Stainless steel has different types and grades, which can divide into five main categories:
- Austenitic stainless steel
- Ferritic stainless steel
- Martensitic stainless steel
- ·Duplex stainless steel
- Precipitation-hardening stainless steel
Most of the furniture is made of austenitic stainless steel, which has good weldability, flexibility, and ease of forming helps it adapt well to the production requirements of furniture. Moreover, austenitic stainless steel is corrosion-resistant and keeps stable performance for long-term furniture use.
In this article, we will compare different austenitic stainless steel grades and advise how to choose the best one for furniture use.
Austenitic stainless steel
Austenitic stainless steel is mainly divided into 200 series and 300 series.
200 Series Austenitic stainless steel
200 series austenitic stainless steel are known as chromium-nickel-manganese alloys, made of chromium, manganese, nitrogen, and low nickel.
Nickel is one of the most commonly used elements in the structure of austenitic stainless steel. After World War II, nickel was short in resources and expensive. Austenitic stainless steel replaced nickel with low-cost manganese and nitrogen for a better solution, reducing the nickel content to make a new type of stainless steel – 200 series stainless steel. More production with lower cost.
The 200 series austenitic stainless steel used in furniture production can be divided into three main grades: SS 201, SS 202, and SS 205; SS 201 is the most popular. Their main chemical composition is as follows:
| AISI Grade | Carbon (C) | Chromium(Cr) | Nickel(Ni) | Manganese(Mn) | Nitrogen(N) | Molybdenum(Mo) |
| 201 | ≤0.15 | 16.0-18.0 | 3.5-5.5 | 5.5-7.5 | ≤0.25. | – |
| 202 | ≤0.15 | 17.0-19.0 | 4.0-6.0 | 7.5-10.0 | ≤0.25 | – |
| 205 | ≤0.15 | 16.5-18.0 | 1.0-1.75 | 14.0-15.5 | 0.32-0.40 | – |
- 200 series stainless steel is highly cost-effective. Since 2005, it has seen a jump in sales and widespread use in Asian countries (especially India).
- 200 series stainless steel performs well in mild environments, with high impact resistance and toughness.
- Due to the low amount of nickel, the percentage of chromium in the 200 series has also been adjusted downward. Whereas chromium is the most important component of stainless steel for corrosion resistance, the low chromium content makes the 200 series slightly less corrosion-resistant.
300 series austenitic stainless steel
The 300 series austenitic stainless steel, known as chromium-nickel alloys, are the highest-selling and most widely used series of austenitic stainless steels.
Mainly used in furniture production can be divided into five grades: SS302, SS303, SS304, SS316, and SS317 grades. Their main chemical composition is as follows:
| AISI Grade | Carbon (C) | Chromium(Cr) | Nickel(Ni) | Manganese(Mn) | Nitrogen(N) | Molybdenum(Mo) |
| 301 | ≤0.15 | 16.0-18.0 | 6.0-8.0 | ≤2.0 | ≤0.1 | – |
| 302 | ≤0.15 | 17.0-19.0 | 8.0-10.0 | ≤2.0 | ≤0.1 | – |
| 303 | ≤0.15 | 17.0-19.0 | 8.0-10.0 | ≤2.0 | – | – |
| 304 | ≤0.08 | 18.0-20.0 | 8.0-11.0 | ≤2.0 | – | – |
| 304L | ≤0.03 | 18.0-20.0 | 8.0-11.0 | ≤2.0 | – | – |
| 316 | ≤0.08 | 16.0-18.0 | 10.0-14.0 | ≤2.0 | – | 2.0-3.0 |
| 316L | ≤0.03 | 16.0-18.0 | 10.0-14.0 | ≤2.0 | – | 2.0-3.0 |
| 317 | ≤0.08 | 18.0-20.0 | 11.0-15.0 | ≤2.0 | ≤0.1 | 3.0-4.0 |
- The most characteristic feature of the 300 series is its high chromium content, which provides excellent corrosion resistance. The most classic ratio is 18/8 of stainless steel 304 (18% chromium, 8% nickel), which is widely used in commerce.
- It is highly weldable, highly ductile, strong, and durable. Its good strength keeps it without deformation at high & sub-zero temperatures.
- As the 300 series contains more nickel, making it is more costly.
Stainless steel 201 VS 304 VS 316
SS201, SS304, and SS316 are the stars of austenitic stainless steel, and more than 95% of stainless steel furniture is made from these three stainless steel. We will compare these three types of stainless steel from furniture material selection.
Corrosion resistance
Furniture is a long-time-use product, and its corrosion resistance greatly impacts its useful life. The secret of stainless steel corrosion resistance is its composition of chromium.
Chromium reacts with water and oxygen in the air to form a layer of chromium oxide on the stainless steel surface, to protect stainless steel from corrosion. The higher the chromium content, the stronger the corrosion resistance.
The 18% chromium of austenitic stainless steel is incompatible with the relatively low content of nickel(6%~8%) in 200 series stainless steel, so SS 201 reduces the chromium content to 15% to 16% or even lower, which leads to SS201 weak in corrosion resistance.
The average chromium content of stainless steel 304 and 316 is 18%, which is higher corrosion resistance than SS 201. Moreover, SS316 added additional 2%~3% molybdenum to enhance its corrosion resistance and make it more resistant, to withstand high temperature and high salt environments, chlorides, and other chemical conditions.
Therefore, in terms of corrosion resistance of furniture, SS316 > SS 304 > SS201
Mechanical Properties
Good physical and mechanical properties are not only good for furniture production but also helpful for long-term use. The following data are the physical and mechanical properties of SS201, SS304, and SS 316:
| AISI Grade | Tensile Strength, KSI | Yield Strength, KSI | Hardness, HB |
| 201 | 30 | 95 | 100 |
| 304 | 30 | 75 | 95 |
| 316 | 45 | 75 | 95 |
Nitrogen helps SS 201 increase its yield and tensile strength, providing excellent impact resistance and toughness, making it harder and stronger than SS 304 and SS 316.
Therefore, in terms of physical and mechanical properties, SS201 > SS304 > SS316.
Note: some furniture styles need to be bent to a special angle, but SS201 is too hard and slightly less ductile; SS304/SS 316 will be better for this situation.
Cost
The cost of raw materials is very important for the furniture budget. 300 series stainless steel is relatively costly due to its higher nickel content, generally speaking, the cost of SS 304 is nearly 1/3 to 1/2 higher than SS 201 (prices fluctuate according to market conditions). And the SS 316 is more expensive than SS 304 as it adds additional molybdenum.
Therefore, in terms of the cost of materials, SS316 > SS 304 > SS201
How to choose the best stainless steel for furniture?
Right-grade use in the right place is helpful for stainless steel’s long-term use.
Indoor use:
- Regular room temperature, low corrosion environment, SS 201 for indoor furniture is ok.
- If the location belongs to the seaside city (more than 10 km from the sea), recommended SS304 for indoor furniture.
- If the location belongs to a chemical environment, such as rich in chloride, acidic, etc., recommended SS316 for indoor furniture.
Outdoor use:
- Regular outdoor environment & temperature (not close to the sea, no chemical environment, such as chlorides, acidic, etc.), SS 304 for outdoor furniture is ok.
- If located in the coastal area (5 ~ 10 km from the sea), in high-temperature & rainy areas, or belonging to a chemical environment, such as chlorine/acid, etc., recommended SS 316 is for outdoor furniture
- If located near the coast (≤ 5 km), recommended choosing SS 316 / SS317 for outdoor furniture. If the stainless steel is polished finished, SS 317 or higher grade duplex 2205 grade is recommended.
Source:
https://matmatch.com/learn/material/austenitic-stainless-steel https://www.essentracomponents.com/en-us/news/guides/understanding-stainless-steel-grades
