Forging defects include surface defects and internal defects. Some forging defects will affect the processing quality of subsequent processes, while others will seriously affect the performance of the forgings, reduce the service life of the finished products, and even endanger the safety. Therefore, in order to improve the quality of forgings and avoid the occurrence of defects in forgings, corresponding technological measures should be taken. At the same time, the quality control in the whole production process should also be strengthened. This chapter gives an overview of three issues: the impact of forging on metal structure, properties, and forging defects; the content and method of forging quality inspection; and the general process of forging quality analysis. (1) Influence of forging on the microstructure and properties of metal Forging production, in addition to the required shape and size of the forging must be ensured, the performance requirements of the part during use must also be met, which mainly include: strength pointer, plastic pointer , impact toughness, fatigue strength, fracture toughness, and stress corrosion resistance, etc., parts that work at high temperatures, high temperature instantaneous tensile properties, long-lasting properties, creep resistance and thermal fatigue properties. The raw materials for forging are ingots, rolled materials, extruded materials, and billets. Rolled materials, extruded materials and forged billets are semi-finished products formed by rolling, extruding and forging of ingots, respectively. Forging production, the use of reasonable process and process parameters, can improve the organization and performance of raw materials through the following aspects: 1) breaking the columnar crystals, improving the macro-segregation, turning the as-cast structure into a forged structure, and suitable In the condition of temperature and stress, the inner pores are welded and the density of the material is increased; 2) The ingot is forged to form fibrous structure, and further through rolling, extrusion, and die forging, so that the forging can obtain a reasonable fiber direction distribution; 3) Control Grain size and uniformity; 4) Improve the distribution of the second phase (for example: alloy carbides in a beryllite steel); 5) Make the structure get deformation strengthening or deformation - transformation strengthening. As a result of the above-mentioned organizational improvements, the plasticity, impact toughness, fatigue strength, and long-lasting properties of the forgings are also improved, and then the required hardness, strength, and plasticity of the parts can be obtained through the later heat treatment of the parts. Comprehensive performance. However, if the quality of raw materials is poor or the forging process used is unreasonable, forging defects may occur, including surface defects, internal defects, or unqualified performance. (2) Influence of raw materials on the quality of forgings The good quality of raw materials is a prerequisite for ensuring the quality of forgings. If there are defects in raw materials, it will affect the forming process of forgings and the final quality of forgings. If the chemical elements of the raw materials exceed the specified range or the content of impurity elements is too high, the forming and quality of the forgings will have a greater impact. For example: S, B, Cu, Sn and other elements are liable to form low-melting phases, making the forgings easy Hot crispness occurs. In order to obtain intrinsically fine-grained steel, the residual aluminum content in the steel must be controlled within a certain range, for example, Al 0.02% to 0.04% (mass fraction). If the content is too small, the effect of grain growth cannot be controlled, and the intrinsic crystal grain size of the forged part is often unacceptable. When the amount of aluminum is too much, a grain-like fracture is easily formed under the condition of forming a fibrous structure during pressure processing. Torn traces and other fractures. For another example, in 1Cr18Ni9Ti austenitic stainless steel, the greater the content of Ti, Si, Al, and Mo, the more ferrite phase, the more likely to form band-like cracks during forging, and to make the parts magnetic. For example, there are defects such as shrinkage tube residue, subcutaneous bubbling, severe carbide segregation, and coarse non-metallic inclusions (slag inclusions) in the raw materials. Forgings easily cause cracks in the forgings. The defects in the raw materials, such as dendrites, severe loosening, non-metallic inclusions, white spots, oxide films, segregation zone, and heterogeneous metals, can easily cause the performance of the forging to decline. Surface cracks, folding, scabs, and coarse crystal rings of raw materials can easily cause cracks in the surface of the forgings. (3) Influence of Forging Process on Forging Quality The forging process generally consists of the following processes, namely, blanking, heating, forming, forging, cooling, pickling, and post-forging heat treatment. If the process is improper during forging, a series of forging defects may occur. The heating process includes furnace temperature, heating temperature, heating rate, holding time, furnace gas composition and the like. If the heating is improper, for example, the heating temperature is too high and the heating time is too long, it will cause defects such as decarburization, overheating, and overheating. For a billet with a large section size and poor thermal conductivity and low plasticity, if the heating speed is too fast and the holding time is too short, the temperature distribution tends to be uneven, causing thermal stress and cracking of the billet. Forging forming process includes deformation mode, deformation degree, deformation temperature, deformation speed, stress state, mold brother and lubrication conditions, etc. If the forming process is improper, it may cause coarse grains, uneven grains, various cracks, fold. Cold current, eddy current, as-cast tissue residue, etc. During the cooling process after forging, cooling cracks, white spots, mesh carbides, etc. may be caused if the process is improper. (d) Effect of forging microstructure on the microstructure and properties of heat-treated stainless steel, austenitic and ferritic heat-resistant stainless steels, high-temperature alloys, aluminum alloys, magnesium alloys, etc. During heating and cooling, there is no isomorphic change. Materials, as well as some copper alloys and titanium alloys, cannot be improved by heat treatment during the forging process. In the heating and cooling process there are materials with allotropic transformation, such as structural steel and martensitic stainless steel, due to certain organizational defects caused by improper forging process or some defects left by raw materials, the quality of the forgings after heat treatment Great influence. An example is illustrated below: 1) The structural defects of some forgings can be improved during heat treatment after forging, and the forgings can still obtain satisfactory structure and properties after final heat treatment. For example, coarse grain and Welsh microstructures in generally overheated structural steel forgings, slightly reticulated carbides due to improper cooling of hypereutectoid steel and bearing steels, etc. 2) Some of the forgings have structural defects that are difficult to eliminate with normal heat treatment and can be improved by high-temperature normalizing, repeated normalizing, low-temperature decomposition, and high-temperature diffusion annealing. For example, low-order coarse crystals, 9Cr18 stainless steel twins, etc. 3) Some defects of the forgings can not be eliminated by the general heat treatment process. As a result, the performance of the forgings after the heat treatment is reduced or even failed. For example, severe stone fractures and prismatic fractures, over-firing, ferritic bands in stainless steel, carbide networks and belts in high-alloy tool steels of the lanthanite, and the like. 4) The structural defects of some forgings will be further developed during the final heat treatment and even cause cracking. For example, coarse-grained microstructures in alloy structural steel forgings, if not improved after heat treatment after forging, often cause martensite needle coarsening and unacceptable performance after carbon and nitrogen sorption and quenching; coarse ribbon carbonization in high-speed steels Material, quenching often causes cracking. Common defects in the forging process and their causes are described in detail in Chapter 2. It should be pointed out that the common defects in various forming methods and the main defects of various types of material forgings are regular. Different forming methods, due to their different stress conditions, have different stress and strain characteristics, and therefore the major defects that may be produced are also different. For example, the main defect when the billet is upset is that the side surface is cracked in the longitudinal or 45° direction. The ingot is upsetting and the upper and lower ends often have as-cast microstructures. The main defect when the rectangular section billet is drawn is the transverse crack of the surface. And angular cracks, internal diagonal cracks and transverse cracks; the main defects in open die forging are insufficient filling, folding and misalignment. The common defects in each major forming process will be described in detail in Chapter 4. Different types of materials, due to their different compositions and textures, have different organizational changes and mechanical behavior during heating, forging, and cooling. Therefore, the forging process is not appropriate and the defects that may occur are also unique. For example, the defects of the high-alloy tool steel forgings of the high-lead alloy are mainly coarse carbide grains, uneven distribution and cracks. The defects of the high-temperature alloy forgings are mainly coarse grains and cracks; the defects of the austenitic stainless steel forgings are mainly intercrystalline chromium lean. Resistance to intergranular corrosion decreases, band structure and cracks in ferrite, etc.; defects in aluminum alloy forgings are mainly coarse crystal, folding, eddy current, and flow through. Laser Projector,130Mw Laser Module,Red 650Nm Laser Module,5Mw Red Line Laser Module Changshu Desheng Optics Electronics Co.,Ltd , https://www.ray-lasertech.com