What is stainless steel?

Stainless steel is a type of steel, steel is refer to the content of carbon(C) below 2%; carbon(C) more than 2% is iron.  When in the smelting the steel process, will add elements chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), titanium (Ti), molybdenum (Mo) and other alloying elements, which improves the performance of the steel and makes the steel corrosion-resistant (That is, no rust). This is the stainless steel.

Why there are different grades of stainless steel?

When in the smelting stainless steel process,  adding different alloying elements and different quantity, which will cause the difference of characteristics; use different grades in order to distinguish their differences. Bellow are the common grades of the stainless steel that we often see, the alloying elements are just for reference:

Grade:  C      Si    Mn    P      S      Cr      Ni  

316  ≤0.08 ≤1.00 ≤2.00 ≤0.035 ≤0.030 16-18.5 10-14

304  ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.03 18-20 8-10

201  ≤0.15 ≤1.00 5.5-7.5 ≤0.05 ≤0.03 16-18 3.5-5.5

Why stainless steel not easy be rusty?

There are three main factors affecting stainless steel corrosion.

1) The content of alloying elements, Generally speaking, the chromium content of 10.5% steel is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, SS304,the content of Nickel is in 8%-10%, chromium content is 18%-20%, so SS304 will not easily corrosion in normal circumstances.

2) The smelting process of the manufacturer will also affect the corrosion resistance of stainless steel. A large stainless steel plant with good smelting technology, advanced equipment and advanced technology can be guaranteed no matter in the control of alloying elements, the removal of impurities, and the control of the cooling temperature of the billet.Therefore, the product quality is stable and reliable, the internal quality is good, and it is not easy to rust. On the contrary, some small steel mills have backward equipment and technology. During the smelting process, impurities cannot be removed, and the products produced will inevitably rust.

3) External environment, stainless steel in dry and ventilated environment is not easy to rust. If the air humidity is high, continuous rainy weather, or the environment with high pH in the air, stainless steel is easy to rust. 304 stainless steel also will be rusty if the surrounding environment is too bad.