Effect of microheterogeneity on the kinetics of phase transformations in large forgings of steel 34KhN3M

Conclusions

• 1. The microheterogeneity of the structure is clearly evident in the central areas of forgings of steel 34KhN3M.

• 2. The phase transformations during heat treatment of large forgings do not conform with the C-shaped curves that are characteristic for the average composition of the steel. Due to the microheterogeneity, the transformation of austenite in the central area of large forgings begins earlier and ends much later than in sections of the steel of average composition. This must be taken into account in heat treatment, particularly annealing after forging, when the absence of segregation ensures the maximum decomposition of austenite.

• 3. The microheterogeneity is retained and may increase during heating for quenching or normalization—the difference in the grain size increases as the result of preferential growth of large grains, and individual microsections are enriched because of the migration of carbon.