The effects of composition and thermal path on hot ductility of forging steels
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.