440 stainless steel is a high-carbon stainless steel material, which is a kind of chromium stainless steel. It contains about 17% to 18% chromium and about 0.6% to 0.75% carbon, and also contains some other alloying elements such as cobalt, copper, manganese, phosphorus, silicon and sulfur. This material has excellent corrosion resistance, hardness and wear resistance, and is widely used in the production of industrial products that require corrosion resistance and high strength, such as knives, bearings, and valves.
Chemical composition of 440 stainless steel
material | 440 |
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chemical composition | C | Mn | Si | P | S | Cr | Mo |
0.6-0.75 | ≦1.00 | ≦1.00 | ≦0.04 | ≦0.03 | 16-18 | ≦0.75 |
Mechanical properties of 440 stainless steel
material | 440 | ||||
Mechanical properties | Tensile Strength (MPa) | Yield Strength 0.2% Proof (MPa) | Elongation (% in 50mm) | Hardness Rockwell (HR C) | Impact Charpy V (J) |
758 | 448 | 14 | 269HB max# | – | |
Physical properties of 440 stainless steel
material | 440 | ||||||||
Physical properties
| Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (μm/m/°C) | Thermal Conductivity (W/m.K) | Specific Heat | Electrical Resistivity (nΩ.m) | |||
0-100°C | 0-200°C | 0-600°C | at 100°C | at 500°C | |||||
7650 | 200 | 10.1 | 10.3 | 11.7 | 24.2 | – | 460 | 600 | |
The main characteristics of 440 stainless steel
440 stainless steel is a high carbon stainless steel with the following key properties:
High hardness: 440 stainless steel has an extremely high hardness, which can be further increased by heat treatment, making it suitable for applications such as manufacturing blades and knives that require excellent cutting performance.
Corrosion resistance: 440 stainless steel has good corrosion resistance and can resist the corrosion of most common acid and alkali solutions, water and gas, so it is widely used in the manufacture of precision instruments and corrosion-resistant parts.
High Toughness: Despite its high hardness, 440 stainless steel still has good toughness, which can resist shock and vibration and increase the service life.
Grinding performance: 440 stainless steel is easy to grind due to its high carbon content and hardness, and can obtain accurate dimensions and surface quality.
Heat treatment plasticity: 440 stainless steel has good plasticity at high temperature, its structure and performance can be changed through heat treatment, and the hardness and strength of the material can be improved.
Heat resistance of 440 stainless steel
440 stainless steel is a high carbon stainless steel with high heat resistance. It can still maintain good strength and hardness at high temperatures, and has excellent oxidation resistance in high-temperature oxidizing environments. The common 440 stainless steel has three grades of 440A, 440B and 440C, among which 440C is the highest quality and has the best heat resistance.
The heat resistance of 440 stainless steel is mainly due to its high carbon content and the addition of alloying elements. The high carbon content increases the hardness and strength of the material, making it less likely to soften or deform at high temperatures. In addition, the addition of alloying elements such as chromium, molybdenum and vanadium can form a dense oxide film, which prevents the erosion of heat and oxidants, and improves the heat resistance of the material.
Generally speaking, 440 stainless steel can be used for a long time in a high temperature environment, and the common use temperature range is 500°C to 600°C. However, it should be noted that although 440 stainless steel has certain heat resistance, intergranular corrosion and oxidation failure may still occur in extreme high temperature environments, such as above 800°C, so the use of materials should be considered in specific applications conditions and requirements.
Heat Treatment of 440 Stainless Steel
440 stainless steel is a kind of high carbon stainless steel, its microstructure and properties can be changed by adjusting temperature and time during heat treatment.
Generally, the heat treatment process of 440 stainless steel includes two steps: annealing and solution treatment.
Annealing: Heat 440 stainless steel to a temperature range of 850-900°C for a period of time, then slowly furnace cool at a temperature of about 600°C and air cool, subcritical annealing is performed at 735 to 785°C, and then slowly furnace cool . During the annealing process, carbides and other non-equilibrium phases will be decomposed again, and the grains will become larger and uniform, thereby improving the toughness and machinability of the material. In addition, annealing also helps to remove residual stress during processing.
Solution treatment: reheat the annealed 440 stainless steel to a temperature range of 1000-1100 ° C, keep it for a period of time, and then cool it rapidly (quenching). Solution treatment can dissolve carbides in stainless steel and generate austenite structure with higher strength and hardness, which improves the hardness and wear resistance of the material.
During heat treatment, temperature, time and cooling rate are the key factors affecting the performance of 440 stainless steel. Different heat treatment conditions can obtain 440 stainless steel with different hardness and structure, which can meet the requirements of different applications.
Grade 440 stainless steel should not be used below the relevant tempering temperature as over-tempering will result in loss of mechanical properties.
Processing of 440 stainless steel
Grade 440 stainless steel can be easily machined in the annealed condition. Machining these grades after hardening is extremely difficult, and in some cases impossible.
Grade 440 stainless steel can be easily machined in the annealed condition. Machining these grades after hardening is extremely difficult, and in some cases impossible.
Therefore, it is necessary to ensure that the material is in an annealed state before processing. During machining, it is recommended to use slow cutting speed and sufficient cooling lubricant to avoid overheating and damage to the tool. In addition, hardened and tempered grade 440 stainless steel should be handled with care so as not to reduce its mechanical properties and hardness.
Welding of 440 stainless steel
During welding, grade 440 stainless steel is preheated at 250°C and then fully annealed. Grade 420 filler rods can be used to achieve high hardness welds. However, grade 309 or 310 filler rods provide soft welds with high ductility. For the welding of 440 stainless steel, the following methods can be used:
Argon arc welding (TIG welding): Argon arc welding is a commonly used welding method for 440 stainless steel. This method uses a tungsten electrode and an inert gas such as argon to shield the weld area from contamination by oxygen and other impurities. Argon arc welding can provide high-quality welds and is suitable for welding thin sheet materials.
Argon arc welding flux (TIG flux welding): For thicker 440 stainless steel materials, argon arc welding flux can be used. Adding a certain amount of welding flux during welding can provide higher welding speed and deeper weld.
Application fields of 440 stainless steel
440 stainless steel is a high-hardness, high-corrosion-resistant stainless steel material, which is mainly used to manufacture various knives, blades and shearing tools. The following are some application areas of 440 stainless steel:
Knife manufacturing: 440 stainless steel is widely used in the manufacture of various knives, such as kitchen knives, hunting knives, folding knives, medical scalpels, etc. Its hardness and corrosion resistance make the blade sharper and more durable.
Industrial blades: 440 stainless steel is often used to manufacture industrial blades, such as cutting blades, lawn mower blades, paper cutting blades, etc. Its high hardness and wear resistance make the blade more durable and effective.
Medical equipment: 440 stainless steel is used in the manufacture of medical equipment, such as scalpels, dental appliances, etc. Its high purity, low magnetic properties and excellent corrosion resistance make medical devices safer and more reliable.
High-end tableware: 440 stainless steel is often used to manufacture high-end tableware, such as knives and forks, spoons, etc., because of its beauty, durability and corrosion resistance.
Production of props: 440 stainless steel is also widely used in the production of film and television props, such as fake knives and swords used by the crew.
In short, 440 stainless steel is widely used in knives, blades, medical equipment, tableware and props production due to its high hardness and high corrosion resistance.
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