Q235 steel is a widely used carbon structural steel, commonly employed in construction, engineering, and general mechanical applications. In the old GB700-79 standard, it was equivalent to A3 steel. The "Q" in the grade represents the yield strength, and "235" indicates a minimum yield strength of 235 MPa. Q235 steel is generally used directly without heat treatment, offering a balance of strength, plasticity, and weldability.
Steel Grade Meaning
The grade designation of Q235 steel follows the format:
Q + number + quality grade + deoxidation method
Q: Yield point of the steel
Number (235): Yield strength in MPa
Quality Grade Symbols: A, B, C, D
Deoxidation Method Symbols:
F: Rimmed steel
B: Semi-killed steel
Z: Killed steel
TZ: Special killed steel
For example, Q235AF indicates Q235 steel, grade A, rimmed steel.
Special-purpose steels, such as bridge steel or marine steel, add a letter at the end of the grade to indicate its use.
Grades and Metallurgical Quality (GB/T 700-2006)
Q235 is divided into four grades based on metallurgical quality:
| Grade | Carbon (C, %) | Manganese (Mn, %) | Silicon (Si, %) | Phosphorus (P, %) | Sulfur (S, %) |
|---|---|---|---|---|---|
| Q235A | ≤ 0.22 | ≤ 1.40 | ≤ 0.35 | ≤ 0.045 | ≤ 0.050 |
| Q235B | ≤ 0.20 | ≤ 1.40 | ≤ 0.35 | ≤ 0.045 | ≤ 0.045 |
| Q235C | ≤ 0.17 | ≤ 1.40 | ≤ 0.35 | ≤ 0.040 | ≤ 0.040 |
| Q235D | ≤ 0.17 | ≤ 1.40 | ≤ 0.35 | ≤ 0.035 | ≤ 0.035 |
A: Basic quality, no impact test required.
B: Standard quality, impact test at +20°C.
C: Cold-resistance grade, impact test at 0°C.
D: Low-temperature grade, impact test at -20°C.
Mechanical Properties
Yield Strength vs. Thickness (MPa)
| Thickness (mm) | Yield Strength (σy) |
|---|---|
| ≤ 16 | ≥ 235 |
| 16 < t ≤ 40 | ≥ 225 |
| 40 < t ≤ 60 | ≥ 215 |
| 60 < t ≤ 100 | ≥ 215 |
| 100 < t ≤ 150 | ≥ 195 |
| 150 < t ≤ 200 | ≥ 185 |
Tensile Strength (MPa): 370–500
Elongation (%):
| Thickness (mm) | Elongation (δ) |
|---|---|
| ≤ 40 | ≥ 26 |
| 40 < t ≤ 60 | ≥ 25 |
| 60 < t ≤ 100 | ≥ 24 |
| 100 < t ≤ 150 | ≥ 22 |
| 150 < t ≤ 200 | ≥ 21 |
Impact Test (J):
| Grade | Test Temperature (°C) | Impact Energy (J) |
|---|---|---|
| A | - | - |
| B | +20 | ≥ 27 |
| C | 0 | ≥ 27 |
| D | -20 | ≥ 27 |
Key Features of Q235 Steel
Moderate carbon content: Ensures good combination of strength, toughness, and plasticity.
Excellent weldability: Suitable for H-beams, plates, and general structural components.
Versatile applications: Used in construction, engineering, and mechanical parts with moderate load requirements.
Wide thickness range: Yield strength varies with thickness, allowing adaptability for different structural needs.
Typical Applications
Construction and Engineering Structures
Steel frames, H-beams, bridges, and non-critical structural components.
Mechanical Parts
Low-stress mechanical components such as mold handles, frames, and brackets.
Punching and Tool Materials
Can be used directly after quenching for punch materials with hardness 36–40 HRC.
Cold-Resistant Components
Grades C and D suitable for low-temperature environments or specialized structures.