The pores produced by welding are the holes formed by the gas in the molten pool that does not escape before the metal solidifies and remains in the weld. The gas may be absorbed by the molten pool from the outside, or it may be generated by the reaction in the welding metallurgy process.
Formation mechanism of pores:
The solubility of the gas in the solid metal at room temperature is only a few tenths to a few hundredths of the solubility of the gas in the high temperature liquid metal. During the solidification process, a large amount of gas escapes from the metal during the solidification process. When the solidification speed is greater than the gas escape velocity, pores are formed.
The main causes of stomata:
The surface of the base metal or filler metal has rust, oil, etc., and the electrode and flux are not dried, which will increase the amount of pores, because the rust, oil and electrode coating, the moisture in the flux is decomposed into gas at high temperature, and the gas in the high temperature metal is increased. content. The welding line energy is too small, and the cooling pool has a high cooling rate, which is not conducive to gas escape. Insufficient deoxidation of the weld metal also increases the oxygen hole.
Hazard of the stomata:
The vents reduce the effective cross-sectional area of ​​the weld and loosen the weld, thereby reducing the strength of the joint, reducing plasticity, and causing leakage. Porosity is also a factor that causes stress concentration. Hydrogen holes may also contribute to cold cracking.
Measures to prevent stomata
A. Remove the oil, rust, moisture and debris from the welding wire, the working groove and its vicinity. B. Use alkaline electrode, flux, and thoroughly dry. C. Use DC reverse connection and apply short-arc welding. D. Preheating before welding to slow down the cooling rate. E. Apply welding with a strong specification.
The slag inclusion refers to the phenomenon that the slag remains in the weld after welding.
(1) Classification of slag inclusions
A. Metal slag: It means that metal particles such as tungsten and copper remain in the weld, which is customarily called tungsten and copper. B. Non-metallic slag inclusions: refers to the unmelted electrode coating or flux, sulfide, oxide, and nitride remaining in the weld. The metallurgical reaction is incomplete and the slag removal is not good.
(2) The distribution and shape of the slag inclusions have a single point slag, strip slag, chain slag and dense slag
(3) Causes of slag inclusion
A, the groove size is unreasonable; B, the groove has dirt; C, multi-layer welding, the interlayer slag is not thorough; D, the welding line energy is small; E, the weld heat dissipation is too fast, the liquid metal solidifies too fast ; F, electrode coating, the chemical composition of the flux is unreasonable, the melting point is too high; G, tungsten inert gas protective welding, the polarity of the power supply is improper, the electricity, the flow density is large, the tungsten melting and falling off in the molten pool. H. When welding by hand, the welding rod is poorly oscillated, which is not conducive to the slag floating. According to the above reasons, corresponding measures can be taken to prevent the occurrence of slag inclusion.