Stainless steel is a steel with stainless and corrosion resistance as the main characteristics, and the chromium content is at least 10.5%, and the carbon content does not exceed 1.2%.

Stainless steel (Stainless Steel) is the abbreviation of stainless acid-resistant steel, which is resistant to weak corrosive media such as air, steam, water, or has stainless steel. Corrosion) Corroded steel is called acid-resistant steel.

Due to the difference in chemical composition of the two, their corrosion resistance is different. Ordinary stainless steel is generally not resistant to chemical medium corrosion, while acid-resistant steel is generally stainless. The term "stainless steel" does not simply refer to one kind of stainless steel, but refers to more than one hundred kinds of industrial stainless steels, and each developed stainless steel has good performance in its specific application field. The key to success is first to understand the purpose, and then to determine the correct steel grade. There are usually only six steel grades relevant to building construction applications. They all contain 17-22% chromium, and the better steel grades also contain nickel. Adding molybdenum can further improve the atmospheric corrosion resistance, especially the resistance to chloride-containing atmosphere corrosion.

Generally speaking, the hardness of stainless steel is higher than that of aluminum alloy, and the cost of stainless steel is higher than that of aluminum alloy.

Main Features

Folding weldability

Different product uses have different requirements for welding performance. Class I tableware generally does not require welding performance, even some pot companies. However, most products require good welding performance of raw materials, such as second-class tableware, thermos cups, steel pipes, water heaters, water dispensers, etc.

Folding Polishing Performance

In today's society, stainless steel products generally go through the polishing process during production, and only a few products such as water heaters, water dispenser inner tanks, etc. do not need polishing. Therefore, this requires the polishing performance of the raw material to be very good. The main factors affecting the polishing performance are as follows:

① surface defects of raw materials. Such as scratches, pitting, pickling, etc.

② The problem of raw materials. If the hardness is too low, it will not be easy to polish during polishing (the BQ property is not good), and if the hardness is too low, orange peel phenomenon will easily appear on the surface during deep drawing, thus affecting the BQ property. BQ properties with high hardness are relatively good.

③For deep-drawn products, small black spots and RIDGING will appear on the surface of the area with a large amount of deformation, which will affect the BQ performance.

Folding heat resistance

Heat resistance means that stainless steel can still maintain its excellent physical and mechanical properties at high temperatures.

Influence of carbon: Carbon is an element in austenitic stainless steel that strongly forms and stabilizes austenite and expands the austenite zone. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is an interstitial element that can significantly increase the strength of austenitic stainless steel through solid solution strengthening. Carbon can also improve the stress corrosion resistance of austenitic stainless steel in high concentration chloride (such as 42% MgCl2 boiling solution).

However, in austenitic stainless steel, carbon is often regarded as a harmful element, mainly because carbon can interact with Chromium forms high-chromium Cr23C6 carbon compounds, which leads to the depletion of local chromium, which reduces the corrosion resistance of steel, especially the resistance to intergranular corrosion. therefore. Most of the newly developed chromium-nickel austenitic stainless steels since the 1960s are ultra-low-carbon types with a carbon content of less than 0.03% or 0.02%. It can be known that as the carbon content decreases, the intergranular corrosion sensitivity of steel decreases. Only 0.02% has the most obvious effect. Some experiments also pointed out that carbon will also increase the tendency of pitting corrosion of chromium austenitic stainless steel. Due to the harmful effect of carbon, not only in the smelting process of austenitic stainless steel, the carbon content should be controlled as low as possible, but also in the subsequent heat, cold processing and heat treatment processes to prevent carbonization on the surface of stainless steel and avoid chromium carbides Precipitate.

Folding Corrosion Resistance

When the atomic number of chromium in the steel is not less than 12.5%, the electrode potential of the steel can change suddenly, from negative potential to positive electrode potential. Prevents galvanic corrosion.

Structural components

The corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, the carbon content of most stainless steels is low, the maximum does not exceed 1.2%, and the ωc (carbon content) of some steels is even lower than 0.03% (such as 00Cr12 ). The main alloying element in stainless steel is Cr (chromium), only when the Cr content reaches a certain.

physical properties

compared to carbon steel

1. Density

The density of carbon steel is slightly higher than that of ferritic and martensitic stainless steel, and slightly lower than that of austenitic stainless steel;

2. Resistivity

Resistivity increases in order of carbon steel, ferritic, martensitic and austenitic stainless steel;

3. The order of linear expansion coefficient is also similar, austenitic stainless steel is the highest and carbon steel is the smallest;

4. Carbon steel, ferritic and martensitic stainless steel are magnetic, and austenitic stainless steel is non-magnetic, but it will produce magnetism when it is cold-work hardened to form martensitic phase transformation, and heat treatment can be used to eliminate this martensite tissue to restore its non-magnetic properties.

Compared with carbon steel, austenitic stainless steel has the following characteristics:

1) High resistivity, about 5 times that of carbon steel.

2) Large linear expansion coefficient, which is 40% larger than that of carbon steel, and as the temperature increases, the value of the linear expansion coefficient increases accordingly.

3) Low thermal conductivity, about 1/3 of carbon steel.

Typical use

Most of the use requirements are to maintain the original appearance of the building for a long time. When determining the type of stainless steel to be selected, the main considerations are the required aesthetic standards, the corrosiveness of the local atmosphere, and the cleaning system to be adopted. Increasingly, however, other applications simply seek structural integrity or impermeability. For example, roofs and side walls of industrial buildings. In these applications, the owner's cost of construction may be more important than aesthetics, and the surface is not very clean. The effect of using 304 stainless steel in a dry indoor environment is quite good.

However, to maintain its appearance outdoors in both the country and the city, frequent washing is required. In heavily polluted industrial areas and coastal areas, the surface will be very dirty and even rusted. However, to obtain the aesthetic effect in the outdoor environment, nickel-containing stainless steel is required. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other construction purposes, but in severely corrosive industries or marine atmospheres, it is best to use 316 stainless steel. There are several design criteria that include 304 and 316 stainless steel.

Because "duplex" stainless steel 2205 has integrated good atmospheric corrosion resistance with high tensile strength and elastic limit strength, this steel is also included in the European standards. Product shape, in fact, stainless steel is manufactured in all standard metal shapes and sizes, and there are many special shapes. The most commonly used products are made of sheet and strip steel, and special products are also produced from medium and thick plates, for example, the production of hot-rolled structural steel and extruded structural steel. There are also round, oval, square, rectangular and hexagonal welded or seamless steel pipes and other forms of products, including profiles, bars, wires and castings. To meet the aesthetic requirements of architects, a number of different commercial finishes have been developed.