Why does the weld bead turn black after stainless steel welding?
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316L stainless steel, 20 mm thick; automatic welding is used, with imported welding materials – wire of type ER316L with a diameter of Φ2.4, and flux of type 805. The welding current is 280–300 A, the voltage is 24–26 V, and the welding speed is 30 m/h. After welding, the weld seam turns black; I’m not sure why All the criteria for weld evaluation are also met. During welding, the interlayer temperature shall be ≤100 degrees
With solid stainless steel welding wire, MIG welding has a relatively fast speed (30–60 cm/min). The shielding gas nozzle reaches the front part of the molten pool, and since the weld is still at a high red-hot temperature, it oxidizes in contact with air, resulting in the formation of oxides on its surface and the weld turning black. The pickling and passivation method can remove the black scale and restore the original surface color of stainless steel.
Blackening is caused by oxidation. Stainless steel usually turns black during welding, but it can be cleaned with acid; after cleaning, it becomes shiny again and regains its original color.
It’s not turning black, right? What I see is a blue color; it oxidizes when in contact with air at high temperatures, and this is also related to the manganese contained in the welding rod
It’s probably because the surface of the weld has oxidized
The temperature is very high during welding, and the iron oxide (as well as oxides of other elements) that forms after the gas protection is discontinued is black in color
After welding, the surface of the material turns blue within a certain range; this is due to the formation of iron tetraoxide on the surface. On the surfaces of some materials, such as firearms, a deliberate \"blueing treatment\" is applied to prevent oxidation over time during use.
It’s been oxidized. Pickling gives better results