Stainless Steel
Stainless Steel
Stainless steel is a kind of alloy steel and is widely used in many fields.
The main component is iron. Chromium is the key alloying element, with a content of at least 10.5%. Chromium can form a dense chromium oxide protective film on the surface of stainless steel, which gives stainless steel its corrosion – resistance. In addition, it may also contain elements such as nickel, molybdenum, titanium, and niobium. Nickel can enhance the toughness and corrosion – resistance of stainless steel; molybdenum can improve the pitting corrosion resistance of stainless steel in a chlorine – containing environment; titanium and niobium are mainly used to stabilize the carbon in stainless steel and prevent intergranular corrosion.
Classification
By Metallographic Structure
– Austenitic Stainless Steel: It contains a relatively high amount of nickel. For example, 304 stainless steel (chromium content is about 18.0 – 20.0%, nickel content is about 8.0 – 10.5%) and 316 stainless steel (chromium content is about 16.0 – 18.0%, nickel content is about 10.0 – 14.0%, and also contains molybdenum). This kind of stainless steel is non – magnetic, has good toughness, corrosion – resistance and processing performance, and is often used in food processing equipment, chemical equipment, medical devices, etc.
– Ferrite Stainless Steel: It has a relatively high chromium content, generally between 11 – 30%, such as 430 stainless steel. It has good corrosion – resistance, is magnetic, and has a small thermal expansion coefficient. It is often used in kitchen utensils, automotive decoration, etc.
– Martensitic Stainless Steel: It has a relatively high carbon content, high strength and hardness, such as 410 stainless steel. After heat treatment, it can obtain high hardness and wear – resistance and is often used in cutting tools, valves, etc.
By Application
– Corrosion – Resistant Stainless Steel: Used to resist various corrosive environments, such as marine environment and chemical environment.
– Heat – Resistant Stainless Steel: Can maintain good performance in high – temperature environments and can be used to manufacture high – temperature equipment such as stoves and boilers.
– Decorative Stainless Steel: Mainly used in the fields of architectural decoration and home decoration, focusing on appearance and corrosion – resistance.
Performance Characteristics
Corrosion Resistance:
This is the most prominent performance of stainless steel. It can resist the corrosion of atmosphere, water, acid, alkali and salt and other media. Different types of stainless steel have different corrosion – resistance. For example, 316 stainless steel has better corrosion – resistance than 304 stainless steel in a chloride – ion – containing environment.
Processing Performance:
It has good processing performance, including cold processing (such as cold rolling and cold bending) and hot processing (such as hot rolling and forging). However, during the processing, attention should be paid to avoid the damage of the surface protective film, otherwise its corrosion – resistance may be affected.
Physical Properties:
It has a relatively low thermal conductivity and a relatively high electrical resistivity. Its density is generally about 7.7 – 8.0g/cm³. Austenitic stainless steel is non – magnetic, while ferrite and martensitic stainless steel are magnetic.
Application Fields
Food Processing Industry:
Used to make food processing equipment and tableware to ensure food hygiene and safety.
Chemical Industry:
Manufactures various chemical containers, pipelines and reactors to resist the corrosion of chemical substances.
Construction Industry:
Used as building decoration materials, such as curtain walls, handrails, doors and windows, which are both beautiful and durable.
Medical Industry:
Used in medical devices, such as surgical knives and medical stents, taking advantage of its corrosion – resistance and biocompatibility.
Metallic materials mainly include the following categories:
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AISI Stainless Steel Designations
200 Series – Chromium – Nickel – Manganese Austenitic Stainless Steels
– Type 201: Can be hardened by cold working. It is relatively inexpensive, with relatively poor corrosion – resistance and processing performance. It is mainly used in applications where the material requirements are not high, such as some decorative fields.
– Type 202: Its corrosion – resistance is better than that of Type 201. It has a certain strength and toughness and is often used in architectural decoration and daily necessities.
300 Series – Chromium – Nickel Austenitic Stainless Steels
– Type 301: It has good ductility and is used for formed products. It has good weldability and its abrasion resistance and fatigue strength are better than those of 304 stainless steel. It is suitable for components that require good formability and a certain strength, such as automotive parts and architectural decoration.
– Type 302: Its corrosion – resistance is similar to that of 304, but it has a relatively high carbon content and thus better strength. It can be used to manufacture structural parts and mechanical parts that require higher strength.
– Type 303: By adding a small amount of sulfur and phosphorus, it is more machinable than 304. It is often used to manufacture parts that require high – precision machining, such as precision instruments and medical devices.
– Type 304: One of the most common austenitic stainless steels, also known as 18/8 stainless steel, containing 18 – 20% chromium and 8 – 10.5% nickel. It has good corrosion – resistance, formability and weldability and is widely used in food processing equipment, kitchen appliances, architectural decoration and other fields.
– Type 309: It has better temperature – resistance than 304 and can be used at higher temperatures. It is often used in high – temperature stoves and heat – resistant equipment.
– Type 310/310S: Highly alloyed and used for high – temperature applications. It has excellent high – temperature resistance and antioxidant performance and is suitable for manufacturing high – temperature furnaces and heat – treatment equipment.
– Type 316: After 304, it is the second most widely used steel type. With the addition of molybdenum, it has better resistance to chloride corrosion and is mainly used in the food industry, surgical instruments and marine environment.
– Type 321: Except for the addition of titanium to reduce the risk of weld corrosion, other properties are similar to 304. It is often used in chemical, aerospace and other fields where high weld corrosion – resistance is required.
400 Series – Ferrite and Martensitic Stainless Steels
– Type 409: The cheapest type, usually used as automotive exhaust pipes. It is a ferrite stainless steel with good heat – resistance and corrosion – resistance and can be used for general corrosion – resistant and heat – resistant components.
– Type 410: It is a martensitic high – strength chromium steel with good wear – resistance but relatively poor corrosion – resistance. It is often used in manufacturing cutting tools, valves, pump shafts, etc.
– Type 420: It is a “cutlery – grade” martensitic steel and can be used in surgical knives, tableware, etc. It can also be used to manufacture parts that require high hardness and wear – resistance.
– Type 430: It is a ferrite stainless steel with good formability and decorativeness and is often used in automotive accessories and home appliance housings.
– Type 440A: It is a high – strength cutlery steel with a relatively high carbon content. After appropriate heat treatment, it can obtain a relatively high yield strength and a hardness of up to 58HRC. It is often used in manufacturing razor blades, cutting tools, etc.
600 Series – Precipitation – Hardening Stainless Steels
– Type 630: The most commonly used precipitation – hardening stainless steel type, usually also called 17 – 4PH, containing 17%Cr – 4%Ni. It has good strength, toughness and corrosion – resistance and is suitable for manufacturing chemical equipment, medical devices, aerospace components, etc.
– Type 631: Usually called 17 – 7PH, it has relatively high strength and good corrosion – resistance and is often used to manufacture parts with high strength and corrosion – resistance, such as springs and aerospace components.
