Understanding Different Stainless Steel Grades

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.

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.

More Resources:

• Austenitic Stainless Steel – Source: TuoLian
• Austenitic SS – Source: Wikipedia
• Austenitic Stainless Steels – Source: Science Direct

Ferritic Stainless Steel Grades

Chemical composition of Ferritic SSS – Photo credits: Wikipedia

Ferritic SS may be a better alternative in metal fabrication. Although there are many Ferritic SS grades, the main characteristics are:

• Carbon composition – approximately 2%
• Chromium composition – between 5% and 27%
• Very little or no nickel content
• Can be cold work hardened
• Harding using heat treatment is not recommended
• For increased hardness, cold working may be necessary
• Does not oxidize due to high temperature
• When subjected to stress, the stainless steel will neither crack or corrode
• Fabrication properties tend to be poor which may require improvements

Some common grades include:

Ferritic Stainless Steel Grade	Description
405	It is a non-hardenable SS grade Post-weld annealing improves the ductility Don’t use oxyacetylene welding on this stainless steel grade Common applications include partitions, steam nozzles, quenching boxes, etc. Can be formed by drawing and spinning
429	Compared to 430 SS, 429 has better welding properties It has good corrosion resistance Applications include making household gadgets, internal decoration for architectural structures, mining equipment, bolts, nuts, automotive parts, etc.
430	Common applications are dishwashers, baskets, automotive trim, chimney liners, fasteners, etc. Best for cosmetic application on both exterior and interior surfaces Post-weld treatment is necessary to restore corrosion resistance Corrosion resistance is almost the same as 304 and 304L It does not work harden faster Can resist nitric acid attack There is the 430F, which is popular for free machining
434	It is simply the 430 SS grade but with molybdenum, which improves corrosion resistance Excellent oxidation and heat resistance
436	Applications include automotive trim, forging wrought products There is the 436L with better oxidation and corrosion resistance than the 409 SS Polishing 436 results in an appearance similar to a chromium plate
442	Resistant to scaling and high temperature Common applications include furnace components A popular precipitation-hardening grade It has high hardness Generally, the strength is good Excellent corrosion resistance properties
446	Suitable for intermittent use Exhibit scaling and high-temperature resistance It is non-heat treatable Excellent resistance to corrosion and high-temperature oxidation
502	A perfect choice for petrochemical equipment It has high strength with heat-resistant properties

More Resources:

• Ferritic Stainless Steel – Source: TuoLian
• Ferritic SS – Source: Wikipedia
• What is Ferritic Stainless Steel – Source: Azom

Martensitic Stainless Steel

Chemical composition of Martensitic SS grade – photo credits: Wikipedia

Martensitic grades of stainless steels are unique due the magnetic properties. The stainless steel metals in this category are known for:

• Chromium varies between 5% and 18%
• Low carbon content of about 1.2% with come containing nickel
• Suitable for heat treatment
• Corrosion resistance is slightly low – Of course, this is because there is low Chromium in the composition
• They have magnetic properties

Grades of martensitic stainless steel grade:

Martensitic Stainless Steel Grade	Description
403	Common applications include turbine blades, bushings, fasteners, rocket components, compressor blades, etc. You can harden 403 SS with heat treatment
409	An example of general-purpose stainless steel grade A perfect choice for construction that does not require heat treatments For making exhaust parts in automobiles, mufflers, catalytic converters, etc. It is cheaper than 304 susceptible to surface rusting Exhibits good thermal properties and strength A more stabilized version of 409 SS grades are S40910, S40930, and S40920 Preheating is necessary before welding (150 to 260°C)
410	Best for making machine parts, exhaust systems, making pipes, valves, nozzles, instruments, etc. Considered general-purpose stainless steel grade Exhibit high strength It is heat treatable You can improve corrosion resistance properties through polishing, hardening, or tempering
414	The application includes making springs, forged spindles, shafts, bolts, nuts, beater bars, valves, etc. It can be heat treated, annealed, and tempered Required post-weld treatment
416	It is a free machining SS – it has the highest machinability Not suitable for marine and chloride exposure Hardening can improve corrosion resistance Poor welding properties Applications include making screws, nuts, shafts, valves, etc.
420	Share most properties with 410 SS grade except for high carbon content Main applications include making surgical instruments, scissors, needles, knife blades, etc. Retain magnetic properties when hardened and annealed Fully hardening 420 SS help achieve maximum resistance to corrosion It has higher carbon compared to 410 SS grade Although you can weld 420 SS grade, it is not a common practice
422	A good choice for making turbine blades, aircraft parts, rotors, heating systems components, etc. Can be a perfect alternative to 403 SS Suitable for high-temperature applications and maximum corrosion resistance is not a priority
431	The perfect grade for beater bars, fittings in the aerospace industry, shafts, bolts, It is considered a special-purpose stainless steel grade Exhibit excellent corrosion resistance It is heat treatable Exceptional toughness and torque strength Not suitable for cold working since they have high-yield strength
440 A, B, and C	Applications include ball bearings, valves, etc. Superior hardenability and toughness than most stainless steel grades 440B exhibit higher toughness and hardness than SS grade 440A 440C has the highest toughness and hardness of all SS grades Highest wear resistance It has High carbon content. Remember, the 440A has a slightly lower percentage than 440B and 440C There is the 440F, which is considered a free-machining version
501	Common applications include petrochemical equipment Highly ductile Heat resistant

More Resources:

• Martensitic Stainless Steel – Source: TuoLian
• What is Martensitic Stainless Steel – Source: Azom
• Martensitic SS – Source: Wikipedia

Duplex Stainless Steel

Chemical composition of Duplex Stainless Steel – Photo credits: Wikipedia

Usually the duplex SS exhibited better properties of Ferritic SS and Austenitic SS. As a result, it is a versatile SS material for many applications.

As a result, this SS grades have:

• 35% to 8% nickel content
• 21% to 27% chromium content
• 05% to 5% copper content

Let’s look at some common duplex SS grades:

Duplex Stainless Steel Grade	Description
318L	Has high molybdenum content Popular for welding Good corrosion resistance
2003	It is a molybdenum enhanced Phase balance is similar to 2205 An affordable alternative to 316L SS
2101	This SS grade is nitrogen enhanced Suitable for general-purpose applications Its corrosion resistance is better than 316L
2205	2205 has high strength with good toughness and better stress corrosion resistance High yield strength It is a popular and common duplex SS grade Enhanced fatigue strength Applications include heat exchanger systems, cargo tanks, marine systems, piping, etc.
2304	Corrosion resistance properties similar to 316L Yield strength is twice that of 304L and 316L Exhibit good welding properties, resistance to stress corrosion cracking, Easy to machine Better fatigue resistance properties
2507	Molybdenum content in 2507 SS is higher than in 2205 SS Strong and resistant to stress corrosion cracking
4501	It is a super duplex stainless steel The toughness, corrosion resistance, and mechanical strength are higher compared to ordinary duplex SS Higher resistance to pitting corrosion Suitable for offshore applications such as extraction rigs, valves, flanges, pumps, etc.
S32750	It is primarily used in the oil and gas industry. Applications include heat exchanger systems, architectural structures, offshore platforms, etc.

More Resources:

• Duplex Stainless Steel – Source: TuoLian
• Duplex SS – Source: BSSA

Precipitation Hardening Stainless Steel

Precipitation hardness SS are unique materials. In fact, through heat treatments, you can get:

• 850 to 1700MPa tensile strength
• 520 to 1500Mpa yield strength

Other unique characteristics are:

• High tensile strength
• 3% to 5% nickel content
• Between 15% and 17.5% chromium
• Suitable for hardening

In precipitation-hardening stainless steel, niobium, aluminum, and copper constitute about 0.5% of the SS total mass.

Let’s look at some of the most common SS grades in this category:

Precipitation Stainless Steel Grade	Description
13-8 PH	This is a martensitic precipitation hardening SS It has high strength, superior toughness, and excellent strength Applications include aerospace parts such as landing gear, nuclear reactor components, parts in the petrochemical industry, etc.
15-5 PH	It is a martensitic precipitation hardening SS Contains about 5% nickel and 15% Chromium Characterized by high hardness and strength Better mechanical properties SS grade is easy to weld Applications include structural components in the aerospace industry, valves, nuclear reactor components, etc.
17-4 PH	It is a martensitic precipitation hardness SS 15% to 17% Chromium and 3% to 5% nickel High strength and hardness Machinability compares to 304 SS grade Heat treatment improves the hardness Improve resistance to stress corrosion cracking Application include aircraft parts and components in petroleum and chemical industries
17-7 PH	Degree of corrosion resistance is nearly similar to 304SS High strength Common applications in aerospace parts, blades, springs, clips, surgical parts, etc.

More Resources:

• PH Stainless Steel – Source: TuoLian
• Precipitation Hardening SS – Source: TWI
• Precipitation Hardening SS – Source: Azom

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

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.

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.

 

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

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
Highly corrosion resistance stainless steel grades	Most stainless steel is highly corrosion resistant However, those with molybdenum have better corrosion resistance properties. Grades 416, 304, and 316 exhibit better corrosion resistance
Exhaust stainless steel grades	Grades 304 and 309 exhaust systems
Hardenable Stainless Steel Grades	Martensitic stainless steels Precipitation hardening stainless steel
Hardest stainless steel	440C is one of the hardest stainless which can be heat treated
Heat-resistant stainless steel	310 with intermittent temp. 1035 °C and continuous temp. 1150 °C 2111HTR intermittent temp. 1150 °C and continuous temp. 1150 °C
High carbon stainless steel grades	Stainless steel with the letter “H” has high carbon. Examples include 304H, 316H
High strength stainless steel grades	Some stainless steel with high tensile strength are 431, and 17-4 PH
Machinability of stainless steel grades	Generally, you can machine all grades of stainless steel However, it is worth noting that when machining stainless steel, there are higher chances of work hardening Adding sulfur improves the stainless steel machining properties like in the case of grade 303 stainless steel. Other SS grades are 304 and 416
Stabilized stainless steel grades	Titanium stabilized SS 321 Niobium stabilized SS grade 347 Titanium or niobium stabilized SS grades 409 High nitrogen and manganese can also stabilize austenitic
Cheapest stainless steel grade	410 is one of the most affordable stainless
Most expensive stainless steel	317 Stainless steel costs vary depending on the element composition.
Weldable Stainless Steel	304L 347 430 439 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.