Shrinkage and shrinkage: These defects form larger holes at the head or inside of the ingot. Shrinkage is caused by the failure of timely replenishment of metal cooling shrinkage, while shrinkage is often caused by improper cutting of risers during forging or poor mold design.
Loose: There is a distribution of fine and micro porous tissue inside the forging, resulting in the material being not dense. This is usually due to insufficient gas discharge or inadequate shrinkage during casting solidification.
Uneven grain size: Some parts of the forging have particularly coarse grains, while others have smaller grains. This may be due to high initial forging temperature, insufficient or uneven deformation, or high final forging temperature.
Surface cracks and folds: Small cracks or folding marks of layered structures can be seen on the surface of forgings. These defects may be caused by stress concentration during the forging process, excessive deformation speed, and incomplete elimination of existing defects on the surface of the billet.
Non metallic inclusions: elongated or broken non-metallic inclusions found on the longitudinal section of the rolled material. This is usually due to poor smelting and casting processes during steelmaking, which result in impurities such as sulfides and oxides being mixed in, or foreign substances such as refractory materials being introduced.
Insufficient forging: The size of the forging does not meet the requirements of the drawing, especially the size is too large in the direction perpendicular to the parting surface. This may be due to insufficient hammering, insufficient deformation, or unreasonable mold design.
Insufficient local filling: occurs in complex shapes such as ribs and convex corners of forged parts, with unclear contours and incomplete filling of the top or edges. This may be due to insufficient forging pressure or unreasonable mold design, resulting in ineffective filling of metal flow lines.
Cast tissue residue: The elongation and fatigue strength of the forging are not qualified, and there are dendritic grains in the microstructure in the original cast state. This is because when forging with ingots as billets, there is not sufficient plastic deformation to eliminate the casting structure.
The main reasons for these defects include:
Poor quality of raw materials: such as defects inside the steel ingot, excessive heating speed leading to high temperature stress, etc.
Improper forging process control: such as excessive deformation speed, unreasonable mold design, improper temperature control, etc.
Unreasonable mold design: such as excessive mold clearance, excessive blade wear, inaccurate installation and adjustment, etc.
Operational errors: such as excessive clearance between cutting dies, equipment defects, improper operation, etc.
In order to prevent the occurrence of these defects, it is necessary to optimize the quality of raw materials from the source, design and manufacture molds reasonably, strictly control forging process parameters (such as temperature, deformation speed, deformation degree), and adopt effective non-destructive testing technology to monitor the quality of forgings.
Grace Ma
Post time: Feb-21-2025
