There are many materials for stainless steel pipes, such as
304, 304L,
316, 321, 310S, etc.In the stainless steel industry, 304 stainless steel pipe and 321 stainless steel pipe are two common materials. They both belong to the 300 series austenitic stainless steel, which have good corrosion resistance and a wide range of applications. However, due to slight differences in composition, they have certain differences in performance and use. This article will explore in detail the main differences between 304 stainless steel pipe and 321 stainless steel pipe, as well as their respective application scenarios.
1. Chemical composition comparison
The main chemical compositions of 304 stainless steel pipe and 321 stainless steel pipe are as follows:
|
Element
|
304 Stainless Steel Pipe
|
321 Stainless Steel Pipe
|
|
Carbon (C)
|
≤0.08%
|
≤0.08%
|
|
Silicon (Si)
|
≤1.00%
|
≤1.00%
|
|
Manganese (Mn)
|
≤2.00%
|
≤2.00%
|
|
Phosphorus (P)
|
≤0.045%
|
≤0.045%
|
|
Sulfur (S)
|
≤0.03%
|
≤0.03%
|
|
Chromium (Cr)
|
18.0-20.0%
|
17.0-19.0%
|
|
Nickel (Ni)
|
8.0-10.5%
|
9.0-12.0%
|
|
Titanium (Ti)
|
-
|
≥5×C%
|
|
304 VS. 321
|
304 Stainless Steel
|
321 Stainless Steel
|
|
Features
|
Corrosion resistance, good toughness
|
Abrasion resistance, high temperature resistance, creep resistance
|
|
Grade
|
0Cr18Ni9 (0Cr19Ni9), 06Cr19Ni9, S30408
|
X10CrNiTi189, 321, S32100, TP321, SUS321
|
|
Chemical Composition
|
C: ≤0.08, Si: ≤1.0, Mn: ≤2.0, Cr: 18.0-20.0, Ni: 8.0-10.5, S: ≤0.03, P: ≤0.035, N≤0.1
|
S: ≤0.030, Ni: 9.00-12.00, Cr: 17.00-19.00, Ti: 5C-0.70
|
|
Tensile Strength (MPa)
|
520
|
≥520
|
|
Conditional Yield Strength (MPa)
|
205-210
|
≥205
|
|
Elongation (%)
|
40%
|
≥40%
|
|
Hardness
|
HB187, HRB90, HV200
|
≤187HB; ≤90HRB; ≤200HV
|
|
Density
|
7.93 g/cm³
|
7.93 g/cm³
|
|
Theoretical Weight
|
Weight (kg) = thickness (mm) * width (m) * length (m) * density value
|
Weight (kg) = thickness (mm) * width (m) * length (m) * density value
|
|
Uses
|
Tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs, auto parts, medical appliances, building materials, chemicals, food industry, agriculture, and ship parts.
|
Outdoor machines for the chemical, coal, and petroleum industries.
|
Main differences:
Addition of titanium: 321 stainless steel pipe adds titanium (Ti) on the basis of 304, and its content is generally 5 times the carbon content (minimum 0.2%). The addition of titanium can improve the resistance of stainless steel to intergranular corrosion in high temperature environments and prevent welding sensitization.
Chromium and nickel content: 304 stainless steel has a slightly higher chromium content, while 321 stainless steel has a slightly higher nickel content, which makes their corrosion resistance in specific environments different.
The appearance and physical properties of 304 and 321 stainless steel are very similar, except for the slight difference in chemical composition:
1) 321 stainless steel requires trace amounts of titanium (Ti) (according to the ASTM A182-2008 standard, the Ti content should not be less than 5 times the carbon (C) content, but not more than 0.7%, another note, 304 and 321 The carbon (C) content is 0.08%, and 304 does not contain titanium (Ti).
2) the requirements for nickel (Ni) content are slightly different. 304 is between 8% and 11%, while 321 is between 9% and 12%.
3) the requirements for chromium (Cr) content are different. 304 is between 18% and 20%, while 321 is between 17% and 19%.
So you can use metal material analyzer or chemical analysis method to verify the composition of these two materials and make judgments.
2. Corrosion resistance comparison
Due to its high chromium content, 304 stainless steel pipe can form a dense oxide film with good corrosion resistance and is suitable for most environments.
However, in high temperature environments (427°C~816°C), 304 stainless steel is prone to intergranular corrosion, that is, chromium carbide precipitation, resulting in a decrease in the corrosion resistance of the material. 321 stainless steel, due to the addition of titanium, can effectively inhibit intergranular corrosion and is suitable for applications in high temperature environments, such as boiler pipes and heat exchange equipment.
3. High temperature resistance comparison
The heat resistance temperature of 304 stainless steel is generally below 800°F (427°C). Chromium carbide precipitation will occur at higher temperatures, resulting in material corrosion failure.
321 stainless steel can work for a long time in an environment of **800°F1500°F (427°C816°C)** due to the presence of titanium, and is suitable for high-temperature structural parts or occasions where annealing cannot be performed after welding.
4. Comparison of mechanical properties
At room temperature, the mechanical properties of 304 and 321 stainless steel are not much different. However, in high temperature environments, 321 stainless steel exhibits better creep resistance and stress fracture resistance, which makes it more reliable in high temperature and pressure environments.
5. Comparison of welding properties
304 stainless steel may produce intergranular corrosion after welding, especially in high temperature environments, where the weld area is susceptible to corrosion damage. However, due to the stabilizing effect of titanium, the corrosion resistance of the weld of 321 stainless steel is stronger, so it is more suitable for high temperature welding structures.
6. Comparison of application fields
Main applications of 304 stainless steel pipes:
Food processing equipment (such as dairy equipment, brewing equipment)
Medical equipment
Handrails, stainless steel decorative materials
Chemical equipment (low temperature and normal temperature environment)
Nuclear energy equipment
Main applications of 321 stainless steel pipes:
High temperature boiler pipes
Heat exchangers
Aerospace industry
Automobile exhaust systems
Petrochemical equipment
High temperature steam pipes
7. Price and economy
Because 321 stainless steel pipes have titanium added to their composition and have better high temperature resistance, their production cost is higher than that of 304 stainless steel pipes, and their market price is relatively expensive. If used in ordinary environments, 304 stainless steel pipes are more cost-effective, while for high temperature, high pressure, and corrosion resistance, 321 stainless steel pipes are a better choice.
8. Conclusion
304 stainless steel pipes are the most widely used stainless steel materials, with good corrosion resistance, mechanical properties and processing properties, suitable for food, chemical and decoration fields.
321 stainless steel pipe adds titanium to 304, making it more resistant to high temperature and intergranular corrosion, and is particularly suitable for high-temperature environments such as boilers, heat exchangers, and aerospace.
The choice of stainless steel pipe depends on the specific application scenario: if the ambient temperature is low and the corrosion resistance requirement is high, 304 can be selected; if it involves a high-temperature environment or long-term high-temperature pressure, 321 stainless steel pipe is recommended.
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