The appearance of Q235 and Q355 is generally invisible. The color difference is related to the material of the steel. This is caused by the difference in cooling method after the steel is rolled out. Generally speaking, the surface will be red after natural cooling. If a rapid cooling method is used and a dense oxide layer is formed on the surface, it will appear black. Q355 is generally used in strength design because Q355 is stronger than Q235 steel and saves steel, 15% to 20% less than Q235. When designing for stability control, it is better to use Q235, and the price difference is 3% to 10%.
There are two opinions on identification:
Method A:
1. Test welding can be used in the factory to roughly distinguish between the two materials. For example, use E43 welding rods to weld a small round steel on two steel plates, and then apply shear force. The materials of the two steel plates can be roughly distinguished based on the damage conditions.
2. The factory can also use grinding wheels to roughly distinguish the two materials. When Q235 steel is polished with a grinding wheel, the sparks spattered are round particles with dark color. The sparks of Q355 are bifurcated and bright in color.
3. In addition, the two steel materials can be roughly distinguished based on the color difference of the shear surface of the two steel materials. Generally, the color of the Q355 shear port is whitish.
Method B:
1. Q235 and Q355 materials can be distinguished according to the color of the steel plate: Q235 is bluish in color and Q355 is somewhat red (this is only for steel that has just entered the market and cannot be distinguished after a long time).
2. The test that can best distinguish materials is chemical analysis. The carbon content of Q235 and Q355 are different, and the chemical content is also different. (This is a foolproof method).
3. To distinguish between Q235 and Q355 materials, use the welding method: connect two steel plates of unknown materials and weld them with ordinary welding rods. If there is a crack on one side of the steel plate, it is proved to be Q355 material.
