The effects of composition and thermal path on hot ductility of forging steels
Abstract
This work examines the effects of composition and thermal handling path on the hot ductility of as-cast steel
forging ingots. Poor ductility of the as-cast structure can lead to cracking of the ingot prior to forging or the
formation of tears early during the forging process. The as-cast structure is particularly susceptible to cracking
due to the large grain size and high degree of microsegregation present.
Experiments were conducted to evaluate the ductility of the as-cast steel with varying levels aluminum and
nitrogen. Multiple thermal handling paths were followed in order to approximate the different thermal conditions
experienced approximately six inches below the surface of a large (~40 MT) steel ingot following solidification.
Hot tension testing after in-situ melting and solidification was used for quantitative measurements of the
material ductility. The majority of testing was carried out on a modified P20 mild tool steel. The experiments
indicate a significant loss of ductility for materials with high aluminum and nitrogen contents
(AlxN = 5.2x10-4) in the temperature range of 950 °C - 1050 °C upon solidification and direct cooling to the
test temperature. This behavior is not present in material with AlxN products below 1.3x10-4. All materials
tested exhibited a loss of ductility when the sample was cooled to 900 °C, immediately reheated to 1000°C and
tested. With increasing hold times at 900 °C prior to reheating to 1000 °C, the material with high aluminum and
nitrogen contents recovers ductility much more quickly than the low aluminum and nitrogen materials.
Funding in part by the Forging Industry Educational & Research Foundation and Ellwood Group, Inc.