Solutions to Common Problems in Forging Processing: Handling Strategies for Post-Forging Deformation, Surface Oxidation, and Internal Porosity

Solutions to Common Problems in Forging Processing: Handling Strategies for Post-Forging Deformation, Surface Oxidation, and Internal Porosity

In forging processing, post-forging deformation, surface oxidation, and internal porosity often lead to product scrapping. It is necessary to develop scientific handling strategies based on the causes of these problems, while strengthening preventive measures to reduce quality risks.

Post-forging deformation is mostly caused by uneven cooling or stress release. When addressing it, the type of deformation must first be analyzed: For bending deformation, the "hot straightening method" can be adopted. Heat the forging to the recrystallization temperature (800-850℃ for carbon steel, 850-900℃ for alloy steel), apply slow pressure with special tooling for straightening, and cover with heat-insulating cotton during cooling to avoid secondary deformation due to excessive temperature differences. For dimensional shrinkage deformation, machining allowances should be supplemented according to the material shrinkage rate (2.5%-3% for stainless steel, 1.5%-2% for carbon steel). When deformation exceeds tolerances, key dimensions can be corrected through CNC milling. To prevent deformation, optimize the cooling process by adopting stepped cooling (first air-cool to 600℃, then slow-cool to room temperature) and conduct stress relief annealing promptly after forging.

Surface oxidation occurs when metal contacts air during heating, forming an oxide scale that affects precision. For mild oxidation (oxide scale thickness < 0.5mm), sandblasting can be used for removal—select 80-120 mesh quartz sand and control the pressure at 0.4-0.6MPa to avoid damaging the forging surface. For severe oxidation (thickness > 1mm), pickling is required first (hydrochloric acid concentration 15%-20%, temperature 40-50℃), followed by rinsing with clean water and passivation treatment. Prevention measures include introducing inert gas (such as nitrogen) into the heating furnace to isolate air, or applying high-temperature anti-oxidation coating on the forging surface to reduce oxidation reactions.

Internal porosity is mainly caused by insufficient forging pressure or poor feeding, which impairs mechanical properties. Minor porosity can be addressed through secondary processing via "isothermal forging"—apply holding pressure (30-50MPa) at a constant temperature (1050-1100℃ for carbon steel) to compact internal voids. Severe porosity requires scrapping and re-forging to prevent defective products from entering downstream processes. Prevention involves controlling forging parameters to ensure the final forging temperature (≥800℃ for carbon steel, ≥850℃ for alloy steel) and deformation amount (single-pass deformation rate 25%-35%) meet standards. For thick-walled forgings, set up a process feeding section to ensure sufficient filling of molten metal.