1. Core positioning & industrial value
А 400 серыял з нержавеючай сталі is the practical bridge between low-cost carbon steels and high-nickel austenitic stainless steels.
Defined by AISI/ASTM and regional standards (ASTM A240, У 10088, Гб/т 1220), it accounts for a large fraction of global stainless steel tonnage because it combines:
- Lower alloy cost (little or no Ni) → attractive economics;
- Magnetic behaviour (ferritic/martensitic) required by many electromechanical applications;
- Heat-treatable strengthenability (martensitic and precipitation-hardening subtypes) enabling very high strength;
- Favourable thermal conductivity and lower thermal expansion compared with austenitics, useful for heat-exposed components.
Industries that benefit most include automotive (выхмы, fuel systems), тэхніка (панэлі, лайнеры), тэхніка (шахты, клапаны), інструмента (арыентыроўка, ляза) and some aerospace/nuclear niches where a balance of cost, strength and moderate corrosion resistance is acceptable.
2. Класіфікацыя, Склад & Microstructural Mechanism
The performance differences of the 400 series stainless steel are essentially determined by their chemical composition and corresponding microstructures.
Below is an in-depth analysis of three core subtypes:
Ферытныя 400 Цыкл (Core Grades: 409, 430, 439, 444)
Ferritic stainless steels are the most widely used subtype, featuring a single-phase ferrite microstructure at room temperature, no phase transformation during heating/cooling, and ultra-low C content (typically ≤0.12 wt.%).
Their core composition is dominated by Cr (10.5–19.5 wt.%), with auxiliary elements such as Ti, НБ, and Mo to optimize stability and corrosion resistance.
- 409: Кр (10.5–11.75 wt.%), C (≤0.08 wt.%), Аб (0.15–0.50 wt.%).
Ti forms TiC precipitates to fix C, avoiding intergranular corrosion caused by Cr carbide precipitation.
The coarse-grained ferrite structure provides basic atmospheric corrosion resistance, making it suitable for low-cost corrosion-resistant scenarios. - 430: Кр (16.0–18.0 wt.%), C (≤0.12 wt.%). Fine-grained ferrite structure with balanced cost and corrosion resistance, being the mainstream cost-effective ferritic grade for home appliances.
- 439: Кр (17.0–19.0 wt.%), C (≤0.03 wt.%), Ti/Nb (0.10–0.60 wt.%).
Ultra-low C and Ti/Nb composite stabilization refine grains, significantly improving weldability and corrosion resistance compared to 430. - 444: Кр (17.5–19.5 wt.%), Мо (1.75–2.50 wt.%), C (≤0.025 wt.%).
Mo addition enhances pitting corrosion resistance (PREN≈25), forming a dense ferrite structure suitable for chloride-containing environments.
Мартэнічны 400 Цыкл (Core Grades: 410, 420, 440A/B/C)
Martensitic stainless steels have higher C content (0.15–0.75 wt.%) and moderate Cr content (11.5–18.0 wt.%).
Пры высокіх тэмпературах, they form austenite, which transforms into hard martensite during quenching—making them the only heat-treatable strengthening subtype in the 400 series stainless steel.
- 410: C (≤0.15 wt.%), Кр (11.5–13.5 wt.%).
As-cast structure is ferrite + мартэнсіт; after quenching/tempering, tensile strength reaches 515–690 MPa, suitable for general structural parts. - 420: C (0.15–0.40 wt.%), Кр (12.0–14.0 wt.%).
Higher C content improves hardness (HRC≥50 after heat treatment), widely used in cutlery and valves. - 440A/B/C: C content gradient (0.60–0.75 wt.%), Кр (16.0–18.0 wt.%).
440C has the highest hardness (HRC≥58) і нашэнне супраціву, ideal for high-precision tools and bearings.
Ападкі-Загартоўка (Ph) 400 Цыкл (Сартаваць: 17-4 Ph, Асі 630)
A special high-performance variant with low C (≤0.07 wt.%), Кр (15.5–17.5 wt.%), У (3.0–5.0 wt.%), and Cu (3.0–5.0 wt.).
It forms austenite at high temperatures, transforms into martensite during cooling, and achieves strengthening via Cu-rich precipitate formation during aging.
Tensile strength can reach 1380 MPa after heat treatment, balancing ultra-high strength and corrosion resistance.
3. Core Comprehensive Properties
Механічныя ўласцівасці
Mechanical properties of 400 series stainless steel vary significantly by subtype, with clear differentiation in strength, пластычнасць, and heat treatment response (data complies with ASTM A240/A480):
- Ferritic types (430, solution-annealed): Tensile strength 415–515 MPa, yield strength 205–275 MPa, elongation 20–25%, hardness ≤183 HBW.
No phase transformation, only annealing for grain refinement. - Martensitic types (420, тунг & загартаваны): Tensile strength 725–930 MPa, yield strength 515–690 MPa, elongation 10–15%, hardness ≥50 HRC.
Тушэнне + tempering significantly improves strength and hardness. - PH type (17-4 Ph, H900 aging): Tensile strength ≥1170 MPa, yield strength ≥1035 MPa, elongation ≥10%, hardness ≥38 HRC.
Precipitation strengthening achieves ultra-high strength without sacrificing ductility.
Каразія супраціву
Corrosion resistance is primarily determined by Cr content, with Mo and low C as auxiliary enhancers. Увесь, it is lower than 300 series but superior to carbon steel:
- Ferritic types: 409 has basic atmospheric corrosion resistance (annual corrosion rate ≤0.03 mm in rural areas); 444 resists dilute acids and chlorides, with a critical pitting temperature ≥30℃.
- Martensitic types: Limited by high C content; 410 is susceptible to rust in humid environments, while 440C has better corrosion resistance due to higher Cr but is unsuitable for marine/acidic media.
- 17-4 Ph: Corrosion resistance comparable to 304 in atmospheric and mild corrosive environments, but prone to pitting in high-chloride media.
Фізічныя ўласцівасці
Inherent magnetism is a signature feature of 400 series stainless steel, with other physical properties consistent across subtypes:
- Шчыльнасць: 7.7–7.8 g/cm³ (lower than 304’s 8.0 g/cm³ due to no Ni addition).
- Цеплаправоднасць: 25–30 W/(м·К) @ 20℃ (higher than 304’s 16 ж/(м·К), favorable for heat dissipation).
- Thermal expansion coefficient: 10–12×10⁻⁶/K (20–400℃), lower than 300 серыял, reducing thermal deformation.
- Magnetic permeability: μ=100–1000 (ferritic/martensitic), far higher than austenitic stainless steels (μ<1.02).
4. Апрацоўка, фабрыкацыя & heat-treatment practice
Фарміраванне & апрацоўванне
- Ferritics: reasonable formability cold; intermediate anneal recommended for heavy forming. Machinability similar to low-alloy steels.
- Martensitics: poor cold formability in hardened condition; form in annealed state or above (гарачая фармоўка). Machinability depends on temper and hardness — higher C grades require robust tooling and slower speeds.
Вінжаванне
- Ferritics: weldable but prone to grain growth and HAZ embrittlement if high heat input used; stabilized grades (Ti/Nb) and low heat input (<10 kJ/cm for some) палепшыць прадукцыйнасць; select ferritic filler metals.
- Martensitics: challenging — preheat (200–300 °C), low hydrogen consumables and post-weld tempering recommended to avoid cracking and restore toughness.
- Ph 17-4: weldable with matched filler and post-weld heat treatment/aging to restore properties.
Тэрмічная апрацоўка
- Ferritics: solution anneal and air cool to relieve stress and refine grains; no quench hardening.
- Martensitics: austenitize (950–1050 °C), патушыць (oil/water depending on grade), then temper (150–650 °C) to reach desired hardness/toughness. 440C typically tempered at 200–300 °C for peak hardness.
- Ph 17-4: Рашэнне лячыць (~1,040–1,060 °C), загасіць вадой, then age (482–621 °C) to produce Cu-rich precipitates and achieve target strength (H900 etc.).
5. Typical Industrial Applications of 400-Series Stainless Steel
The 400-series family serves a broad range of industries because its subtypes map cleanly onto different engineering needs:
гаспадарка + Умераная ўстойлівасць да карозіі (ferritics), high hardness/wear (martensitics), і very high strength with reasonable corrosion resistance (PH alloys).
Аўтамабільная прамысловасць
Common parts & гатункі
- Выцяжныя сістэмы, muffler components, reaction pipes — 409, часам 439 for improved weldability.
- Аздабленне, decorative panels — 430.
- Engine and transmission shafts, сядла клапанаў / small wear components — 410 / 420 where heat treatment is required.
Why 4xx is used
- Low nickel content gives a strong cost advantage for very high-volume components.
Ferritic grades resist cyclic oxidation in hot exhaust environments and have suitable thermal conductivity and expansion. Martensitic grades offer hardened surfaces for wear-critical small parts.
Key considerations
- For welded exhaust systems, use Ti/Nb-stabilized ferritics (409Ti/439) or control heat input to avoid HAZ embrittlement.
- Абарона ад карозіі (паверхневыя пакрыцця, aluminizing) is frequently applied to extend life in road-salt environments.
Household appliances and consumer products
Common parts & гатункі
- Refrigerator doors, oven liners, dishwasher interiors, control panels — 430 А часам 439/444 for better corrosion resistance.
- Cutlery and kitchen knives — 420 / 440C (мартенситный), polished and tempered.
Why 4xx is used
- Attractive surface finish, добрая формуемость (ferritics), magnetic response where needed (e.g., induction cooking indicators), and much lower cost than austenitics make ferritic 4xx the default for decorative and internal appliance parts.
Key considerations
- Avoid 4xx in salt-spray or coastal exposures unless coated or specifically a Mo-bearing variant (444).
For cutlery, select high-C martensitics and control tempering to balance edge retention and corrosion resistance.
Heat-exchange, HVAC and thermal systems
Common parts & гатункі
- Heat-exchanger fins, ducting, кампаненты печы, boiler cladding — 409, 430, 444.
Why 4xx is used
- Ferritics combine good thermal conductivity, low thermal expansion and oxidation resistance at elevated temperatures with lower cost than 300-series, making them well suited to heat-transfer hardware and exhaust heat management.
Key considerations
- For wet, chloride-containing streams or high pitting risk, prefer Mo-bearing ferritics (444) or step up to duplex/300-series where necessary.
Хімічны, process and water handling industries
Common parts & гатункі
- Intermediate duty tanks, piping fittings, heat exchangers for non-extreme chemistries — 444 (where chloride resistance matters), 439 for welded tanks.
Why 4xx is used
- When service is moderately aggressive but full austenitic or duplex alloys are not justified economically, Mo-stabilized ferritics offer an acceptable middle ground.
Key considerations
- Specify mill certificates and corrosion testing. For continuous chloride exposure (process brines, seawater cooling) validate grade choice against measured chloride, temperature and crevice conditions.
Змазваць & бензін, нафтахімічны (selected components)
Common parts & гатункі
- Зашпількі, non-critical valve components, pump shafts — 410, 431 (martensitic high-strength), 17-4 Ph for high-strength, устойлівыя да карозіі кампаненты (where post-weld aging is feasible).
Why 4xx is used
- Martensitic and PH grades provide very high strength for pressure and mechanical loadings; 17-4 PH is often chosen where strength plus reasonable corrosion resistance is required and welding/aging cycles can be controlled.
Key considerations
- Martensitic parts in sour or chloride environments must be qualified for hydrogen embrittlement and SSC risk. Post-weld tempering/aging is often mandatory.
Марская, desalination and seawater equipment (limited use)
Common parts & гатункі
- Seawater strainers, non-critical housings — 444 in mild chloride exposure; otherwise designers prefer duplex or higher-PREN alloys.
Why 4xx is used (selectively)
- Mo-bearing ferritics can manage some seawater duties at lower cost, but long-term pitting and crevice risk often rule them out for continuously submerged structural parts.
Key considerations
- When 4xx is used in marine contexts, combine with cathodic protection, пакрыцці, and a stringent inspection regime. Avoid where heat-affected or crevice conditions exist.
Выпрацоўка электраэнергіі & energy systems
Common parts & гатункі
- Heat-exchangers, flue gas ducts, turbine seals — 409, 444.
- High-strength bolting and shafting — 17-4 Ph or martensitics where applicable.
Why 4xx is used
- Ferritic grades endure cyclic oxidation and thermal stress well; PH grades are used for high-stress fasteners and components where austenitic alloys would be unnecessarily expensive.
Key considerations
- Watch for long-term sigma phase embrittlement in some high-Cr alloys at intermediate temperatures; specify operating temperature limits and inspection intervals.
Медычны, tooling and precision instruments (selected)
Common parts & гатункі
- Surgical instrument blades — 420 / 440C (мартенситный, high polish and edge retention).
- Precision mold inserts and high-wear tooling — 440C.
Why 4xx is used
- High hardness and edge retention make martensitics attractive, provided corrosion exposure is controlled and surface finishing/passivation is excellent.
Key considerations
- For implants or long-term body exposure, 300-series or medical-grade alloys are preferred; 4xx for instruments only when sterilization and passivation are acceptable and medical standards are followed.
6. Перавагі & Абмежаванні
The 400-series stainless steels occupy a distinct position between carbon steels and nickel-bearing austenitic stainless steels.
Key Advantages of 400-Series Stainless Steel
Cost efficiency and price stability
400-series stainless steels contain little or no nickel, relying primarily on chromium for corrosion resistance.
This significantly reduces raw material cost and shields procurement from nickel price volatility, making these grades economically attractive for large-volume applications.
Inherent magnetic properties
Ferritic and martensitic 400-series grades are naturally magnetic, enabling their use in electromagnetic devices, датчыкі, выканаўчыя механізмы, and components requiring magnetic response—applications where austenitic stainless steels are unsuitable.
Heat-treatable strength (martensitic and PH grades)
У адрозненне ад аўстэнітных нержавеючых сталей, martensitic and precipitation-hardening 400-series alloys can be strengthened through quenching, загармаванне, and aging.
This allows tensile strengths ranging from moderate levels to well above 1000 МПА, supporting wear-resistant, нясе, and high-stress components.
Good thermal conductivity and low thermal expansion
Ferritic 400-series steels exhibit higher thermal conductivity and lower coefficients of thermal expansion than 300-series stainless steels.
This improves resistance to thermal fatigue and distortion, making them suitable for exhaust systems, цеплаабменнікі, and thermal cycling environments.
Adequate corrosion resistance for moderate environments
With chromium contents typically above 10.5 wt.%, 400-series steels provide reliable resistance to atmospheric corrosion, мяккія хімікаты, and high-temperature oxidation—far superior to carbon steel and sufficient for many industrial and consumer applications.
Simplified alloy design and recyclability
Lower alloy complexity facilitates melting, перапрацоўка, and reuse within stainless steel streams, aligning with cost control and sustainability objectives in large-scale manufacturing.
Key Limitations of 400-Series Stainless Steel
Inferior corrosion resistance compared with austenitic grades
Most 400-series steels lack the nickel and, in many cases, sufficient molybdenum needed for strong resistance to pitting, карозія шчыліны, and stress corrosion cracking in chloride-rich or strongly acidic environments.
They cannot generally replace 304 або 316 in harsh chemical or marine service.
Limited weldability
Ferritic grades are prone to grain coarsening and toughness loss in the heat-affected zone, while martensitic grades are susceptible to cold cracking and hydrogen embrittlement.
Successful welding often requires strict heat-input control, stabilizing elements (Аб, НБ), папярэдні нагрэў, і тэрмічная апрацоўка пасля зваркі.
Reduced low-temperature toughness
Ferritic 400-series stainless steels exhibit a ductile-to-brittle transition temperature, typically around sub-zero to slightly above freezing conditions.
This limits their suitability for cryogenic or cold-climate structural applications.
Lower formability than austenitic stainless steels
Ferritic grades have moderate cold-forming capability but limited stretch formability, while martensitic grades are difficult to cold form due to high hardness.
Complex deep-drawn components are generally better suited to 300-series stainless steels.
Sensitivity to improper heat treatment and service exposure
Martensitic and PH grades require carefully controlled heat-treatment cycles.
Inappropriate tempering, prolonged exposure to intermediate temperatures, or improper welding practices can lead to embrittlement, loss of corrosion resistance, or premature failure.
Narrower application window for severe environments
In highly corrosive, high-chloride, or high-purity process environments, the performance margin of 400-series steels is limited, often necessitating the use of austenitic, дуплекс, or super stainless steels.
7. Comparative analysis vs 300-series & other alternatives
- Ўстойлівасць да карозіі: 300-серыял (304/316) >> 400-series in aggressive chloride/acid environments.
- Моц (тэрмічнаму апрацаваны): Martensitic/PH 400 >> 300-серыял (can far exceed 1,000 МПА).
- Каштаваць: 400-series typically 30–50% cheaper than 304 due to low Ni.
- Зварачнасць & Фармальнасць: 300-series superior; 400-series requires more care.
- Магнетызм: 400-series magnetic — an advantage if magnetic response is needed.
- High-temperature behaviour (акіленне): ferritic 4xx are often better than austenitics for cyclic oxidation and thermal conductivity applications.
Selection rule of thumb: choose 400-series when cost, magnetic response or very high hardness/strength is required and corrosion environment is moderate or manageable with coatings; choose 300-series/duplex/nickel alloys when corrosion resistance is primary.
8. Conclusion
А 400 series stainless steels are a versatile and widely used family that delivers a pragmatic balance of гаспадарка, магнітныя ўласцівасці, thermal performance and attainable strength. Their role spans everyday appliances to demanding mechanical parts.
Successful use requires informed grade selection and disciplined processing: welding and heat treatment have outsized influence on final performance.
Where corrosion exposure is moderate and cost or magnetic response matter, the 400-series often represents the optimal engineering choice.
Where aggressive corrosion resistance or extreme low-temperature toughness is required, higher-alloy families should be evaluated.
FAQ
Are 400-series steels “stainless”?
Yes — they form a chromium oxide passive film and resist corrosion much better than carbon steels, but they are less corrosion-resistant than 300-series alloys in many aggressive media.
Can 400-series replace 304 in consumer appliances?
Often yes for decorative and many appliance applications (e.g., 430), but avoid where frequent exposure to chlorides, acidic detergents or marine atmospheres occur.
Why are some 400-series magnetic and others not?
Ferritic and martensitic microstructures are magnetic; austenitic microstructures (typical of 300-series) are essentially non-magnetic. 400-series are designed to be ferritic/martensitic.
How to weld 17-4 PH safely?
Use qualified procedures, control heat input, and apply post-weld solution/age cycles or localized aging per supplier instructions to restore strength and corrosion resistance.
Is 440C suitable for marine bearings?
No — while 440C offers high hardness and wear resistance, its corrosion resistance in marine chloride environments is limited; consider stainless bearings with higher PREN or coatings.
