17-4 Stainless Steel vs 304: 8 Key Distinctions!

Stainless steel is a popular material used in the manufacture of a wide range of products. Manufacturers use this material due to its excellent strength, machinability, and corrosion resistance. Stainless steel comes in various grades, and 17-4 and 304 are among them. However, when these two grades are compared, it sparks a debate on 17-4 Stainless Steel vs. 304.

 

304 stainless steel has a higher chromium composition. Due to this, people consider it superior in terms of corrosion resistance. However, 17-4 strength is something that helps it stand out in the comparison. In this article, I’ll explain all the differences between 17-4 and 304 stainless steel. This will help you select the appropriate stainless steel grade for your specific needs.

 

 

Overview of 17-4 PH & 304 Stainless Steel

 

As I mentioned earlier, stainless steel comes in various grades. Those grades differ from each other in terms of their composition and properties. The 304 and 17-4 PH are two popular grades that are widely used across various industries.

 

The 304 grade is from the austenitic family and has higher chromium content. It consists of 17% chromium and around 8% nickel. Apart from these two elements, this material also consists of many traces. Its high chromium content makes the 304 grade highly resistant to rust and corrosion. 

 

What I like about the 304 grade is that it comes with excellent surface finishing. The part made from this type of stainless steel does not require a post-processing step for finishing. The primary reason for the extensive usability of this material lies in its low pricing.

 

17-4 PH stainless steel is known for its strength and hardness. It contains 17% of chromium and 4% of nickel (As indicated 17-4 in their names). This type of stainless steel undergoes a precipitation hardening process. It is exposed to heat treatment, followed by cooling (quenching), and then heat treatment (aging) to increase its strength.

 

Those additional heat treatments increase the cost of 17-4 stainless steel. Due to its superior strength, this material is used in high-end parts. The aerospace, automobile, nuclear, and marine industries utilize these materials. However, the corrosion resistance of this grade is compromised as compared to 304 stainless steel.

 

Quick Highlight: You will see 17-4 grade written as 17-4 PH. This PH indicates the precipitation hardness. As I mentioned earlier, this process exposes the grade to a heating, cooling, and aging process. This PH, or precipitation hardening, increases the strength and hardness of this material. PH is written in this grade name to indicate its higher strength.

 

Differences Between 17-4 Stainless Steel and 304 Stainless Steel

 

In the above section, I discussed some basics of these two grades of stainless steel. However, these two grades have several distinct differences from each other. Therefore, their usability and overall value proposition also differ. Let’s dive in and discuss all the fundamental differences between 304 and 17-4 stainless steel. 

 

1- Chemical Composition

The primary difference between these stainless steels lies in their composition. Generally, both consist of the same elements. However, the content of each component differs between the two types. Due to the difference in proportion of content, the properties of these grades differ. Here is a table showing the chemical composition of 304 and 17-4 PH stainless steel grades:

Element	304 Stainless Steel	17-4 PH Stainless Steel
Iron (Fe)	70.0%	73.0%
Chromium (Cr)	18.0%	17.0%
Nickel (Ni)	8.0%	4.0%
Copper (Cu)	0.0%	4.0%
Manganese (Mn)	2.0%	1.0%
Silicon (Si)	1.0%	1.0%
Carbon (C)	0.08%	0.07%
Phosphorus (P)	0.04%	0.04%
Sulfur (S)	0.03%	0.03%

 

Grade 304 and 17-4 mainly differ in the proportion of the two elements. Those include chromium and nickel. The 304 grade consists of 18% chromium and 8% nickel. On the other hand, 17-4 stainless steel has lower chromium (17%) and nickel (4%) content.  

Due to high chromium, the 304 grades are more corrosion-resistant and long-lasting than their counterparts. Generally, the presence of higher nickel makes a material stronger. However, 17-4 PH, having less nickel, is stronger and more complex. This is due to the heat treatment that this material undergoes.

 

2- Heat Treatment Capability

Grade 304 stainless steel cannot be hardened. Its heat treatment does not make it harder and stronger. Even if you heat this material at high temperatures, you won’t see any change in its mechanical properties. On the other hand, the 17-4 grade can be hardened through heat treatment. 

This material undergoes a precipitation hardening process. In this process, this material undergoes heat at higher temperatures. After that, it is cooled down to increase its strength. After this cooling, the material undergoes heating again at a relatively lower temperature. 

This process is called precipitation hardening or aging. It increases the mechanical strength of this stainless steel grade. Due to this process, the material is widely used in heavy-duty applications. Many parts in the aerospace, marine, and nuclear sectors are made using 17-4 stainless steel grade. 

 

3- Corrosion Resistance

As I mentioned earlier, the 304 stainless steel grade contains 18% chromium. When this material is exposed to air, the chromium reacts with oxygen. Due to this reaction, a chromium oxide layer is produced. This layer or coat is powerful and protects the base material from further corrosion. Parts made with 304 stainless steel can be used in moist or salty conditions. 

You might say 17-4 stainless also has 17% chromium. So the corrosion resistance of both materials should be the same. In reality, the corrosion resistance of 304 grade is superior to that of 17-4 grade. The reason is that 17-4 PH stainless steel has some proportion of copper. The presence of this copper does not support the formation of chromium layers.

In the presence of copper, a weaker chromium layer is produced on the surface of the material. This layer can deteriorate, affecting the corrosion resistance of 17-4 stainless steel material. In some cases, copper even promotes and accelerates the corrosion of this material. Therefore, I consider the 304 grade ideal for corrosion resistance. 

 

4- Weldability & Formability

I consider Grade 304 a superior option in terms of weldability and formability. This 304 grade can be heated and melted easily to create joints. You can use any welding technique, such as TIG, MIG, or laser welding, to complete the job. Additionally, this grade is less complicated and can be formed and shaped. Manufacturers use this material to make parts of complex shapes. 

On the flip side, 17-4 PH stainless steel is less suitable for the welding process. You’ll have to be very careful while welding them. As I said earlier, the heat treatment (aging) process increases the strength and hardness of this material. Due to this, material deforming, bending, and shaping become challenging. Therefore, it is not ideal for formability. 

 

5- Strength & Hardness

The 17-4 stainless steel grade is stronger and more complex than its counterpart. The reason is that this material undergoes precipitation hardening, also known as aging. In this process, the stainless steel grade is heated at a very high temperature. Once done, it then undergoes quenching. In this process, the hot material suddenly undergoes cooling. 

This sudden temperature change makes the stainless steel very strong. This cooled stainless steel further heats at a lower temperature, and this process is called aging. As a result of aging, small particles combine and form with the base material, increasing its strength. The 304 stainless steel cannot undergo this additional heat treatment. Therefore, 17-4 stainless steel is considered superior to 304 grade.

 

6- Durability & Longevity

When it comes to durability and longevity, both of these grades are top-notch. They are durable in different conditions. As I mentioned earlier, stainless steel is corrosion-resistant. Parts made from this material can remain in good condition in environments with high salt content. Their longevity will be top-notch even if they stay in contact with water. 

However, if these parts undergo stress, they can break or be damaged. Their strength is compromised, which is a drawback. On the other hand, the 17-4 comes with lower corrosion resistance. If you use this material in moist conditions, it will start to deteriorate and corrode quickly. However, its mechanical strength is top-notch, which is a significant advantage. 

You can use it in conditions where the part is subjected to stress and load. In such usage, this material will last longer and withstand the extreme load. Both of these materials are durable and long-lasting, but in different ways. For the marine industry, I recommend choosing the 304 grade. On the other hand, 17-4 PH is excellent in the aerospace industry, where parts are subjected to consistent loads and stress.

 

7- Magnetism & Machinability

The magnetism of stainless steel material varies depending on its type and grade. The 304 grade is highly non-magnetic. Even if you heat this material, its magnetic behavior won’t change from non-magnetic to magnetic. Therefore, this material is ideal for use where magnetic interference needs to be avoided.  On the flip side, 17-4 grade is magnetic. 

As I said earlier, this material undergoes a heat treatment process. Even after undergoing intense heat treatment, 17-4 stainless steel remains magnetic. CNC machining becomes more challenging as materials get harder and stronger. The 304 grade is relatively less intense and can be machined easily. 

On the other hand, 17-4 PH stainless steel is tough and strong. Machining this stainless steel can be tedious and time-consuming. Therefore, manufacturers generally cut, drill, and shape this material before its aging process. After aging, this material becomes extremely strong and less suitable for machining. 

 

8- Cost & Application

The 304 stainless steel grade is less expensive compared to the 17-4 grade. The reason is that the 304 stainless steel production process is straightforward. It does not undergo any additional heat treatment. On the flip side, the 17-4 grade is tough, premium, and very expensive. The primary reason behind its high price is the heat treatment it undergoes. 

This treatment increases its mechanical strength, which is worth the higher price. The 304 is less ideal in applications where high mechanical strength is needed. Its usage is more suitable in parts that require corrosion resistance. On the other hand, 17-4 is used to make products that are the toughest. Here is a table showing their different applications:

 

304 Stainless Steel Applications	17-4 Stainless Steel Applications
Kitchen sinks and appliances.	Aerospace components
Food processing equipment.	Marine shafts and propellers
Chemical containers and tanks.	Nuclear reactor components
Medical instruments and surgical tools	High-pressure valves and pumps
Brewing and dairy equipment.	Oil & gas equipment
Heat exchangers and piping systems.	Injection molds and tooling
Automotive trim and exhaust parts.	Military-grade hardware and firearm parts

 

Concluding: Which One Should You Opt for, 304 or 17-4 PH Stainless Steel?

 

It depends on the type of part you’re making. There is no one-size-fits-all solution when it comes to choosing between 304 vs 17-4 stainless steel.

 

I recommend choosing a 304 stainless steel grade if you want corrosion-resistant parts. This grade offers optimal strength without being too heavy. Additionally, the cost of the 304 stainless steel grade is very low, which is a big plus. However, parts made with this material may not withstand heavy loads.

 

If you want material to withstand extreme loads, 17-4 PH grade is the best suited for you. This stainless steel undergoes extreme heating, which increases its strength and hardness. It can withstand harsh usage and bear heavy loads effectively. However, this material has a higher price and is less corrosion-resistant. These two are the most significant disadvantages you’ll face if you choose 17-4 PH stainless steel.