Everything You Need to Know About Ferritic Stainless Steel

Ferritic stainless steel, as the second most common type of stainless steel in the stainless steel family, has become a frequently used material in many industries due to its characteristics and advantages. This blog will provide you with a detailed introduction to ferritic stainless steel from the aspects of features, applications, and benefits, helping you with your customized metal products.

What is Ferritic Stainless Steel?

تعريف

Ferritic stainless steel is a type of stainless steel with iron as the base, characterized by chromium(typicallly 10.5%-30%), and low or no nickel content.

It maintains a body-centered cubic (BCC) crystal structure from room temperature up to high temperatures.

What is Ferritic?

Ferrite is a crystal structure formed by the arrangement of iron atoms in a body-centered cubic pattern. This metallographic structure determines that all ferritic steels possess magnetism and provides them with characteristic formability and toughness.

Chemical Components

Main Properties of Ferritic Stainless Steel

الخصائص الفيزيائية

• مغناطيسي
• Good thermal conductivity
• Low thermal expansion

الخواص الكيميائية

• Good corrosion resistance: especially in mild atmospheric environments, freshwater environments, and environments containing light chemical media.
• Good oxidation resistance: even in high temperature environment of 600-800℃.

الخواص الميكانيكية

• Moderate tensile strength and yield strength.
• Toughness: It has a certain degree of toughness at room temperature, but the lower the temperature, the worse the toughness becomes.
• Formability: It typically has poor plasticity, especially at low temperatures.

Common Ferritic Stainless Steel Grades

430 الفولاذ المقاوم للصدأ

430 stainless steel contains 16-18% chromium and is the most common and versatile ferritic stainless steel.

It exhibits good corrosion resistance in dry, mild environments.

Its weldability is relatively poor, making it suitable for sheet metal fabrication methods such as cutting and bending for integrated forming.

Common applications of 430 include microwave oven casings, elevator wall panels, and kitchen sinks.

434 الفولاذ المقاوم للصدأ

434 stainless steel adds approximately 1% molybdenum to the base of 430. The addition of molybdenum enhances the pitting and crevice corrosion resistance of the stainless steel, while also slightly increasing its cost.

Common 434 components include car door handles, wiper arms, and dishwasher liners.

409 الفولاذ المقاوم للصدأ

409 stainless steel has a chromium content of about 11% and contains titanium, a stable element.

The addition of titanium improves its resistance to intergranular corrosion, giving it excellent welding performance.

Due to its low chromium content, its cost is reduced, but its corrosion resistance is significantly weakened.

Common applications of 409 are automotive exhaust pipes, automotive mufflers, and agricultural equipment exhaust pipes.

439 الفولاذ المقاوم للصدأ

The chromium content of 439 stainless steel is about 17-19%, and titanium is used as a stabilizing element to improve the resistance to intergranular corrosion, so the welding performance is excellent.

Parts that require high welding performance and good corrosion resistance can be made of 439, such as water heater liners, gas pipelines, etc.

444 Stainless Steel

444 stainless steel is a high-molybdenum ferritic stainless steel containing 18-20% chromium, approximately 2% molybdenum, and niobium as a stabilizing element—effectively preventing intergranular corrosion.

The presence of molybdenum gives it extremely strong resistance to chloride stress corrosion and pitting corrosion.

Common 444 products include hot water storage tanks and roofing materials for coastal buildings.

446 الفولاذ المقاوم للصدأ

446 stainless steel is a high-chromium ferritic stainless steel with a chromium content of 23-27%, giving it extremely high high-temperature oxidation resistance and a maximum heat resistance temperature of up to 1100℃.

However, its cost is relatively high among ferritic stainless steels, and its machinability is generally average.

Common 446 stainless steel products include industrial furnace annealing tubes and heat treatment equipment.

International Standards & Grade Equivalents

Advantages and Disadvantages of Ferritic Stainless Steel

المزايا

1. The chromium content in ferritic stainless steel ensures its good corrosion resistance. If your custom product needs to withstand moderately corrosive environments, ferritic stainless steel can meet your long-term use needs.
2. Ferritic stainless steel has good oxidation resistance at high temperatures and has a low coefficient of thermal expansion, ensuring that ferritic stainless steel products can still maintain good performance in high-temperature use environments.
3. The plasticity and toughness of ferritic stainless steel make it excellent in processing at room temperature, and if you choose ferritic stainless steel as your production material, then the whole production process will be very efficient.
4. Ferritic stainless steel contains very little or no nickel, resulting in lower production costs. If your product prioritizes cost-effectiveness, ferritic stainless steel is a good choice.

العيوب

Compared with other types of stainless steel, ferritic stainless steel has some disadvantages in specific applications.

1. Compared to austenitic stainless steel, ferritic stainless steel has relatively lower corrosion resistance, especially in humid, chemical, and chlorine-containing environments.
2. Ferritic stainless steel has poor weldability, and after welding, it will become embrittled, develop hot cracks, and lead to intergranular corrosion, resulting in generally poor weld quality.
3. Ferritic stainless steel is not as strong as austenitic stainless steel and PH stainless steel, so it does not have much advantage in applications with high strength requirements.
4. In low-temperature environments, ferritic stainless steel has poor plasticity and toughness, making it unsuitable for low-temperature applications or scenarios requiring high tensile strength in components.

Processing Methods of Ferritic Stainless Steel

التصنيع باستخدام الحاسب الآلي

CNC machining is the most common processing method for ferritic stainless steel, producing products with high precision, smooth surfaces, and excellent performance, making it highly suitable for small to medium-batch custom projects.

However, it is important to note that localized temperature increases during cutting can cause surface hardening and accelerate tool wear.

It is recommended to use high-speed steel or carbide tools, combined with medium to low cutting speeds and cutting fluid, to achieve better machining results.

التشكيل الساخن

Ferritic stainless steel can be hot-processed, but it is necessary to accurately control the workpiece temperature between 950~1250°C during processing. 

Too low a temperature will lead to work hardening, while too high a temperature will lead to coarse grains, decreased mechanical properties and corrosion resistance.

Therefore, it is less used for thermal processing and is mainly used for a small number of parts with large thickness or special shapes.

الاستثمار في الصب

While ferritic stainless steel can be used for investment casting, its poor fluidity and susceptibility to cold cracking and intergranular cracking during rapid cooling limit its application.

Therefore, it is typically used only for small-batch casting of complex shapes and high-precision parts.

Strict control of melting temperature, pouring speed, and cooling method is required during the casting process to prevent cracking.

Furthermore, post-casting annealing is necessary to relieve stress and ensure mechanical properties and corrosion resistance.

Cutting &  Bending

Cold working processes, such as bending and stamping, are the most common industrial processing methods for ferritic stainless steel, mainly for the following two reasons:

1. Low cost and good corrosion resistance, offering cost advantages for large-scale applications.
2. Cold working uses thin sheets, which effectively avoids the disadvantages of limited plasticity and work hardening of ferritic stainless steel.

اللحام

The weldability of ferritic stainless steel is generally average. If the welding heat input and interpass temperature are not strictly controlled during the production process, hot cracks may occur at the weld, affecting the product’s performance.

However, selecting grades with good weldability, such as 439 and 444, can effectively prevent intergranular corrosion after welding.

معالجة السطح

• Functional treatment: pickling, passivation, electropolishing…
• Decorative treatments: polishing, sandblasting, coating…

Application of Ferritic Stainless Steel

• Automotive: exhaust pipes, exhaust manifolds, mufflers, door handles， wiper parts…
• Home appliances and kitchenware: water heater liners, washing machine drums, microwave oven shells, sinks, induction cookers and pans…
• Architecture and decoration: elevator door panels, door and window hinges, coastal building structural…
• Industry and energy: boiler drum, chemical transport pipeline, heat exchanger tube…
• Durable consumer goods: motorcycle frames, fasteners (bolts, nuts)…

ملخص

The blog has given you a general understanding of the characteristics, advantages, and application scenarios of ferritic stainless steel. If you are interested in customizing ferritic stainless steel products, please feel free to contact us for a quote. We offer one-stop services, including machining, investment casting, sheet metal fabrication, and surface treatment.

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