The appearance of Q235 steel plate and Q345 steel plate is generally invisible. The color difference has nothing to do with the material of the steel, but is caused by the different cooling method after the steel is rolled. Under normal circumstances, the surface is red after natural cooling. If a rapid cooling method is used, a dense oxide layer is formed on the surface, and it will appear black.
Q345 steel plate is used for general strength design, because Q345 steel plate has higher strength than Q235 steel plate and saves steel, which is 15%-20% less than Q235 steel plate. It is better to use Q235 steel plate when designing with stability control, and the price difference is 3%-8%.
So, how to distinguish whether the steel plate material is Q235 steel plate or Q345 steel plate?
1. According to the color of the steel plate, the material of Q235 steel plate and Q345 steel plate can be distinguished: for the steel that has just entered the field, the color of Q235 steel plate is green, and the color of Q345 steel plate is a little red.
2. The test that can distinguish the material of the steel plate is the chemical analysis. The carbon content of Q235 steel plate and Q345 steel plate are different, and the chemical content is also different.
3. The material of Q235 steel plate and Q345 steel plate is distinguished by welding method: butt two steel plates of unknown material and weld them with ordinary welding rod. If the steel plate on the side with cracks is proved to be the material of Q345 steel plate.
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