Influence of in-service thermal softening on wear and plastic deformation in remanufactured hot forging dies

Abstract

The need for economic and greener production methods necessitates remanufacturing of used hot forging dies. However, it has been reported from industries that the remanufactured forging dies show higher wear rate, and plastic deformation as compared to new dies. In this work wear and plastic deformation behaviour in new, and remanufactured hot forging dies at different stages of forging cycles are experimentally studied. Die geometry was digitised using three dimensional optical scanner to analyse the wear depth, and plastic deformation. Compared to new dies, significant wear and plastic deformation was found in remanufactured dies. Since in-service microstructural changes are expected to influence wear and plastic deformation behaviour, microhardness tests were conducted on die specimen to measure the variations in hardness from surface to core regions of die. This study reveals that a thermally softened layer grow on the die surface with each forging cycle and in subsequent cycles, this layer gets removed by in-service wear and plastic deformation. In addition, the core hardness in new and remanufactured dies was found to decrease with increasing hot forging test duration. Consequently, remanufactured dies exhibits a lower core hardness, as compared to new dies, which eventually results in higher wear loss and plastic deformation.

Influence of full annealing on microstructure and mechanical properties of AISI 1035 steel

“…From figure 11, it can be observed that the optimum hardness and impact energy can be obtained in samples annealed within 940 °C and 980 °C. These observations are similar to the studies conducted in previous research [9]. After this optimum range of temperature, the hardness drops significantly.…”

“…This helps to stabilize the temperature inside the specimen and prevents thermal shocks. Such thermal shocks can produce internal cracks inside the specimens [9] which will reduce the strength of such specimens. Further, the specimens were heated to austenitising temperature of 900 °C, 940 °C, 980 °C and 1020 °C, and these were furnace cooled to obtain full-annealed ferritic-pearlitic microstructure [8].…”

Design of a forging process to individually examine thermal, mechanical and tribological stress in the tool surface zone

“…The loss of strength of the material in the tool surface layer is caused by the thermal loads and results in wear. During forging, peak temperatures in the thermally highly stressed tool areas exceed the tempering temperature of the tool material, thus softening the tool surface layer [3].…”

Load-Adapted Surface Modifications to Increase Lifetime of Forging Dies

“…Cyclical processes with high rates in the temperature changes act during die forging simultaneously with high forces. They promote several wear mechanisms such as abrasive and/or adhesive wear, plastic deformation and tribochemical reactions [2]. In addition, crack formation and propagation are observed on the tool surface [3].…”