(I) Influence of forging on metal structure and properties In forging production, in addition to the shape and size required for forgings, the performance requirements of the parts must be met, including: strength pointers, plastic pointers. , impact toughness, fatigue strength, fracture toughness and stress corrosion resistance, high temperature working parts, high temperature instantaneous tensile properties, long-term performance, creep resistance and thermal fatigue properties. The raw materials for forging are ingots, rolled products, extruded materials and forged billets. The rolled material, the extruded material and the forged blank are respectively semi-finished products formed after the ingot is subjected to rolling, extrusion and forging processing. In forging production, using reasonable process and process parameters, the microstructure and properties of the raw materials can be improved by: 1) breaking the columnar crystals, improving the macrosegregation, changing the as-cast microstructure to the forged structure, and at the appropriate Under the condition of temperature and stress, the internal pores are welded to increase the density of the material; 2) the ingot is forged to form the fibrous structure, and further, through rolling, extrusion and die forging, the forgings are reasonably distributed in the fiber direction; 3) Control The size and uniformity of the grains; 4) improving the distribution of the second phase (for example, alloy carbides in the Leysite steel); 5) obtaining deformation strengthening or deformation of the structure - phase transformation strengthening, and the like. Due to the improvement of the above-mentioned structure, the plasticity, impact toughness, fatigue strength and durability of the forgings are also improved, and then the final heat treatment of the parts can obtain a good combination of hardness, strength and plasticity required for the parts. performance. However, if the quality of the raw materials is poor or the forging process used is unreasonable, forging defects, including surface defects, internal defects or performance failure, may occur.
(II) Influence of raw materials on the quality of forgings The good quality of raw materials is a prerequisite for ensuring the quality of forgings. For example, defects in raw materials will affect the forming process of forgings and the final quality of forgings. If the chemical element of the raw material exceeds the specified range or the impurity element content is too high, it will have a great influence on the forming and quality of the forging. For example, S, B, Cu, Sn and other elements are easy to form a low melting point phase, making the forging easy. It appears hot and crisp. In order to obtain the intrinsic fine-grain steel, the residual aluminum content in the steel needs to be controlled within a certain range, for example, 0.02% to 0.04% (mass fraction) of Al acid. If the content is too small, the effect of controlling the grain growth will not be achieved, and the intrinsic grain size of the forging is often unsatisfactory; the aluminum content is too much, and the grain-like fracture is easily formed under the condition of forming the fiber structure during the pressure processing. A tear-like fracture, etc. For example, in the 1Cr18Ni9Ti austenitic stainless steel, the more the content of Ti, Si, Al, and Mo is, the more the ferrite phase is, and the more the band-shaped crack is formed during forging, and the part is magnetic. For example, there are defects such as shrinkage of the shrinkage tube, subcutaneous foaming, severe carbide segregation, and coarse non-metallic inclusions (slag inclusion), which may cause cracks in the forging. Defects such as dendritic crystals, severe looseness, non-metallic inclusions, white spots, oxide film, segregation zone and mixed metal in the raw materials are likely to cause a decline in the performance of the forgings. Surface cracks, folding, crusting, and coarse crystal rings of raw materials are liable to cause surface cracks in forgings.
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