If you don’t know much about stainless steel yet, be sure to read this article. It will give you a comprehensive and systematic understanding of stainless steel types, characteristics, applications, and more. By the end, you’ll find that this article covers almost all the knowledge about stainless steel. I hope it helps you.
The History of Stainless Steel
Before the invention of stainless steel, humans explored the world using bronze and iron tools. However, both bronze and iron had a major drawback: they rusted, especially when exposed to harsh environments for extended periods, leading to performance degradation.
In the early 20th century, scientists discovered that combining chromium, nickel, and other elements with iron could create a metal with unprecedented properties—corrosion resistance. This discovery marked the birth of stainless steel.
With technological advancements, stainless steel has evolved from a single type to multiple grades with varying properties. Its presence can now be seen in various fields, and it is widely used across many applications.
Production of different types of stainless steel
Different types of stainless steel are made by adding various chemical elements during production, with different proportions of each element. This results in stainless steel with different characteristics that suit various purposes.
Carbon
The carbon content in stainless steel significantly affects its properties. For example, stainless steel with high carbon content will exhibit high hardness and strength but lower toughness and corrosion resistance. Conversely, low carbon content reduces hardness and strength while increasing toughness and corrosion resistance.
Chromium
Adding chromium during the production of stainless steel imparts many important characteristics:
- Corrosion Resistance: Chromium reacts with oxygen in the air to form a layer of chromium oxide on the surface, effectively preventing corrosion. The higher the chromium content, the better the effect.
- High-Temperature Resistance: Chromium significantly improves the high-temperature performance of stainless steel.
- Strength and Hardness: Chromium also increases the hardness and strength of stainless steel, making it more durable.
Nickel
Adding the right amount of nickel to stainless steel makes it more resistant to corrosion; it also increases the strength and toughness of the stainless steel, allowing it to withstand greater pressure and impact. Nickel improves its formability and weldability, and it makes the surface smoother and easier to clean.
Five main types and characteristics of stainless steel:
Although there are over 1,000 different types of stainless steel produced by controlling the proportion of added elements, they can all be classified into the following three main categories.
Austenitic stainless steel
To produce austenitic stainless steel, the main elements are chromium and nickel, with nickel content being at least 8%. This is because nickel stabilizes the austenitic structure, giving the stainless steel excellent corrosion resistance, toughness, and formability.
When observing austenite under a metallographic microscope, you will find it consists of equiaxed polygonal grains with twins inside, which is known as the face-centered cubic structure. This type of stainless steel, such as 304, 316, and 301, is the most common, non-magnetic, highly corrosion-resistant, and easy to form and weld.
Ferritic Stainless Steel
Unlike austenitic stainless steel, ferritic stainless steel primarily contains chromium and may also include elements like manganese and nickel, but there is no requirement for nickel content. Ferritic stainless steel also has good corrosion resistance.
It is characterized by a body-centered cubic lattice structure and is magnetic. However, it has lower strength and toughness, with common types being 409, 430, and 434.
Martensitic Stainless Steel
Like other stainless steels, martensitic stainless steel is an alloy of iron, chromium, and some other elements. It has a body-centered cubic lattice structure and is magnetic. You can adjust its mechanical properties through heat treatment, significantly improving its strength, hardness, and wear resistance, but its toughness and corrosion resistance are relatively poor.
The high hardness and strength of martensitic stainless steel are due to its unique crystal structure and high carbon content, making it suitable for use in stamping, forging dies, and various cutting tools.
Duplex (Ferritic-Austenitic) Stainless Steel
Dual-phase stainless steel, as the name suggests, consists of roughly equal parts of ferrite and austenite phases. This combination integrates the characteristics of both ferritic and austenitic stainless steels. The proportion of these phases can be adjusted according to specific needs:
- 70% Ferrite – 30% Austenite: This is the most common ratio, offering good overall performance.
- 50% Ferrite – 50% Austenite: This ratio provides higher strength and toughness, making it ideal for certain applications.
The ratio can be tailored based on specific requirements:
- For higher strength and toughness, increase the austenite content.
- For better corrosion resistance, increase the ferrite content.
- To enhance formability (which is characteristic of austenite), increase the austenite content.
- Since austenite contains more nickel, which increases costs, reducing the austenite content can help lower costs.
Dual-phase stainless steel exhibits excellent strength, toughness, corrosion resistance, and impact resistance, making it suitable for extreme environments such as petroleum, natural gas, shipbuilding, nuclear power, and other fields.
Precipitation-hardening (PH) Stainless Steel
PH steel is stainless steel that undergoes a heat treatment process called precipitation hardening, which further enhances its strength and hardness while maintaining its original stainless steel properties. This makes it exceptionally durable.
PH steel boasts the highest hardness and strength among all stainless steels, comparable even to some low-carbon steels. It also exhibits good wear resistance and high-temperature resistance, making it suitable for a wide range of applications. It is used in advanced industries such as aerospace, defense, and oil drilling.
Common Types of Austenitic Stainless Steel
Grade 301 Stainless Steel
301 stainless steel consists of 17% chromium, 7% nickel, 2% manganese, ≤0.15% carbon, ≤1.0% silicon, ≤0.03% sulfur, and ≤0.04% phosphorus. It has a melting point between 1399-1421°C, a density of 7.88 g/cm³, and a tensile modulus of elasticity of 193 GPa.
301 stainless steel exhibits excellent strength, hardness, corrosion resistance, and ductility. When cold-worked, it maintains good strength and ductility.
It resists most corrosion media such as chemicals and saltwater to some extent. However, its corrosion resistance may be inadequate in high-temperature or highly corrosive environments.
Applications for 301 stainless steel include automotive exhaust systems, springs, fasteners, medical devices, and food processing equipment.
Grade 302 Stainless Steel
302 stainless steel consists of 17.00% to 19.00% chromium, 8.00% to 10.00% nickel, ≤1.00% silicon, ≤0.030% sulfur, ≤0.045% phosphorus, ≤2.00% manganese, and ≤0.15% carbon. It has a melting point between 1398 to 1420°C, a density of 8.03 g/cm³, and a tensile strength (RM/MPa) of ≥520.
302 stainless steel exhibits good corrosion resistance, especially in mild atmospheres and seawater. It is also easily workable through processes like stamping and stretching, with cold working enhancing its strength and hardness.
Applications for 302 stainless steel include storage tanks, medical instruments, kitchenware, and architectural materials.
Grade 303 Stainless Steel
303 stainless steel primarily consists of chromium (18%) and nickel (9%). It also contains sulfur and selenium to improve machinability, making it popular in the machining industry. However, the addition of sulfur can slightly affect its corrosion resistance, although it maintains decent corrosion resistance in typical environments.
It’s important to note that 303 stainless steel is non-magnetic, but after heavy cold working, it may exhibit slight magnetism. Additionally, it cannot be hardened through heat treatment.
As a result, 303 stainless steel is suitable for manufacturing high-precision gears, shafts, bushings, valve bodies, and valves.
Grade 304 Stainless Steel
304 stainless steel is a common austenitic stainless steel known for its excellent machinability, allowing for turning, milling, drilling, stamping, welding, and other processes, making it widely used in many industries.
Its high chromium and nickel content provides outstanding corrosion resistance in various environments and can withstand temperatures up to 800°C.
304 stainless steel excels in overall performance, making it a preferred material in industries such as food and medical sectors, dairy equipment, household appliances, and even in SpaceX rocket casings.
Grade 309 Stainless Steel
Compared to 304 stainless steel (18%-20% chromium, 8%-10.5% nickel), 309 stainless steel has higher chromium (23.00-25.00%) and nickel (12.00-15.00%) content. This gives it better corrosion resistance and superior oxidation resistance at high temperatures. It can maintain stability for long periods at temperatures as high as 980°C.
Due to these characteristics, 309 stainless steel is an ideal material for equipment requiring high-temperature operation and excellent oxidation resistance.
Grade 316 Stainless Steel
316 stainless steel is also a common type of austenitic stainless steel. It enhances its basic austenitic composition by adding about 2% to 3% molybdenum, significantly improving its resistance to pitting and crevice corrosion, especially in chloride environments.
The carbon content of 316 stainless steel needs to be controlled below 0.08% to enhance its weldability.
316 stainless steel is predominantly used in the food and medical industries, including corrosion-resistant containers, pipes, and equipment for food contact applications.
Grade 317 Stainless Steel
317 stainless steel builds upon the composition of 316 by increasing the content of chromium, nickel, and molybdenum. This enhancement gives it superior corrosion resistance, strength, and toughness compared to 316. It can withstand both acidic and alkaline environments effectively.
Additionally, the production of 317 stainless steel results in less waste and wastewater, with higher rates of recycling.
Industries with demanding environments, such as chemical processing, oil and gas, nuclear, and marine sectors, find 317 stainless steel particularly suitable for their applications.
Grade 321 Stainless Steel
321 stainless steel can be considered a variant of 304 stainless steel, with similar performance characteristics. However, 321 stainless steel incorporates titanium, which enhances its resistance to intergranular corrosion and high-temperature strength.
Through testing, 321 stainless steel has shown excellent stress rupture performance and creep resistance at high temperatures, making it suitable for welded structures used in high-temperature environments.
321 stainless steel is suitable for manufacturing machinery and equipment exposed to outdoor environments in industries such as petroleum, coal, and chemicals.
Grade 347 Stainless Steel
Similar to 321 stainless steel, 347 stainless steel also adds a metal element to the base of 304, but instead of titanium, it uses niobium. The main purpose is to stabilize the austenitic phase and enhance its resistance to intergranular corrosion. Some variants of 347 stainless steel may also include titanium and molybdenum to further improve its performance.
347 stainless steel exhibits good machinability and weldability, meeting the fabrication requirements of various complex parts. Its excellent corrosion resistance and high-temperature properties make it suitable for manufacturing equipment used in petroleum refining and natural gas desulfurization.
Common Types of Ferritic Stainless Steel
| Grade | Standard | Main Elements | Characteristics | Applications |
|---|---|---|---|---|
| 409 | AISI | Cr10.5-11.75 | Low price, easy to process, general corrosion resistance | Automotive exhaust system components, appliance trim |
| 430 | AISI | Cr16-18 | Good corrosion resistance, formability, and weldability | Decorative parts, cookware, building components |
| 430F | AISI | Cr16-18 (Ti) | Excellent formability and weldability | Low-carbon steel substitute |
| 430LX | AISI | Cr16-18 (low carbon) | Excellent welding performance | Deep-drawn parts, automotive exhaust system components |
| 434 | AISI | Cr17-19 | Good corrosion resistance and weldability | Automotive trim, appliance parts |
| 439 | AISI | Cr17-19 (Nb) | Excellent formability and high-temperature resistance | Deep-drawn parts, sinks |
| 441 | AISI | Cr18-20 | Good corrosion resistance and high-temperature resistance | Heat exchangers, catalytic converters |
| 444 | AISI | Cr18-20 (Nb, Mo) | Excellent high-temperature resistance and oxidation resistance | Exhaust manifolds, high-temperature components |
| 446 | AISI | Cr23-26 | Excellent high-temperature resistance and oxidation resistance | Deep-drawn parts sinks |
Common Types of Martensitic Stainless Steel
| Grade | Standard | Main Elements | Characteristics | Applications |
|---|---|---|---|---|
| 403 | AISI | Cr12Mo0.5 | Low price, high strength, good wear resistance | Knives, scissors, bearings |
| 410 | AISI | Cr12Mo0.5 | Good wear resistance and corrosion resistance | Knives, valves, pumps |
| 414 | AISI | Cr14Mo0.5 | Higher hardness and strength | Knives, dies |
| 416 | AISI | Cr12Mo0.5S | Good machinability and wear resistance | Screws, bolts, bearings |
| 420 | AISI | Cr13Mo0.4 | Good hardness and wear resistance, heat treatable | Knives, cutlery, mechanical parts |
| 422 | AISI | Cr13Mo0.7 | Improved corrosion resistance and toughness | Good hardness and wear resistance, heat-treatable |
Common Types of Duplex (Ferritic-Austenitic) Stainless Steels
| Grade | Standard | Main Elements | Characteristics | Applications |
|---|---|---|---|---|
| 201N | AISI | Cr18Mn6Ni5N | Low price, strong resistance to nitrogen corrosion | Food processing, chemical industry |
| 2205 | AISI | Cr18Mn6Ni4Mo0.5Cu | Good corrosion resistance, strength, and toughness | Flue gas desulfurization, marine aquaculture |
| 2304 | AISI | Cr18Ni10Mo2 | Excellent corrosion resistance, strength, and toughness | Petrochemical industry, offshore engineering |
| 2505 | AISI | Cr21Ni5Mo3Cu1.5 | Excellent corrosion resistance, strength, and toughness | Flue gas desulfurization, marine aquaculture |
| S31803 | UNS | Cr18Ni5Mo3Cu | Good corrosion resistance, strength, and toughness | Shipbuilding, offshore engineering |
| S32205 | UNS | Cr18Ni5Mo3Cu0.5 | Good corrosion resistance, strength, and toughness | Petrochemical industry, offshore engineering |
| SAF 2205 | ASTM | Cr18Mn6Ni4Mo0.5Cu | Good resistance to chloride corrosion | Flue gas desulfurization, marine aquaculture |
Common Types of Precipitation Hardening (PH) Stainless Steels
| Grade | Standard | Main Elements | Characteristics | Applications |
|---|---|---|---|---|
| 17-4PH | AISI | Cr17Ni4MoCu | High strength, high toughness, good corrosion resistance | Aerospace, nuclear industry, petrochemical industry |
| 17-7PH | AISI | Cr17Ni7Mo | Extremely high strength and hardness | Knives, dies, bearings |
| A286 | AISI | Cr15Ni25Ti2MoAl | Good high-temperature strength and corrosion resistance | Aerospace, gas turbines |
| 630 | AISI | Cr17Ni4CuNb | Good strength, toughness, and corrosion resistance | Chemical, petrochemical, shipbuilding |
What do the grades of stainless steel mean?
The grades of stainless steel represent their material properties, composition, and applications. These grades are typically denoted by a series of numbers or numbers followed by letters, indicating:
Numbers:
- 200 Series: Represents austenitic stainless steels with chromium and manganese as primary components and lower nickel content. They have good corrosion resistance and are easy to process and weld, but they have lower strength.
- 300 Series: Also represents austenitic stainless steels primarily composed of chromium and nickel. They exhibit good corrosion resistance, as well as good strength and toughness. 304 and 316 are the most common in this series.
- 400 Series: Represents ferritic stainless steel. Unlike the 300 series, these steels primarily contain chromium with little to no nickel, resulting in some magnetic properties. They have good strength and wear resistance but lower corrosion resistance compared to the 200 and 300 series.
- 500 Series: Represents martensitic stainless steels, primarily composed of chromium and nickel. These steels have high strength and hardness but relatively poor corrosion resistance.
- 600 Series: Represents precipitation hardening stainless steels, which involve adding elements like copper, molybdenum, and titanium to improve strength and hardness. They exhibit strong comprehensive performance including strength, hardness, corrosion resistance, and high-temperature resistance.
Letters:
- L: Indicates low-carbon stainless steel with carbon content usually below 0.03%. They are easier to weld and have better resistance to intergranular corrosion.
- N: Indicates nitrogen-containing stainless steel, where nitrogen enhances strength and toughness.
- S: Indicates sulfur-containing stainless steel, which facilitates easier machining.
- Ti: Indicates titanium-containing stainless steel, which enhances corrosion resistance and high-temperature performance.
- Mo: Indicates molybdenum-containing stainless steel, which improves corrosion resistance, especially against chlorides.
- Cu: Indicates copper-containing stainless steel, which enhances strength and hardness.
For example, austenitic stainless steel 316 has a carbon content of approximately 0.08%, while 316L has a carbon content below 0.03%.
What are the different standards for stainless steel grades?
- American Standard (ASTM): This standard is set by the American Society for Testing and Materials (ASTM) and is widely used globally. When we refer to 304, it is a simplified version of ASTM304 (American Standard). Similarly, 316 is a simplified version of ASTM316.
- European Standard (EN): This standard is set by the European Committee for Standardization (CEN) and is used by many European countries. The standards typically start with “EN” followed by a series of numbers. For example, EN 1.4301 represents 304 stainless steel.
- Japanese Standard (JIS): This standard is set by the Japanese Industrial Standards Committee (JISC). The prefix “SUS” is added before the grade, so SUS304 represents 304 stainless steel.
- China National Standard (GB): This standard is set by the Standardization Administration of China (SAC). The grades are typically represented by their elemental composition. For example, GB 1Cr18Ni9 stainless steel is equivalent to 304 stainless steel.
Here are some common stainless steel grades and their corresponding standards:
| Grade | ASTM | EN | JIS | GB |
|---|---|---|---|---|
| 304 | ASTM304 | EN1.4301 | SUS304 | 1Cr18Ni9 |
| 316 | ASTM316 | EN1.4401 | SUS316 | 00Cr18Ni14Mo2 |
| 201 | ASTM201 | EN1.4306 | SUS201 | 1Cr18Ni5 |
| 430 | ASTM430 | EN1.4016 | SUS430 | 1Cr13Ni4 |
| 17-4PH | A17-4PH | EN1.405 | SUS416 | 00Cr17Ni7Mo4 |
How do you decide which type is right for your needs?
To determine the right type of stainless steel for your needs, especially if you’re not very familiar with it, consider the following aspects based on our extensive experience in stainless steel processing:
Your Environment
Firstly, think about where your stainless steel product will be used. Consider exposure to chemicals and potential impacts. For instance, if it will be exposed to seawater or acidic environments over a long period, prioritize stainless steels known for their corrosion resistance, such as 316 or 2205.
Formability or Weldability
Next, assess whether you’ll need to shape or process the stainless steel. Processes like welding, forging, stamping, or machining require stainless steels that are easy to work with. Austenitic and ferritic stainless steels generally offer good formability and are suitable choices for such applications.
Strength
Next, you need to consider how much load you want the stainless steel to bear and whether you require high strength. If you need high-strength stainless steel, you might consider using martensitic stainless steel or precipitation-hardening stainless steel, both of which have high hardness.
Toughness
Also, consider the toughness of the stainless steel you need. Will it need to withstand impact and vibration during use? If so, austenitic and duplex stainless steel are good choices, as they offer good toughness.
Cost and Availability
Cost may be a significant factor in your stainless steel procurement decision. There are many types of stainless steel, and the price differences between them can be substantial. However, when purchasing, prioritize meeting your operational requirements first, then work to reduce costs based on those needs.
Best Types of Stainless Steel by Industry
Each industry has different demands for stainless steel performance, so choosing the right stainless steel is crucial to meet specific industry needs. Here are some recommended stainless steel grades for various industries:
Aerospace Industry
We all know the aerospace industry operates in harsh environments where stainless steel must withstand heavy loads, impacts, and vibrations. Therefore, martensitic and precipitation-hardening stainless steels are excellent choices. They offer great strength and toughness and perform well at high temperatures.
Medical Industry
The medical industry is unique, with some medical devices possibly being implanted directly into the body, making rust unacceptable. Here, 316L stainless steel is highly recommended for its lower carbon content, effectively reducing the risk of intergranular corrosion. Common instruments and equipment can use 304 stainless steel.
Marine Industry
The marine industry faces harsh conditions with prolonged exposure to seawater and occasional impact from waves. Recommended choices include 316 stainless steel and duplex stainless steel. They are suitable for marine environments, effectively preventing chloride solution corrosion, and they boast good hardness and strength.
Oil and Gas Industry
In the oil and natural gas industry, 316 stainless steel is ideal for production, storage, and transportation due to its effective resistance to corrosion from oil and gas. Duplex stainless steel is suitable for specialized applications such as subsea pipelines and drilling equipment.
Chemical Industry
In the chemical industry, which deals with corrosive gases and liquids, stainless steels like 316 and 2205 are excellent choices because they resist corrosion well and offer good strength and toughness.
Food processing industry
In the food processing industry, stainless steels like 304 and 316 are widely used and trusted after years of market testing. They are commonly found in stainless steel cutlery, kitchenware, and cups.
Misconceptions about stainless steel
“All Stainless Steel is the same”
Stainless steel comes in over 1,000 different types, each with its own specific uses and characteristics. In today’s industrial classification, stainless steels are typically categorized by their crystal structure: austenitic, ferritic, martensitic, duplex (a combination of austenite and ferrite), and precipitation-hardening stainless steels. Each of these main categories further includes numerous subtypes.
“Stainless Steel doesn’t rust”
Stainless steel gets its name because it has excellent corrosion resistance compared to other metals. This ability primarily depends on its chromium content and the thickness of its passive oxide layer. The higher the chromium content and the thicker the oxide layer, the better its corrosion resistance. However, stainless steel is not completely immune to rusting and can still rust under certain conditions.
Some low-chromium stainless steels, like 403, can rust in moist or corrosive environments. Even high-chromium stainless steels like 304 can rust if their surface is damaged, scratched, or welded.
“Stainless Steel is not magnetic”
Many people believe stainless steel is non-magnetic and anything that a magnet can attract isn’t stainless steel. This is actually incorrect. For instance, austenitic stainless steels are non-magnetic or slightly magnetic in their annealed state. However, they can become magnetic if they undergo cold working or welding. On the other hand, martensitic and ferritic stainless steels are magnetic in their annealed state.
“Stainless Steel is expensive”
Stainless steel is indeed more expensive compared to carbon steel, typically costing 1/3 to 1/2 more. However, the additional performance benefits of stainless steel often justify its higher price. Due to its excellent properties, stainless steel is irreplaceable in many applications. If your application requires materials with corrosion resistance, strength, toughness, and other qualities, stainless steel is a great choice.
In contrast, if you use carbon steel, you’ll need to paint it to prevent rusting. While this may seem cost-effective initially, the maintenance costs later on are likely to be higher compared to using stainless steel.
“All Stainless Steels have the same corrosion resistance”
This viewpoint is actually incorrect. While they are all called stainless steel, their corrosion resistance capabilities vary. The factors that cause this difference are the chromium content and the addition of other metals such as nickel, molybdenum, copper, etc. These elements effectively prevent corrosion, but their corrosion resistance varies depending on the amount added.
Choosing the Right Stainless Steel Fabrication Partner
If you want to purchase stainless steel or stainless steel parts, here are a few suggestions that I hope will help you.
Experience and expertise
When choosing partners, their experience and expertise in stainless steel manufacturing are crucial. This allows them to recommend suitable materials and manufacturing processes based on your needs. They can also share case studies relevant to your industry or application area. Visiting their factories allows you to inspect their manufacturing equipment firsthand.
QC
Stainless steel manufacturing requires strict quality control measures. You can inquire about their process control methods and review their quality certification documents. When receiving deliveries, ask your supplier for inspection and testing reports.
Price and delivery time
You can approach multiple suppliers to obtain several quotes and compare their prices and delivery times. The quotes should be detailed, covering costs for materials, transportation, tooling, and other expenses.
Communication and Service
This depends on your personal feelings. Evaluate how comfortable you are communicating with them, whether they understand your needs, and if they respond promptly and effectively to any questions or issues you have.
Conclusion
By exploring the main types of stainless steel in depth, it’s clear that stainless steel offers excellent overall performance and has a wide range of applications. This article aims to help you understand their characteristics and uses. Whether you are selecting materials, designing products, or choosing suppliers, this knowledge will be beneficial.
