining becomes more difficult and probably impossible.
Applications
AISI 440 steel is used for the manufacture of bearing parts that operate in corrosive environments, as well as for the manufacture of high-quality tools (medical scalpels, scissors and blades, surgical and dental instruments), molds, springs, cutlery, valves and valve components, cams, gears, shafts, ball bearings, nozzles, and measuring tools.