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How to choose between 303 and 304 stainless steel

CNC Milling Parts-316 Stainless Steel


What is 303 Stainless Steel

303 stainless steel is a kind of free-cutting stainless steel. It is mainly used in occasions requiring free cutting and a high surface finish. From the above table, we could find that 303 contains 0.15% of added sulfur(S).

Although the addition of sulfur slightly reduces its corrosion resistance, it improves machinability. So 303 is widely used to make accurate machining parts. For example, pins, shafts, bushings, bearings, nuts, bolts and some other fasteners.

303 stainless steel still has strong corrosion resistance, but for an added boost, we recommend 304.


304 Stainless Steel

304 stainless steel is also known as 18/8 or A2. It’s the most commonly used type of austenitic stainless steel. 18/8 means this material contains a minimum of 18% chromium (Cr) and 8% nickel(Ni). So it has the alternate name 18/8 stainless steel.

This stainless steel type is oxidation-resistant and corrosion-resistant. It’s harder than 303 stainless steel but more cost-effective compared to 316.


Which stainless steel is harder to processing?

In the machining industry, 303 material is the most popular part of the production factory. From the material point of view, 303 is a free-cutting material, which is easy to process. Almost all the CNC machine shops can process 303 stainless steel parts. However, 304 has a higher hardness. And this makes it more difficult to process and more expensive than 303.

Can every machining factory process stainless steel 304? On the whole, this is not the case. Because 304 is harder and it needs a good CNC machine with better rigidity. So some metal parts manufacturers can process 303 parts but failed to manufacture stainless steel 304 parts.

The Advantages of Stainless Steel

Of its many properties, stainless steel is most famous for its corrosion resistance, from which it takes its name. Stainless steel is remarkable for its ability to resist stains and corrosion. At a minimum, stainless steel is a low-carbon iron alloy with at least 10.5 percent chromium added. Unlike carbon steel, which starts to rust when exposed to air and moisture, stainless steel does not readily corrode, rust, or stain in normal exposure environments.

The chromium in stainless steel allows the metal to form a chromium oxide film on its surface that is invisible to the eye. The corrosion resistance works so well that it actually is self-healing. When the metal is scratched or damaged, the film reacts with oxygen and repairs itself, one of the biggest reasons for stainless steel’s durability.

Additionally, other elements can be added to the alloy, such as nickel, nitrogen, and molybdenum, to bolster the corrosion resistance even further. All together, dozens of stainless steel grades are available, and they can be categorized into five alloy classes by the elements that have been added. They are:

Ferretic, alloyed with chromium and less than .10% carbon;
Martensitic, alloyed with chromium and up to 1% carbon;
Precipitation Hardening, alloyed with elements such as copper, niobium, and aluminum to be very high strength;
Austentic, alloyed with chromium, molybdenum, nitrogen, nickel, and manganese;
Duplex, which is about 50% ferretic and 50% austentic.
Other prominent benefits of stainless steel include the high strength-to-weight ratio, a resistance to heat and chemical damage, and cost advantages over other materials. Furthermore, stainless steel is fully recyclable, and the majority of new stainless steel in the United States comes from scrap metal. This helps lower the cost of using stainless steel and helps to fit in with the modern desire for increased sustainability.

What are the benefits of austenitic stainless steel?

303 and 304 are both from the family of austenitic stainless steels. This means that they are a metallic, non-magnetic iron allotrope containing chromium and nickel, with other elements added for particular grades. They have a eutectoid point of at least 727°C (1,341°F). The austenite allotrope exists at room temperature in stainless steel and was originally named for Sir William Chandler Roberts-Austen. These metals are generally labeled in the 200 and 300 series of stainless steel.

The peculiar characteristics of austenitic steels include high ductility and toughness. When they are in what is known as a quench-annealed state, they can be very soft and formable. However, when they have been cold stretched or hard rolled, their hardness and strength are bolstered. Their strength can be further increased by adding carbon, nitrogen, or molybdenum.

These steels are known to have excellent weldability and do not need any post-weld treatment. Conventional arc welding methods that can be used on austenitic stainless steel include shielded metal, plasma, gas metal, gas tungsten, and submerged welding. They also have the excellent corrosion resistance properties common to stainless steel.

How to chose between 303 and 304 stainless steel alloys?

303 stainless steel is a free-machining grade of 304 that has sulfur added to increase its machinability. It is particularly desired for automatic machining operations for this reason. It also maintains the mechanical and corrosion resistance common to stainless steel. While the sulfur content does decrease its corrosion resistance and toughness when compared to 304, the increased machineability is worth it for certain applications.

304 stainless steel, among the most popular stainless steel alloys, has a minimum of 18% chromium and 8% nickel. Clinton Aluminum keeps a grade known as 304L #4 finish stainless steel sheet in stock. Its low carbon content makes it suitable for most welding operations that are common in construction and other industries. 304L also provides for excellent rust resistance and low intergranular corrosion. 304, like all austenitic steels, is non-magnetic in nature, and it also features low electrical and thermal conductivity. It also is recognized for its higher corrosion resistance than most other stainless steel alloys.

Choosing between the two most often comes down to whether machining is a prominent part of your application. 303 stainless steel is specifically made for machining applications, whereas many 304 grades can be difficult to machine. This increased machinability will often make up for the increased cost, and the lowered toughness and corrosion resistance of 303.

What are common applications for 303 and 304 alloys?

As pointed out, 303 stainless steel is most often used for parts that will need to be heavily machined. This includes small parts like screws, nuts, and bolts, aircraft fittings, gears, bushings, and electrical components. 304, on the other hand, as one of the most popular stainless steel alloys around, is commonly found in kitchen appliances, utensils, and surfaces, chemical containers, food or liquid processing equipment, heat exchangers, automotive parts, construction materials, architectural trim, and aerospace fixtures. Moreover, because of the increased corrosion resistance over 303, the 304 alloy is often used for screws, nuts, and bolts in a marine environment.

No matter what your particular industrial application, you will find the stainless steel alloy right for you at Clinton Aluminum. We take pride in working with our customers to be a technical resource partner. That means we will always do our best to help you select the correct material for your production needs.

XTJ is a leading OEM Manufacturer that is dedicated to providing one-stop manufacturing solutions of 303 steel,304 steel from prototype to production. We are proud to be an ISO 9001 certified system quality management company and we are determined to create value in every customer relationship. We do that through collaboration, innovation, process improvements, and exceptional workmanship.



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