How to distinguish the steel plate material is Q235 and Q345?

Q235 Steel Plate and Q345 Steel Plate are generally not visible on the outside. The color difference has nothing to do with the material of the steel, but is caused by the different cooling methods after the steel is rolled out. Generally, the surface is red after natural cooling. If the method used is rapid cooling, the surface of the formation of dense oxide layer, it will show black.
General strength design with Q345, because Q345 than Q235 steel strength, save steel, than 235 save 15% - 20%. To stability control design with Q235 good. Price difference of 3% --- 8%.

As for identification, there are several statements:
A.
1, the factory can be used to test welding methods to roughly distinguish between the two materials. For example, in two pieces of steel plate with E43 welding rod were welded a small round steel, and then apply the shear force, according to the destruction of the situation to distinguish between the two types of steel plate material.
2, the factory can also use the grinding wheel to roughly distinguish between the two materials. Q235 steel with a grinding wheel when grinding, the sparks are a round particle, dark color. And Q345 sparks are bifurcated, bright color.
3, there is also according to the two steel shear surface color difference can also distinguish between the two kinds of steel. General, Q345 shear mouth color whitish
B.
1, according to the color of the steel plate can distinguish between Q235 and Q345 material: the color of Q235 for the green, Q345 some red (this is only for just into the field of steel, time can not be distinguished)
2, the most distinguishable material test is chemical analysis, Q235 and Q345 carbon content is not the same, while the chemical content is not the same. (This is a foolproof method)
3, the distinction between Q235 and Q345 material, with welding: two pieces of unidentified material of steel butt, with ordinary welding rod to weld, if there is a crack on one side of the steel plate is proved to be Q345 material. (This is practical experience)