Stainless steel is a type of steel, steel refers to the amount of carbon (C) less than 2% is called steel, more than 2% is iron. Steel in the smelting process to add chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), titanium (Ti), molybdenum (Mo) and other alloying elements to improve the performance of steel so that steel has corrosion resistance (that is, no rust) is what we often say stainless steel.

"Steel" and "iron" are what, what characteristics, and what relationship, we usually say 304, 304L, 316, 316L is how to come, and what is the difference between each other?

Steel: Material with iron as the main element, carbon content is generally less than 2%, and contains other elements. -- GB/T 13304-91 "Steel Classification"

Iron: a metallic element, atomic number 26. Iron materials have strong ferromagnetism, and have good plasticity and thermal conductivity.

Stainless steel: resistant to air, steam, water and other weak corrosive media or stainless steel. The steel grades usually used are 304, 304L, 316, 316L, which are 300 series steel of austenitic stainless steel.

Second, why does stainless steel have different steel numbers?

In the process of stainless steel smelting, due to the different varieties of alloying elements added, the amount of different varieties added is different. Its characteristics are also different, in order to make a difference, the crown on the different steel numbers, the following is the common decorative stainless steel with different steel numbers "alloying elements" content table for reference only: chemical composition (mass fraction, %)

Common categories:

Usually divided by metallographic organization:

Generally, according to the metallographic organization, the ordinary stainless steel is divided into three categories: Austenitic stainless steel, ferritic stainless steel, martensitic stainless steel. On the basis of these three basic metallographic structures, for specific needs and purposes, and derived from the duplex steel, precipitation hardening stainless steel and iron content of less than 50% of the high alloy steel.

1, Austenitic stainless steel

The matrix is mainly stainless steel with a face-centered cubic crystal structure of austenitic structure (CY phase), non-magnetic, mainly through cold working to strengthen it (and may result in a certain magnetic). The American Iron and Steel Institute uses 200 and 300 series numbers, such as 304.

2, iron type stainless steel

The matrix is dominated by a ferrite structure (phase A) of body-centered cubic crystal structure, magnetic, generally can not be hardened by heat treatment, but cold working can make it slightly strengthened stainless steel. The American Iron and Steel Institute is marked 430 and 446.

3. Martensitic stainless steel

The matrix is martensitic structure (body-centered cubic or cubic), magnetic stainless steel, its mechanical properties can be adjusted by heat treatment. The American Iron and Steel Institute uses numbers 410, 420, and 440. Martensite has an austenitic structure at high temperatures, and when cooled to room temperature at an appropriate rate, the austenitic structure is able to convert to martensite (i.e., hardened).

4, austenitic ferritic (duplex) stainless steel

The matrix has both austenitic and ferritic two-phase structure, of which the content of the less phase matrix is generally greater than 15%, is magnetic, and can be strengthened by cold working stainless steel, 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex steel has higher strength, higher resistance to intergranular corrosion, chloride stress corrosion and point corrosion.

5, precipitation hardening stainless steel

Stainless steel whose matrix is austenitic or martensitic and can be hardened by precipitation hardening. The American Iron and Steel Institute uses 600 series numbers, such as 630, which is 17-4PH.

In general, in addition to alloys, the corrosion resistance of austenitic stainless steel is relatively excellent, in a less corrosive environment, ferritic stainless steel can be used, in a mildly corrosive environment, if the material is required to have high strength or high hardness, martensitic stainless steel and precipitation hardened stainless steel can be used.

Features and uses

Surface technology

Thickness differentiation

1, because the steel mill machinery in the rolling process, the roll heat appears slight deformation, resulting in the thickness of the rolled out board deviation, generally thick on both sides of the thin. When measuring the thickness of the board, the state stipulates that the middle part of the board head should be measured.

2, the reason for the tolerance is according to the market and customer demand, generally divided into large tolerances and small tolerances: for example

304 stainless steel -

Performance description:

304 stainless steel is a common steel, as a widely used steel, has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; Stamping, bending and other hot processing is good, no heat treatment hardening phenomenon (non-magnetic, then use the temperature -196℃ ~ 800℃).

Scope of application:

Household goods (Class 1 and 2 tableware, cabinets, indoor plumbing, water heater, boiler, bathtub)

Auto parts (windshield wipers, mufflers, molding products)

Medical equipment, building materials, chemicals, food industry, agriculture, Marine components

- 304L stainless steel -

Performance description:

As a low-carbon 304 steel, in the general state, its corrosion resistance is similar to that of 304, but after welding or stress relief, its grain boundary corrosion resistance is strong; In the absence of heat treatment, it can also maintain good corrosion resistance, and the use temperature is -196℃ ~ 800℃.

Scope of application:

It is used in chemical, coal and petroleum industry with high grain boundary corrosion resistance, heat resistant parts of building materials and parts with difficulty in heat treatment.

316 stainless steel -

Performance description:

316 stainless steel due to the addition of molybdenum, so its corrosion resistance, atmospheric corrosion resistance and high temperature strength is particularly good, can be used under harsh conditions; Excellent work hardening (non-magnetic).

Scope of application

Seawater equipment, chemicals, dyes, papermaking, oxalic acid, fertilizer and other production equipment; Photography, food industry, coastal facilities, ropes, CD rods, bolts, nuts.

- 316L stainless steel -

Performance description:

As a low-carbon series of 316 steel, in addition to having the same characteristics as 316 steel, its resistance to grain boundary corrosion is excellent.

Scope of application:

Products with special requirements for resistance to grain boundary corrosion.

What kind of stainless steel is not easy to rust?

There are three main factors affecting stainless steel corrosion:

1, the content of alloying elements.

Generally speaking, the content of chromium in 10.5% steel is not easy to rust. The higher the content of chromium nickel, the better the corrosion resistance, such as 304 material nickel content in 8-10%, chromium content reached 18-20%, such stainless steel in general circumstances will not rust.

2, the smelting process of the production enterprise will also affect the corrosion resistance of stainless steel.

Large stainless steel plants with good smelting technology, advanced equipment and advanced technology can be guaranteed whether in the control of alloying elements, the removal of impurities, and the control of billet cooling temperature, so 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 are backward in equipment and technology, and impurities cannot be removed in the smelting process, and the products produced will inevitably rust.

3, the external environment, the climate is dry and ventilated environment is not easy to rust.

The air humidity is large, continuous rainy weather, or environmental areas with high pH in the air are easy to rust. 304 stainless steel, if the surrounding environment is too poor will rust.

Stainless steel appears rust spot how to deal with?

1. Chemical methods

Use pickling paste or spray to assist its rust parts to re-passivate to form chromium oxide film to restore its corrosion resistance. After pickling, in order to remove all contaminants and acid residues, it is very important to properly rinse with water. After all treatment, re-polish with polishing equipment, and seal with polishing wax. For local slight rust spots can also be used 1:1 gasoline, oil mixture with a clean cloth to wipe rust spots.

2. Mechanical method

Sand blasting, shot blasting with glass or ceramic particles, annihilation, brushing and polishing. With mechanical methods it is possible to erase contamination caused by previously removed, polished or annihilated materials. All kinds of pollution, especially foreign iron particles, can be a source of corrosion, especially in humid environments. Therefore, the mechanical cleaning surface should be regularly cleaned under dry conditions. The use of mechanical methods can only clean the surface, can not change the corrosion resistance of the material itself. Therefore, it is recommended to re-polish with polishing equipment after mechanical cleaning and seal with polishing wax.

Stainless steel why some also rust

Why does stainless steel rust? When the surface of the stainless steel pipe appears brown rust spots (spots), people are surprised: think that "stainless steel is not rusty, rust is not stainless steel, there may be a problem with the steel." 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 has the ability to resist atmospheric oxidation - that is, rust, but also has the ability to corrosion in the medium containing acid, alkali, salt - that is, corrosion resistance. However, the size of its corrosion resistance is changed with the chemical composition of the steel itself, the protection state, the use conditions and the type of environmental media. Such as 304 steel pipe, in a dry and clean atmosphere, has excellent corrosion resistance, but it is moved to the seaside area, in the sea fog containing a lot of salt, it will soon rust; The 316 steel pipe performed well. Therefore, not any kind of stainless steel, in any environment can resist corrosion, does not rust.