Forgings defects including surface defects and internal defects. Some forgings defect will affect the follow-up process of machining quality, some are in serious influence the performance of forgings, reduced the service life of a manufactured goods, even compromise safety. Therefore, in order to improve the quality of forgings, avoid the generation of forgings defect, should take corresponding countermeasures of the process, but also should strengthen the whole production process quality control. This chapter briefly introduce three problems: the forging of metal organization, and influence on the performance of the forgings defect; Forging quality inspection content and methods; General process of forgings quality analysis.
(a) to metal forging organization and influence on the performance of the forging production, besides must ensure that forging the required shape and size, also must satisfy the parts in use process proposed performance requirements, which mainly includes: strength pointer, plastic pointer, impact toughness, fatigue strength and fracture toughness and stress corrosion resistance performance, high temperature parts of work, and high temperature instantaneous tensile properties, and lasting performance, creep resistance and thermal fatigue property, etc. Forging raw materials is with bubble, rolling material, a kind of special material and crowded. And rolling material, a kind of special material and crowded respectively by the bubble is rolling, extrusion and the forging of the formation of the processing of the semi-finished products. Forging production, the use of reasonable technology and process parameters and can be improved through the following a few the raw material of the organization and performance: 1) broken columnar crystal, improve macro segregation, the as-cast organization into forging state organization, and in the right temperature and stress conditions, welding and internal pore, improve the density of material;
(1) bubble after forging form fibres organization, further through extrusion, rolling, forging, make forgings get reasonable distribution of fiber direction; 3) control the size of the grain and the homogeneous degree; 4) improve the second phase (for example: ledebrite steel alloy of carbide) distribution; 5) make the organization get deformation strengthen or deformation-strengthening phase. Due to the improvement of the organization, the forging of plastic, impact toughness, fatigue strength and lasting performance has improved, and then through the components of the final heat treatment can get parts required hardness, strength and the plastic and good comprehensive performance. If, however, the quality of the raw materials used by bad or forging process is not reasonable, it may produce forgings defects, including surface defect, internal defects or performance not qualified, etc.
(2) the influence on the quality of raw material on forging the raw material of the good quality is the precondition of forgings quality guarantee, such as raw material defects, will influence the forming process of forging and forging final quality. Such as the raw material of the chemical elements beyond the prescribed scope or impurity element content too high to the forming of the quality of forging and will bring greater influence, such as: S and B, Cu, Sn elements such as easy to form in low melting point, make easy appear hot forging crisp. In order to get the essence fine grain steel, steel of residual aluminum content must control within a certain range, such as Al acid 0.02% ~ 0.04% (mass fraction). Content too little, do not rise to control the role of grain growth, often to the essence of forgings grain degree is unqualified;
Alumina is too much, the pressure process in the form of fibrous tissue under the condition of the formation of grain to fracture, tear mark shape fracture, etc. Be like again, in 1 Cr18Ni9Ti austenitic stainless steel, Ti, Si, Al, Mo content is more, the more ferritic phase, forging the easier when form bands crack, and make a magnetic parts. Raw materials such as exist inside the residual, subcutaneous shrinkage blister, serious carbide segregation, bulky non-metallic inclusions (slag), and other defects, forging easily to make forgings crack. The branches of the crystal shape in raw materials, serious osteoporosis, non-metallic inclusions, white, oxidation film, segregation belt and different metal mixed defects such as people, easy cause forgings, slow performance. The raw material surface crack, fold, scarred, coarse grain ring forgings easy cause such as surface crack.
(3) forging process of forging process of the influence on the quality of forging process by the general process composition, namely next makings, heating, cooling, after forming, forged pickling and forging after heat treatment. The process of forging process will be if not produce a series of forgings defects. Heating process including outfit furnace temperature and heating temperature, heating speed, holding time, furnace gas composition, etc. If heating improper, for example the heating temperature is too high and heating time is too long, will cause the decarburization, too overheat, burn, and other defects. For the section size and the thermal conductivity is bad, the plastic low stock, if heating speed too fast, holding time too short, often make temperature distribution uneven, cause thermal stress, and make blank produce craze. Forging process including deformation way, the deformation degree, deformation temperature, the deformation and stress state, the labor, the speed of the die and lubrication conditions feeling brother, if forming technology is undeserved, may cause bulky grain, grain, all kinds of crack, folding uneven. Cold snap, eddy current, as-cast tissue residues, etc. After forging cooling process, if not process may cause cooling crack, white, mesh carbide, etc.
(4) forging on final after heat treatment of organization organization and influence on the performance of the austenitic and ferritic heat-resistant stainless steel, high temperature alloy, aluminum alloy, magnesium alloy etc in heating and cooling process, not with element of the transformation of heterogeneous materials, and some of the copper alloy and titanium alloy, in the process of forging produce organization with the heat treatment to defect not improve. In the process of heating and cooling with element of the transformation of heterogeneous materials, such as structural steel and martensitic stainless steel, etc, due to improper forging process of some defects or raw material of some defects left, after heat treatment of forgings quality has very big effect. Now for example as follows:
1) some forgings defects, in forging when after heat treatment can be improved, and eventually after heat treatment can still be forging a satisfactory organization and performance. For example, in general the structural steel forgings overheating the coarse grain and were organization, GuoGongXiGang and bearing steel due to improper cooling the slight mesh carbide, etc.
2) some forgings defects, with normal heat treatment more difficult to eliminate, need high temperature is fire, and repeatedly is fire, low temperature decomposition, high temperature diffusion annealing and other measures to improve. For example, low power coarse grain, 9 Cr18 stainless steel crystal non-infarct-related carbide, etc.
3) some forgings defects, using general heat treatment process can't eliminate, the results of the final after heat treatment of forgings performance drop, even not qualified. For example, serious fracture and the edges of the stone face fracture, burning, stainless steel with the ferrite
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