跳至主要内容

WHY DOES STAINLESS STEEL RUST?

Stainless steel widely used to produce all kinds of machinery part to avoid rust. But Stainless steel will rust under certain conditions.

Why does stainless steel rust?

When there are brown rust spots (spots) on the surface of stainless steel pipes, people are surprised to think that “stainless steel is not rusty, rust is not stainless steel, maybe there is a problem with the steel quality”. In fact, this is a one-sided wrong view of the lack of understanding of stainless steel. Stainless steel will rust under certain conditions.
stainless steel CNC turned part
stainless steel CNC turned part

Stainless steel does not rust

It also produces an oxide on the surface. At present, all stainless steel on the market is due to the presence of Cr element. The basic reason (mechanism) of stainless steel corrosion resistance is passivation film theory. The so-called passivation film is a layer of Cr2O3 based film on the surface of stainless steel. Due to the existence of this film, the corrosion of stainless steel matrix in various media is blocked, which is called passivation.

THERE ARE TWO CONDITIONS FOR THE FORMATION OF THIS PASSIVATION FILM.

1.One is that stainless steel itself has the ability of self passivation, which is accelerated with the increase of chromium content, so it has rust resistance;
2.The other is that stainless steel in various aqueous solutions (electrolytes) forms a passivation film in the process of corrosion, which hinders corrosion. When the passive film is damaged, a new passive film can be formed immediately.
hexagon end bar(stainless steel)
hexagon end bar(stainless steel)

THE PASSIVATION FILM OF STAINLESS STEEL HAS THREE CHARACTERISTICS:

1. the thickness of the passivation film is very thin, generally only a few microns when the chromium content is more than 10.5%;
2. the proportion of the passivation film is greater than the proportion of the substrate. These two characteristics show that the passivation film is thin and dense, so it is difficult for the passivation film to be broken down by the corrosion medium to quickly corrode the base body.
3. Third characteristic is that the chromium concentration of the passivation film is three times higher than that of the substrate, so the passivation film has high corrosion resistance.
stainless steel machined part
stainless steel machined part

Stainless steel will be corroded under certain conditions

The application environment of stainless steel is very complex, and the pure chromium oxide passivation film can not meet the requirements of high corrosion resistance. In order to improve the composition of passivation film and the corrosion resistance of stainless steel, molybdenum (MO), copper (Cu), nitrogen (n) and other elements should be added to the steel according to the different service conditions.

1.WHEN MO IS ADDED

the corrosion product MoO2 – is close to the substrate, which strongly promotes the collective passivation and prevents the corrosion of the substrate;

2.WHEN CU IS ADDED

the passivation film on the stainless steel surface contains CuCl, which improves the corrosion resistance because it does not interact with the corrosion medium;

3.WHEN N IS ADDED

the passivation film is rich in Cr2N, which increases the Cr concentration in the passivation film, thus improving the corrosion resistance of stainless steel.
CNC lathing parts
CNC lathing parts

THE CORROSION RESISTANCE OF STAINLESS STEEL IS CONDITIONAL.

One grade of stainless steel is corrosion-resistant in one medium, but it may be damaged in another medium. At the same time, the corrosion resistance of stainless steel is also relative. So far, no stainless steel is absolutely non corrosive in all environments.
Stainless steel has the ability to resist atmospheric oxidation, i.e. rust resistance, but also the ability to corrode in the medium containing acid, alkali and salt, i.e. corrosion resistance. However, the corrosion resistance of the steel varies with the chemical composition of the steel itself, the state of reinforcement, the conditions of use and the type of environmental medium.
For example, 304 steel pipe has absolutely excellent corrosion resistance in dry and clean atmosphere, but when it is moved to the seaside area, it will soon rust in the sea fog containing a lot of salt, while 316 steel pipe performs well. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.
KYLT Precision CNC machining services (milling & turning service), Fast prototyping, Fixture/Jig/Tooling making, Aluminum die casting & plastic injection parts. Email:cnkylt@aliyun.com +008615195010186
KYLT CNC Machining Services:
KYLT CNC Precision Machined Parts:
More information about Machining Technology:
标签：

评论

发表评论

此博客中的热门博文

How to choose Distribution Transformer?

The Key Selection points of   Oil-Immersed Distribution Transformer . Load Properties of Distribution Transformer: 1) When there are a large number of primary or secondary loads, it is advisable to install two or more transformers. When one transformer is disconnected, the capacity of the remaining transformers can meet the demand of primary and secondary loads. First, the secondary loads should be concentrated as far as possible and should not be too dispersed. 2) When seasonal load capacity is large, special transformer should be installed. For example, in large civil buildings, the load of air conditioning refrigerators, heating electricity and heat, etc. 3) When the concentrated load is large, special transformer should be installed. Such as large heating equipment, large X-ray machine, electric arc furnace, etc. 4) When the lighting load is large or the power and lighting use common transformer seriously affects the lighting quality and lamp life, special lighting tra
1 条评论
阅读全文

JTFY AUTO CORRUGATED FIN WALL PRODUCTION LINE REACH KAILI POWER FACTORY

Shandong Kaili Power is a new national factory, which focus on all kinds of Electrical Distribution Transformer manufacturing. electrical power transformer factory This time, they purchased  JTFY 1300*400 full automatic transformer tank corrugated fin wall production line . The whole production line involve:  Hydraulic decoiler  ( steel roll holding & feeding machine ),  Corrugated fin wall folding machine ,  Corrugated fin wall steel ribs insert and fin seam welding machine . JTFY transformer tank corrugated fin wall making line Corrugated Fin Wall Forming Machine , automatic controlled by PLC. Which is used to make  Corrugated Fins Wall  for  Distribution Transformer Tanks . By  Folding  and  Forming  Metal Sheet to demand shapes,so this machine also named  Corrugated Fins Wall Folding Machine ,  Corrugated fin wall Pressing Machine  or  Corrugated Wall Making Machine . Folding machine usage :   Corrugated fin forming length 300-2000mm, width 300-1300mm, height 50-400m
发表评论
阅读全文

What is Die Casting Machine - Types of Die Casting Machine | KYLT Industrial

  What is Die Casting Machine - Die Casting Machine Types, Die-casting mould & Die casting parts Die casting process , by injecting molten metal under pressure into die casting dies or molds.  Die casting mould  consists two halves: fixed die half, movable die half. Metal shapes are formed by mold cavity. When mold open, we can obtain the cast metal parts.  The machine which used to finish the die casting process is named Die casting machine. It has two mechanism:  Cold chamber  &  Hot Chamber . Here, we will introduce the equipment for this process, what is die casting machine, die casting machine types, their mechanism & features, how to choose suitable die casting machine. What is Die Casting Machine? Die casting machine  is one kind non-ferrous metal products making mechinery. It is a metal casting process, by inject molten metal into the mold cavity, the shape of the  die casting parts  will be formed when the metal is cool and solidified. This manufacturing method can
发表评论
阅读全文