300 Series Stainless Steel

304 stainless steel

304 stainless steel is a common material in stainless steel, with a density of 7.93 g/cm³, which is also called 18/8 stainless steel in the industry. High temperature resistant to 800℃, with good processing performance and high toughness, it is widely used in industry and furniture decoration industry and food and medical industry.

Common labeling methods on the market include 06Cr19Ni10 and SUS304, among which 06Cr19Ni10 generally means national standard production, 304 generally means ASTM standard production, and SUS 304 means Japanese standard production.

304 is a versatile stainless steel, which is widely used to make equipment and parts that require good overall performance (corrosion resistance and formability). In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 18% chromium and more than 8% nickel. 304 stainless steel is a grade of stainless steel produced in accordance with the American ASTM standard.

Name: 304 stainless steel/SUS304
Alias: SUS304, food grade stainless steel, food grade 304 stainless steel, 18/8
Features: corrosion resistance (not completely uncorrosive), good toughness
Semi-finished product status: hot-rolled plate, cold-drawn tube
Magnetism: weak magnetism, the magnetism will become stronger after cold working such as stretching/pressing (can be attracted by magnet)
National standard: GB/T 3280-2015

Physical properties

Tensile strength σb (MPa)≥515-1035
Conditional yield strength σ0.2 (MPa)≥205
Elongation δ5 (%)≥40
Hardness: ≤201HBW; ≤92HRB; ≤210HV
Density (20℃, g/cm³): 7.93
Melting point (℃): 1398~1454
Specific heat capacity (0~100℃, KJ·kg-1K-1): 0.50
Thermal conductivity (W·m-1·K-1): (100℃) 16.3, (500℃) 21.5
Linear expansion coefficient (10-6·K-1): (0~100℃) 17.2, (0~500℃) 18.4
Resistivity (20℃, 10-6Ω·m2/m): 0.73
Longitudinal elastic modulus (20℃, KN/mm2): 193

Product Standards:

For 304 stainless steel, the Ni element in its composition is very important, which directly determines the corrosion resistance and value of 304 stainless steel.

The most important elements in 304 are Ni and Cr, but they are not limited to these two elements. The specific requirements are stipulated by the product standards. The common judgment in the industry is that as long as the Ni content is greater than 8% and the Cr content is greater than 18%, it can be considered as 304 stainless steel. This is why the industry will call this type of stainless steel 18/8 stainless steel. In fact, the relevant product standards have very clear regulations on 304, and these product standards have some differences for different shapes of stainless steel.

To determine whether a material is 304 stainless steel, it must meet the requirements of each element in the product standard. As long as one does not meet the requirements, it cannot be called 304 stainless steel.

Scope of application

System description: 304 stainless steel is the most widely used chromium-nickel stainless steel. As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; it has good hot workability such as stamping and bending. , No heat treatment hardening phenomenon (use temperature -196℃～800℃).

It is resistant to corrosion in the atmosphere. If it is an industrial atmosphere or heavily polluted area, it needs to be cleaned in time to avoid corrosion. It is suitable for food processing, storage and transportation. Has good processing properties and weldability. Plate heat exchangers, bellows, household products (category 1, 2 tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs), auto parts (windshield wipers, mufflers, molded products), medical appliances, building materials, chemicals, food industry , Agriculture, ship parts, etc.

304 stainless steel is a nationally recognized food-grade stainless steel.

Most of the requirements for use are to maintain the original appearance of the building for a long time. When determining the type of stainless steel to be selected, the main considerations are the required aesthetic standards, the corrosiveness of the local atmosphere, and the cleaning system to be adopted.

However, other applications are increasingly seeking structural integrity or impermeability. For example, roofs and side walls of industrial buildings. In these applications, the owner’s construction cost may be more important than the aesthetics, and the surface may not be very clean. The effect of using 304 stainless steel in a dry indoor environment is quite good. However, if you want to maintain its appearance outdoors in the countryside and cities, you need to wash it frequently. In heavily polluted industrial areas and coastal areas, the surface will be very dirty and even rusty.

However, to obtain the aesthetic effect in the outdoor environment, nickel-containing stainless steel is required. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other construction purposes. However, 316 stainless steel is best used in severely corrosive industries or marine atmospheres.

With stainless steel sliding doors, people have fully realized the advantages of using stainless steel in structural applications. There are several design criteria that include 304 and 316 stainless steel. Because “duplex” stainless steel 2205 has integrated good atmospheric corrosion resistance with high tensile strength and elastic limit strength, this steel is also included in the European standards. Product shape In fact, stainless steel is manufactured in full-standard metal shapes and sizes, and there are many special shapes.

The most commonly used products are made of thin plates and strip steel, and medium and heavy plates are also used to produce special products, such as the production of hot-rolled structural steel and extruded structural steel. There are also round, oval, square, rectangular and hexagonal welded pipes or seamless steel pipes and other forms of products, including profiles, bars, wires and castings.

Product Standards

International stainless steel marking method

The American Iron and Steel Institute uses three digits to indicate various standard grades of forgeable stainless steel. in:

①Austenitic stainless steels are marked with 200 and 300 series numbers. For example, some common austenitic stainless steels are marked with 201, 304, 316 and 310.

②Ferritic and martensitic stainless steels are represented by numbers in the 400 series.

③Ferritic stainless steel is marked with 430 and 446, and martensitic stainless steel is marked with 410, 420 and 440C.

④ Duplex (austenite-ferrite), stainless steel, precipitation hardening stainless steel, and high alloys with iron content less than 50% are usually named by patent names or trademarks.

4). Standard classification and classification

4-1 Classification:

①National Standard GB
②Industry standard YB
③Local standards
④Enterprise standard Q/CB

4-2 Classification:

①Product standard
②Packaging standard
③Method standard
④Basic standards

4-3 Standard level (divided into three levels):

Y level: International advanced level
Level I: International general level
H level: domestic advanced level

4-4 National Standard:

GB1220-2007 Stainless Steel Bar (Grade I) GB4241-84 Stainless Steel Welded Disc (Grade H)
GB4356-2002 Stainless Steel Welded Panel (Grade I) GB1270-80 Stainless Steel Pipe (Grade I)
GB12771-2000 stainless steel welded pipe (Y grade) GB3280-2007 stainless steel cold plate (I grade)
GB4237-2007 stainless steel hot plate (level I) GB4239-91 stainless steel cold strip (level I)

processing methods

Etching

The etching process is to screen-print an acid-resistant protective film on the surface of stainless steel, and then etch with ferrous chloride liquid to form an artistic pattern.

Spray color

The color spray method is to spray pigment particles after screen printing to form a pear-like surface and form an artistic pattern.

crafting process

The process of the color spray art processing method of stainless steel products is: stainless steel products → silk screen → etching → alkali treatment → silk screen → oxidation coloring → alkali treatment → finished product.

The process of the etching art processing method of stainless steel products is: stainless steel products → silk screen → etching → alkali treatment → oxidation coloring → finished product.

The chemical coloring method of stainless steel does not use pigments and dyes. Instead, the stainless steel is soaked in a heated concentrated chromium sulfate solution for chemical coloring. It is characterized by good food resistance. The ink used in this processing method must have very strong acid resistance, and generally use UV vulcanized ink with special properties that is compatible with the treatment process.

Stamping

Stainless steel products, especially stainless steel strips, are often the most primitive processing method of the factory is to use a punch for stamping products. Stamping includes two methods: straight punching and stretching. Generally, the hardness lower than 1/2 is used for stretching and bending, and the hardness higher than 1/2 is harder, all of which are straight punching.

Cause of rust

The rust of 304 stainless steel may have the following reasons:

Chloride

Chloride ions are widespread, such as salt/sweat traces/sea water/sea breeze/soil and so on. Stainless steel corrodes quickly in the presence of chloride ions, even exceeding that of ordinary low-carbon steel. Therefore, there are requirements for the use environment of stainless steel, and it needs to be wiped frequently to remove dust and keep it clean and dry.

Solution treatment

The alloy elements are not dissolved into the matrix, resulting in low alloy content of the matrix structure and poor corrosion resistance.

Intergranular corrosion

This material without titanium and niobium has a tendency to intergranular corrosion. Adding titanium and niobium, together with stabilization treatment, can reduce intergranular corrosion. A high-alloy steel that can resist corrosion in the air or in chemical corrosive media. Stainless steel has a beautiful surface and good corrosion resistance. It does not need to undergo surface treatments such as plating, and exerts the inherent surface properties of stainless steel. It is used in many applications. A kind of steel, usually called stainless steel. High-alloy steels such as 13 chrome steel and 18-8 chrome-nickel steel represent performance.

From a metallographic point of view, because stainless steel contains chromium, a very thin chromium film is formed on the surface. This film isolates the oxygen from the intrusion of the steel and acts as a corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 12% chromium. Used in occasions where welding is required. The lower carbon content minimizes the precipitation of carbides in the heat-affected zone near the weld, and the precipitation of carbides may cause stainless steel to produce intergranular corrosion (welding erosion) in certain environments.

Surface mark phenomenon

The phenomenon of surface marks refers to the occurrence of wire-mounted or dot-shaped dent marks on the surface of 304 stainless steel after deep processing or grinding of processed products.

Reason: There are foreign bodies on the surface and the surface of the mold, and there are scars on the surface of the edge holder.

Countermeasures: Remove foreign bodies and scars before processing, and you can also remove orange peel by adequate grinding.

Orange peel phenomenon refers to the phenomenon that the surface of 304 stainless steel molded products has a shape like orange peel under grinding or other conditions.

Reason: Insufficient grinding, the larger the processing, the more serious the orange peel, the coarser grains of the raw materials, and the softening of heat treatment.

Countermeasures: Fully grind deep-processed products, select suitable heat treatment conditions, and control the grain size of raw materials.

 

301 (Stainless steel band grade)

301 is a stainless steel strip grade Cr17Ni7. Tensile strength ≥520.

Composition analysis:

Cr17Ni7.
C: ≤0.15,
Si ：≤1.0,
Mn: ≤2.0,
Cr: 16.0～18.0,
Ni: 6.0-8.0,
S: ≤0.03,
P: ≤0.045

Basic performance

301 stainless steel yield strength (N/mm2) ≥205
Tensile strength ≥520
Elongation (%) ≥40
Hardness HB ≤187 HRB≤90 HV ≤200
Density 7.93 g cm-3
Specific heat c(20℃)0.502 J·(g·C)-1
Thermal conductivity λ/W(m·℃)-1 (at the following temperature/℃)
20 100 500
12.1 16.3 21.4
Linear expansion coefficient α/(10-6/℃) (between the following temperatures/℃):
20～100 20～200 20～300 20～400
16.0 16.8 17.5 18.1
Resistivity: 0.73 Ω·mm2·m-1
Melting point: 1398～1420℃

●Mechanical properties:

Tensile strength σb (MPa): ≥520
Conditional yield strength σ0.2 (MPa): ≥205
Elongation δ5 (%): ≥40
Reduction of area ψ (%): ≥60
Hardness: ≤187HB; ≤90HRB; ≤200HV

● Heat treatment specification and metallographic structure:

Heat treatment specification:

solid solution 1010～1150℃ and fast cooling.

Metallographic structure:

The structure is characterized by austenite type.

A high-alloy steel that can resist corrosion in the air or in chemical corrosive media. Stainless steel has a beautiful surface and good corrosion resistance. It does not need to undergo surface treatments such as plating, and exerts the inherent surface properties of stainless steel. It is used in many applications. A kind of steel, usually called stainless steel. High-alloy steels such as 13 chrome steel and 18-8 chrome-nickel steel represent performance.

From a metallographic point of view, because stainless steel contains chromium, a very thin chromium film is formed on the surface. This film isolates the oxygen from the intrusion of the steel and acts as a corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 12% chromium. 304 is a versatile stainless steel, which is widely used to make equipment and parts that require good overall performance (corrosion resistance and formability).

304 stainless steel is a grade of stainless steel produced in accordance with the American ASTM standard. 304 is equivalent to our country’s 0Cr19Ni9 (0Cr18Ni9) stainless steel. 304 contains 17% chromium and 7% nickel. 301 is the most widely used stainless steel and heat-resistant steel. Used in food production equipment, Xitong chemical equipment, nuclear energy, etc.

301 (17Cr-7Ni-carbon) material: Compared with 304 steel, the content of Cr and Ni is less, the tensile strength and hardness are increased during cold working, and it is non-magnetic, but it is magnetic after cold working.

Uses:

trains, aircraft, conveyor belts, vehicles, bolts, springs, screens.

Remarks:

L stands for low carbon, such as 304L has a lower carbon content than 304. H and S stand for high temperature resistance. For example, 310S is more resistant to high temperatures than 310, and 304H is more resistant to heat than 304.

 

321 stainless steel

321 stainless steel is a material with excellent high-temperature stress rupture (Stress Rupture) performance and high-temperature creep resistance (Creep Resistance) stress mechanical properties are better than 304 stainless steel.

Stainless steel

A material of stainless steel. The details are as follows:
321 Chemical composition: carbon: 0.08 silicon: 1.00 manganese: 2.00 phosphorus: 0.045 sulfur: 0.030 nickel: 9.00-12.00 chromium: 17.00-19.00 titanium: 5C-0.70

German brand:

X10CrNiTi189

Austenitic stainless steel is equivalent to domestic grade 0Cr18Ni10Ti 　321 stainless steel is Ni-Cr-Mo austenitic stainless steel, its performance is very similar to 304, but due to the addition of metallic titanium, it has better resistance to intergranular corrosion and High temperature strength. Due to the addition of titanium, it effectively controls the formation of chromium carbide.

321 austenitic stainless steel has good corrosion resistance in the atmosphere and is widely used in petrochemical, electric power, bridge and automobile industries [1]. However, the “stainlessness” of stainless steel is not absolute. Due to the special service environment, stainless steel will also corrode. Factors such as medium concentration, pH value, and temperature will have a greater impact on the corrosion resistance of stainless steel.

For example, if used for a long time within the sensitization temperature range of 450~850℃, stainless steel will undergo intergranular corrosion. The mechanism is that C combines with Cr at the grain boundary to form Cr23C6 and precipitate, which reduces the Cr content at the grain boundary. This is the so-called “chromium depletion”. The Cr element is one of the main elements that inhibit intergranular corrosion. When the Cr content at the grain boundary is less than 12%, the probability of intergranular corrosion will increase.

Industry application:

It is used in the field machines in the chemical, coal, and petroleum industries that require high resistance to grain boundary corrosion, heat-resistant parts of building materials, and parts that have difficulty in heat treatment.

1. Petroleum waste gas combustion pipeline
2. Engine exhaust pipe
3. Boiler shell, heat exchanger, heating furnace parts
4. Silencer parts for diesel engines
5. Boiler pressure vessel
6. Chemical Transport Truck
7. Expansion joint
8. Spiral welded pipes for furnace pipes and dryers

316L

316L is a grade of stainless steel material, AISI 316L is the corresponding American grade, and sus 316L is the corresponding Japanese grade. The unified digital code in my country is S31603, the standard brand is 022Cr17Ni12Mo2 (new standard), and the old brand is 00Cr17Ni14Mo2, which means that it mainly contains Cr, Ni, and Mo, and the number indicates the approximate percentage. The national standard is GB/T 20878-2007 (current edition).

chemical composition

Carbon C: ≤0.030
Silicon Si: ≤1.00
Manganese Mn: ≤2.00
Sulfur S: ≤0.030
Phosphorus P: ≤0.045
Chromium Cr: 16.00～18.00
Nickel Ni: 10.00～14.00
Molybdenum Mo: 2.00～3.00

Corrosion resistance

316L is widely used in the chemical industry due to its excellent corrosion resistance. 316L is also a derivative steel of 18-8 type austenitic stainless steel, with 2 to 3% Mo element added. On the basis of 316L, many steel grades are also derived. For example, 316Ti is derived from adding a small amount of Ti, 316N is derived from adding a small amount of N, and 317L is derived from increasing the content of Ni and Mo.

Most of the existing 316L on the market is produced in accordance with American standards. For cost considerations, steel mills generally keep the Ni content of their products as low as possible. The American standard stipulates that the Ni content of 316L is 10-14%, and the Japanese standard stipulates that the Ni content of 316L is 12-15%. According to the minimum standard, there is a 2% difference in Ni content between the American standard and the Japanese standard, which is still quite huge in terms of price. Therefore, customers still need to see clearly when purchasing 316L products, whether the product is based on ASTM or JIS standards.
The Mo content of 316L makes the steel have excellent resistance to pitting corrosion and can be safely used in environments containing halogen ions such as Cl-. Because 316L is mainly used for its chemical properties, steel mills have slightly lower requirements for surface inspection of 316L (relative to 304). Customers with higher requirements on the surface should strengthen the surface inspection.

Mechanical properties

Tensile strength σb (MPa): ≥480
Conditional yield strength σ0.2 (MPa): ≥177
Elongation δ5 (%): ≥40
Reduction of area ψ (%): ≥60
Hardness: ≤187HB; ≤90HRB; ≤200HV
Density: 7.98g/cm3;
Specific heat ratio (20℃): 0.502J/(g*K)
Thermal conductivity (W/(m*K))
100℃ 300℃ 500℃
15.1 18.4 20.9

Heat treatment

Solid solution 1010～1150℃ and fast cooling.

Microstructure

The structure is characterized by austenitic stainless steel.

Distinction

The two most commonly used stainless steels 304 and 316 (or 1.4308 and 1.4408 corresponding to German/European standards). The main difference in chemical composition between 316 and 304 is that 316 contains Mo, and it is generally recognized that 316 has better corrosion resistance. It is more corrosion resistant than 304 in high temperature environment. Therefore, in high-temperature environments, engineers generally choose 316 material components. But the so-called nothing is absolute, in a concentrated sulfuric acid environment, no matter how high the temperature is, don’t use 316. Otherwise, this matter can be a big problem.

Anyone who learns machinery has learned threads, and remember that in order to prevent the threads from being seized at high temperatures, you need to apply a dark solid lubricant: molybdenum disulfide (MoS2), from which two conclusions can be drawn:

One: Mo is indeed a high-temperature resistant substance (do you know what crucible is used to melt gold? Molybdenum crucible!).

Two: Molybdenum easily reacts with high-valent sulfide ions to form sulfides.

Therefore, no stainless steel is super invincible and corrosion-resistant. After all, stainless steel is a piece of steel with more impurities (but these impurities are more resistant to corrosion than steel). It is steel that can react with other substances.