It is generally not possible to distinguish between Q235 and Q345 based on appearance alone. The difference in color is not related to the material of the steel, but instead to the different cooling method used after rolling. Typically, the surface is red after natural cooling, but if a quenching method is used, a dense oxide layer is formed on the surface and appears black.
For general strength design, Q345 is often used as it is stronger than Q235 and also saves 15-20% steel compared to Q235 steel. However, for stability control design, Q235 steel is preferred. The price difference between the two materials is approximately 3-8%.
There are several methods to distinguish steel plates made of Q235 and Q345:
Distinguish Q345 and Q235 A method:
There are a few methods for rough differentiation between Q235 and Q345 materials. One method is through test welding. For example, small round steel can be welded with the E43 electrode on two plates, then the shear force can be applied to determine the material of the two steel plates based on the condition of the damage.
Another method is through grinding. The factory can use a grinding wheel to make a rough distinction between the two materials. When Q235 steel is polished with a grinding wheel, the sparks produced are rounded particles with dark colors, whereas the sparks from Q345 steel are bifurcated and have a bright color.
Additionally, the color difference between the two steel shearing surfaces can also be used to distinguish between the two types of steel. In general, the shear mouth of Q345 is white.
Distinguish Q345 and Q235 B method:
The color of the steel plate can be used to distinguish between Q235 and Q345 materials. The color of Q 235 is blue, while the color of Q345 is red (however, this method is only applicable for freshly produced steel and may not be reliable over time).
The most reliable method for differentiation is chemical analysis, as the carbon content and chemical composition of Q 235 and Q345 differ.
Another practical method is through welding. By welding two steel plates of unknown materials together with ordinary welds, steel plates with cracks can be identified as Q345 materials.