High-Carbon Wire Rods for Prestressed Concrete Steel Strand

Prestressed steel strands are steel cables made of multiple high-strength steel wires, mainly used in prestressed concrete structures. The specifications and performance of its raw materials (wire rods) directly affect the final quality of the steel strands. SWRH82B is a representative steel grade for prestressed steel strands, and we will introduce this material in details.

Specifications and requirements of high-carbon wire rods:

Material and diameter of wire rods:

- Steel type: high carbon steel (such as SWRH82B, SWRH77B, etc.), carbon content 0.80%~0.85%, manganese content 0.60%~0.90%.

- Standard: in accordance with GB/T 24238-2009 (China), JIS G3506 (Japan), ASTM A416 (USA), etc.

- Common diameters: 5.5mm, 6.5mm, 8.0mm, 10mm, 12mm, 13mm

- Drawing process: The wire rod is gradually reduced to the target wire diameter through the cold drawing process (such as 5.0mm steel wire needs to be drawn from 13mm wire rod).

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ADVANTAGES

Specifications and requirements of wire rods:

1. Material and diameter of wire rods:

- Steel type: high carbon steel (such as SWRH82B, SWRH77B, etc.), carbon content 0.80%~0.85%, manganese content 0.60%~0.90%.

- Standard: in accordance with GB/T 24238-2009 (China), JIS G3506 (Japan), ASTM A416 (USA), etc.

- Common diameters: 5.5mm, 6.5mm, 8.0mm, 10mm, 12mm, 13mm.

- Drawing process: The wire rod is gradually reduced to the target wire diameter through the cold drawing process (such as 5.0mm steel wire needs to be drawn from 13mm wire rod).

2. Key performance indicators:

- Tensile strength: original wire rod strength ≥1200MPa (can reach more than 1860MPa after drawing).

- Sectional shrinkage: ≥30% (to ensure cold working performance).

- Surface quality: no cracks, folds, scars and other defects.

- Composition control: low sulfur (S≤0.025%), low phosphorus (P≤0.025%) to reduce brittleness.

3. Wire rod specifications:

- Conventional steel strand strength level: 1860MPa.

- Surface quality requirements: The surface of the wire rod should be smooth, without cracks, folds, ears, scars, delamination and inclusions and other harmful defects.

- 82B is a representative steel grade for prestressed steel strands, and the corresponding specifications and properties are as follows:

USE

Common specifications of prestressed steel strands:

1. 1×7 wire structure (most commonly used):

- Diameter: 15.2mm (standard type), 12.7mm (compact type), 17.8mm (large diameter).

- Tensile strength: 1860MPa, 1960MPa, 2000MPa (common grades).

2. Other structures:

- 1×3, 1×19 (special uses, such as cable-stayed bridge cables).

Precautions:

1. Wire rod selection: the material needs to be matched according to the strength grade of the steel strand (such as SWRH82B+microalloying treatment is required for 2000MPa grade).

2. Surface treatment: the quality of the phosphating film affects the drawing efficiency and the life of the steel wire.

3. Fatigue performance: the purity of the wire rod (control of non-metallic inclusions) is crucial to the fatigue strength of the steel strand.

SPECIFICATIONS

SWRH82B standard quality indicators (refer to GB/T24238 or JIS G3506 standards).

1) Chemical composition (unit: %)

Grade	C	Si	Mn	P	S	Cu	Cr	Ni	V
SWRH 82B	0.79 ~ 0.86	0.10 ~ 0.30	0.6 ~ 0.9	≤ 0.025		≤ 0.2	≤ 0.35	≤ 0.1	≤ 0.15

2) Mechanical properties (after aging)

Grade	Tensile Strength, MPa	Reduction of area, Z / %
SWRH 82B	1130 - 1280	≥ 30

Usage requirements:

Tensile strength of steel strand: not less than 1860MPa.

Requirements for raw materials: The wire breakage rate of drawing and stranding (twisting) should be low (generally less than 3 times per 100 tons).

Tensile strength requirements: generally 1150-1250MPa, with as little fluctuation as possible.

Cross-sectional shrinkage requirements: not less than 30%.

3) Mechanical properties:

Grade	Diameter / mm	Tensile Strength, R_m / MPa	Elongation after fracture, A / %	Reduction of area, Z / %
SWRH 82B	11.0	1150 ~ 1250	≥ 8	≥ 30
	12.0	1140 ~ 1240	≥ 8	≥ 30
	12.5	1140 ~ 1240	≥ 8	≥ 30
	13.0	1120 ~ 1220	≥ 8	≥ 30
	12.5	1260 ~ 1350	≥ 8	≥ 30
	13.0	1250 ~ 1240	≥ 8	≥ 30

Production process:

1. Wire rod pretreatment: pickling (removing oxide scale) → phosphating/copper plating (lubrication and rust prevention).

2. Drawing: multiple cold drawing to reduce the diameter to the target wire diameter (such as Φ5.0mm).

3. Twisting: 7 steel wires are twisted into steel strands in a spiral manner, and pre-tensioning is used to eliminate stress.

4. Stabilization treatment: low temperature tempering (350~450℃) to improve stress relaxation resistance.

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