Why is rebar chemically analyzed? Where does it come from?

Code for Acceptance of Construction Quality of Concrete Structure Engineering GB50204-2002

When it is found that the steel bar is brittle, the welding performance is poor or the mechanical properties are significantly abnormal, the chemical composition of the batch of steel bars should be tested or other special inspections.

In addition to the main chemical component iron (Fe), steel also contains a small amount of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), oxygen (O), nitrogen (N), titanium (Ti), vanadium (V) and other elements. These elements, although present in small amounts, have a great impact on the properties of steel:

1 carbon. Carbon is the most important element that determines the properties of steel. When the carbon content in the steel is below, with the increase of carbon content, the strength and hardness of the steel increase, while the plasticity and toughness decrease; However, when the carbon content is above, the strength of the steel decreases as the carbon content increases.

With the increase of carbon content, the welding performance of steel deteriorates (the weldability of steel with greater carbon content decreases significantly), the sensitivity of cold brittleness and aging increases, and the resistance to atmospheric corrosion decreases. 2。Silicon (Si) and manganese (Mn) can improve the strength of steel, among other properties.

3。Phosphorus (P), sulfur (S), and oxygen (O) are all harmful elements.

According to the Code for Acceptance of Construction Quality of Concrete Structure Engineering GB50204-2002, when it is found that the steel bar is brittle, the welding performance is poor or the mechanical properties are significantly abnormal, the chemical composition of the batch of steel bars should be tested or other special inspections.

At the same time, according to the requirements of the construction quality acceptance specification, the chemical composition analysis of imported steel must be carried out.

Only when the environmental factors of the site have high requirements for corrosion, etc., the chemical composition of the steel bar is considered; Of course, the chemical content of the aggregate of the concrete, such as alkali, is also considered.

There are also imported steel bars from abroad.

If one of the following conditions occurs in the steel bar, the chemical composition test must be done:

1) There is no factory certificate or the steel grade and steel number are unknown;

2) Imported steel bars with welding requirements;

3) In the process of processing, brittleness, poor welding performance and significant abnormal mechanical properties occur.

Analysis of the chemical composition of steel.

The analysis of chemical products using steel includes wet analysis and spectral analysis, as follows: the main test items of wet analysis of steel: C, S, P, MN, SI, CR, NI, CU, MO, V, TI, AL, MG, NB, B, CEQ and PCM;

Spectral analysis of carbon steels and low- and medium-alloy steels: C, S, P, MN, SI, CR, NI, CU, MO, V, TI, AL, W, NB, B; Stainless steel: C, S, P, MN, SI, CR, NI, CU, MO, TI, AL, W.

If the steel bar has one of the following conditions, the chemical composition must be tested: (1) there is no factory certificate or the steel number of the steel is unknown; 2) Imported steel bars with welding requirements; 3) In the process of processing, brittleness, poor welding performance and significant abnormal mechanical properties occur.

Chemical composition In addition to the main chemical component Fe iron, steel also contains a small amount of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), oxygen (0), nitrogen (N), titanium (To, vanadium (V) and other elements, although the content of these elements is very small, but it has a great impact on the performance of steel.

What are the categories according to the chemical composition of steel bars?

1. Carbon steel bar: Carbon steel bar is rolled from carbon steel. According to the provisions of the national standard "Technical Standard for Ordinary Carbon Structural Steel" (GB700-79), ordinary carbon structural steel is divided into the following three categories according to the guarantee conditions of the factory:

Class A steel - steel that guarantees mechanical properties; It is denoted by the symbol A.

Class B steel – steel with a guaranteed chemical composition; It is denoted by the symbol B.

Special steel - steel that guarantees both mechanical properties and chemical composition. It is denoted by the symbol C.

The larger the steel grade, the higher the carbon content, the higher the strength and hardness, but the plasticity, toughness, cold bending and weldability are reduced.

2. Ordinary low-alloy steel bars: Ordinary low-alloy steel bars are steel bars made by adding a small amount of elements (silicon, manganese, titanium, rare earths, etc.) to the composition of low-carbon and medium-carbon steel.

Its steel number and representation method: The steel grade of ordinary low-alloy steel is expressed according to the type of carbon content and gold element. The first number represents the average carbon content of 10,000 parts per thousand, the following chemical element names are the alloying elements added, and the number after the alloying elements indicates the content of alloying elements.

When the average content of alloying elements is 5 to 50 a ......, the number should be written as 2, 3, 4 ...... accordinglyIf the average content of alloying elements is less than 1 5, no number is attached to the alloying elements. For example, "20 mnsi" is read as 20 manganese silicon steel, which means that the carbon content is 20 parts per 10,000, and it is composed of two alloying elements, manganese and silicon, and the average content of alloying elements is less than 1 5%.

The main advantages of ordinary low-alloy steel bars are high strength, good comprehensive performance, and the amount of steel used is about 20 less than that of carbon steel.

Commonly used ordinary low-alloy steels include 20 manganese silicon, 25 manganese silicon, 40 silicon, manganese vanadium and other varieties.