The appearance of Q235 and Q345 is generally not visible. 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 of rapid cooling is used, the surface forms a dense oxide layer, which will show black.
General strength design with Q345, because Q345 than Q235 steel high strength, save steel, than 235 save 15% - 20%. To stability control design with Q235 is good. The price difference of 3% --- 8%.
As for identification, there are several statements:
1, The factory can use the test welding 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 shear force, according to the destruction of the situation to roughly distinguish between the two steel plate material.
2、The factory can also use the grinding wheel to roughly distinguish the two materials. q235 steel with grinding wheel grinding, the sparks are a round particle, while the Q345 sparks are bifurcated.
3, There is also according to the color difference between the two steel shear surface can also be roughly distinguished between the two steel. In general, the color of Q345 shear mouth is white
4, According to the color of the steel plate can be distinguished between Q235 and Q345 material: Q235 color is greenish, Q345 some red (this is only for the steel that just entered the field, and can not be distinguished after a long time)
5, The most distinguishable material test is the chemical analysis, Q235 and Q345 carbon content is not the same, while the chemical content is also different. (This is the method that can be foolproof)
6, The distinction between Q235 and Q345 material, with welding: two pieces of unknown material steel plate butt, with ordinary welding rod to weld, if the side of the steel plate with cracks is proved to be Q345 material. (This is practical experience)
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