The Effect of Forging Conditions on Final Macrostructure of Slab Ingot from the 55NiCrMoV7 Tool Steel

Abstract

The paper presents numerical modelling and an operational experiment to forge a slab ingot P40N from 55NiCrMoV7 tool steel and the procedure for the optimization of its production. The aim of the numerical simulation of forging was to verify the existing procedure of forging a plate from a conventional polygonal 8K forging ingot and a slab ingot with a polygonal shape of P40N surfaces. The effect of the shape of the ingot on the achievement of the required forging reduction and strain after the cross section of the forging of the plate, with final dimensions of approximately 1010 mm width × 310 mm thickness × 5350 mm length, was studied. The results obtained in the operational experiment showed satisfactory qualitative parameters of the steel forging from the slab P40N ingot which were in accordance with the predicted results of numerical simulations. The results indicated that in selected cases the use of a slab P40N ingot instead of the conventional polygonal 8K forging ingot can be considered in the production of certain plate-type forgings.

Formation mechanism of inspection defects in hundred-ton class 55NiCrMoV7 die steel forging

“…[20][21][22] The selective crystallization of S element in the solid and liquid phases during the solidification process occurs, with S atoms dissolving minimally in the solid phase and completely in the liquid phase. The concentration of S w[j] L at the solidification front can be calculated using equation (1).…”

“…Hundred-ton class 55NiCrMoV7 die steel forgings are utilised as the material for bolster plates in ten-thousand-ton level large-scale die forging machines, owing to their uniform hardness across large cross-sections and exceptional resistance to load impact. 1 In service, they support forging dies and forgings, requiring them to endure substantial pressure and wear. Usage conditions impose stringent metallurgical quality requirements on die steel, and user manufacturing technology agreements explicitly forbid the presence of internal defects.…”

“…The production of this material includes processes such as steel ingot smelting, forming, and heat treatment. In recent years, numerous studies have been conducted on this material, concentrating on optimising heat treatment process parameters, [2][3][4] thermal deformation behaviour, 5 macrosegregation control, 6 microstructure evolution, 1,[7][8][9] the relationship between microstructure and properties, 10,11 and cavity defect closure behaviour. 12 Most of these studies have focused on laboratory-scale or small to medium-sized steel ingot forging and heat treatment process optimisation in industrial practices.…”