Quality Control Techniques in Forging Processing: Prevention and Inspection Methods for Cracks, Inclusions, and Dimensional Deviations

The quality of forgings directly determines the safety and stability of downstream equipment. Cracks, inclusions, and dimensional deviations are key defects that require strict control during processing, and a dual approach of "prevention + inspection" is necessary to build a solid quality defense line.

Crack prevention must start from the source of the process. During the heating stage, the heating rate must be strictly controlled: the heating rate for carbon steel forgings should not exceed 150℃/h, and for alloy steel forgings, it should not exceed 100℃/h to avoid thermal stress caused by excessive temperature differences. During forging, the deformation amount should be controlled, with a single-pass deformation rate not exceeding 30% to prevent internal stress concentration in the metal. If small surface cracks occur, an angle grinder can be used to grind and remove them; if the crack depth exceeds 2mm, repair welding is required followed by re-forging. For inspection, magnetic particle testing (MT) can be used, which achieves a detection rate of over 98% for surface and near-surface cracks in carbon steel and alloy steel forgings. Before testing, oil stains and scale on the forging surface must be thoroughly cleaned.

Inclusion defects are mostly caused by raw material impurities or contamination during heating. For prevention, raw materials with low impurity content should be selected (e.g., sulfur and phosphorus content ≤ 0.03%). During heating, it is necessary to prevent fuel impurities from falling into the metal billet, and during forging, multiple passes of forging are used to "break up" internal inclusions and expel them. Ultrasonic testing (UT) can be adopted for inspection, which can accurately locate the position and size of non-metallic inclusions larger than 2mm inside the forging. For critical forgings (such as those used in aerospace), penetrant testing (PT) should be combined to ensure no omission of tiny surface inclusions.

Prevention of dimensional deviations requires enhanced process control. Before forging, machining allowances must be reserved based on the material shrinkage rate (3-5mm for carbon steel and 5-8mm for stainless steel). During forging, numerical control (NC) forging equipment should be used to monitor the forging dimensions in real time, and pressure parameters should be adjusted promptly when deviations exceed 0.5mm. For inspection, a coordinate measuring machine (CMM) can be used to conduct precision testing on key dimensions of the forging (such as hole diameter and step height), with tolerances controlled within ±0.1mm. For mass production, special gauges can be used to improve inspection efficiency and prevent defective products from entering the next process.