SS is the general indication of the iron-based alloy featuring stainless characteristics due to its Cr content over 12%.

 

What is the general SS model for decoration?

Currently so-called SUS304(Japan label standards),i.e,0Cr18Ni9 for our country.

 

Not sure. Due to the limitation of material and production technology, some recycled material has a higher C content and contains small amount of nitrogen which shall enhance hardness; additionally the decreasing content of Cr and Ni shall also enhance hardness. Such two types of material shall have a lowered malleability and corrosion resistance.

 

Does SS never rust? In what conditions the decoration-purposed SS shall become easy to rust?

Sometimes. In addition to inherent defects, the environment conditions shall also be greatly associated with the rusting of decoration-purposed SS ,such as the humidity and temperature of air, flow velocity and direction, composition and quantity of impurities contained in air, etc. In atmosphere or weak corrosion with its speed lower than 0.01mm/year shall be deemed as complete anti-corrosion. However in case rust is formed in CL media (ex, salt),sulfuric acid ,oxalic acid (often used to wash the external wall of constructions),hydrochloric acid and porcelain cleanser(for internal decoration cleaning),the neutral substance(such as clean water )shall be often used during maintenance to reduce the corrosive substances adhered to SS. Besides, the scratches caused by some sharp articles(such as blades, brass wire brush, etc.)shall be avoided to maintain its appearance and intercrystalline structure against rust.

 

After SS experiences bending, twisting and folding, the dislocation, i.e. damage of internal intercrystalline bond, shall occur, which may result in pitting corrosion to cause rust.

 

SS can be generally classified in terms of usages, chemical composition and fine texture.

Based on the austenite steel containing 18% Cr to 8% Ni, various purpose-based steels can be developed by adding various elements in different amount.

Classified according to chemical composition:

1.CR series: ferrite series and marten site series

2.CR-NI series: austenite series, abnormity series, precipitation hardening series.

Classified according to fine texture:

1.austenite SS 2. ferrite SS 3. marten site 4.two-phase SS 5. precipitation hardening SS

 

The property of SS is determined by one element, that is, Cr. All SSs contain Cr in a certain amount. Until now, a kind of SS free of Cr has not been invented.

The root cause for Cr to be the major element determine the property of SS is that Cr element can drive the internal movement of steel towards the direction beneficial

1.Cr can upgrade the electrode potential of iron-based solid solution

2.Cr can absorb the electron of iron to have iron passivated

Passivation is a kind of phenomenon that the metal or alloy has an improved anti-corrosion performance by the inhibition of positive reaction. There are many theories on the formation of passivation for metal or alloy, mainly including membrane theory, absorption theory and electron configuration theory.

 

Ni is the excellent anti-corrosive material and also the important element to form alloy steel. Ni is an element to form austenite in steel. The content of Ni must reach 24%if low C-Ni steel shall get pure austenite texture. And only that the content of Ni reaches 27%,the anti-corrosive property of steel in some media can be significantly improved. So single Ni can not form SS. However when Ni and Cr are co-existing in the SS, many precious performances can be available.

Based on the above mentioned, as an alloy element, Ni can change the texture of high Cr steel, thus improving the anti-corrosive and process performances of SS.