Both Q235 and Q235A are ordinary carbon structural steel defined in GB/T 700 of China's national standard. Their main differences lie in the quality grade and specific requirements for some performance indexes.

Here are the main differences in performance between the two materials:

chemical composition

• Q235: For the Q235 grade, the requirements for chemical composition are relatively loose, especially for the content control of harmful elements sulfur (S) and phosphorus (P) is not particularly strict.

• Q235A: Compared to Q235, Q235A has more stringent limits on chemical composition, especially sulfur (S) and phosphorus (P). In general, Q235A has lower sulfur and phosphorus content, which helps improve the purity and mechanical properties of steel.

Specific chemical composition requirements (take GB/T 700 standard as an example)

Carbon (C): 0.22% or less (for all Q235 series)

Manganese (Mn): 0.30%-0.70%

• sulphur (S):

•Q235: ≤0.050%

•Q235A: ≤0.045%

• phosphorus (P):

•Q235: ≤0.045%

•Q235A: ≤0.045%

Although the maximum allowable content of sulfur and phosphorus is the same, in actual production process, Q235A often has more strict internal control to ensure that the actual content of these harmful elements is as low as possible.

mechanical property

• Yield strength (ReL): The two are basically the same, and both are required to be no less than 235MPa.

• Tensile strength (Rm): The two are basically the same, generally 370-500MPa.

• Elongation (A): The requirements are similar, usually not less than 26% (for plates with a thickness of less than 16mm).

Impact energy (KV2): This is an important aspect to distinguish Q235 from Q235A.

Q235A needs to meet certain impact absorption energy requirements at a specific temperature (usually room temperature or specified low temperature), while Q235 does not necessarily have this requirement or the requirement is lower.

application

•Q235: Suitable for general construction projects, Bridges, machinery manufacturing and other applications that do not require particularly high purity or special performance.

• Q235A: Due to its low sulfur and phosphorus content, it has better weldability and toughness, which is suitable for occasions with certain requirements on material purity, weldability or low temperature toughness, such as shipbuilding, pressure vessel manufacturing and other fields.

Summary: Although Q235 and Q235A are very similar in basic mechanical properties, Q235A offers better purity and mechanical performance through stricter control of chemical composition (mainly sulfur and phosphorus content), especially in weldability and low-temperature toughness. Therefore, when selecting materials, if the project has high requirements for these properties, Q235A should be given priority. For general structural applications, Q235 can also meet the needs.