Jan Sińczak

Prediction of mechanical properties of heavy forgings

Abstract This paper deals with the problem of forging of heavy parts. The stock material for this process has the microstructure of the casted material, which is characterised by strong inhomogeneity of grains and the presence of pores. This structure is altered during forging by subsequent processes of plastic deformation and recrystallization. Therefore, the problem of penetration of plastic deformation inside the forging becomes essential. The general objective of the work is an evaluation of the minimum reduction of the cross-section of the forging, which still allows the required mechanical properties to be obtained. The research included both experimental tests and finite-element simulation of the forging process. The tested material was middle carbon steel containing 0.4% C and 1.3% Mn. The experiments consisted of the measurement of yield stress, tensile strength and hardness for samples cut from various parts of the forging. The results were compared with the local values of strains and temperatures during the forging process predicted by the finite-element program. The microstructure evolution models were implemented into the finite-element code, which allowed the prediction of distributions of grain size in the volume of the forging. Analysis of all the results allowed conclusions to be drawn regarding a design of forging technology that will guarantee required properties of forging.

Automated Determination and On-Line Correction of Emissivity Coefficient in Controlled Cooling of Drop Forgings

The paper presents the methodology of determination of emissivity coefficient of steel in the direct cooling temperature range, which allow self-definition of this parameter in automated temperature control system used for direct cooling of drop-forged parts. Based on the actual temperature of the surface of the workpiece, the system automatically adjusts the velocity of fan-forced air to produce desired cooling rate and course of cooling curves. To enable automatic correction of cooling rate, the system must rely on exact remote temperature measurements. This is conditioned by correct definition of emissivity in pyrometer gauge system. Traditionally, pyrometers use presets of a constant value, selected as to get optimum consistency for the temperature range concerned. As the emissivity is time-dependent, the idea of the approach presented in the paper is to use time dependent characteristics, to attain the minimum discrepancy between actual and measured values during the whole cooling cycle.