Stainless Steel(SUS) Grades & Composition Chart | BELINKER
Stainless Steel Grades Explained: Composition, Properties, and CNC Machining
Choosing stainless steel involves more than deciding whether a part needs corrosion resistance.
A machined shaft, welded enclosure, precision fitting, and spring can require very different combinations of strength, hardness, formability, and environmental resistance. The material that works well for one component may add unnecessary cost—or create performance problems—in another.
This guide compares 40 commonly encountered stainless steel grades across five major families. It explains their key chemical compositions, practical differences, and implications for CNC machining and sourcing.
If you are comparing 304 vs. 316 stainless steel, considering 430 as a lower-nickel alternative, or selecting 17-4 PH for a high-strength component, start with the requirements of the finished part.
What Makes Stainless Steel Different?
Stainless steel contains at least approximately 10.5% chromium. Chromium helps form a thin protective surface film, which gives stainless steel its characteristic corrosion resistance.
Other elements change how the material behaves:
Element | Why it matters |
|---|---|
Chromium — Cr | Supports the protective passive film and oxidation resistance. |
Nickel — Ni | Helps stabilize the austenitic structure and supports toughness and formability. |
Molybdenum — Mo | Improves resistance to localized corrosion, including pitting in many chloride environments. |
Carbon — C | Influences hardenability and strength; its effect depends strongly on the stainless family. |
Nitrogen — N | Can improve strength and localized corrosion resistance in suitable alloys. |
Sulfur — S | Improves machinability in free-machining grades, with corrosion and welding tradeoffs. |
Titanium / Niobium — Ti / Nb | Used to stabilize certain grades against carbide-related sensitization. |
Copper / Aluminum — Cu / Al | Contribute to precipitation strengthening in certain PH stainless steels. |
The effect of an element depends on the overall alloy and processing history. Chromium percentage alone does not establish which stainless steel will perform best. Outokumpu: Stainless steel types, Nickel Institute: The nickel advantage.
The Five Main Types of Stainless Steel
Family | Common examples | Main selection considerations |
|---|---|---|
Austenitic | 304, 316, 303, 321 | Corrosion resistance, toughness, forming, and welding |
Ferritic | 409, 430, 439, 444 | Low nickel content, magnetic behavior, and application-specific corrosion resistance |
Martensitic | 410, 420, 440C | Hardness, wear resistance, and heat-treatment response |
Precipitation-hardening — PH | 17-4 PH, 15-5 PH, 17-7 PH | High strength obtained through controlled processing and aging |
Duplex | 2101, 2304, 2205, 2507 | Strength combined with corrosion resistance; careful fabrication control |
Austenitic grades are generally nonmagnetic in the annealed condition, although cold working can make some grades magnetic. Ferritic, martensitic, and duplex stainless steels are magnetic. A magnet test alone cannot identify a specific grade. Outokumpu: Stainless steel families.
304 vs. 316 vs. 430: The Practical Difference
304 stainless steel is a common starting point for general-purpose components. It offers a useful combination of corrosion resistance, formability, and weldability.
316 stainless steel contains molybdenum, which improves resistance to pitting and crevice corrosion in many chloride-containing environments. It deserves consideration when the exposure is more demanding than ordinary indoor service.
430 stainless steel is ferritic and contains much less nickel than 304 or 316. It is often considered for appliance components, trim, and other applications where its corrosion resistance and fabrication characteristics are sufficient. Outokumpu: Core, Supra, Moda.
Question | 304 | 316 | 430 |
|---|---|---|---|
Stainless family | Austenitic | Austenitic | Ferritic |
Molybdenum addition | Not a defining addition | Typically specified at 2–3% | Not a defining addition |
Typical reason to consider it | General-purpose balance | Greater localized corrosion resistance | Low-nickel option for suitable environments |
Welding considerations | Widely used; consider 304L | Widely used; consider 316L | Requires grade-appropriate process control |
Magnetic behavior | Can become magnetic after cold work | Can become magnetic after cold work | Magnetic |
316 is not automatically suitable for continuous seawater exposure. Temperature, chloride concentration, crevices, deposits, and cleaning conditions all influence corrosion. More highly alloyed materials may be necessary. Nickel Institute: Stainless steel in water applications.
How to Read the Stainless Steel Composition Charts
All numerical composition values below are weight percentages, wt%.
≤ means a maximum.
≥ means a minimum.
A range specifies lower and upper limits.
— means the element is not reported in this selected comparison; it does not necessarily mean zero.
Iron is the balance after alloying and residual elements.
These tables show selected major elements, not every chemical requirement.
The charts summarize published reference ranges. Product form, purchasing specification, and revision can affect the applicable limits. The 304 and 304L entries below use the A276 bar compositions reported by BSSA; sheet and plate references may differ.
Use the specified standard and material test report to verify purchased material. A grade name by itself is not a complete procurement specification. BSSA: Austenitic composition tables and product-form differences.
1. Austenitic Stainless Steel: 200 and 300 Series
Austenitic stainless steels cover a wide range of applications, from formed sheet components to machined fittings and corrosion-resistant process equipment.
General-purpose and forming grades
Grade | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
201 | ≤0.15 | 16–18 | 3.5–5.5 | — | Mn 5.5–7.5; N ≤0.25 |
202 | ≤0.15 | 17–19 | 4–6 | — | Mn 7.5–10; N ≤0.25 |
301 | ≤0.15 | 16–18 | 6–8 | — | N ≤0.10 |
302 | ≤0.15 | 17–19 | 8–10 | — | N ≤0.10 |
303 | ≤0.15 | 17–19 | 8–10 | — | S ≥0.15 |
304* | ≤0.08 | 18–20 | 8–11 | — | — |
304L* | ≤0.03 | 18–20 | 8–12 | — | — |
305 | ≤0.12 | 17–19 | 10.5–13 | — | — |
304 and 304L: bar-reference compositions described above. Chemistry reference: BSSA austenitic grades.
201 and 202 use more manganese and less nickel than conventional 304-type alloys. They should be evaluated against the actual environment and fabrication requirements before being substituted.
301 and 302 are frequently associated with cold-worked products. Their delivered condition matters: annealed material and heavily cold-worked material can behave very differently.
304 and 304L are widely used general-purpose options. The lower carbon limit of 304L helps reduce susceptibility to sensitization associated with welding.
305 is selected particularly for forming operations where a lower work-hardening rate is useful. Outokumpu: Core product range, Ulbrich: Alloy reference brochure.
303 deserves separate attention for machining. Sulfur additions improve chip breaking and machinability, making it attractive for suitable turned components. The tradeoff is reduced suitability for some corrosive environments and welded assemblies. Carpenter Technology: Machining austenitic stainless steels.
Corrosion-resistant, stabilized, and heat-resistant grades
Grade | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
304H | 0.04–0.10 | 18–20 | 8–10.5 | — | Controlled carbon range |
309S | ≤0.08 | 22–24 | 12–15 | — | — |
310S | ≤0.08 | 24–26 | 19–22 | — | — |
316 | ≤0.08 | 16–18 | 10–14 | 2–3 | — |
316L | ≤0.03 | 16–18 | 10–14 | 2–3 | — |
316Ti | ≤0.08 | 16–18 | 10–14 | 2–3 | Ti stabilized |
317L | ≤0.03 | 18–20 | 11–15 | 3–4 | — |
321 | ≤0.08 | 17–19 | 9–12 | — | Ti stabilized |
347 | ≤0.08 | 17–19 | 9–13 | — | Nb/Ta stabilized |
904L — N08904 | ≤0.02 | 19–23 | 23–28 | 4–5 | Cu 1–2 |
254 SMO — S31254 | ≤0.02 | 19.5–20.5 | 17.5–18.5 | 6–6.5 | N 0.18–0.22; Cu 0.5–1 |
Chemistry references: BSSA heat-resistant grades, BSSA austenitic grades, Ulbrich alloy data.
316 and 316L are common candidates when molybdenum-bearing stainless steel is required. Choose the low-carbon variant when the specification or welding requirements call for it.
317L, 904L, and 254 SMO extend the available choices for more demanding corrosion conditions. They require an environment-specific assessment; their higher alloy content does not make them universally interchangeable.
316Ti, 321, and 347 are stabilized grades. Titanium or niobium additions help address sensitization concerns in appropriate thermal service.
304H, 309S, and 310S are associated with elevated-temperature applications. Selection must account for the atmosphere, loading, exposure duration, and thermal cycling. There is no single maximum service temperature that applies to every installation. Outokumpu: Supra, Ultra, Therma.
2. Ferritic Stainless Steel: 409, 430, 439, and More
Ferritic grades offer options with low nickel content. They are magnetic and are not hardened through conventional quench-and-temper treatment.
Grade | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
409 family — S40910 reference | ≤0.03 | 10.5–11.7 | ≤0.50 | — | Ti stabilized |
430 | ≤0.12 | 16–18 | — | — | — |
430F | ≤0.12 | 16–18 | ≤0.75 | — | S ≥0.15 |
434 | ≤0.12 | 16–18 | — | 0.75–1.25 | — |
439 — S43035 reference | ≤0.03 | 17–19 | ≤0.50 | — | Ti stabilized |
444 | ≤0.025 | 17.5–19.5 | ≤1.00 | 1.75–2.50 | Ti/Nb stabilized |
446 | ≤0.20 | 23–27 | ≤0.75 | — | N ≤0.25 |
409 includes multiple UNS variants with different stabilization requirements. The row above specifically represents S40910.
Chemistry references: BSSA ferritic grades, Rolled Metal Products: 439, BSSA heat-resistant grades.
409 is associated with automotive exhaust applications. 430 is common in appliance and decorative applications where its corrosion resistance is sufficient.
430F is a free-machining grade. Its sulfur addition improves machinability but requires attention to corrosion and joining requirements.
434 adds molybdenum to a chromium-based ferritic composition. 439 uses titanium stabilization and is used in applications including exhaust components. 444 combines molybdenum with stabilization for more demanding corrosion applications.
446 is a high-chromium ferritic option associated with oxidation resistance at elevated temperatures. Its suitability still depends on the operating and fabrication conditions. Outokumpu: Moda, Supra, Carpenter Technology: 430F datasheet.
3. Martensitic Stainless Steel: Hardness and Wear Resistance
Martensitic stainless steels can be hardened through appropriate heat treatment. They are useful when hardness, wear resistance, and mechanical performance are central requirements.
Grade | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
410 | 0.08–0.15 | 11.5–13.5 | ≤0.75 | — | — |
416 | ≤0.15 | 12–14 | — | — | S ≥0.15 |
420 | ≥0.15 | 12–14 | — | — | Carbon varies among related specifications |
431 | ≤0.20 | 15–17 | 1.25–2.50 | — | — |
440A | 0.60–0.75 | 16–18 | — | ≤0.75 | — |
440B | 0.75–0.95 | 16–18 | — | ≤0.75 | — |
440C | 0.95–1.20 | 16–18 | — | ≤0.75 | — |
Chemistry reference: BSSA martensitic and PH grades.
410 is a general-purpose hardenable stainless steel. 416 adds machinability for suitable turned components.
420 is used where hardenability and a polished surface are valuable. Specify the exact grade and standard: “420” does not fully describe every related product sold under that name.
431 offers a combination of strength, toughness, and corrosion resistance after appropriate processing.
440A, 440B, and 440C contain progressively higher carbon ranges. 440C is commonly considered for high-hardness and wear-resistant components, including bearing-related applications.
The grade name alone does not guarantee a final hardness. Heat treatment and subsequent finishing must be included in the manufacturing plan. Carpenter Technology: Stainless selection guide, Carpenter Technology: 431.
4. Precipitation-Hardening Stainless Steel: 17-4 PH, 15-5 PH, and 17-7 PH
PH stainless steels develop strength through controlled processing and precipitation hardening.
Grade | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
17-4 PH — S17400 | ≤0.07 | 15–17.5 | 3–5 | — | Cu 3–5; Nb+Ta 0.15–0.45 |
15-5 PH — S15500 | ≤0.07 | 14–15.5 | 3.5–5.5 | — | Cu 2.5–4.5; Nb+Ta 0.15–0.45 |
17-7 PH — S17700 | ≤0.09 | 16–18 | 6.5–7.75 | — | Al 0.75–1.50 |
Chemistry reference: BSSA PH composition data.
17-4 PH is a widely used option for high-strength machined parts. A drawing should specify the required material condition, rather than only “17-4 stainless.”
15-5 PH is considered when strength and transverse toughness are important.
17-7 PH is frequently associated with springs and formed components that require high strength after processing.
For CNC machining, establish whether critical dimensions must be achieved before or after aging. Heat-treatment condition affects mechanical properties and can affect dimensional planning. Carpenter Technology: 17-4 PH datasheet, 15-5 PH datasheet, Outokumpu: Dura.
5. Duplex Stainless Steel: 2101, 2304, 2205, and 2507
Duplex stainless steel combines austenitic and ferritic phases. These grades offer useful combinations of strength and corrosion resistance, with fabrication requirements that differ from conventional 304 and 316.
Grade / reference UNS | C | Cr | Ni | Mo | Other selected chemistry |
|---|---|---|---|---|---|
2101 — S32101 | ≤0.04 | 21–22 | 1.35–1.70 | 0.10–0.80 | N 0.20–0.25; Mn 4–6 |
2304 — S32304 | ≤0.03 | 21.5–24.5 | 3–5.5 | 0.05–0.60 | N 0.05–0.20 |
2205 — S32205 | ≤0.03 | 22–23 | 4.5–6.5 | 3–3.5 | N 0.14–0.20 |
2507 — S32750 | ≤0.03 | 24–26 | 6–8 | 3–5 | N 0.24–0.32 |
2205 is also associated with UNS S31803, which has different composition limits. Specify the required UNS designation and certification.
Chemistry reference: BSSA duplex composition data.
2101 and 2304 are lean duplex options. 2205 is a widely used duplex grade for applications requiring strength and enhanced corrosion resistance. 2507 is a super duplex option for more demanding environments.
Machining, welding, and thermal exposure require grade-specific planning. A duplex grade should not be treated as a direct process substitution for 304 or 316. Outokumpu: Forta duplex range.
Which Stainless Steel Is Best for CNC Machining?
The best grade is the one that meets the part’s requirements at an acceptable total manufacturing cost.
Main requirement | Grades to evaluate | What to check |
|---|---|---|
General-purpose machined part | 304 / 304L | Environment, welding, tolerances |
Improved chip control for turning | 303 | Corrosion exposure and joining requirements |
Greater resistance to chloride-related pitting | 316 / 316L | Actual temperature, concentration, and crevice conditions |
Hardenable, machinable shaft | 416 | Corrosion requirements and final heat treatment |
High hardness and wear resistance | 420 / 440C | Required hardness, distortion, and finishing sequence |
High-strength precision component | 17-4 PH / 15-5 PH | Aging condition and final dimensional requirements |
Strength plus demanding corrosion service | 2205 / 2507 | Fabrication capability and environmental suitability |
Austenitic stainless steels can work-harden during machining. Tooling, engagement, coolant delivery, and chip evacuation affect productivity and surface quality. Free-machining grades may reduce machining difficulty, but their other properties must still satisfy the application. Carpenter Technology: Austenitic stainless machining guidance.
What Affects the Cost of Stainless Steel Machined Parts?
Raw material price is only one part of the quotation.
A useful cost review also considers stock availability, material removal, tool access, tolerances, setup count, heat treatment, finishing, inspection, quantity, and delivery requirements.
For example, a lower-priced alloy may offer little advantage if it requires additional processing or cannot meet the service conditions. Conversely, specifying a highly alloyed grade without a functional reason can increase purchasing and manufacturing costs.
Compare quotations against the same drawing, material condition, inspection scope, and delivery terms.
What Should U.S. Buyers Include in a Stainless Steel RFQ?
A clear request for quotation should include:
Material designation: grade and UNS number where applicable.
Purchasing standard: the relevant product specification.
Material condition: annealed, cold-worked, hardened, or aged.
Drawings: dimensions, tolerances, threads, and surface finish.
Post-processing: heat treatment, passivation, polishing, or other requirements.
Documentation: material certification, traceability, and inspection reports.
Commercial requirements: quantity, delivery destination, and target date.
Common specifications include ASTM A276 for stainless bars and shapes, ASTM A240 for plate, sheet, and strip, and ASTM A564 for age-hardening stainless bars and shapes. Specify the applicable revision and requirements. ASTM: Steel standards.
Frequently Asked Questions
Is SUS304 the same as 304 stainless steel?
SUS304 is a Japanese designation closely associated with Type 304. However, matching grade numbers do not automatically establish compliance with a particular ASTM purchase requirement. Verify the standard, product form, chemistry, and required properties. BSSA: Grade designations and composition differences.
Is 316L always better than 316?
The “L” indicates a lower carbon limit. Its main advantage is relevant to sensitization and welding requirements; it does not mean universally better performance in every application. Outokumpu: Supra range.
Can stainless steel rust?
Yes. An unsuitable grade, aggressive exposure, contamination, or poor surface condition can lead to corrosion. Cleaning and appropriate passivation can help address free-iron contamination, but they cannot compensate for selecting the wrong alloy. Carpenter Technology: Passivating stainless steel parts.
Source Stainless Steel CNC-Machined Parts from South Korea with BELINKER
Material selection becomes more useful when it is connected to a practical manufacturing plan.
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Share your drawing, material specification, quantity, finishing requirements, and delivery target with BELINKER. Whether you already have a specified grade or need to discuss suitable manufacturing options, a clear technical review helps establish the scope of the project.
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