List of SUS stainless steel types｜Complete guide to selecting stainless steel by features, applications, and comparison

 

Here what can be used for machine materials"SUS (Stainless Steel) Materials"I'm taking notes that will be helpful for mechanical design.

 

In the field of mechanical design, selecting the optimal stainless steel (SUS) from numerous materials is a crucial process that influences product quality and cost. However, even with JIS standards alone...Finding the one stainless steel that perfectly meets a project's requirements among over 60 varieties is not an easy task, even for experienced designers.

 

This article presents a comprehensive list of the main types of SUS stainless steel, offering an in-depth comparative analysis of their unique characteristics and specific applications from a professional perspective.

 

Furthermore, we will delve into selection criteria from practical perspectives such as workability and cost. By the time you finish reading this article, your concerns about material selection should be resolved, and you will have acquired the knowledge to confidently choose the optimal stainless steel.

SUS Stainless Steel Types: Basics | The 5 Major Systems and Their Characteristics

Mechanism of passive film for rust prevention

The primary reason stainless steel is considered "rust-resistant" is the presence of an extremely thin protective layer on its surface called a "passive film."It is located in stainless steel. This is a dense, stable chromium oxide film that is spontaneously formed when chromium contained in stainless steel reacts with oxygen in the air and water.

 

This passive film acts as a strong barrier, preventing the underlying iron from rusting. Furthermore, it is remarkable that even if the film is damaged by scratches on the surface, it has the ability to instantly self-heal as long as there is oxygen. This feature allows stainless steel to maintain excellent corrosion resistance over a long period of time.

 

However, thisMembranes are not a panacea.In environments containing chloride ions in seawater, or under highly acidic or alkaline conditions, it can be damaged and corrosion can progress. Also, "stray rust," which occurs when iron powder adheres and rusts, can happen, so understanding the usage environment is important.

 

 

Properties imparted by chromium and nickel

The two major elements that determine the properties of stainless steel are chromium (Cr) and nickel (Ni). The properties of stainless steel change significantly depending on the balance of their content.

 

First, chromium is an essential element for stainless steel, and iron alloys with a chromium content of 10.5%%or more are defined as stainless steel. As mentioned above, chromium forms a strong passive film on the surface and plays a fundamental role in corrosion resistance. Generally, the higher the chromium content, the better the corrosion resistance.

 

Meanwhile, nickel is an important element that primarily stabilizes the metallic structure and imparts toughness and ductility (ease of processing) to materials. Adding nickel makes it easier to form a stable "austenite" metallic structure even at room temperature, which results in excellent workability and weldability. However,Because nickel is an expensive rare metal, its content directly affects material costs.　I will do so.

 

 

All-around austenitic stainless steel

Austenitic stainless steel is the most widely used type, accounting for about 60% of all stainless steel production. The representative steel grade, SUS304, contains a well-balanced amount of chromium and nickel, demonstrating high performance in terms of corrosion resistance, workability, and weldability.

 

A major characteristic of this type is that it does not have magnetic properties (does not stick to magnets) in the solution heat treated state.Furthermore, its high ductility makes it suitable for cold working into complex shapes such as deep drawing and bending.

 

However, it's important to note that it cannot be hardened by quenching, and it is prone to a phenomenon called "work hardening," where the surface hardens when subjected to processing such as cutting. This work hardening may also cause it to become slightly magnetic after processing.

 

 

Economical and easy-to-process ferritic stainless steel

Ferritic stainless steel's main characteristic is that it primarily contains iron and chromium, with little to no expensive nickel.This offers the advantage of lower material costs and stable pricing compared to austenitic stainless steel.

 

This series, represented by the representative steel grade SUS430, exhibits ferromagnetism and is attracted to magnets because it has the same ferritic structure as iron.It has good workability and weldability, but it falls short of austenitic stainless steel in terms of strength and corrosion resistance.

 

On the other hand, it has the excellent advantage of showing extremely high resistance to "stress corrosion cracking" in chloride environments, which is a weakness of austenitic stainless steel. For this reason, it is a more suitable option than austenitic stainless steel in certain environments.

 

 

Martensitic stainless steel that achieves high hardness

Martensitic stainless steel's greatest feature, unlike other stainless steels, is its ability to achieve extremely high hardness and strength by changing its structure through heat treatment (quenching and tempering).This is due to the fact that it contains a relatively large amount of carbon as a component.

 

Representative steel types include SUS410 and SUS440C, which are widely used in machine parts requiring high durability, such as blades, bearings, and shafts, due to their excellent hardness and wear resistance.

 

This alloy exhibits ferromagnetism and is attracted to magnets.However, as a trade-off for achieving high hardness, corrosion resistance tends to be the lowest among other stainless steel families. Therefore, selection requires careful consideration of the usage environment.

 

Thorough Comparison of Key Properties of SUS Stainless Steel Types

Duplex stainless steel with excellent strength and corrosion resistance

Duplex stainless steel, as the name suggests, is a relatively new high-performance material characterized by a microstructure where austenite and ferrite phases coexist in approximately equal proportions. This unique structure allows it to combine the advantages of both systems.

 

Its greatest feature is the combination of high strength and excellent corrosion resistance. It exhibits very balanced performance, possessing approximately twice the strength of general austenite steels (like SUS304) while also being resistant to stress corrosion cracking in chloride environments.

 

Steel types like SUS329J4L demonstrate their true value in extremely harsh environments, such as plant equipment and marine structures exposed to seawater and chemicals.It contains ferrite phases and is therefore magnetic, but its high performance is leading to increased adoption in specialized applications.

 

 

Precipitation hardening stainless steel that becomes even stronger with heat treatment

Precipitation hardening stainless steel ishardeningIt is a high-performance material that can drastically increase strength by precipitating fine particles within the metal structure through methods such as "". It is also called PH stainless steel.

 

The appeal of this system lies in its ability to achieve a high level of compatibility between seemingly contradictory properties: high strength comparable to or exceeding that of martensitic systems, and good corrosion resistance close to that of austenitic systems.

 

The representative steel grade, SUS630, is supplied in a relatively easy-to-machine condition. After the parts are machined to their final shape, they are hardened by applying an aging treatment at a relatively low temperature. Because this heat treatment causes very little distortion, it is ideal for manufacturing high-strength parts that require high dimensional accuracy, such as aerospace components and precision machinery.　It is.

 

 

The balance between strength and hardness in design.

In mechanical design, material strength and hardness are among the most fundamental selection criteria, but these two are not necessarily the same. A material with high strength is not always hard, nor isIf you only pursue hardness, materials tend to become brittle (toughness decreases).　There are

 

When selecting stainless steel, it is essential to consider the balance between strength, hardness, and toughness.

• Martensitic stainless steel (e.g., SUS440C)While heat treatment can achieve maximum hardness and high strength, it has low toughness and is weak against impact.
• Austenitic (e.g., SUS304)It has moderate hardness and strength, but very high toughness and excellent impact absorption capabilities.
• Precipitation hardening system (e.g., SUS630) and two-phase systemIt is located in between these, and balances high strength with good toughness.

 

Analyzing the forces applied to the designed part and the expected failure modes, and then selecting a system with an optimal balance of properties, leads to a reliable design.

 

 

The presence or absence of magnetism is key to material selection.

The magnetism of stainless steel is determined by its metallic structure and serves as an important design criterion. Whether or not it is attracted to a magnet is a simple method for identifying the material and, at the same time, a mandatory performance requirement for specific applications.

System classification	Presence or absence of magnetism (standard state)
Austenitic	nashi (Pyrus pyrifolia, esp. var. culta)
Ferritic	ant
Martensitic	ant
Two-phase system	ant
Precipitation hardening system	ant

 

 

Applications where magnetism is a concern

In environments where magnetism affects performance, such as with medical equipment (especially MRI-related), electronic devices, and peripheral components for magnetic sensors, being non-magnetic is an absolute requirement. In such cases, austenitic stainless steel is generally selected. However, as mentioned earlier, caution is advised because even austenitic stainless steel can become magnetized through strong cold working.

 

Applications that utilize magnetism

On the other hand, there are also cases where magnetism is actively utilized. For example, in IH cooking appliances like pots and pans, the bottom surface uses ferritic stainless steel (such as SUS430) that has magnetic properties, as they generate heat through electromagnetic induction. This property is also utilized in magnetic kitchen panels and whiteboards.

 

Classification and symbols according to JIS standards

When specifying stainless steel in Japan, it is common to use symbols defined by JIS (Japanese Industrial Standards). These symbols serve as a common language for accurately conveying materials on design drawings and specifications.

 

Stainless steel isIt usually starts with the symbol "SUS." This is an acronym for "Steel Use Stainless."The three digits following SUS indicate the specific steel grade.

• SUS304, SUS316, etc. (300 series)Mainly shows austenite.
• SUS430, SUS410, etc. (Series 400)Mainly shows ferritic and martensitic systems.
• SUS630 and similar (600 series)Mainly precipitation hardening systems.

Is there anything else?Symbols may also be added to indicate low carbon content (e.g., "L" in SUS316L) or the addition of specific elements.As a designer, understanding which system these symbols belong to and what their basic characteristics are is the first step in rapid material selection.

 

SUS Stainless Steel Types: Representative Steel Grades and Specific Applications

Most Representative SUS304 and Its Wide Range of Applications

SUS304 is the most representative type of stainless steel and has the largest market distribution.　です。　クロム18%、ニッケル8%を基本成分とすることから「18-8ステンレス」とも呼ばれ、その優れた特性バランスからあらゆる産業分野で基準材として使用されています。

 

Main characteristics of SUS304

Its greatest advantages are an excellent balance of corrosion resistance, workability, weldability, and cost. It exhibits sufficient corrosion resistance in atmospheric and general water environments and is also suitable for cold working such as pressing and bending.

 

Specific use cases

Thanks to its high versatility, it is used in a very wide range of applications, from everyday objects to cutting-edge industrial equipment.

• Household goods and kitchen appliancesSink, cookware, dishes, thermos, refrigerator door
• ArchitectureHandrails, interior and exterior panels, automatic doors, elevator interiors
• CarMuffler, decorative trim, wheel caps
• Industrial equipmentPiping and tanks for food and chemical plants, structural members for various machinery, bolts, and nuts

Thus, unless there are special requirements, the basic approach to material selection is to first consider SUS304.

 

 

Improved corrosion resistance of SUS316 with molybdenum

SUS316 is a higher-performance austenitic stainless steel made by adding the element molybdenum (Mo) to the composition of SUS304. The addition of this molybdenum is key to dramatically improving its corrosion resistance.

 

Main characteristics of SUS316

Specifically, it has remarkably superior resistance to chloride ions contained in seawater and coastal sea breezes.Even in harsh corrosive environments where SUS304 would rust, SUS316 maintains high corrosion resistance. This characteristic is called "pitting corrosion resistance."

 

Additionally, for structures involving welding, SUS316L, which has a low carbon content to prevent decreased corrosion resistance in the welded areas, is commonly used.

 

Specific use cases

Due to its excellent corrosion resistance, it is used in more severe environments where SUS304 cannot be used.

• Marine-relatedShip parts, marine structures, architectural components for coastal areas
• Chemical and Pharmaceutical PlantsReactor tank, piping, valve
• Medical devicesSurgical instruments, implants, and other items that require a high degree of cleanliness and chemical resistance.
• Food manufacturing equipmentLine that uses cleaning agents with strict hygiene management

Although the cost is higher than SUS304, it is often an economical choice in the long run when considering the frequency of part replacement and maintenance due to corrosion.

 

 

Features of SUS430, also used in household goods

SUS430は、フェライト系ステンレス鋼の中で最も代表的で、広く使用されている鋼種です。　クロムを18%含むことから「18クロムステンレス」とも呼ばれます。

 

 

Key Features of SUS430

Its greatest advantage is that it is relatively inexpensive among stainless steels because it does not contain expensive nickel.It also has the property of adhering to magnets like iron, and has the advantage of being less prone to deformation due to temperature changes because it expands little with heat. Workability is also good, and it is particularly suitable for bending and shallow drawing.

 

However, in terms of corrosion resistance, it is inferior to SUS304, so caution is required when used in places that are always wet or in environments with high salt content.

 

Specific use cases

Due to their economy and ease of processing, they are used in many products familiar in our daily lives.

• Kitchen & Home AppliancesCommercial refrigerator panels, washing machine drums, gas stove parts, spoons, and forks
• CarExhaust system parts such as mufflers and exhaust manifolds
• ArchitectureInterior materials, decorative trim, roofing materials
• OtherIH cookware base material (utilizing magnetism)

This material is a very strong contender for applications where cost-performance is key.

 

 

Examples of SUS440C with highest hardness

SUS440C is a special type of martensitic stainless steel with a particularly high carbon content. When heat-treated, it can achieve the highest hardness among stainless steels (capable of reaching HRC60).

 

SUS440C's main characteristics

Its exceptional hardness provides excellent wear resistance, meaning it has a property of being resistant to wear from friction.This characteristic creates a unique value that cannot be replaced by other stainless steels.

 

On the other hand, because it is a very hard material, its toughness is low (brittle) and it is not easy to machine. Furthermore, its corrosion resistance is inferior compared to other types, so proper management is necessary to prevent rust.

 

Specific use cases

Its application is limited to high-performance parts where hardness and wear resistance are paramount.

• BearingParts such as the balls of ball bearings and the races, which need to maintain smooth rotation under high loads
• BladeItems requiring long-lasting sharpness, such as high-quality knives, kitchen knives, and surgical scalpels
• Precision measuring instrumentsTools that need to maintain dimensional accuracy over long periods, such as gauge blocks
• OtherNozzles, valve seats, and other parts requiring wear resistance

This is truly a material that can be called a specialist in pursuing "hardness."

 

 

Performance of SUS630 in the Aerospace Field

SUS630は、析出硬化系ステンレス鋼の中で最も代表的で、広く使用されている鋼種です。その名称は、公称組成がクロム17%-ニッケル4%であることに由来し、「17-4PH」とも呼ばれます。

 

Key features of SUS630

The greatest appeal is that it achieves a high level of compatibility between opposing properties: high strength comparable to martensitic stainless steels and good corrosion resistance close to austenitic stainless steels.　It is.

 

Furthermore, a significant design and manufacturing advantage is that the material hardens through relatively low-temperature heat treatment (aging), resulting in extremely low distortion and dimensional changes during heat treatment. This allows for increased strength to be achieved even with complex shapes while maintaining high dimensional accuracy.

 

Specific use cases

Due to its high performance and reliability, it is active in fields with extremely high demands.

• AerospaceComponents requiring light weight and high strength, such as engine parts, airframe structural members, and actuator rods.
• Chemical and Petroleum PlantsValve parts and pump shafts that withstand high pressure
• Industrial machineryInjection molds, high-pressure equipment parts
• OtherShip propeller shafts, high-performance spring parts

Although the material cost is high, it is a very valuable option when considering the total manufacturing process cost and product reliability.

 

How to Smartly Choose and Important Considerations for Processing SUS Stainless Steel Types

Material selection considering processability and weldability

Not only the performance of the material itself, but also the perspective of "manufacturability" – how a part is manufactured – is an important factor that influences both cost and quality. Stainless steel, in particular, varies greatly in ease of processing depending on its type.

 

machining

When manufacturing parts by cutting from round bars, like bolts or shafts, machinability directly relates to production efficiency. SUS304 and SUS316 are highly viscous and are representative difficult-to-cut materials.On the other hand,SUS303 is a "free-cutting steel" with significantly improved machinability due to the addition of sulfur, etc., and is extremely effective for mass production on automatic lathes.I will.Stainless steel machiningIt is necessary to know the characteristics of each stainless steel material.

 

Welding

When creating a structure by welding parts together, weldability becomes extremely important. SUS304 and SUS316L have good weldability and are widely used.However, SUS303, which is a free-cutting stainless steel, cannot be welded in principle because the added sulfur causes cracks (hot cracks) in the welded area. It is necessary to confirm the presence or absence of welding during the design stage and select appropriate materials.

 

Press bending

In processes like bending and drawing sheet metal, material ductility is important.Austenitic stainless steel SUS304 has high ductility and is suitable for complex forming, such as deep drawing. Ferritic stainless steel SUS430 also has good workability, but its deep drawing performance is not as good as SUS304.

 

Work hardening phenomenon and its design implications

Work hardening, a characteristic phenomenon particularly observed in austenitic stainless steels, is the property of the material becoming harder due to cold working such as bending or cutting.This refers to. This occurs because the energy added by processing triggers a portion of the stable metal structure to transform into a hard structure called "martensite."

 

This phenomenon has two aspects for designers.

 

Drawbacks

One is the risk that the properties of the materials will change unintentionally. For example,Even if you design a part that requires non-magnetic properties with SUS304, it may become magnetized through processing.Additionally, hardening can reduce ductility, making further processing difficult, and slightly decrease corrosion resistance.

 

As a benefit

Meanwhile, this phenomenon can also be actively utilized. For example, in parts that require high elasticity and strength, like springs, a design is employed where steels that readily undergo work hardening (such as SUS301) are deliberately chosen, and the desired strength is obtained by utilizing the cold rolling and forming processes themselves.This allows for high strength without heat treatment.can be achieved.

 

 

Stress corrosion cracking risks and countermeasures

Stress Corrosion Cracking (SCC) is a fracture phenomenon accompanied by cracking that occurs when a material is exposed to a specific corrosive environment while under tensile stress. Austenitic stainless steels (SUS304 and SUS316) in particular have a weakness in that they are prone to this phenomenon in environments containing chloride ions, such as hot water and seawater.

 

This type of failure is extremely dangerous because it can occur suddenly, despite showing little visible corrosion. This risk must be thoroughly considered in areas where stress and corrosive environments overlap, such as in the piping of water heaters or heat exchangers in chemical plants.

 

To counter this, the most effective approach is to select materials with high resistance to stress corrosion cracking. Specifically,Ferritic stainless steel (such as SUS430) and duplex stainless steel, which has even better corrosion resistance, are strong alternative material options for such environments.　The first two are the following.

 

 

Correctly evaluate corrosion resistance according to the environment

While there's a common perception that "stainless steel doesn't rust," this is only true to the extent that it's "rust-resistant." Corrosion can still occur depending on the environment in which it's used.Designers must specifically evaluate what kind of corrosion will be a problem in what kind of environment, rather than vaguely understanding the term "corrosion resistance."

 

General corrosion

Corrosion where the entire surface is uniformly attacked in a very strong acidic or alkaline environment.In such an environment, it is necessary to consider higher alloy stainless steels and special corrosion-resistant alloys.

 

Pitting corrosion

Corrosion that occurs locally, deeply, and in a spot-like manner due to the localized breakdown of passive films by chloride ions contained in seawater and industrial water.For this countermeasure, SUS316 with added molybdenum and duplex stainless steel with even higher corrosion resistance are effective.

 

Crevice corrosion

Corrosion that occurs in the gaps between members, such as bolt joints and gasket contact surfacesCorrosion progresses through a mechanism similar to pitting because oxygen supply is limited within the crevice, making it prone to chloride ion concentration. SUS316 and duplex systems are also effective countermeasures for this.

 

It is essential to accurately understand the usage environment, predict potential corrosion forms, and select steel types with optimal resistance to ensure product longevity and safety.

 

Mastering the knowledge of SUS stainless steel types and applying it to design

Balancing cost and performance

When selecting the optimal stainless steel, considering the balance between performance and cost is unavoidable.What's important here is the perspective of judging based on the "total manufacturing cost," which includes not only the price of the material itself (material unit cost) but also processing, heat treatment, assembly, and future maintenance.　It is.

 

For example, let's consider designing a part where cutting is the primary manufacturing process. Looking solely at material cost, SUS304 might be cheaper than SUS303. However, SUS304 is a difficult-to-machine material, leading to longer processing times and increased tool wear. On the other hand, SUS303, being a free-cutting steel, allows for significantly shorter processing times. Consequently, when considering the total cost including machining expenses, SUS303 often becomes less expensive than SUS304.

 

Similarly, when producing high-precision, high-strength parts, selecting precipitation-hardenable SUS630, which has a higher material cost, can eliminate the need for costly finishing grinding after heat treatment required for martensitic types, potentially reducing overall costs.

 

In this way, overlooking the entire manufacturing process from the early stages of design and having a perspective to optimize total cost leads to competitive product development.

 

 

Select the optimal SUS stainless steel type and utilize it in design

This article comprehensively explains stainless steel, which is essential for mechanical design, covering its basic principles, characteristics of each system, representative steel types, and practical selection methods. Finally, it summarizes the key points and a table for selecting the optimal material and utilizing it in excellent designs.

 

• The corrosion resistance of stainless steel is due to the passive film on its surface.
• They are broadly classified into five systems by their metallic structure: austenite, ferrite, martensite, duplex, and precipitation hardening.
• Austenitic stainless steel is the most common general-purpose material, excelling in corrosion resistance and workability.
• Ferritic stainless steel does not contain nickel, is economical, and has magnetic properties.
• Martensitic stainless steels offer the highest hardness among stainless steels through heat treatment.
• The two-phase system combines the advantages of austenite and ferrite, achieving both high strength and high corrosion resistance.
• Precipitation hardening systems achieve ultra-high strength and good corrosion resistance through special heat treatment, making them ideal for precision parts.
• SUS304 is a standard steel grade used in all fields
• SUS316 excels in corrosion resistance in harsh environments such as seawater due to the addition of molybdenum.
• SUS303 is also called free-cutting steel and greatly improves productivity in cutting operations.
• SUS430 is a strong contender when cost reduction is desired and is widely used in household goods.
• SUS440C is used in special applications where wear resistance is crucial, such as bearings and cutting tools.
• SUS630 is suitable for high-strength parts that require high precision with minimal distortion during heat treatment.
• The optimal material differs depending on processing methods such as cutting, welding, and pressing.
• It is important to make decisions based on the total manufacturing cost, including processing fees, not just the material cost.

 

SUS Stainless Steel: List of Properties by Type

Here is a table summarizing the properties of the representative stainless steel (SUS) types explained in this article. We hope this will be useful for your material selection comparison.

JIS Steel Types	System	Main Features	magnetism	corrosion resistance	Strength/Hardness	Workability	relative cost
SUS304	Austenitic	Most versatile. Good balance of corrosion resistance, workability, and cost.	None	優	中	Cutting: Difficult Welding: Good Molding: Excellent	Standard
SUS316/316L	Austenitic	Corrosion resistance improved with Mo addition. Resistant to seawater and chemicals.	nashi (Pyrus pyrifolia, esp. var. culta)	Special grade	中	Cutting: Difficult Welding: Good Molding: Excellent	Slightly high
SUS303	Austenitic Free-cutting steel	With the addition of S and P, machinability is extremely high.	None	Slightly inferior	中	Cutting: Excellent Welding: Not Allowed Molding: Possible	Standard
SUS430	Ferritic	Inexpensive. Excellent resistance to stress corrosion cracking.	ant	良	中	Cutting: Good Welding: Caution Molding: Good	安
SUS410	Martensitic	Hardened by heat treatment. High strength, wear resistance.	ant	劣	高	Machining: Available Welding: Difficult Molding: Possible	Standard
SUS440C	Martensitic	Highest hardness in stainless steel. Extremely high wear resistance.	ant	劣	The best	Cutting: Difficult Welding: Difficult Shaping: Difficult	高
SUS329J4L	Two-phase system	Achieves both high strength and high corrosion resistance. Extremely excellent in stress corrosion cracking resistance.	ant	Special grade	高	Cutting: Difficult Welding: Caution Molding: Possible	高
SUS630	Precipitation hardening system	Achieves both high strength and excellent corrosion resistance. Minimal heat treatment distortion.	ant	優	Extremely high	Cutting: Good Welding: Possible Molding: Good	高

Austenitic stainless steels are generally non-magnetic, but their structure can change due to cold working, which can cause them to become magnetic.

 

That's it.