Knowing the existing stainless steel grades will help you choose the perfect material for any fabrication process. With the varying alloying composition, you can classify stainless steel depending on elements, functionality, and ease of fabrication, among other variables.
Today’s guide will help you choose a perfect grade of stainless steel for any application.
So, if you want to learn about the classification criteria, applications, or characteristics of various stainless steel grades – then, this is the right guide for you.
Table of Contents
Austenitic Stainless Steel Grade
Austenitic Stainless Steel Chemical Composition – Photo credits: Wikipedia
They are mainly the 300 series and 200 series.
Although there exist some variations in austenitic stainless steels, usually, there is a broad similarity. Take, for example, the grades of stainless steel in this category are distinguished by the following key variables:
Maximum nickel composition – 35%
Structure – face-centered cubic
Superior corrosion resistance
Chromium content varies between 16% and 26%
Carbon composition by weight is relatively low
Can perform well in most low-temperature or cryogenic applications
Most are non-magnetic SS grades
Common austenitic SS grades:
Austenitic Stainless Steel Grade
Description
201
It has low nickel content and was developed to address the shortage of nickel during the 1950s.
The yield strength is better than 301
Resistance is lower compared to other austenitic SS grades
In most cases, it can substitute the 301 SS
Suitable for flatware, cooking utensils, door parts, washing machine, etc.
202
Has low nickel content
Low toughness
Low corrosion resistance
An affordable alternative that can substitute 304SS
Suitable for kitchenware, hose clamps kitchen sinks, etc.
205
Perfect for spin-forming applications
Good ductility and formability
It is common when making the stainless steel precipitation hardening grade
Possess good corrosion resistance
Ductile and soft when solution annealed condition
301
Good corrosion resistance
For cold working, it has a slightly high carbon content
Best for stretch forming in the annealed condition
Suitable for fasteners, car parts, and trailer body construction
It has a high work-hardening rate
301LN has low carbon content to improve ductility, with high nitrogen composition
301L is another variant of 301LN, except that the latter has a high nitrogen content
302
It is a general-purpose SS grade
302 and 304 share most properties; however, 302 has a higher carbon content
Restrictions in the application are due to the carbide precipitation formation
Suitable for spinning, wire forming, and stamping applications when making springs, cables, or washers
In 302HQ, there is 3% to 4% copper making a good wire alloy
303
Increased machinability
Suitable for parts requiring heavy machining such as gears, screws, bolts, nuts, etc.
303 is similar to 304 SS except for the extra sulfur to improve its machining properties
However, sulfur lowers corrosion resistance
There is the grade 303Se without sulfur but contains selenium. Consequently, it has better hot-forming and cold-forming properties
304
It is a low-carbon and economical stainless steel grade
Although the 304 is weldable, the grade is not resistant to seawater
It is common and a perfect choice for many applications today
Applications include piping systems, heat exchangers, home appliances, building structures, etc.
Also referred to as 18/8
Good welding and forming properties
Best for deep-drawn stainless steel parts such as sinks, or hollow-ware
304L
A 304 version but with low carbon composition
Suitable for heavy gauge fabrication since it does not require post-weld annealing operations
Low post-welding corrosion
304H grade has high carbon content making it a perfect choice for high-temperature applications
305
Suitable for blanking, spin forming, and deep drawing applications
It has low work hardening rate. This is contributed by the high nickel content in this SS grade.
Excellent corrosion resistance though may discolor or pit in high chloride or saltwater
Oxyacetylene welding is not suitable for 305 stainless steel grade
Applications may include cold-headed rivets, barrels, shells, etc.
308
It is a common filler material in 304 stainless steel grade welding
It is a high-alloy steel
20% chromium – As a result, this SS has exceptional resistance to any corrosive element or environment
Suitable for making pump parts, bolts, lever parts, etc.
309
The SS grade highly resists any possible oxidation even at high temperature
Resistance to deformation and creep
May experience intergranular corrosion after a long time of exposure
Resistant to scaling
Strength matches 304 stainless steel grade
Oxyacetylene welding is not suitable for 309 SS grade
Common applications include heat exchanger systems, boiler systems, fireboxes, furnace components, etc.
310
Resistant to high temperature and scaling
Highly resistant to oxidation
310S has a low carbon and excellent corrosion resistance in salty environments
Not suitable for regular liquid quenching due to the risk of thermal shock
Both 310 and 310s can be cold formed
Common applications include furnace systems, kilns, steam boilers, radiant tubes, heat exchanger systems, etc.
314
Resistant to scaling and high temperature
It is similar to 310S except for the extra silicon to enhance oxidation and carburization resistance properties
Suitable for making radiant tubes, furnace parts, heat treatment systems, etc.
316
Adding molybdenum increases corrosion resistance in seawater and acidic environment
Excellent resistance to pitting and crevice corrosion
Excellent welding properties and do not require post-weld annealing
Common applications include chemical tanks, machine components, medical equipment, etc.
316L
It shares the same properties as 316. However, it has low carbon thereby improving corrosion resistance after welding
316h has high carbon content making it suitable for extremely high-temperature applications
316Ti is a titanium-stabilized stainless steel grade. Stabilization help eliminate the possibility of losing excellent corrosion resistance properties in heat-affected zones
317
Better corrosion and creep resistance
Unlike the 316 with 2 to 3% molybdenum, 317 has more than 3% molybdenum
Tougher than 304 SS
317L has low carbon content than 317
Oxyacetylene not recommended
Suitable for the textile industry, chemical equipment, or pulping paper
321
Excellent performance in high-temperature applications
High titanium content
Excellent resistance to intergranular corrosion after heating
Excellent resistance to scaling
Perfect choice for applications with temperatures going above 900 °C
321H has higher carbon content, thereby improving strength in high-temperature applications
Not suitable for welding consumables hence you can choose 347 instead
If the performance requirement only requires resistance to intergranular corrosion, then 304L is a better alternative.
329
It is duplex austenitic stainless steel
Even at high temperatures, it is resistant to stress-crack and pitting
Exhibits improved machinability
Slightly difficult to weld
Best for centrifugal equipment
330
More nickel makes 330 SS resistant to oxidation even at high temperature
It is resistant to stress corrosion, thermal shock, or carburization
Specially designed for industrial applications at high temperatures such as heat treatment equipment, heat exchanges, gas turbines, etc.
GAW welding technique is highly recommended
High strength makes cold working difficult
347
Known for high creep-strength
Excellent intergranular corrosion resistance
A perfect choice for making jet engine components
It is a stabilized austenitic stainless steel with columbium and tantalum
348
Stabilized with columbium/tantalum
Excellent resistance to intergranular corrosion
Good choice for applications requiring intermittent heating
It is tougher than 304 SS grade
Avoid Oxyacetylene welding
Suitable for blanking, stamping, stamping, or drawing
It suitable for most nuclear applications
384
Has low tensile strength
Suitable for making bolts, screws
Best for forming wrought products
904L
Softer than 316L
Resistant to pitting and crevice corrosion
Processing 904L is difficult compared to 316L
904L is costly
Applications include heat exchanger systems, piping, bleaching systems, etc.
Now, throughout the first section of this guide, we were simply classifying stainless steel grades based on the chemical elements.
However, to make it easier to choose the perfect grades of stainless steel for your metal fabrication process, we shall be more specific. Apart from the stainless steel grade charts above, we shall focus on other variables including fabrication, and applications, among other vital aspects.
Let’s explore more:
Food Grade Stainless Steel
Food grade stainless steel in pharmaceutical machines
Currently, stainless steel grade 304 and stainless steel grades 316 are common in most food industries.
The term “food-grade stainless steel” refers to materials that can safely handle food products. That is, you will find these SS in food processing industries or at home.
Furthermore, the best food-grade stainless steel materials are also used to make machine parts and components. These may include:
Food-grade stainless steel pipes
Food-grade stainless steel tubing
Kitchen-grade stainless steel accessories or stainless steel cookware grade
Moreover, food-grade stainless steel is best for utensils, tumblers, pans, etc. Let’s look at some common stainless steel types in the food industry:
Type of Food Grade Stainless Steel
Remarks
Stainless Steel 316
Can withstand high temperature
Safe for food handling
Exceptional resistance to chlorides, most acids, and alkali
The most popular food-handling accessories
Stainless Steel 304
Common in kitchen appliances
Safe when handling foods
Mostly referred to as 18-10 or 18-8
May experience pitting on exposure to salt, making 316 a better substitute
Stainless Steel Grade 430
Properties are similar to 316 SS
Affordable option compared to 316
Superior resistance to organic and nitric acids
Marine Grade Stainless Steel
Marine environments are mostly corrosive. Therefore, the place requires materials that have been modified for high performance such as the marine stainless steel grades.
Although there are different grades of stainless steel, marine grade SS has molybdenum as a key element composition. It is for this reason that 316 stainless steel is popular in most machine applications. 316 SS has about 2% molybdenum.
Marine grade 316 stainless steel is popular for its high resistance to pitting corrosion. For example, marine-grade stainless steel screws offer exceptional performance in marine environments.
Remember, there are other variations of 316 stainless steel such as:
316H – adding carbon improved creep rupture strength. This is critical, especially at a higher temperature
316L (Hi)N – it has a higher amount of nitrogen
316Ti – this grade has titanium for stabilization
316Cb – there is niobium for stabilization
Furthermore, there are other classifications for stainless steel for marine applications such as:
Super austenitic stainless such as the UNS S31254 or N08367
Super duplex stainless steels such as the UNS S32760 or S32750
Finally, there is also the nitronic. It is one of those grades of stainless steel suitable for offshore applications.
Marine grade stainless steel for boats
Medical Grade Stainless Steel
Medical grade stainless steel or surgical steel is suitable for most medical applications. Ideally, the best stainless steel grades for medical applications are known for enhanced corrosion resistance.
That is, surgical grade stainless steels have additional elements such as molybdenum. At the same time, to prevent surgical steel about 0.2% carbon. Additionally, they should have nickel, which reduces brittleness.
Medical grade stainless steels are suitable for making:
Stainless steel surgical equipment and accessories
Medical-grade stainless steel is best for implant equipment due to its hypoallergenic properties
Suturing devices, tubes, instrument components, and medical and medical instruments are made from stainless steel
Currently, stainless steel 304 and stainless steel 316 are popular materials in the medical industry.
Stainless steel medical equipment
Magnetic Stainless Steel Grades
Most austenitic is non-magnetic stainless steel grades. Usually, the magnetic properties in stainless steel depend on two critical aspects:
Stainless steel grade should have iron
The crystal structure must allow for magnetism
Ideally, most magnetic stainless steel grades are Ferritic or martensitic. Some common grades of stainless steel in this category include:
409, 430, and 439 which are Ferritic stainless steel
410, 420, and 440 which are Martensitic stainless steel
Again, it is important to note that certain processes such as work-hardening or thermal treatments may make certain stainless steels magnetic.
Aerospace Stainless Steel Grades
Stainless steel in aerospace industry
Aircraft grade stainless steel has been adopted to make many parts and components. But of course, from the stainless steel classification based on element composition, you can choose an equivalent grade.
Some practical examples include:
304L and 316L are suitable for fuel tanks
309 and 310 can withstand high temperatures hence suitable for making exhaust components
321 which has been stabilized with titanium play an integral role in the piston engine exhaust system, flanges, and exhausts systems
Apart from the stainless steel grading above, you can classify stainless steel further as illustrated in the table below:
Stainless Steel Classification Criteria
Remarks
Cast stainless Steel Grades
When it comes to casting stainless steel, you can choose any of these grades – 303, 304 (L), 310, 316 (L), 410, 416, 418, 420c, 430, 436, 440A, 440C, 15-5, 17-4, 2205 and 2207
These SS grades are readily weldable. When it comes to welding, avoid martensitic stainless steel.
In addition to these, you can also grade stainless steel by standards such as the:
ASTM Stainless Steel Grades
European Stainless Steel Grades
ISO Stainless Steel Grades
SAE Stainless Steel Grades
FDA Approved stainless steel grades
JIS Stainless Steel Grades
Finally, there has always been a questions of the highest-grade stainless steel. Well, there is never a straightforward answer to this. It will depend on whether your focus is on material strength, magnetism, or corrosion resistance.
However, it is worth noting at the moment, it is only 440C stainless steel that can be heat treated to achieve the highest hardness.
Conclusion
In short, you should choose stainless steel grade depending on your applications requirements. Although the main classification criterion is material composition, other variables such as fabrication and uses play a pivotal role.
For all your graded of stainless steel, – contact us now.