Publish Time: 2023-04-11 Origin: Site
A correct understanding of the main factors affecting the quality of forged products is of great significance for the purchase and use of forged products
1. Defects in raw materials
If there are residual shrinkage cavities, air bubbles, porosity, inclusions, etc. in the raw materials, it may lead to cracking of forgings. Jiahangaero believes that forging cracks are often accompanied by a large number of inclusions such as oxides, sulfides, and silicates. Scratches, scars, folds, and cracks on the surface of raw materials will bring defects to forgings. Therefore, raw materials must be inspected in die forging production.
2. Whether the heating is standardized
When forging large-scale forged products, if the heating rate is too fast and the temperature difference between the inner and outer layers is too large, the temperature stress and tissue stress will cause cracks in the central part.
When the heating temperature is too high and the holding time is too long to cause slight overheating, there will be lustrous, crystalline, and intergranular fractures with coarse-grained fractures. Slightly overheated coarse grains can be corrected by annealing or normalizing and recrystallization. In case of severe overheating, naphthalene-like fracture or stone-like fracture will occur. Forging blanks with severe overheating have extremely poor mechanical properties. The naphthalene-like fracture can be normalized at high temperature to eliminate the intragranular texture, while the stone-like fracture is difficult to correct by heat treatment. After the die forging is formed, once the stone-like fracture is found, it is irreparable.
The forging heating temperature is low, and when it is not heated through, there may be cracks that propagate through the grain, and the tail ends are sharp. When there is no subsequent heating process, there is no oxidation and decarburization on the crack surface.
If the final forging temperature is too low, the steel is in the dual-phase region, the inclusions are distributed along the main deformation direction of the blank, and the ferrite precipitated from the austenite preferentially adheres to the surface of the inclusions to form a banded structure. The Widmanstatten and banded structures reduce the mechanical properties of forgings, especially the impact toughness. In order to refine the grain, improve the structure, and improve the mechanical properties, the steel with this type of structure must be completely annealed to cause recrystallization.
3. Die forging process
Jiahangaero believes that the use of different die forging deformation methods, such as open die forging, closed die forging, extrusion, upsetting, high-speed die forging, rolling, etc.
The die forging process parameters such as deformation temperature, deformation speed and deformation degree are obviously directly related to the quality of die forgings. Especially high-strength aluminum alloys, magnesium alloys, etc., require a small deformation speed and an appropriate degree of deformation, and are suitable for forming on a press, which helps to avoid cracks.
The quality of forged products is also related to design. The selection of machining allowance and forging tolerance should proceed from the actual situation, surface defects and dimensional errors will easily cause waste products after machining; forging parting surface, die forging strip belly, fillet radius, continuous skin size and flash structure, etc. Whether the design is appropriate or not will affect the quality of metal flow filling; if the lock is ignored, the forging size will be out of tolerance due to the wrong movement of the upper and lower dies.
Jiahangaero believes that every link in the production will have a non-negligible impact on the quality of forged products. Therefore, forging is not simply plasticity, but requires sufficient experience and strict checks on each link.