The reason why stainless steel is “stainless” is due to the chromium contained in it has a significant corrosion resistance.
Ferritic stainless steel is no exception.
Ferritic stainless steel is the main element of chromium (≥10.5%) and iron, and some grades only chromium, some grades in addition to chromium, but also contains other elements (such as Mo, Ti, Nb, etc.) to get some special performance.
Ferritic stainless steel containing chromium does not contain nickel, and the price of chromium in the history of relatively stable, and nickel-containing austenitic stainless steel compared to its lower cost, more stable.
Ferritic stainless steels have most of the mechanical properties and corrosion resistance of austenitic stainless steels, and there are many unique properties over austenitic stainless steels. So ferritic stainless steel can:
- Complement the 304 stainless steel in the stainless steel family (304 is still the most widely used and most commonly used grade);
- Replacement of 200 series stainless steel (usually with better performance);
- Because of its special performance, it can be used in many fields instead of other materials such as carbon steel, Cu, Zn, Al, plastic, etc., even in the original area can only use austenitic stainless steel, may also become excellent alternative materials.
Users of ferritic stainless steel typically benefit from their technical performance and low life cycle cost.
Ferritic stainless steel “magnetic” is not “negative”, but it is different from other stainless steel a special performance.
Well-known standard ferrite stainless steels 409, 410 and 430 are available all over the world. They are widely used in the washing machine drums, exhaust systems and many other important applications, are very successful developed. In fact, ferritic stainless steel in all areas have great potential applications.
Newly developed ferritic stainless steel such as 439,441, etc., can be used for a wide range of fields. They can be processed into complex shapes such as seamless stainless steel tubes, welded round pipes or square pipes, ferritic stainless steel mechanical parts, ferritic stainless steel Stamping parts, ferritic stainless welding parts and structures and so on. And ferritic stainless steel can be connected and welded in the most common connection.
The addition of molybdenum ferrite stainless steel 444 to the local corrosion corrosion resistance at least comparable with the austenitic stainless steel 316.
Ferritic stainless steel as the cost, characteristics and supply channels of the advantages, become the ideal material.
Five categories of ferritic stainless steel
Ferritic stainless steel is divided into five categories, of which 1-3 categories for the standard grades, 4-5 categories for the special grades. So far, the largest amount and the application of the most extensive focus on the standard steel. Therefore, the standard ferritic stainless steel is generally fully able to meet and apply the requirements of most applications.
Class 1 – Cr content: 10% -14%; typical grades 409, 410, 410L.
This type of steel has the lowest chromium content in all stainless steels and is therefore the cheapest and most suitable for use in environments where no corrosion or slight corrosion is allowed and local rust is localized. The 409 stainless steel was originally designed for automotive exhaust system silencers (corrosion is not externally) designed. 410L stainless steel commonly used in containers, buses and long-distance cars, recently used as a liquid crystal display frame.
Class 2 – Cr content: 14% -18%; typical grade 430.
It is a class of the most widely used ferritic stainless steel, containing a high chromium, with good corrosion resistance, the majority of its performance and 304 similar. In some applications, replaceable 304 stainless steel, generally used indoors with sufficient corrosion resistance. Typical uses include washing machine drums, interior panels and the like. Typical 430 is often used as an alternative to 304 for kitchen facilities, dishwashers, pots and pots.
Class 3 – Cr content: 14% -18%, containing stabilizing elements Ti, Nb, etc .; typical grades 430Ti, 439,441 and so on.
Compared with the second category, this type of brand has good weldability and formability. In most cases, its performance is even better than 304. Typical uses include sinks, heat exchange tubes (sugar, energy, etc.), automotive exhaust systems (longer than 409 long life) and welding parts of the washing machine. Class 3 grades may even replace 304 for higher performance requirements.
Class 4 – Mo content above 0.5%; typical grades include 434,436,444 and so on.
These grades add corrosion resistance by adding molybdenum, and their typical applications are hot water tanks, solar water heaters, automotive exhaust systems, electric heating pots and microwave components, car trim and outdoor panels. 444 stainless steel corrosion resistance and 316 stainless steel quite.
Category 5 – Cr content: 18% -30%; typical grades include 446,445 / 447 and so on.
These grades increase the corrosion resistance and oxidation resistance by adding more chromium and containing molybdenum. The corrosion resistance and oxidation resistance of these grades are better than 316. Typical use Coastal and other highly resistant environments. The corrosion resistance of JIS 447 is equivalent to that of metallic titanium.
Modern ferritic stainless steel excellent performance
High-quality ferritic stainless steel has been around for many years, has now formed a series of excellent performance of the commercial grade.
430 stainless steel was once the only recognized ferrite grade, but the early use of this grade, especially in the use of welding or severe corrosion conditions, did not get enough technical support, there have been some events, so that later The formation of ferritic stainless steel poor performance and excellent performance of Austenitic stainless steel misunderstanding.
In fact, ferritic stainless steel has long been improved. The full support of modern technology and the addition and diversification of steel grades ensure that the user’s needs are met in terms of performance. Ferritic stainless steel performance can be compared with austenitic stainless steel, that ferritic stainless steel performance is poor or particularly good are wrong, they are only between the performance and use different.
In fact, in many conditions, compared with the expensive materials, ferritic stainless steel is becoming a better choice. This type of stainless steel is more suitable for some special requirements of the environmental conditions, performance is not high is not low, just to meet the requirements.
Excellent forming performance
Ferritic stainless steel ductility and carbon steel, like most of the molding operations are no problem, but no austenitic stainless steel ductility is good. Austenitic stainless steel has excellent ductility, but in many cases is “excellent performance.”
Ferritic stainless steel and carbon steel exhibit the same formability. So, as long as you can now think of carbon steel can be processed into a variety of complex shapes (such as car body), will realize that ferritic stainless steel also has the same possibility. As long as the tools and grades are selected correctly, ferritic stainless steel can be machined into various shapes.
Unique magnetic properties
A general misunderstanding of ferritic stainless steel is that because ferritic stainless steel has magnetic properties, so this type of steel is not “real” stainless steel, and will rust like carbon steel. This is not justified. Some of the stainless steel is magnetic and some of the real cause of no magneticity is that the atomic structure between them is different. Corrosion resistance has nothing to do with the atomic structure, but with the chemical composition, that is, the specific chromium content. And magnetic and corrosion resistance is not related.
In fact, the magnetic properties of ferritic stainless steels are one of the important properties of this material, with many current or potential uses and advantages. The closure of refrigerators and knives and other metal tools takes advantage of this performance. Practical application, “induction fever” cooker in the basic performance of the pot is magnetic, because the heat process is the cooking itself into the thermal energy of the process.
Unique technical advantages
Ferritic stainless steel is a particularly durable and low maintenance material that has a much lower life cycle cost than carbon steel and 100% recyclable.
Compared with carbon steel, ferritic stainless steel has all the advantages of stainless steel: corrosion resistance, low life cycle cost and long life. In addition, compared with the same kind of steel austenitic stainless steel, its advantages are not only in its low cost of this one, in fact, ferritic stainless steel in many properties are better than austenitic stainless steel.
Ferritic stainless steel unique “ace” performance
Ferritic stainless steel is magnetic.
Ferritic stainless steel has a low coefficient of thermal expansion (less than austenitic stainless steel when heated).
Ferritic stainless steel high temperature oxidation resistance (compared with the austenitic stainless steel, the surface is not easy to form oxide)
Ferritic stainless steel has a high thermal conductivity (heat transfer is more uniform than austenitic stainless steel).
Ferritic stainless steels containing stabilized niobium have good creep resistance (strain under long stress is smaller than that of austenitic stainless steels).
Ferritic stainless steel is easier to cut and process than austenitic stainless steel (austenitic stainless steel machining requires special tools and high power machinery, resulting in greater tool wear).
In the cold forming, the ferritic stainless steel rebound tendency is much smaller than the austenitic stainless steel.
Ferritic stainless steel yield strength higher than 304 stainless steel (equivalent to carbon steel).
Ferritic stainless steel is less prone to stress corrosion cracking
Match is perfect
In the current market situation, the user in the specific application environment for material selection, the first to avoid the material selected “overcapacity.”
In the past, the development of austenitic stainless steel 304 has a wide range of applicability, has become the most widely used, the most readily available stainless steel grades. As long as the rational selection, modern ferritic stainless steel can often effectively replace 304 stainless steel.
After careful and practical inspections of the quality of manufacture and use, the results show that ferritic stainless steel with cost advantages is sufficient to meet the performance requirements of processors and end users.
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