There Is Also Stainless "iron"? How Much Do You Know about Stainless Steel？

The stainless steel knowledge crash course is now open! Everyone knows stainless steel, but how much do you know about it? The following is a detailed introduction to the categories, characteristics and uses of stainless steel, so that all screw friends can quickly absorb stainless steel knowledge.

Classification of stainless steel

"Stainless steel iron" that can be absorbed and stainless steel that cannot be absorbed

Stainless steel can be roughly divided into three categories: 200 series, 300 series and 400 series. Among them, the 300 series is the most commonly used. The 200 series and 400 series are substitutes for the 300 series to a certain extent. Strictly speaking, the 400 series is not called stainless steel, but stainless iron, because it does not contain nickel, so it can be attracted by magnets. The 200 series and 300 series have nickel, are not magnetic, and cannot be attracted by magnets.

304 is the most common variety in the 300 series, so the price trend of the entire stainless steel can generally be judged from the price changes of 304. The 200 series contains less nickel, the 400 series contains no nickel, and the 300 series contains the most nickel, so the 300 series is the most affected by the nickel price.

The 300 series can be simply divided into 304, 304L, 316, 316L, 321, 309S, 310S, etc. The basis for distinction is the different contents of various metal elements. The characteristics of stainless steel with different contents are also different. The difference between 304 and 304L lies in the different carbon (C) content. The one with L means low carbon content, also called low carbon. The difference between 316 and 316L is the same.

The form of stainless steel

Stainless steel can be divided into five categories: coils, plates, profiles, steel pipes and parts. The most important ones are coils and plates. Profiles are various types of materials made of plates, including angle steel, flat steel, I-beams, and channel steel. Steel pipes mainly refer to seamless steel pipes. The opposite of seamless steel pipes is welded pipes. The difference lies in whether they are formed in one go. Parts mainly refer to elbows, flanges and other small things.

Coils and plates are actually the same, but they are shipped in different forms. Coils are shipped in rolls, while plates are shipped one by one. If they are shipped in the form of plates, they are also called original plates, which are usually thick plates. If they are very thick, they cannot be rolled. Generally, they cannot be rolled if they are thicker than 16 mm.

The prices of coils and plates are also different. If you purchase coils, they are calculated based on actual weight, so the price is high. Plates are calculated based on theory, so the price is low. For example, a 10mm thick plate may actually be 9.6mm, so there will be a price difference.

Stainless steel plates are divided into hot rolling and cold rolling according to the different rolling processes of the rolling mill (rolling mill is the name of the machine that rolls the plate). Hot rolling is usually marked ; cold rolling is marked as 2B or BA (BA has a better and brighter surface than 2B, close to a mirror. The best is the mirror surface. The mirror surface is not available in stock and needs to be processed). For example, 304 is often purchased plate, which means that the coil must be flattened into a plate by machine. This machine is a flattening machine.

The steel plate can be cut into different lengths by a flattening machine. If it is not a regular length, it is called a fixed length, which means a fixed length. Because customers often put forward different length requirements according to actual needs, the coil becomes important at this time, and the conventional plate cannot meet the requirements.

The domestic cold-rolled steel plate is generally below 3 mm, and the hot-rolled steel plate is generally above 3 mm. The 3 mm thickness is both hot-rolled and cold-rolled, but the imported cold-rolled steel plate can reach a thickness of 4 mm or even below 6 mm. The hot-rolled steel plate of 3 mm to 12 mm is called a medium plate, and the steel plate above 12 mm is called a thick plate, which can be thicker than 120 mm and is called a hot-rolled medium and thick plate, while the cold-rolled steel plate is a cold-rolled thin plate.

Calculation of the theoretical weight of stainless steel plate

Steel weight = specific gravity × thickness (mm) × width (m) × length (m)

In the field of engineering machinery, due to the emphasis on precision dimensions, the world uses millimeters as units, 1000 mm = 1 meter, 1 mm = 100 wires.

The weight obtained by this formula is kilograms (KG), which must be accurate to two decimal places. Because stainless steel is expensive and the transaction volume is large, the numbers after the decimal point are very important, so the money must also be accurate to two decimal places.

Specific gravity of stainless steel (KG)

Different stainless steels have different specific gravity:

• -400 series specific gravity is 7.75

• -304, 321, 304N, 201, 202, 304L, 301 specific gravity is 7.93

• -310S, 309S, 316, 316L specific gravity is 7.98

  
  

Stainless steel number comparison table

Countries around the world have different names for stainless steel. The ones commonly encountered in the market are China and the United States, called national standards and American standards. The 200 series, 300 series, and 400 series mentioned above are American standards.

National standard ============ American Standard 

1cr17mn6ni5n========201 

1cr18mn8ni5n========202 

0cr18ni9============304 

00cr19ni10==========304L 

0cr18ni12mo2t=======316Ti 

00cr17ni14mo2=======316L 

0cr17ni12mo2========316 

1cr18ni9ti==========321 

0cr18ni10ti=========321 

0cr23ni1 3===========309S

1cr20ni14============309S

0cr25ni20============310S

1cr25ni20============310s

0cr13===============405

1cr13===============410

2cr13===============420

3cr13===============420

4cr3================430

The element content in the national standard generally refers to the middle value of the content, which is a theoretical value and can be large or small.

What is tolerance?

This is a very important term. Tolerance is the generally accepted length or thickness deviation. Because in the production process of the plate, for various reasons, the actual thickness often cannot reach the theoretical thickness. For example, a 6 mm plate is only 5.6 mm. This is the tolerance. In China, the tolerance is often a negative tolerance. Of course, there is also a positive tolerance, but it is rare.

When buying and selling plates, it is usually calculated according to the theoretical thickness. This is why the theoretical price is lower than the weighing price. Tolerances also have different sizes and prices. The price of large tolerances is cheap. For example, if the 6 mm plate is less than 5.5, it is a large tolerance.

Characteristics and uses of main stainless steel types

• As a widely used steel, 304 has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, good hot processing properties such as stamping and bending, no heat treatment hardening phenomenon, no magnetism, and an operating temperature of minus 193 degrees to plus 800 degrees.

Applications: tableware, kitchenware, water heaters, boilers, auto parts, medical equipment, food machinery, wine storage utensils, pressure vessels (chemical machinery, chemical equipment).

• 304L is a low-carbon 304 steel. Under normal conditions, its corrosion resistance is similar to that of 304, but after welding and stress relief, it has good resistance to intergranular corrosion. It can also maintain good corrosion resistance without heat treatment and is generally used at 400 degrees.

Applications: petrochemical industry, building materials.

• 321 adds Ti element to 304 steel to prevent intergranular corrosion. It is suitable for temperatures below 430 to 900 degrees and is non-magnetic.

Applications: automotive exhaust, heat exchangers, containers and other products that are not heat treated after welding. Due to the addition of Ti element, they are not suitable for making food processing equipment.

• 316 is low-carbon and has MO element added, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength are particularly good. It can be used under harsh conditions and is suitable for use below 900 degrees. It is non-magnetic.

Application: Equipment used in seawater, production equipment for chemicals, dyes, papermaking, acetic acid, fertilizers, etc., food industry and coastal facilities, products with special requirements for resistance to intergranular corrosion.

• 309S/310S are two materials with relatively high nickel and chromium content, and the content of Si is increased, making them resistant to high temperatures and corrosion. Among them, 309S can withstand repeated heating below 980 degrees, and the use temperature of 310S reaches 1200 degrees, and the continuous use temperature can be 1150 degrees, and it is non-magnetic.

Application: Suitable for key parts such as high-temperature electric furnace equipment, drying equipment, furnace materials, aviation, petrochemicals, electricity, etc.

• 200 series is similar to 304 and is cheap and economical.

Application: Food processing utensils, kitchen equipment, food processing equipment, filters, milk cans, durable consumer goods, washing machine accessories, water heaters, steel furniture, building decoration, decoration.

In terms of fatigue resistance, 201 has a higher hardness and is not as tough as 304, but 304 has better fatigue resistance.