I. Introduction to 321 Stainless Steel
321 stainless steel is a Ni-Cr-Ti austenitic stainless steel used in the manufacture of acid-resistant containers and wear-resistant equipment linings and piping.
- Japanese degree: SUS321
- UK Grade: 304S12, 321920
- German grade: X10CrNiTi189
- Also known as: Austenitic Stainless Steel
- Features: Wear resistance, high temperature resistance, creep resistance
- Applications: Industrial applications with high requirements for resistance to intergranular corrosion.
321 stainless steel is created by adding a titanium element to the base composition of 304 stainless steel. Its performance is very similar to that of 304 stainless steel.
The addition of titanium results in exceptional resistance to acid and alkaline corrosion. Even a small amount of titanium (about 1%) added to stainless steel can significantly increase its resistance to rust.
Austenitic stainless steel is prone to sensitization when exposed to temperatures between 450℃ and 850℃.
During sensitization, carbides, mainly chromium carbide (C23C6), precipitate along grains and at double boundaries, which results in damage to neighboring alloy elements. This leads to intergranular corrosion in specific corrosive environments.
321 stainless steel is able to withstand the formation of chromium carbide between 426℃ and 815℃ due to the addition of titanium as a stabilizing element. As a result, it exhibits better resistance to intergranular corrosion, high temperature performance, and greater resistance to creep and stress fractures than 304 and 304L.
In addition, 321 also has excellent low temperature toughness, formability and welding properties. Does not require annealing after welding.
The characteristic of 321 stainless steel is the presence of Ti as a stabilizing element.
However, it is also a heat-resistant variety of steel with a much better high-temperature appearance compared to 316L.
At different concentrations and temperatures of organic and inorganic acids, especially in oxidizing media, 321 stainless steel shows excellent resistance to wear and corrosion. It is used in the manufacture of wear-resistant acid containers, linings and piping.
321 stainless steel is a type of Ni-Cr-Ti austenitic stainless steel. Its performance is very similar to 304, but the addition of titanium metal provides better resistance to intergranular corrosion and high temperature resistance. The addition of titanium effectively controls the formation of chromium carbide.
321 stainless steel has excellent high-temperature stress rupture and high-temperature creep resistance. Its tensile mechanical properties are superior to those of 304 stainless steel.
II. 321 stainless steel composition
| Standard | GB/T20878 | ASTM A276 | JIS G4303 | DIN EN10088-3 |
| Note | 06Cr18Ni11Ti（0Cr18Ni10Ti） | S32100321 | SUS 321 | X6CrNiTi18-101.4541 |
| W | ≤0.08 | ≤0.08 | ≤0.08 | 0.08 |
| Yes | 1.00 | 1.00 | ≤1.00 | 1.00 |
| Mn | ≤2.00 | ≤2.00 | 2:00 | ≤2.00 |
| P | 0.045 | 0.045 | 0.045 | 0.045 |
| s | ≤0.030 | ≤0.030 | ≤0.030 | 0.030 |
| No | 9:00 ~ 12:00 | 9:00 ~ 12:00 | 9:00~13:00 | 9:00 ~ 12:00 |
| Cr | 17.0~19.0 | 17.0~19.0 | 17.0~19.0 | 17.0~19.0 |
| You | 5C~0.70 | 5（C+N）~0.70 | >5×C% | 5×C~0.70 |
III. 321 Stainless Steel Physical Property
| Density (g/ cm3 ) 20℃ |
8.03 | |
| Melting point (℃) | 1398~1427 | |
| Specific thermal capacity (kJ/(kgK)) 0~100 ℃ |
0.50 | |
| Thermal conductivity (W/(mK)) |
100°C | 16.3 |
| 500°C | 22.2 | |
| Linear expansion coefficient (10 -6 /K) |
0~100°C | 16.6 |
| 0~500°C | 18.6 | |
| Resistivity ( Ωmm2 /m) 20 ℃ |
0.72 | |
| Longitudinal modulus of elasticity (kN/ mm2 ) 20 ℃ |
193 | |
| Magnetic | Slightly magnetic after cold deformation | |
Mechanical properties
- Tensile strength (σb) (MPa): ≥520
- Yield strength (σ0.2) (MPa): ≥205
- Elongation (δs) (%): ≥40
- Area Reduction (ψ) (%): ≥50
- Hardness: ≤187HB; ≤90HRB; ≤200HV
4. Applications of 321 stainless steel
The addition of titanium to 321 stainless steel increases its suitability for high temperature applications, making it a better choice than 304 stainless steel, which can undergo sensitization reactions, and 304L stainless steel, which may not have sufficient resistance to high temperatures.
Common uses for 321 stainless steel plates and tubes include thermal expansion joints, corrugated tubes, components for aircraft exhaust systems, coatings for heating elements, furnace body components, and heat exchangers.
Furthermore, it can be used in areas where high resistance to anti-grain corrosion is required, such as in the chemical, coal and petroleum industries, for outdoor machinery exposed to the elements, heat-resistant building materials and parts that are difficult to treat. thermal, such as:
- Petroleum waste gas combustion pipes
- Engine exhaust pipes
- Boiler casings, heat exchangers, heating furnace components
- Silent components for diesel engines
- Boiler Pressure Vessels
- Chemical transport vehicles
- Expansion joints
- Spiral welded tubes for furnace and dryer piping
V. 321 Stainless Steel Tolerances
Dimensions and allowable deviations of stainless steel 321.
| Degree of Deviation | Permissible Deviation from Standard Outside Diameter |
| D1 | ±1.5%, with a minimum of ±0.75 mm. |
| D2 | ±1.0%, with a minimum of ±0.5 mm. |
| D3 | ±0.75%, with a minimum of ±0.30 mm. |
| D4 | ±0.50%, with a minimum of ±0.10 mm. |
The weight formula for stainless steel pipes: ((Outer Diameter – Wall Thickness) * Wall Thickness) * 0.02491 = kg/m (weight per meter).
SAW. Heat Treatment and Microstructure Specifications
Heat treatment specifications:
1) Solution heat treatment at 920-1150℃ with rapid cooling;
2) Stabilization treatment can be carried out upon request at a heat treatment temperature of 850-930°C, but must be specified in the contract.
3) The solution temperature should not exceed 1066°C. If this happens, a stabilization treatment must be carried out to prevent chromium precipitation.
Microstructure:
Characterized by an austenitic structure.
Delivery condition: The product is generally delivered under heat treatment conditions. The type of heat treatment is specified in the contract. If not specified, the product is delivered untreated.
VII. Differences between 304 and 321 stainless steel
Both 304 and 321 belong to the 300 series of stainless steel and have little difference in corrosion resistance.
However, under heat-resistant conditions of 500-600 degrees Celsius, 321 stainless steel is mainly used. A type of heat-resistant steel called 321H, with a slightly higher carbon content than 321, similar to China's 1Cr18Ni9Ti, has been specially developed abroad.
A moderate amount of Ti is added to stainless steel to increase its resistance to intergranular corrosion.
This was due to the inability to reduce the carbon content of steel at the beginning of stainless steel production due to low smelting technology, so the method of adding other elements was used.
With technological advancement, low and ultra-low carbon varieties of stainless steel can now be produced, hence the widespread use of the 304 material.
At this point, the heat resistance characteristics of 321, 321H or 1Cr18Ni9Ti become apparent.
304 is 0Cr18Ni9Ti and 321 is 304 with added Ti to improve intergranular corrosion tendencies.
The Ti in 321 stainless steel acts as a stabilizing element, but it is also a heat-resistant type of steel that is much better at high temperatures than 316L.
321 stainless steel has excellent wear resistance at different concentrations and temperatures of organic acids, especially in oxidizing media, and is used to manufacture wear-resistant acid containers and wear-resistant equipment linings and conveying pipes.
321 stainless steel is a Ni-Cr-Mo austenitic stainless steel, its performance is very similar to 304, but the addition of titanium metal provides better intergranular corrosion resistance and high temperature resistance.
The addition of titanium metal effectively controls the formation of chromium carbide.
321 stainless steel exhibits superior mechanical properties of high-temperature stress rupture and high-temperature creep resistance than 304 stainless steel.
The main components of 304 stainless steel and 304L stainless steel contain 18% chromium (Cr) and 8% nickel (Ni); its main difference is that 304L stainless steel is a low carbon 304 steel, under normal conditions, the corrosion resistance of 304L stainless steel is similar to that of 304 stainless steel, but after welding or stress relieving, 304L stainless steel has excellent resistance to intergranular corrosion.
In terms of price, 304L stainless steel is superior to 304 stainless steel. 304L stainless steel is a low-carbon stainless steel, mainly suitable for welding processes. During welding, the use of 304L stainless steel can effectively reduce welding corrosion.
According to hardness standards, 304 stainless steel is superior to 304L stainless steel because the carbon content directly affects the hardness of stainless steel. There is also 304H stainless steel series, where H means high carbon content.
304L is a variant of 304 stainless steel with lower carbon content, used for welding occasions.
The lower carbon content minimizes precipitated carbides in the heat-affected zone near the weld, and carbide precipitation can cause intergranular corrosion (weld deterioration) of stainless steel in certain environments.
304 vs 321 stainless steel
304 and 321 are austenitic stainless steels and their appearance and physical properties are very similar. The only slight difference lies in their chemical composition:
Firstly, 321 stainless steel requires trace amounts of element titanium (Ti) (according to ASTM A182-2008 standard, its Ti content should not be less than 5 times the carbon content (C), but not more than 0.7%. Note that both 304 and 321 have a carbon (C) content of 0.08%), while 304 does not contain titanium (Ti).
Secondly, the requirements for nickel (Ni) content are slightly different, with 304 between 8% and 11% and 321 between 9% and 12%.
Thirdly, the requirements for chromium (Cr) content are slightly different, with 304 between 18-20% and 321 between 17-19%.
