1. What is carbon steel?
Carbon steel is essentially low carbon steel without any added elements (excluding trace impurities). Under the effect of corrosive media, the surface of carbon steel quickly forms a loose layer of iron oxide (Fe3O4), commonly known as rust.
This layer is unable to isolate the metal from the environment, causing oxygen atoms from the outside to continually diffuse inwards and perpetuate the rust and corrosion of the steel piece until it is completely destroyed.
2. What is stainless steel?
Stainless steel is a type of steel cast by adding a certain amount of chromium (Cr) to carbon steel. Why doesn't it rust or corrode? The main reason is the presence of chromium in the steel.
Due to the influence of chromium, under the impact of corrosive media, a resistant and dense layer of chromium oxide film, known as “passivation film”, forms on the surface of the steel part. This film is extremely thin and transparent, making it almost invisible to the naked eye.
Consequently, the shiny metallic surface is still visible. This film isolates the metal from the external environment, preventing further corrosion of the metal. Furthermore, it has the ability to self-repair.
If the film is scratched or damaged by external forces, the chromium on the exposed steel surface will react with the oxygen in the medium to regenerate the passivation film, continuing its protective function.
3. The difference between SUS304 stainless steel and SUS444 stainless steel
Our company consistently uses food-grade aircraft stainless steel material, SUS304, as the base material for water tanks to ensure the quality of stainless steel water tanks and establish our brand. The main component of this stainless steel is low carbon steel, with a chromium content of not less than 17%.
In addition, the nickel (Ni) content is not less than 10.5% and the proportion of other elements such as molybdenum, manganese and nitrogen is relatively small.
As the price of nickel, a strategic resource for stainless steel, continues to rise, the development of high-performance, nickel-saving stainless steel has become a major research focus for stainless steel manufacturers.
SUS444 high purity ferritic stainless steel is a kind of environmentally friendly and nickel-saving ferritic stainless steel product. It has excellent corrosion resistance and has been widely used in water treatment systems abroad, but its application in our country is just beginning.
The casting difficulty of SUS444 stainless steel is much greater than SUS304, which required importing from abroad. Due to the complexity of purchasing channels, there are few manufacturers in our country that use SUS444 stainless steel.
At present, Baosteel Company has successfully produced high-purity SUS444 ferritic stainless steel that meets the standard. This new nickel-saving and environmentally friendly stainless steel product has been highly sought after since its inception.
Now, let's compare SUS304 stainless steel and SUS444 stainless steel:
| SUS304 | SUS444 |
| 0Cr18Ni9 | 00Cr18Mo2 |
| Non-magnetic | Magnetic |
| Low carbon | Ultra-low carbon |
| It has good rust resistance and corrosion resistance. | It has superior resistance to rust and corrosion. |
| The surface has a glossy shine. | The surface has a moderate shine. |
| Harmless to the human body, edible product. | Harmless to the human body, edible product. |
| Approximately 40 yuan per kilogram. | Approximately 30 yuan per kilogram. |
4. Specific Properties of SUS444
Here we will discuss the specific properties of SUS444 stainless steel:
The yield strength of SUS444 stainless steel is about 1.5 times that of carbon steel and six times that of fiberglass, making it exceptionally resistant to shaking, snow accumulation, wind pressure and impact.
SUS444 ferritic stainless steel has high thermal conductivity, approximately 130%-150% of that of chrome-nickel austenitic stainless steel, making it highly suitable for heat exchange applications.
Its coefficient of thermal expansion is small, only about 60%-70% of that of chrome-nickel austenitic stainless steel, making it highly suitable for applications involving thermal expansion and contraction and thermal cycling without deformation.
This type of steel has good ductility and toughness, making it suitable for drawing, drawing and stamping manufacturing. In terms of corrosion resistance, this type of steel is excellent.
Its corrosion resistance in high chloride media is superior to that of regular ferritic stainless steel and austenitic stainless steel, and it does not suffer from chloride stress corrosion cracking.
This type of steel can be welded using the methods normally used for other stainless steels, making it especially suitable for food processing equipment, heat exchangers, hot water tanks, storage tanks, solar collection panels, etc.
The only disadvantage of this type of steel, compared to other stainless steels, is its magnetism. With this in mind, it is not suitable for use on sensitive electronic equipment, aviation equipment susceptible to electromagnetic waves or magnetic noise interference.
5. Conclusion
Considering the overall performance and price, our company intends to replace SUS304 with SUS444 as the main material for our stainless steel water tanks. Its superior performance can fully meet our brand requirements for water tanks.
We hope that our business elites can fully promote this new type of stainless steel material, inform our customers about its advantages, and break the traditional mentality that only SUS304 can be used in water tanks.
