There will inevitably be some defects in the production of forgings, some of which are unpredictable and some can be avoided, so it is necessary to avoid defects as much as possible in the forging process. Common endogenous inclusions in forgings are mainly sulfides, silicates, oxides, etc. Their quantity and composition in steel are related to steel composition, smelting quality, casting process, and deoxidation method. Endogenous inclusions with a high melting point solidify before the base metal, and the crystallization is not hindered, showing a regular angular shape. Dendrites are distributed along grain boundaries. Sulfide and silicate components with good plasticity, when the ingot is deformed by forging, extend along the main deformation direction and form a strip.
The oxides and silicate inclusions with poor plasticity are broken into small particles during forging deformation, which is distributed in a chain spherical shape. Small-sized, diffusely distributed endogenous inclusions are mostly microscopic defects, and the degree of damage is small. Large or dense cloud-like distribution of inclusions constitutes macroscopic defects, which have extremely adverse effects on the use of forgings and are prone to serious failure accidents.
Foreign inclusions refer to slag, mold slag, oxide film, refractory materials, and dissimilar metal blocks in the mixed steel. Usually, the foreign inclusions are relatively coarse, and the serious distribution will destroy the continuity of the steel and be scrapped.
With the development of high parameters and large-scale machinery and equipment, more stringent requirements are placed on the quality of large forgings. For this reason, trace elements such as lead, antimony, tin, bismuth, and arsenic in steel need to be controlled to improve the strength of forgings. toughness level. The general countermeasures to reduce inclusions in forgings are:
1. Vacuum treatment of molten steel, refining outside the furnace, and control the quality of molten steel;
2. Clean pouring to prevent foreign contamination and foreign metals from entering;
3. Reasonable forging deformation and improved inclusion distribution.
From the above, I now understand the reasons for the defects of some forgings. It is necessary to reduce the occurrence of inclusions as much as possible in production. If there are inclusions in the forgings, the above countermeasures and measures can be taken to reduce them and eliminate them in production. Defects can make the forgings achieve the best results after the final completion.
