Generally, from the appearance of Q235 and Q345, it is not able to distinguish them.
The color difference is not related to the material of the steel, but the different cooling method after rolling.
Generally, the surface is red after natural cooling. If using the quenching method, a dense oxide layer will be formed on the surface and present the black color.
When the general strength design is presented, Q345 is used because Q345 is not only strengthened than Q235 but also save 15% to 20% steel compared to Q235 steel.
However, for stability control design, Q235 steel is better.
The price difference is 3%- 8%.
Regarding how to distinguish the steel plate from Q235 and Q345, there’re several methods:
Distinguish Q345 and Q235 A method:
There are two kinds of materials that can be roughly differentiated by test welding.
For example, small round steel is welded with the E43 electrode on two plates, then the shear force is applied to distinguish the material of the two steel plates according to the condition of the damage.
The factory can also use the grinding wheel to make a rough distinction between the two materials.
When the steel of Q235 is polished with grinding wheels, the sparks flying are rounded particles and dark colors.
And the spark of Q345 is bifurcated, the color is bright.
Also, according to the color difference between the two steel shearing surfaces, it is possible to distinguish between two types of steel.
In general, the shear mouth of Q345 is white.
Distinguish Q345 and Q235 B method:
According to the color of the steel plate, the Q235 and Q345 materials can be distinguished: the color of Q235 is blue, and the Q345 is red (this is only for the steel that just came into the market, and if the time is long then it also cannot be distinguished).
The most distinguishable test is chemical analysis. Q235 is different from Q345’s carbon content, and its chemical content is different.
(this is a foolproof method)
The distinction between Q235 and Q345 is made by welding: the two steel plates of unknown materials are welded together with ordinary welds, and the steel plates with cracks are shown as Q345 materials.
(this is practical experience)