Large Ingot Metallurgical Defects In The Evolution Of Hot Forging Conditions

As the installed capacity of electric power equipment becomes upsizing, the ingot used in heavy forgings also becomes larger and larger. At present, the biggest ingot of million KW grade nuclear heavy forgings has already been to 600 ton grade. Ingot inevitably exist metallurgical defects such as loose during smelting and casting process. With the increasing of ingot size, the metallurgical defects are more likely to produce. Therefore, studying the evolvement situation of metallurgical defects inside the heavy ingot during hot forging process is very important to produce quality heavy forgings and improve its production level in our country.For the metallurgical defects inside heavy ingot on hot forging condition, this paper put forwards for the first time to establish loose material model based on porous material on FE software DEFORM-3D, and to make relative density as evaluation index to assess the loose compaction process. At the same time, this paper makes a preliminary exploration on dendrite evolutionary process during hot forging. Firstly, this paper ascertains technique parameters of FM method theoretically, establishes and optimizes loose material model based on porous material. Then, the physical experiments about upsetting and FM method stretching have been carried on, the main researches are density and dendrite changing situations under different forging condition, and verifying the healed conditions of defects by the changes of mechanical properties. Finally, in the foundation of physical experiments, using the loose material model and dense matierial model which has been founded, this paper carries numerial simulation on the physical experiment, observe relative density changing rule of loose material and the feasibility that using porous material instead of loose material and taking relative density as evaluation index to assess loose compaction process. The main conclusions are as follows: (1)Density diversification of loose material can reflects as-cast material loose compaction process, it indicates that it is feasible to establish loose models through porous materials and take relative density as evaluation index of loose compaction. (2)Physical experiment and numerical simulation shows the same rules: both the density and loose compaction degree improves following the forging ratio increasing. The more closed to the dense material, the more difficult to compact the loose. (3)With the increasing of forging ratio, dendrite turn to flow line, the flow line direction of upsetting sample tends to coincide with the material flowing direction during upsetting, the angle between the flow line direction and main deformation direction of stretching sample decreases gradually. (4)After twice heat treatment, the mechanical properties of the samples in different forging ratios have been improved greatly, and it shows that the primary metallurgical defects of material have been healed to some extent in hot forging.