Influence of Temperature and Holding Time on the Interaction of V, Al, and N in Microalloyed Forging Steels

A medium-carbon vanadium microalloyed steel (38MnSiVS5) with three different aluminum levels (0.006, 0.020, and 0.03 wt pct) was used to examine the interaction of vanadium, aluminum, and nitrogen during the heating and cooling cycle for forging. The thermal cycle was simulated using a Gleeble ® 1500. Hold times varied from 5 to 45 minutes and temperature varied from 1323 K to 1523 K (1050 °C to 1250 °C). Thermal simulation specimens and as-received material were characterized by quantitative metallography, hardness, and chemical analysis of electrolytically extracted precipitates. The hardness was observed to be relatively constant for all aluminum levels after all thermal simulations at and above 1423 K (1150 °C). Hardness, pearlite fraction, and austenite grain size decreased with increasing aluminum content at the two lowest temperatures examined, which were 1323 K and 1373 K (1050 °C and 1100 °C). The amount of vanadium precipitated in the lowest aluminum steel was very consistent, approximately 70 pct, for the thermal simulations. The amount of precipitated vanadium decreased with increasing amount of aluminum nitride for the 0.03 wt pct Al level.