Hazard classification and identification of welding defects

1.Non fusion

During welding, for the part where there is no complete fusion between the weld bead and the base metal or between the weld bead and the weld bead, the incomplete fusion can be divided into groove incomplete fusion, weld bead incomplete fusion and weld root incomplete fusion. According to the different components, it can be divided into white incomplete fusion and black incomplete fusion.

2.Incomplete penetration

The welding current is too small, the speed is too fast, the groove angle is too small, the root blunt edge is too thick, the arc is too long or partial blowing, etc.

The harmfulness of incomplete penetration depends on the shape, length and depth of the defect, which not only reduces the weld strength, but also easily expands into cracks in the incomplete penetration area and leads to fracture.

3.Slag inclusion

It refers to the defects caused by foreign solid substances remaining in the weld metal and metal particles remaining in the weld after welding. Slag inclusion is an easy defect in the welding process, especially the slag inclusion caused by flux remaining in the weld metal.

Flux slag inclusion refers to slag inclusion caused by electrode coating or flux insoluble matter. Metal slag inclusion refers to residual metal particles in weld metal, such as tungsten metal.

4.Air hole

Pores refer to the holes formed by bubbles in the molten pool during solidification during welding. They can be divided into insect pores, pinholes and column holes. The positions and shapes of pores can be divided into internal pores and external pores. Pores are due to the melting of gas in liquid metal, which reduces the melting degree of metal during cooling. Some gases enter the atmosphere and encounter the resistance of metal crystallization, It cannot escape smoothly and remains in the metal, forming internal pores.

The main causes of pores are that there are unclean electrodes such as rust and oil on the surface of metal or filler materials, the arc energy is too small or the welding speed is too fast, and the deoxidation of weld metal is insufficient.

The residual pores in the weld will reduce the effective section of the weld metal, thus reducing the strength of the welded joint, especially the dense pores will make the weld less dense, reduce the joint plasticity and cause leakage at the weld.

Compared with incomplete penetration, porosity is less harmful. It is allowed to exist in a limited amount in the standard, but the weld shall be free of porosity or reduce the number of pores.