5 types of stainless steel：grades and characteristics

Many engineers face constant headaches when choosing the right material stainless steel for performance-critical parts. Selecting the wrong alloy leads to corrosion, cracking, high scrap rates, and unexpected CNC machining delays. These issues grow worse when a design demands tight tolerances, cosmetic finishes, or long-term durability.

This guide gives you a practical understanding of stainless steel material, and the five core types of stainless steel used across modern manufacturing. You will learn how each stainless steel alloy behaves, how the classes of stainless steel differ. After reading, you will confidently select the best alloy for your  parts and avoid costly material mistakes.

What Are the 5 Types of Stainless Steel?

There are five main types of stainless steel used in industry: Austenitic Stainless Steel, Ferritic Stainless Steel, Martensitic Stainless Steel, Duplex Stainless Steel, and Precipitation Hardening Stainless Steel. These five groups cover all common stainless steel grades, stainless alloys, and ss material types you will encounter in CNC machining and manufacturing.

Type 1: Austenitic Stainless Steel

Austenitic Stainless Steel is the most widely used type among all stainless steel types. It features high corrosion resistance, excellent ductility, and stable performance during CNC machining. Its stainless steel composition of chromium and nickel allows for smooth cutting, precise tolerances, and clean surface finishes. These qualities make it ideal for medical, food, marine, optical, and high-precision industrial applications.

Austenitic Stainless Steel Grades

Austenitic stainless steel includes many stainless steel grades, each designed for specific corrosion resistance, weldability, and temperature requirements. The table below shows the most common common stainless steel alloys for reference.

Grade	Key Features	Typical Uses
301 / 301L	High strength after cold work, good fatigue resistance	Springs, clips, structural brackets
302	Similar to 304 but higher strength	Fasteners, washers, industrial connectors
303	Best machinability due to added sulfur	Screws, bushings, fittings, mass-production parts
304 / 304L	Most common stainless steel alloy, strong corrosion resistance	Consumer housings, kitchen equipment, general structures
305	Very good cold formability	Deep-drawn shells, containers, enclosures
309	Improved high-temperature oxidation resistance	Heat shields, oven parts, thermal assemblies
310 / 310S	High Cr-Ni, excellent heat resistance	Furnace parts, burners, high-temperature brackets
316 / 316L	Molybdenum improves chloride resistance	Marine hardware, chemical processing, medical devices
317 / 317L	Higher Mo, stronger pitting resistance	Pumps, valves, offshore systems
321	Titanium-stabilized for weld durability	Exhaust manifolds, welded thermal structures
347 / 347H	Niobium-stabilized for high-temp strength	Aerospace manifolds, refinery components
904L	Super austenitic, very high Ni and Mo	Acid-resistant parts, luxury hardware, process equipment
254SMO	Extreme pitting and seawater resistance	Desalination, seawater cooling systems, offshore engineering

Austenitic Stainless Steel Characteristics

Below is a detailed overview of the key characteristics for the most common Austenitic Stainless Steel Grades, including mechanical, thermal, and chemical properties relevant for CNC machining and industrial applications.

Grade	Tensile Strength	Hardness (HRB)	Maximum Use Temp	Melting Point	Density (g/cm³)	Corrosion Resistance
301 / 301L	515 MPa	70	871 °C	1399–1421 °C	7.9	Excellent general corrosion, good oxidation resistance
302	585 MPa	75	870 °C	1400–1420 °C	7.9	Excellent corrosion resistance
303	515 MPa	75	870 °C	1400–1420 °C	7.9	Good corrosion, best machinability
304 / 304L	520–720 MPa	70–80	870 °C	1398–1440 °C	8.0	Excellent corrosion and oxidation resistance
305	485 MPa	70	870 °C	1400–1420 °C	7.9	Good corrosion, very ductile
309	515 MPa	75	980 °C	1400–1450 °C	8.0	Excellent high-temperature oxidation resistance
310 / 310S	515–620 MPa	75	1050 °C	1400–1450 °C	8.0	High temperature corrosion resistance
316 / 316L	515–690 MPa	75–80	870 °C	1398–1424 °C	8.0	Excellent resistance to chlorides
317 / 317L	620–700 MPa	75–80	870 °C	1400–1425 °C	8.0	Superior pitting resistance
321	515 MPa	75	900 °C	1400–1450 °C	8.0	High temp corrosion resistance, weldable
347 / 347H	515–620 MPa	75–80	900 °C	1400–1450 °C	8.0	Excellent weld corrosion resistance
904L	620–760 MPa	80	925 °C	1398–1450 °C	8.0	Super austenitic, strong acid resistance
254SMO	620–760 MPa	80	925 °C	1398–1450 °C	8.0	Extremely high pitting & crevice resistance

Type 2: Ferritic Stainless Steel

Ferritic Stainless Steel is a chromium-rich stainless steel alloy with low carbon content. Unlike austenitic types, ferritic steels are magnetic, offer moderate corrosion resistance, and resist stress corrosion cracking. They are dimensionally stable during CNC machining and easier to cut and grind than austenitic steels, making them suitable for automotive panels, kitchen equipment, and industrial components.

Ferritic Stainless Steel Grades

Ferritic stainless steels include many stainless steel grades, each optimized for corrosion resistance, weldability, or high-temperature performance. Engineers can select the exact grade depending on the application. Below is an expanded list of commonly used ferritic grades:

Grade	Key Features	Typical Uses
409	Good corrosion resistance, mainly automotive exhaust, weldable	Automotive exhaust systems, mufflers, catalytic converter housings
430	Excellent corrosion resistance in mild environments, magnetic	Kitchen equipment, decorative panels, automotive trim
434	Improved corrosion resistance, good formability	Industrial panels, HVAC components
436	High chromium for superior oxidation resistance	High-temp furnace components, heat exchangers
439	Superior stress corrosion cracking resistance, weldable	Automotive exhaust, chemical processing equipment
444	High corrosion resistance, good weldability, dimensional stability	Chemical tanks, heat exchangers, piping systems
446	High temperature oxidation resistance, some chemical resistance	Furnace parts, high-temp ducting
445	Extra high chromium for harsh chemical environments	Aggressive chemical environments, offshore structures
451	Good scaling resistance at high temperatures, magnetic	Heat-resistant panels, industrial ovens
409L	Low carbon version of 409, better weld performance	Automotive welded components, exhaust assemblies
439L	Low carbon version of 439, improved weldability	Chemical tanks, welded piping, marine components

Ferritic Stainless Steel Characteristics

Below is a detailed overview of key mechanical, thermal, and chemical characteristics for the most common Ferritic Stainless Steel Grades. These properties are important for CNC machining, fabrication, and industrial applications.

Grade	Tensile Strength	Hardness (HRB)	Maximum Use Temp	Melting Point	Density (g/cm³)	Corrosion Resistance
409	450 MPa	60	815 °C	1425–1440 °C	7.7	Good general corrosion, weldable
430	505 MPa	65	815 °C	1425–1440 °C	7.7	Excellent corrosion resistance in mild environments
434	520 MPa	65	815 °C	1425–1440 °C	7.7	Improved corrosion resistance, good formability
436	530 MPa	65	830 °C	1425–1445 °C	7.8	High chromium, good oxidation resistance
439	520 MPa	65	815 °C	1425–1440 °C	7.7	Superior stress corrosion cracking resistance
444	550 MPa	68	870 °C	1420–1450 °C	7.8	High corrosion resistance, weldable, dimensionally stable
446	620 MPa	70	870 °C	1420–1450 °C	7.8	High temperature oxidation resistance
445	630 MPa	70	870 °C	1420–1450 °C	7.8	Extra high chromium for harsh chemical environments
451	515 MPa	65	880 °C	1425–1450 °C	7.8	Good scaling resistance at high temperatures
409L	440 MPa	60	815 °C	1425–1440 °C	7.7	Low carbon, excellent weldability
439L	520 MPa	65	815 °C	1425–1440 °C	7.7	Low carbon, improved weldability, corrosion resistant

Type 3: Martensitic Stainless Steel

Martensitic Stainless Steel is a stainless steel alloy with higher carbon content compared to ferritic types. It is magnetic, can be hardened by heat treatment, and offers high strength and moderate corrosion resistance. These properties make it suitable for cutting tools, valves, turbine components, and wear-resistant parts.

Martensitic Stainless Steel Grades

The most commonly used Martensitic Stainless Steel Grades include:

Grade	Key Features	Typical Uses
410	Moderate corrosion resistance, hardenable, magnetic	Cutlery, valves, pump shafts
410S	Low carbon version of 410, better weldability	Industrial blades, moderate corrosion components
420	High carbon, good wear resistance, magnetic	Surgical instruments, knives, cutting tools
420F	Free-machining version of 420	Precision CNC components, blades
431	High strength, hardenable, good corrosion resistance	Aerospace fasteners, shafts, automotive parts
440A	Good corrosion resistance, moderate hardness	Knives, industrial tools
440B	Higher carbon than 440A, better wear resistance	Precision blades, industrial cutting tools
440C	Maximum hardness, wear-resistant, magnetic	High-end knives, precision bearings, shafts
630 / 17-4PH	Precipitation hardening capable, high strength, corrosion resistant	Aerospace fittings, pump shafts, valve components
630F	Free-machining version of 17-4PH	Precision CNC fasteners, machined components
431L	Low carbon version of 431, improved weldability	Shafts, fasteners, precision machined parts
440F	Free-machining version of 440	CNC cutting tools, precision components

Martensitic Stainless Steel Characteristics

The following table highlights the key mechanical, thermal, and chemical properties of the most common Martensitic stainless steel grades. Understanding these characteristics helps engineers and CNC machinists select the right grade for strength, hardness, and corrosion requirements.

Grade	Tensile Strength	Hardness (HRC)	Maximum Use Temp	Melting Point	Density (g/cm³)	Corrosion Resistance
410	480 MPa	50 HRC	870 °C	1425–1440 °C	7.7	Moderate corrosion resistance, magnetic
410S	450 MPa	48 HRC	870 °C	1425–1440 °C	7.7	Improved weldability, moderate corrosion
420	700 MPa	55–60 HRC	815 °C	1425–1450 °C	7.8	Good corrosion, excellent wear resistance
420F	680 MPa	52–57 HRC	815 °C	1425–1450 °C	7.8	Free-machining, wear-resistant
431	850 MPa	55–60 HRC	870 °C	1425–1450 °C	7.8	High strength, good corrosion resistance
431L	830 MPa	53–58 HRC	870 °C	1425–1450 °C	7.8	Low carbon, better weldability
440A	760 MPa	57 HRC	815 °C	1425–1450 °C	7.8	Moderate corrosion resistance, good wear
440B	820 MPa	58–60 HRC	815 °C	1425–1450 °C	7.8	Higher wear resistance than 440A
440C	900 MPa	60–65 HRC	815 °C	1425–1450 °C	7.8	Maximum hardness and wear resistance
440F	880 MPa	58–63 HRC	815 °C	1425–1450 °C	7.8	Free-machining, wear-resistant
630 / 17-4PH	1000 MPa	40–45 HRC	315 °C	1400–1450 °C	7.8	High strength, corrosion resistant, precipitation hardenable
630F	980 MPa	38–43 HRC	315 °C	1400–1450 °C	7.8	Free-machining 17-4PH, corrosion resistant

Type 4: Duplex Stainless Steel

Duplex Stainless Steel combines the austenitic and ferritic microstructures, offering a balanced mix of high strength and excellent corrosion resistance. It is partially magnetic, resistant to stress corrosion cracking, and ideal for chemical processing, marine, and offshore applications.

Duplex Stainless Steel Grades

The most commonly used Duplex Stainless Steel Grades include:

Grade	Key Features	Typical Uses
2205	Balanced austenitic-ferritic, high strength, excellent corrosion resistance	Chemical tanks, piping, heat exchangers, marine structures
2507 / Super Duplex	Very high chromium and molybdenum, superior pitting and crevice corrosion resistance	Offshore platforms, seawater equipment, aggressive chemical processing
2304	Good corrosion resistance, moderate strength	Pressure vessels, structural components
2001	Cost-effective lean duplex, good corrosion and strength	Industrial piping, tanks, general marine applications
2101	Lean duplex, moderate corrosion resistance, high strength	Automotive exhaust, general structural applications
2201	Balanced strength and corrosion resistance	Piping, welded assemblies in chemical plants

Duplex Stainless Steel Characteristics

The following table presents the key mechanical, thermal, and chemical properties of common Duplex stainless steel grades.

Grade	Tensile Strength	Hardness (HRB)	Maximum Use Temp	Melting Point	Density (g/cm³)	Corrosion Resistance
2205	620 MPa	32 HRB	300 °C	1390–1430 °C	7.8	Excellent chloride and stress corrosion resistance
2507 / Super Duplex	850 MPa	35 HRB	300 °C	1390–1430 °C	7.9	Superior pitting and crevice corrosion resistance
2304	600 MPa	30 HRB	300 °C	1385–1425 °C	7.8	Good general corrosion resistance
2001	580 MPa	30 HRB	300 °C	1385–1425 °C	7.8	Cost-effective, moderate corrosion resistance
2101	600 MPa	32 HRB	300 °C	1385–1425 °C	7.8	Lean duplex, moderate corrosion resistance
2201	620 MPa	33 HRB	300 °C	1390–1430 °C	7.8	Balanced strength and corrosion resistance

Type 5: Precipitation Hardening (PH) Stainless Steel

Precipitation Hardening Stainless Steel is a high-strength stainless steel alloy that gains exceptional hardness through precipitation heat treatment. It combines corrosion resistance with mechanical performance, making it ideal for aerospace, automotive, and high-precision CNC components.

PH Stainless Steel Grades

The most commonly used PH stainless steel grades include:

Grade	Key Features	Typical Uses
17-4PH / 630	High strength, corrosion resistant, precipitation hardenable	Aerospace fittings, pump shafts, valves, precision CNC components
15-5PH / 651	Excellent toughness and corrosion resistance	Aerospace fasteners, structural components, CNC machined parts
13-8PH	High strength and hardness, moderate corrosion resistance	Aircraft landing gear, shafts, high-strength fasteners
17-7PH	Good corrosion resistance, excellent fatigue strength	Springs, aerospace components, CNC precision parts
17-4PH F	Free-machining version of 17-4PH	Precision fasteners, machined components

PH Stainless Steel Characteristics

The following table presents the mechanical, thermal, and chemical properties of common PH stainless steel grades.

Grade	Tensile Strength	Hardness (HRC)	Maximum Use Temp	Melting Point	Density (g/cm³)	Corrosion Resistance
17-4PH / 630	1000 MPa	40–45 HRC	315 °C	1400–1450 °C	7.8	High strength, corrosion resistant, precipitation hardenable
15-5PH / 651	1100 MPa	42–46 HRC	315 °C	1400–1450 °C	7.8	Excellent toughness, corrosion resistant
13-8PH	1200 MPa	44–48 HRC	300 °C	1400–1450 °C	7.8	High strength, moderate corrosion resistance
17-7PH	950 MPa	38–42 HRC	315 °C	1400–1450 °C	7.8	Good corrosion resistance, excellent fatigue strength
17-4PH F	980 MPa	38–43 HRC	315 °C	1400–1450 °C	7.8	Free-machining version, corrosion resistant

International Equivalents

All the stainless steel grades discussed earlier—including Austenitic, Ferritic, Martensitic, Duplex, and PH types—are based on AISI / ASTM standards. When sourcing or specifying materials internationally, engineers often need to cross-reference these grades with other national standards to ensure correct selection for CNC machining or industrial applications.

The table below shows common international standards and how they compare to the American Iron and Steel Institute (AISI) names:

Standard	Example	Notes
European Standard (EN)	1.4301	Stainless steel names are identified numerically starting with 1.4, followed by three digits denoting the composition
Japanese International Standard (JIS)	SUS304	Japan uses the AISI standard but adds the SUS prefix
British Standard (BS)	BS 970	Britain has adopted the AISI standard as well
Chinese National Standard (GB)	—	Depends on the steel source and its composition
German Standard (DIN)	DIN X12CrNi17-7	Governed by DIN17006, X indicates alloying elements content over 5%
International Organization for Standardization (ISO)	ISO15510	ISO has adopted Germany’s DIN standard

VMT Case: CNC Machining Austenitic Stainless Steel 304L

A client in the medical equipment industry in Germany required Austenitic stainless steel 304L parts with extremely tight tolerances and high-quality surface finishes. They had faced repeated issues with part failures, tool wear, and delayed delivery when working with standard suppliers.

VMT addressed these challenges by:

• Material Evaluation – Our engineers reviewed the stainless steel composition to select the optimal stainless steel grades suitable for CNC machining and corrosion resistance.
• CNC Machining Optimization – Using 4 & 5-axis CNC centers, we controlled feeds, cutting forces, and tool paths to maintain tolerances of 0.01 mm.
• Surface Treatment Control – Specialized engineers performed polishing and passivation to achieve the desired appearance without compromising material integrity.
• Quality Assurance – Key procedures were monitored with CPK ≥ 68, ensuring each part met ISO and IATF standards.

Over 500 precision parts were produced with consistent surface quality, dimensional accuracy, and corrosion resistance. The client reported significant improvements in assembly efficiency and product reliability, demonstrating how VMT transforms common stainless steel alloys into high-precision, high-performance components. If you need similar results for your CNC machined stainless steel parts, contact VMT to discuss your project and get expert guidance from material selection to final finishing.

Conclusion

Understanding the different types of stainless steel—Austenitic, Ferritic, Martensitic, Duplex, and Precipitation Hardening—is essential for selecting the right stainless steel grades. Each type has distinct stainless steel composition, mechanical properties, and corrosion resistance, which affect CNC machinability and application suitability. Comparing international equivalents ensures correct material selection across global standards.