Effect of Pre-Aging Treatment on the Strain Aging Characteristics of Hard Drawn Eutectoid Carbon Steel Wire

Abstract

The effect of quench aging and intermediate strain aging on the aging characteristics of cold worked eutectoid carbon steels containing different quantities of free nitrogen has been examined by means of torsional pendulum damping, electrical resistivity, and room temperature tensile test.
It is found that the strength increase by aging in the temperature range from room temperature to about 150deg;C (1st stage aging) is enhanced by the introduction of an intermediate strain aging at 220deg;C or 350deg;C put in between two sets of wire drawing practices. During strain aging at 220deg;C or 350deg;C, locking or pinning of dislocations by carbon supplied from lamellar cementite is brought about. The following cold drawing unlocks the dislocations and results in the dissolution of the carbon atoms in normal lattice sites. These carbon atoms in solution lock dislocations again during 1st stage aging.
By cold drawing after strain aging, nitrogen atoms also can enter in normal lattice sites as a result of dislocation depinning. During the following aging at 1st stage, nitrogen atoms relock dislocations and age strengthening occurs.,
Quench aging at 100°C can, however, diminish much of the redissolution of nitrogen by cold work on Fe-0.8% C-0.01%N specimen. This may suggest thatthe iron nitride formed during quench aging is more stable to cold work than Cottrell atmosphere.