Q235A is a Chinese steel grade that belongs to the category of carbon structural steel. The "Q" in Q235A stands for "yield", and the number 235 represents the yield strength of the material, which is 235Mpa. The "A" in Q235A indicates that the steel has a lower carbon content and slightly inferior mechanical properties to Q235B.
Q235B is another steel grade in the Q235 family that differs from Q235A in mechanical properties and chemical composition. Q235B is often considered a stronger and more versatile option than Q235A.
The main difference between Q235A and Q235B steel plates is that Q235B requires a mandatory impact test at 20°C (room temp) for toughness, which Q235A doesn't need, leading to better low-temperature performance for B grade, along with slightly stricter limits on carbon (0.2% vs 0.22% max) and sulfur (0.045% vs 0.05% max), making Q235B a higher-quality, tougher steel for demanding applications.
Chemical Composition:
|
Grade |
C % |
Si % |
Mn % |
P % |
S % |
|
Q235A |
≤0.22 |
≤0.35 |
≤1.4 |
≤0.045 |
≤0.050 |
|
Q235B |
≤0.20 |
≤0.35 |
≤1.4 |
≤0.045 |
≤0.045 |
Mechanical Properties：
| Property | Q235A (typical) | Q235B (typical) |
|---|---|---|
| Yield strength (nominal) | 235 MPa (design basis for grade name) | 235 MPa |
| Tensile strength (typical) | ~370–500 MPa (depends on thickness/process) | ~370–500 MPa (similar range) |
| Elongation (A%) | ~20–26% (varies with thickness) | ~20–26% (similar or slightly better at low temperature) |
| Impact toughness | Not specified by standard for A; varies by mill | Specified at 0°C (commonly a Charpy V-notch minimum, e.g., ~27 J) |
| Hardness | Typical mild-steel hardness range; not a primary spec | Similar to Q235A under like processing |
Q235B steel performs better in mechanical properties, thanks to the strict requirements of its room temperature impact test (V-notch). In contrast, the mechanical properties of Q235A steel are slightly inferior. In addition, there are differences in impact tests for different grades of Q235 steel. For example, Q235C and Q235D steels need to be impact tested at specific temperatures and meet the corresponding strength requirements. These differences are crucial to evaluating the performance of steel in practical applications.
Application Areas:
Q235A steel is often used in a hot-rolled state, and its rolled steel sections, steel bars, steel plates and steel pipes are widely used in the manufacture of various welded structural parts, bridges and ordinary machine parts, such as bolts, tie rods, rivets, collars and connecting rods.
Q235B spiral steel pipes are widely used, covering water supply, oil, natural gas and urban construction.
Weldability And Formability：
Due to the different carbon content, Q235A is generally easier to weld and form than Q235B. Higher elongation makes Q235A less likely to break or crack when bent and stretched.
However, Q235B's higher tensile strength makes it more resistant to deformation under load, so Q235B has an advantage over Q235A in structural applications.
Corrosion Resistance：
While both Q235A and Q235B have similar corrosion resistance, Q235B is slightly more resistant to atmospheric corrosion than Q235A due to its higher manganese content. Manganese helps improve the corrosion resistance of steel, so Q235B may be more durable in some harsh environment applications.
In Simple Terms
Think of it like this: Q235A is the basic version, good for general construction. Q235B is a slightly refined version with better low-temperature toughness and stricter impurity limits (less sulfur), making it better for more critical parts that need to withstand cold or stress without cracking.
