While 18-8, 304, and 316 are all types of austenitic stainless steels known for their excellent corrosion resistance, their primary differences lie in their chemical composition and specific applications. 18-8 is a general designation referring to stainless steels with approximately 18% chromium and 8% nickel (which includes 304), while 304 is the most common and versatile grade. 316 stainless steel, however, adds molybdenum, significantly enhancing its resistance to pitting and crevice corrosion, particularly in chloride environments.
Customers ordering stainless steel parts can easily get tripped up by the sheer variety of stainless steel grades. Today, there are more than 50 common grades of the material, spanning different material families.
That is a lot of variation in itself, but matters are complicated further by the different designation systems used around the world. The United States uses both the UNS (Unified Numbering System) and AISI/SAE (Society of Automotive Engineers) naming systems, while ISO (the International Organization for Standardization) has its own system, as does the European Union, Japan, and other locations.
That basically means that a single grade of stainless steel can have many different names depending on where it is manufactured and sold. For example, the names 430, 1.4016, X12Cr17, and Z10CD17 can all be used to refer to the same alloy. As a company with a presence in both the United States and China, we regularly encounter customers confused by this.
This article focuses on 18-8 vs. 316 vs. 304 stainless steels, as this is a question that regularly surfaces. However, the answer involves both differences in chemical composition and differences between alloy naming systems.
How Are Stainless Steel Grades Named?
The best place to start when discussing 18-8 vs. 316 vs. 304 stainless steels is not the physical differences between those materials or the differences in how they are used. First, we need to look at what exactly we are talking about when we use those numbers.
All three of those stainless steel grades are regularly specified by customers in their technical drawings. However, you will notice that they do not follow the same format. 304 and 316 appear to belong to the same category, but 18-8 does not.
This is because:
- 304and 316 are both designations given by the SAE steel grades system used in the United States. These two stainless steel grades have three-digit codes beginning with the number “3” because they are both austenitic chromium-nickel alloys, making them part of the SAE “300 Series.”
- 18-8(sometimes written 18/8), on the other hand, is not a designation given by the SAE steel grade system. Passed down from older naming conventions, it is a general and descriptive term for a stainless steel that contains 18% chromium and 8% nickel.
As it so happens, SAE 304 contains 18–20% chromium and 8–11% nickel, making it effectively the same thing as 18-8.
Why only effectively the same? Because other stainless steels with SAE designations can technically also contain 18% chromium and 8% nickel. For example, SAE 302 allows for a range of 17–19% chromium and 8–10% nickel.
This is just the tip of the iceberg, as different naming systems refer to these materials in their own ways.
18-8 vs. 316 vs. 304 Stainless Steels Comparison
The section above touched on the differences and similarities between stainless steels with different names. This section offers a direct comparison of our three stainless steel grades—both in terms of their naming conventions and their actual physical and chemical properties.
Note that this section does not include a direct comparison between 18-8 vs 316 stainless steel, as 18-8 is chemically the same as 304. For a de facto 316 vs 18-8 stainless steel comparison, see the section “304 vs 316 Stainless Steel.”
18-8 vs 304 Stainless Steel: Semantic Differences
First off, what is the difference between 18-8 and 304 stainless steel? As we have discussed, 18-8 stainless steel vs 304 is primarily a distinction between different naming conventions.
- 18-8is a general term for a stainless steel that contains 18% chromium and 8% nickel.
- 304is an SAE designation for a stainless steel that contains 18–20% chromium and 8–11% nickel.
That means that “18-8” and “304” essentially refer to identical grades of stainless steel. In practice, they are often used interchangeably.
However, there is no perfect overlap between the two. 18-8 could also include SAE grades like 302 (which has a higher maximum carbon content than 304 but similar chromium and nickel content), while 304 could also fall under the umbrella of 18-10 stainless steel (a grade with 10% nickel content rather than 8%).
304 vs 316 Stainless Steel: Real Differences
304 and 316 are chemically different grades of stainless steel within the SAE 300 Series of austenitic chromium-nickel alloys.
- 304, also known as A2 stainless steel or 18-8, is the most common grade of austenitic stainless steel.
- 316, sometimes known as marine-grade stainless steel, is the second most common grade and contains molybdenum to prevent corrosion.
In terms of chemical composition, the key difference between 304 and 316 stainless steel is the presence of molybdenum in 316.
Practically speaking, the main difference between 316 stainless steel and 304 is the former’s superior corrosion resistance. However, despite its “marine-grade” tag, 316 does show brown staining after prolonged exposure to seawater.
The stainless steel 304 vs 316 strength differences are minor, but the presence of molybdenum in 316 gives it a greater level of hardness.
The 304 stainless steel temperature limits are about 870 °C in intermittent service. For 316, the limit is about the same. Grades 304H and 316H, both of which have higher carbon content, have higher strength at elevated temperatures than their regular counterparts.
In the food processing and household goods industries, food-grade stainless steel 304 vs 316 comes down to whether the product requires extra corrosion resistance due to salt or chemical exposure. Use of stainless steel 304 is widespread for kitchen equipment and utensils.
304 Stainless Steel Application – Kitchen Utensils
Both 304 and 316 have low-carbon stainless steel variants. 304L is often used in welding to reduce corrosion at welds, while 316L provides weldability and other advantages such as even higher corrosion resistance and lowered risk of contamination in industries like medicine and food processing. For high-temperature applications, high-carbon variants may be chosen instead. These are called 304H and 316H.
316 Stainless Steel Application – Lab Equipment
316 also has a nitrogen-strengthened grade called 316N and a titanium-stabilized grade called 316Ti that is suitable for very high temperatures and high pressures. Stabilization is achieved through intermediate-temperature heat treatment, which allows titanium carbides to form.
The table below shows the main differences between 304 and 316 stainless steel:
| 304 | 316 | |
| UNS number | S30400 | S31600 |
| Chromium content | 18–20% | 16–18% |
| Nickel content | 8–11% | 10–14% |
| Molybdenum content | / | 2–3% |
| Corrosion resistance | Very good but sensitive to pitting and crevice corrosion by chlorides | Higher |
| Tensile strength (MPa, min) | 515 | 515 |
| Yield strength (MPa, min) | 205 | 205 |
| Magnetism | Non-magnetic | Non-magnetic |
| Machinability during CNC machining | Higher | Lower (gummier and work-hardens faster) |
| Cost | Lower | Higher |
| Main uses | Food processing, machine parts, fasteners, utensils, transport, storage, architectural panelling, heat exchangers | Food processing, chemical storage, laboratory equipment, marine parts, architectural panelling, medical implants |
Engineering Considerations for Stainless Steel Parts
This section looks at the two main areas of consideration for engineers designing parts for 304 or 316 stainless steel: which material is best for their particular situation, and which manufacturing process should be used.
Material Selection
Choosing between 304 (or 18-8) and 316 stainless steel typically comes down to the corrosion resistance requirements of the parts in question. However, other factors include whether the parts need to be biocompatible, budget, etcetera.
Overall, we could advise engineers to consider the following factors when choosing stainless steel:
- Corrosion resistance: 316 offers superior performance when it comes to salts and acids, making it an obvious candidate for seawater applications. However, 304 (18-8) still offers very good corrosion resistance compared to other metals.
- Application: This typically relates to corrosion resistance. 304 serves a wide variety of end-uses, but 316 is more suitable for harsh environments, chemical processing, and medical implants (particularly the low-carbon 316L grade).
- Strength: The molybdenum content of 316 makes it harder than 304, but this is typically not significant enough to be a major consideration given the cost difference between the materials and the availability of other high-strength alloys.
- Cost: The cost of 304 is about 2/3 that of 316, making it the more budget-friendly option if the above factors do not come into play.
- Specificity: It is worth pointing out that engineers often simply specify “300 Series” stainless steel for parts, which indicates that the manufacturer can use any stainless steel within that category. This may result in shorter lead times and cost savings, as the manufacturer does not have to acquire one particular material.
Manufacturing Considerations
These stainless steel grades are suitable for a variety of manufacturing processes and post-processing techniques.
- CNC machining: 304 (18-8) is slightly more machinable than 306, which is gummier and harder. However, both are suitable. We offer both stainless steel grades as part of our stainless steel CNC machining
- Welding: 304 is slightly easier to weld but the corrosion resistance of 316 serves it well for preventing sensitization near welds. 304L and 316L are both more weldable than their regular counterparts.
- Forming: Stainless steels 304 and 316 are both suitable for hot extrusion and certain casting processes.
- Sheet metal: In sheet metal fabrication and related areas, both grades are suitable for processes like stamping, rolling, and drawing. But the slightly more ductile 304 is more amenable.
- 3D printing: Metal additive manufacturing processes like DMLS and binder jetting can be used for the 3D printing of 304 and 316L. Metal extrusion 3D printing processes can be used with materials like BASF’s Ultrafuse 316L.
Our guide to stainless steel machining has more information about the best stainless steels for CNC processes.
Ordering Stainless Steel Parts from 3ERP
3ERP is a trusted provider of services such as CNC machining, sheet metal fabrication, low-volume prototyping, finishing, and bridge production.
Our many years of experience producing stainless steel parts allow us to help you develop and manufacture your parts and prototypes, regardless of your chosen grades of stainless steel. We can also help you choose between different stainless steel types if you have any doubts.
For your next project, contact 3ERP for a free quote.
FAQs
Is 18-8 the same as 304 stainless steel?
If 304 contains 18% chromium and 8% nickel, then what is 18-8 stainless steel? For all intents and purposes, 18-8 and 304 are equivalent, with 18-8 being a less precise term. However, the overlap is not perfect. For example, a material could be labelled both 18-8 and 302, while another could be labelled both 18-10 and 304.
Does 316 stainless steel rust?
316 or marine grade steel is highly corrosion-resistant and less likely to rust than other grades of stainless steel like 304. However, it can still rust when subjected to extreme conditions. Known as a “super austenitic” stainless steel, 904L is perhaps the most corrosion-resistant stainless steel available to engineers.
Which stainless steel is best?
The best stainless steel grades are those best suited to the part in question. 304 is the most popular austenitic stainless steel alloy because of its performance, versatility, and affordability, but other alloys like 316 offer specific benefits suited to certain applications.
Is 18/8 stainless steel good?
18/8 or 18-8 stainless steel, usually called 304 stainless steel in the United States, is a popular and high-performing alloy.
Why is 304 stainless steel called that?
The designation “304” comes from the AISI/SAE (Society of Automotive Engineers) classification system. The 3 indicates that it is part of the 300 Series, which means it is an austenitic chromium-nickel alloy. The other two digits do not have a particular meaning, but they differentiate the alloy from others in the 300 series. (This is in contrast to the four-digit SAE numbering system for carbon steels, in which the digits indicate elements and carbon content.)
What is 304L and 316L stainless steel? And what is 304H and 316H?
304L stainless steel is a low-carbon version of 304 that does not require annealing after welding. 304H stainless steel, on the other hand, is a high-carbon version of 304 that performs better than the standard grade at elevated temperatures. The same applies to the variants of 316.
