1. Introduction to rebar

1. **Definition and commonly known as **: Rebar is a surface ribbed steel, also known as ribbed steel bar, usually with two longitudinal ribs and transverse ribs evenly distributed along the length direction. The shapes of the horizontal ribs are spiral, herringbone, and crescent.

2. **Grade and Classification**:

* Grade: The grade of ordinary hot-rolled steel bars consists of the yield point minimum of HRB and grades, where H, R, and B are three words: Hotrolled, Ribbed, and Bars. first letter of English. Hot-rolled ribbed steel bars are divided into four grades: HRB335 (old brand is 20MnSi), HRB400 (old brand is 20MnSiV, 20MnSiNb, 20Mnti), HRB500 and HRB600 (according to the new national standards).

* Classification: There are two commonly used classification methods for rebar. One is to classify by geometric shape, and classify or type according to the cross-sectional shape of the cross-rib and the spacing of the ribs; the other is to classify by performance, and according to the strength level (yield point/ Tensile strength) divides rebar into different grades. In addition, rebar can also be classified according to its purpose, such as ordinary steel bars for reinforced concrete and heat-treated steel bars for prestressed reinforced concrete.

3. **Specification and supply length**:

* Specifications: The specifications and models of rebar are generally divided into nominal diameters of 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, 22mm, 25mm, 28mm, 32mm, 40mm, 50mm and other specifications.

* Supply length: It is divided into two types: fixed ruler and double ruler, usually the fixed ruler is 9m and 12m.

4. **Main uses**: Rebar is widely used in civil engineering construction such as houses, bridges, roads, etc. From highways, railways, bridges, culverts, tunnels, flood control, dams and other public facilities, to small buildings, foundations, beams, columns, walls, and plates of house buildings, rebars are indispensable structural materials.

### 2. Rebar technical indicators

1. **Strength**: Strength is one of the most important technical indicators of rebar. It is usually expressed as tensile strength (yield strength and tensile strength), which refers to the ability of steel to resist breaking during tensile process. The tensile and compressive design strength of HRB335 grade steel bars is 300MPa, and the tensile and compressive design strength of HRB400 grade steel bars is 360MPa.

2. **Chemical components**: The chemical composition of rebar has a significant impact on its performance. Important elements include carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulfur (S), etc.

3. **Extension**: Extension refers to the ability of rebar to undergo plastic deformation during stretching, which can be evaluated by measuring the elongation of fracture.

4. **Formability**: Formability refers to the plasticity of rebar during cold processing or hot processing. If rebar is easily processed into the desired shape, it has better formability.

5. **Toughness**: Toughness refers to the ability of rebar to not easily break under external forces such as extrusion or impact. Good toughness is the key to the application of rebar to durable structures.

6. **Surface state**: The surface state includes smoothness and surface defects, etc. The surface smoothness plays an important role in the embedded concrete of rebar.