Ferritic Stainless Steel: Everything You Need to Know

Choosing the wrong stainless steel can cause CNC machining issues, costly rework, or poor durability. Many engineers struggle with corrosion, magnetic requirements, or forming limits. Without proper guidance, selecting a material wastes time and drives up production costs. Understanding Ferritic Stainless Steels helps you avoid these pitfalls and ensures high-quality parts.

Ferritic Stainless Steels feature a Ferritic Structure with low carbon content. They provide strong Ferritic Stainless Steel Properties, including good formability and magnetic behavior. This article explains Ferritic Stainless Steel Composition, Grades, Microstructure, and key characteristics. You will learn how to choose the right grade, compare with other stainless steels.

What is Ferritic Stainless Steel?

Ferritic Stainless Steels are a category of stainless steel defined by their Ferritic Structure, which is primarily composed of chromium with very low carbon content. This structure gives the steel natural corrosion resistance and makes it magnetic. They are often referred to as plain chromium stainless steel or magnetic stainless steel. These steels generally have a simple microstructure, which provides stable mechanical properties and good dimensional stability.

Ferritic Stainless Steel Chemical Composition

The chemical composition of Ferritic Stainless Steels determines their corrosion resistance, magnetic properties, and machinability. Chromium is the main element, ranging from 10.5 to 30 percent, while carbon is very low, typically below 0.12 percent. Other common elements include nickel, molybdenum, manganese, silicon, titanium, and aluminum, which help improve corrosion resistance, strength, and heat stability.

Below is a table showing common Ferritic Stainless Steel Grades and their typical composition, which helps engineers select the right material for CNC machining and forming.

Grade	Chromium (%)	Carbon (%)	Nickel (%)	Molybdenum (%)	Manganese (%)	Silicon (%)	Titanium (%)	Aluminum (%)
AISI 430	16 – 18	≤ 0.12	≤ 0.75	0 – 0.75	1	1	0	0
AISI 439	17 – 19	≤ 0.03	≤ 0.5	0 – 0.5	1	1	0.2	0
AISI 446	23 – 27	≤ 0.2	≤ 0.5	2 – 3	1	1	0	0
AISI 409	10.5 – 11.75	≤ 0.08	≤ 0.5	0	0.5	0.5	0	0

Ferritic Stainless Steel Microstructure

The Ferritic Stainless Steel Microstructure consists of a body-centered cubic crystal(BCC), known as Ferritic Structure. This structure gives the steel magnetic properties and stable mechanical behavior. It also provides excellent dimensional stability during CNC machining. Unlike other stainless steels, the Ferritic Structure contains no significant austenite, which reduces distortion during forming and heat treatment.

Ferritic Stainless Steel Grades and Five Groups

Ferritic Stainless Steels can be divided into five distinct groups. Each group differs in metal content and performance. Below are typical grades and their equivalent materials across multiple standards.

Group 1

Group 1 ferritic steels are among the least expensive types of stainless steel. They have extremely low chromium levels, which makes them prone to developing a thin layer of localized surface rust over time. These steels are typically selected for applications where cost is a priority, and corrosion resistance is not critical.The table below lists the most common Group 1 ferritic steels and their equivalents in different standards:

AISI	EN / DIN	JIS	GB	UNS	BS
409	1.4512	SUS 445J1	06Cr19	S40900	409S
430	1.4016	SUS 430	06Cr17	S43000	430S
439	1.4510	SUS 439	06Cr18Mo	S43900	439S

Group 2

Group 2 ferritic steels are the most commonly used type. Because of their higher chromium levels, these steels possess greater corrosion resistance. They are generally applied in building features, interior appliances, and other CNC-machined parts where moderate corrosion resistance is sufficient. These steels provide a good balance of cost, formability, and corrosion protection.The table below shows typical Group 2 ferritic steels with equivalents across different standards:

AISI	EN / DIN	JIS	GB	UNS	BS
430	1.4016	SUS 430	06Cr17	S43000	430S
434	1.4116	SUS 434	08Cr17	S43400	434S
436	1.4510	SUS 436	06Cr18Mo	S43600	436S
439	1.4510	SUS 439	06Cr18Mo	S43900	439S

Group 3

Group 3 ferritic steels are well known for their ease of forming and welding. This makes them suitable for a wide range of applications, including CNC-machined components that require moderate strength, excellent ductility, and consistent dimensional stability. Their combination of formability, weldability, and corrosion resistance makes them highly versatile in both industrial and consumer products.The table below lists common Group 3 ferritic steels and their equivalent materials in multiple standards:

AISI	EN / DIN	JIS	GB	UNS	BS
444	1.4521	SUS 444	19Cr19Ni	S44400	444S
445	1.4541	SUS 445	18Cr20Ni	S44500	445S
439	1.4510	SUS 439	06Cr18Mo	S43900	439S

Group 4

Group 4 ferritic stainless steels contain higher amounts of molybdenum, further improving their corrosion resistance. This type of steel is commonly used for high-moisture applications like exhaust systems, hot water tanks, and other environments exposed to moisture or mild chemicals. Their enhanced corrosion resistance allows CNC-machined parts to maintain durability under harsher conditions.The table below shows Group 4 ferritic steels with their equivalent materials:

AISI	EN / DIN	JIS	GB	UNS	BS
446	1.4864	SUS 446	24Cr20Ni	S44600	446S
447	1.4529	SUS 447	23Cr18Ni	S44700	447S
444	1.4521	SUS 444	19Cr19Ni	S44400	444S

Group 5

Group 5 ferritic steels have the highest chromium levels, giving them a degree of corrosion resistance which is unmatched by all but a handful of other metals. These steels are used for highly demanding applications where both corrosion resistance and mechanical stability are critical. CNC-machined components made from Group 5 steels can endure aggressive environments and provide long-term reliability.The table below lists Group 5 ferritic steels and their equivalents in multiple standards:

AISI	EN / DIN	JIS	GB	UNS	BS
445	1.4541	SUS 445	18Cr20Ni	S44500	445S
446	1.4864	SUS 446	24Cr20Ni	S44600	446S
454	1.4529	SUS 454	25Cr22Ni	S45400	454S

Confused about which grade suits your CNC project? Our engineers can help you balance corrosion resistance and cost. [Get a Material Recommendation]

Ferritic Stainless Steel Characteristics

Ferritic Stainless Steels have key characteristics including strong magnetism, good corrosion resistance, excellent ductility and formability, thermal stability, moderate weldability, toughness, and resistance to oxidation. These properties make them ideal for CNC-machined components. The table below summarizes these characteristics:

Characteristic	Typical Performance	Notes
Magnetic	Ferromagnetic	BCC structure, strong magnetism retained after machining
Corrosion Resistance	Good	Oxidizing environments, SCC resistant
Ductility / Formability	Good	Cold-workable, maintains tight tolerances
Thermal Properties	Good	Low thermal expansion, good conductivity
Weldability	Moderate	Thick sections may require annealing
Toughness	Lower than Austenitic	Not suitable for cryogenic
Oxidation Resistance	High	Stable at elevated temperatures

Magnetic

They have a Body-Centered Cubic (BCC) structure, which makes them inherently ferromagnetic. Unlike austenitic grades, they retain strong magnetism even after forming or machining. This property is critical for CNC parts used in magnetic sensors, electric motors, and actuators. Their magnetic behavior also allows for easy detection and separation in industrial processes.

Corrosion Resistance

These steels resist corrosion effectively in oxidizing environments, such as air and mild acids. They are immune to chloride stress corrosion cracking (SCC), which is a common failure mode in harsh environments. This makes them suitable for automotive components, household appliances, and industrial equipment exposed to moisture or moderate chemicals. Surface treatments can further enhance longevity and prevent surface staining.

Ductility and Formability

Ferritic stainless steels exhibit good ductility, allowing them to be cold-worked into complex shapes. They are not heat-treatable for hardening, but their formability ensures CNC-machined parts can maintain tight tolerances and smooth finishes. This combination of flexibility and dimensional stability makes them ideal for precision enclosures, brackets, and decorative metal parts.

Thermal Properties

They have good thermal conductivity and low thermal expansion, ensuring dimensional stability during temperature fluctuations. This is valuable for precision CNC parts in machinery and electronics.

Weldability

Weldability is moderate. Thick sections may experience grain growth, requiring annealing to restore toughness. Proper welding procedures are necessary to prevent stress and ensure structural integrity in CNC-fabricated components.

Toughness

Toughness is lower than austenitic steels, making them unsuitable for sub-zero or cryogenic applications. They perform reliably at room temperature and moderate heat.

Resistance to Oxidation

Ferritic stainless steels resist oxidation effectively at elevated temperatures. This ensures that CNC-machined parts maintain their appearance and structural integrity even under prolonged exposure to air and heat.

Ferritic Stainless Steel Uses

Ferritic Stainless Steels are widely used in many industry due to their combination of Ferritic Stainless Steel Properties, corrosion resistance, and magnetic behavior. Typical Ferritic Stainless Steel Uses include:

• Automotive: Exhaust pipes, mufflers, catalytic converters, heat shields, trim, engine brackets, suspension components, and turbocharger housings.
• Appliances: Washing machine drums, dishwasher parts, microwave oven components, kitchen sinks, cooking utensils, refrigerator panels, oven trays, and mixer housings.
• Architecture: Building facades, roofing, elevator panels, decorative elements, window frames, stair railings, door handles, and cladding panels.
• Industrial: Heat exchangers, boilers, chemical processing equipment, storage tanks, conveyor components, pressure vessels, and piping fittings.
• Electrical: Transformer cores, magnetic shielding, electric motor housings, inductors, relays, and sensor brackets.
• Food & Beverage: Food processing machinery, storage equipment, conveyor parts, mixers, slicers, and packaging machinery components.

Ferritic Stainless Steel Price

The Ferritic Stainless Steel Price varies depending on grade, chemical composition, thickness, and market conditions. Steels with higher chromium or molybdenum content offer better corrosion resistance but cost more. CNC machining requirements, such as complex geometries, tight tolerances, and fine surface finishes, can also increase the overall price. Production volume, supply chain fluctuations, and regional availability further influence costs. Generally, ferritic steels are more affordable than austenitic grades, making them a cost-effective choice for CNC-machined parts that need durability, magnetic behavior, and corrosion resistance without a high expense.

Ferritic vs Martensitic Stainless Steel

The Difference Between Austenitic and Ferritic Stainless Steel is mainly in structure and performance. Ferritic Stainless Steels have a Body-Centered Cubic (BCC) structure, are magnetic, and offer good corrosion resistance and formability. Martensitic Stainless Steels have a Body-Centered Tetragonal (BCT) structure, are harder and stronger after heat treatment, but less corrosion-resistant and magnetic.

The table below shows the comparison between Ferritic and Martensitic Stainless Steels.

Feature	Ferritic Stainless Steel	Martensitic Stainless Steel
Crystal Structure	BCC (Body-Centered Cubic)	BCT (Body-Centered Tetragonal)
Magnetic	Yes	Yes, but weaker after machining
Corrosion Resistance	Good	Moderate, less than ferritic
Hardness	Moderate	High after heat treatment
Ductility / Formability	Good	Lower, harder to machine complex shapes
CNC Machining Suitability	Excellent for precision parts	Suitable for high-strength parts, more tool wear
Typical Applications	Automotive panels, appliance components, architectural parts	Cutting tools, shafts, pump components

VMT Case：CNC Machining of Ferritic Stainless Steel

A German automotive supplier approached VMT with a challenge. They needed CNC-machined exhaust system brackets made of Ferritic Stainless Steels with tight tolerances (±0.01 mm), smooth surface finish, and consistent magnetic behavior. Previous suppliers struggled with work hardening, dimensional deviations, and surface defects, causing assembly delays and performance inconsistencies.

VMT addressed the problem with a structured approach:

• Selected AISI 430 for its good corrosion resistance, formability, and stable magnetic behavior to meet client specifications.
• Optimized cutting parameters and tooling to handle moderate machinability and prevent work hardening.
• Applied multi-step finishing and polishing to achieve the required surface quality.
• Monitored dimensional tolerances using CMM and maintained CPK ≥ 68 for key features.
• Controlled heat input during welding and performed post-weld annealing for thick sections.
• Specialized engineers supervised surface treatments to ensure corrosion resistance and magnetic performance.

The results exceeded expectations. The client received brackets with precise dimensions, excellent surface finish, and stable magnetic behavior. Production efficiency improved, and assembly issues were eliminated. If you also want your CNC parts to achieve the same high-quality standards, or if you face similar challenges with Ferritic Stainless Steels, contact VMT to Get a free quote and customized CNC machining solution.

Conclusion

Ferritic Stainless Steels combine magnetic behavior, good corrosion resistance, ductility, and thermal stability. They are suitable for CNC-machined components in automotive, appliances, architecture, industrial, electrical, and food & beverage sectors. Proper grade selection, machining, and surface treatment ensure parts meet tight tolerances, maintain durability, and perform reliably in demanding applications.