Steel is unquestionably among the most widely used materials. It is an alloy made out of iron and carbon. You can add alloying agents to enhance the material’s properties. When you add chromium to your steel, an extremely important alloy called stainless steel is formed.
Stainless steels are known for their superior corrosion resistance. These steels have excellent mechanical properties and good manufacturing characteristics, making them suitable for various diverse applications.
An important class of stainless steel is austenitic stainless steel. These steels are known for their excellent resistance to corrosive forces, high flexibility, and ability to be formed into different shapes.
One such austenitic stainless steel is AISI 303. It belongs to the 300 austenitic series, and the number 303 helps you uniquely identify its grade and properties.
Compared to other grades of austenitic steels, the AISI 303 is known for its excellent machinability. So you can’t use it in applications requiring extensive processing and machining.
This article will review the properties, manufacturing techniques, applications, and limitations of the AISI 303 stainless steel.
The Components of SS AISI 303.
Like most austenitic steels, the AISI 303 stainless steel also has a high amount of chromium and nickel. It also contains higher sulfur, phosphorus, and molybdenum levels than other austenitic steels. The composition of the AISI 303 grade is as follows:
| Element | Minimum % | Maximum % |
| Carbon | – | 0.12 |
| Manganese | 1.00 | 2.00 |
| Sulphur | 0.15 | 0.30 |
| Phosphorus | – | 0.045 |
| Silicon | 0.2 | 1 |
| Chromium | 17 | 19 |
| Nickel | 8 | 11 |
| Iron | Balance | Balance |
Table 1: Composition of the AISI 303 stainless steel
Properties of Austenitic AISI 303 Stainless Steel
AISI 303 has various mechanical and physical properties that make it suitable for different industries. These include:
1.Mechanical Properties
The mechanical properties of AISI 303 grade are as follows:
| Property | Value |
| Compressive Strength | 190 MPa |
| Tensile Strength | 500 – 700 MPa |
| Hardness | 262 HB max |
| Elongation | 35% |
2.Physical Properties
| Property | Magnitude |
| Melting Point. | 1455 °C. |
| Thermal Expansion Coefficient. | 17.2 x 10-6 /K. |
| Density. | 8.03 Kg/m3. |
| Modulus of Elasticity. | 193 GPa. |
| Electrical Resistivity. | 0.072 x 10-6 Ω .m. |
| Thermal Conductivity. | 16.3W/m.K. |
How Does the Composition of Austenitic AISI 303 Stainless Steel Affect Its Properties?
Different factors, such as the type of alloying elements, impurities, and heat treatment methods, affect the properties of the AISI 303 steel. The effect of different alloying elements is:
1.Carbon
Carbon is the primary alloying in all steels, and it significantly increases the strength of your steel. In stainless steels like AISI 303, carbon is only added in small amounts. Carbon reduces the resistance to intergranular corrosion due to carbide formation.
2.Chromium
At least 10.5% chromium is present in all stainless steels, providing basic corrosion resistance. The resistance to corrosion increases with an increase in chromium content.
Adding chromium can also increase the high-temperature oxidation resistance of the AISI 303 grade.
3.Nickel
Nickel is present in austenitic steels as it is an austenite phase stabilizer. It increases the corrosion resistance of the AISI 303, especially in acidic environments.
4.Phosphorus
Phosphorus improves the machinability of your steel by minimizing the formation of long and stringy chips during machining operations.
5.Silicon
The addition of silicon can improve the high-temperature oxidation resistance of your steel.
6.Sufur.
Sulfur is primarily added to AISI 303 to improve its machinability. However, the presence of sulfur reduces the steel’s weldability, formability, and corrosion resistance.
7.Manganese
Manganese is also an austenite stabilizer. You can improve the hot ductility of the AISI 303 stainless steel by adding manganese. It also forms manganese sulfide, which acts as a chip breaker during machining, improving machinability.
Applications of Austenitic AISI 303 Stainless Steel
You can use the AISI 303 grade in different industries. It is, however, mostly used for smaller components where heavy machining is required. The applications of the AISI 303 grade include:
1.Food Industry Applications.
You can manufacture various food and beverage processing equipment using the AISI 303 stainless steel. It is considerably resistant to corrosive forces, making it suitable for the job.
AISI 303’s non-porous surface also prevents microbial growth. And you can easily clean food processing equipment made of AISI 303 stainless steel.
2.Aerospace Applications
AISI 303 steel is also in the aerospace industry. Its high machinability allows for the formation of complex shapes.
You can use these steels to manufacture components like aircraft gear. These steels are also often used to manufacture aircraft fittings.
3.Electronic Equipment
You can use the AISI 303 stainless steel in sensitive electronic equipment due to its low magnetic permeability.
4.Fasteners
Fasteners such as nuts, bolts, and screws have intricate shapes, making them difficult to machine.
However, you can use AISI 303 stainless steel to machine these fasteners. The fasteners made out of this steel will also have high strength, corrosion resistance, and temperature resistance.
5.Chemical Processing Equipment
Materials used to manufacture chemical processing equipment should be stable against chemical reactions and corrosive forces. Due to its chemical stability and corrosion resistance, you can use AISI 303 stainless steel for these applications.
6.Medical Applications
The AISI 303 stainless steel is often used in various medical applications, such as manufacturing surgical equipment.
You can use this steel to manufacture various surgical tools. Good corrosion resistance and ease of sterilization make it ideal for such applications.
Due to AISI 303’s excellent machinability and corrosion resistance, you can also use it to manufacture dental equipment such as drills. Other devices that come in contact with the body can also be made using AISI 303 stainless steel.
Fabrication Methods for Austenitic AISI 303 Stainless Steel
Austenitic AISI 303 stainless steel can be manufactured using various techniques. These include:
1.Machining
Due to this alloy’s excellent machinability, machining is one of the most common AISI 303 stainless steel manufacturing methods. It involves cutting, drilling, and shaping to obtain intricate shapes and features. You can use conventional methods such as milling and turning for manufacturing the AISI 303 stainless steel. Precision machining processes can also be used if you want more intricate features to be present.
2.Hot Rolling
In this process, you deform the metal by heating and rolling it. The deformation is carried out by passing the billets through a series of rollers to decrease their thickness and change their shape.
The grain structure is broken down, allowing the grains to recrystallize to obtain a uniform and equiaxed microstructure. Mill scale is formed on the surface of your alloy due to oxidation during the hot rolling process. You can remove the mill scale and obtain a shiny, smooth surface by picking your AISI 303 stainless steel.
3.Annealing
Annealing involves heating your AISI 303 stainless steel to 1010-1120°C, soaking it, and slowly cooling it.
The soaking time should be sufficient for the temperature to become homogenous throughout the cross-section of the part. It depends mainly on the part’s size and the alloy’s composition. You then cool it inside a furnace below its austenitizing temperature.
Annealing will help reverse any work-hardening effects on your AISI 303 stainless steel. It also helps to obtain a refined grain structure, remove any microstructural irregularities and improve the machinability of the alloy.
4.Welding Capability of AISI 303 Stainless Steel
The AISI 303 has poor weldability due to the presence of sulfur, which causes problems like hot cracking. High porosities can also arise during the welding process. Sensitization can also occur, where the chromium carbides are segregated to the grain boundaries at high temperatures and can cause corrosion.
If welding is necessary, use filler rods of grades 308L and 309 steel to weld the AISI 303 stainless steel. Post-weld annealing also helps to improve the corrosion resistance of the alloy.
5.Heat Treatment of Austenitic AISI 303.
You can not harden AISI 303 through thermal methods. However, the steel can be heated to 1010°C-1120°C followed by rapid cooling for annealing or solution treatment.
Properties of AISI 303 Stainless Steel
AISI 303 has a range of properties that make it suitable for a variety of industrial applications. These properties include:
1.Magnetic Properties
Similar to other austenitic steels, the AISI 303 is also non-magnetic. The lack of magnetism is due to the high level of symmetry in the Face Centered Cubic(FCC) structure of austenitic steels. Hence, you cannot stick a magnet to the AISI 303 stainless steel.
2.Corrosion Resistance
All austenitic stainless steels show excellent corrosion resistance that varies per their composition.
AISI 303 is stable in mild environments. However, its corrosion resistance is lower than the AISI 304 grade. Sulfur is present, creating sites for pit formation and can cause pitting corrosion.
You should not use the AISI 303 in marine environments as it can cause rapid pitting and crevice corrosion. In chloride-rich environments, stress corrosion cracking can occur at temperatures above 60°C.
You can improve the corrosion resistance in such aggressive environments by adding molybdenum.
3.Thermal Properties
The AISI 303 stainless steel shows good oxidation resistance at high temperatures up to 760°C upon intermittent exposure. Good oxidation resistance is also seen at temperatures up to 870 °C when subjected to continuous service.
However, you should not use this steel around this temperature for extended periods. At extended periods, carbide precipitation happens on the grain boundaries at 425-860°C.
4.Machinability
Austenitic AISI 303 has excellent machinability, especially in comparison with other austenitic steels. This is because of the presence of alloying elements such as phosphorus and sulfur.
When machining it, you should use lubricants in large quantities to avoid the build-up of heat on cutting edges. You should ensure that cutting edges are sharp, as dull edges can cause work hardening. Make light but deep cuts on the surface and use chip breakers.
Comparison of Austenitic AISI 303 Stainless Steel to Other Stainless Steels
The Austenitic AISI 303 stainless steel is also known as a free-machining grade. It has good formability and can be machined easily because of sulfur and phosphorus. However, their presence reduces the corrosion resistance and weldability of the alloy.
It has better machinability than other steels, such as AISI 304. AISI 304 is not easy to machine but easy to weld. In contrast, AISI 303 is easy to machine but difficult to weld.
Even though stainless steels are generally corrosion resistant, the AISI 303 is less stable against corrosive forces than AISI 304 or 316.
You can use the AISI 304 for marine applications, but the AISI 303 is not suitable for marine applications. The AISI 316 has higher pitting and crevice corrosion due to high amounts of molybdenum and nickel.
Compared to the AISI 304 and AISI 316, the AISI 303 has lower strength and toughness due to the presence of sulfur.
The price of the stainless steel varies with the application you are using it for. Generally, AISI 303 might cost you more than AISI 304. However, the AISI 303 is a heavy machining grade and does not require excess work for forming, so the price of the AISI 303 can vary depending on your application.
Limitations of the AISI 303 Stainless Steel
Let’s discuss some limitations of AISI 303:
1.Strength
The AISI 303 stainless steel has a lower strength and hardness than other steels, such as AISI 304 and AISI 316.
2.Weldability
Due to the presence of sulfur, the AISI 303 has poor weldability. Hot cracks and porosities can arise in your steel during welding.
3.Corrosion Resistance.
The AISI 303 provides considerable corrosion resistance in milder conditions. You cannot, however, use these steels in marine conditions as they are prone to pitting and crevice corrosion.
4.Hot Working, Cold Working, and Forging Capabilities
Due to the high sulfur content, you cannot cold work AISI 303 stainless steel. 304 steel is a better choice for cold working applications.
Hot working of the AISI 303 is possible using processes such as forging around 982°C – 1204°C.
However, the hot working of this steel is not recommended due to the presence of sulfur. The 304 steel is once again a better choice for such applications.
Endnote.
The AISI 303 is austenitic steel with excellent machinability and versatile properties.
Often small and intricate parts are manufactured using the AISI 303 stainless steel. You can use these steels to manufacture parts in the aerospace, food, and beverage industries and fasteners.
If you require steel with high strength, good corrosion resistance, and excellent machinability, then AISI 303 is a perfect choice. For any information or queries regarding your steel needs, please contact us!
FAQs
1.What differentiates AISI 303 and AISI 304?
Grade AISI 303 contains more phosphorus, sulfur, carbon, and silicon than AISI 304. AISI 303 is more machinable but offers lower corrosion resistance than AISI 304.
AISI 303 stainless steel is also more expensive compared to 304 because it is less commonly available and is produced in lower quantities.
2.Is AISI 303 Stainless Steel suitable for medical implants?
AISI 303 is suitable for medical implants as it is biocompatible and non-toxic to the human body.
