Investigation of the quality of metal in large forgings formed from steel 25Kh2NMFA in the annealed state

1. The quality of the metal in axial trepans, which was sampled from two large forgings, is satisfactory along the entire length: no cracks, flakes, or other defects that disturb the metal's continuity are detected. 2. Nonmetallic inclusions are observed in the metal of the trepan: sulfides, oxides, and oxysulfides, arranged in the form of chains along the grain boundaries, and small lines in the direction of deformation; this exerts an unfavorable influence on the plastic and ductile properties of the forgings. 3. The presence of a dendritic and banded macrostructure suggests inadequacies in plastic-deformation technology. 4. The level of strength, plastic, and ductile characteristics of the metal after treatment in accordance with the new regime is lower, and the critical brittleness temperature higher by 30° C than after treatment in accordance with the regime previously adopted. 5. The new regime for the preliminary heat treatment of large forgings ensures decomposition of the austenite in accordance with a diffusion mechanism and the production of a grain corresponding to Nos. 5–7 in the central zones; this is positively manifested in the properties of the metal after final heat treatment.