Effects of vanadium and nitrogen on recovery and recrystallization during and after hot-working some HSLA steels |
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Authors: | M J White W S Owen |
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Affiliation: | (1) Norton Company, New Bond Road, 01601 Worcester, MA;(2) Department of Materials Science and Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA |
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Abstract: | The effects of vanadium/nitrogen additions on dynamic and static recovery and recrystallization have been studied in a set
of aluminum-killed HSLA steels containing 0.1 pct carbon, 0.01 to 0.02 pct nitrogen, and either vanadium (0.1 or 0.2 pct),
niobium (Cb) (0.03 pct), or vanadium and niobium together. Most, but not all, of the tests were carried out at 1173 K (900°C),
a temperature at which precipitation of VN might be expected under some conditions. The net effect of dynamic recovery, recrystallization,
and precipitation was monitored by measuring the change in compressive flow stress with strain at a constant temperature.
Static changes were followed by measuring the change in compressive flow stress on isothermally holding unloaded specimens
after a hot precompression. These kinetic data were supplemented by metallographic and electron-microscopic examinations of
quenched specimens and of carbon extraction replicas taken from them. Evidence is presented which indicates that, at a holding
temperature of 1173 K (900°C), static recrystallization occurs in vanadium steels containing 0.1 pct vanadium before any precipitation
is detected. The progress of this recrystallization is arrested by the precipitation of vanadium nitride. At a higher vanadium
concentration, 0.2 pct, recrystallization does not start. The effects of V/N ratio, austenitizing temperature (between 1373
K (1100°C) and 1523 K (1250°C), and isothermal holding temperature (between 1173 K (900°C) and 1273 K (1000°C)) on the kinetics
of static softening and hardening are compared in some vanadium steels and plain-carbon and niobium steels of similar base-composition. |
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