Kinetics of strain aging in drawn pearlitic steels

Abstract

The kinetics of strain aging in a drawn pearlitic steel wire were analyzed based on measurements from three different experimental techniques: tensile testing, electrical resistivity, and internal friction. The progress of aging after a total reduction in area of 86 pct by drawing and heating between 60 ЊC and 200 ЊC was evaluated in terms of the changes in yield strength, electrical resistivity, and temperature-dependent background damping. The kinetic law and the apparent activation energies of the processes occurring in this temperature range were determined by the isothermal variation of the transformed fraction, obtained from the changes in properties with aging time. Under the conditions considered, static strain aging of drawn pearlitic steels seems to occur in two distinct stages, each associated with different atomic mechanisms. The first stage takes place between 60 ЊC and 100 ЊC and is characterized by a small increase in yield strength and a decrease in electrical resistivity and background damping. The second stage of aging occurs at higher temperatures or longer aging times and is marked by a sharp increase in yield strength and an increase in electrical resistivity, while the background damping reaches very small values. The probable mechanisms related to this behavior are discussed in terms of the empirical law and the apparent activation energy found.

An Empirical Model for Carbon Diffusion in Austenite Incorporating Alloying Element Effects

“…Figures 1 and 2 show the predicted carbon diffusivities using Eqs. (2) to (12) in Table 1 compared with measured values. Table 2 provides the experimental temperature conditions and carbon ranges used for the comparisons.…”

“…For example, strain aging and dynamic strain aging at low temperatures are controlled in part by carbon diffusion in ferrite, and models that predict aging times rely on expressions for carbon (and nitrogen) diffusion. 1,2) At higher temperatures, carbon diffusion governs phase transformation kinetics during heating and cooling or during isothermal holding processes, and in several analyses, an accurate expression for carbon diffusivity in austenite is critical. As one example, carburizing models 3,4) for low alloy steels require a carbon diffusivity expression that incorporates a complete assessment of the effects of alloy additions on carbon diffusion in austenite.…”

Macroscopic Characterization of Mechanical Properties in Electric Current Treated Dry Drawn High Strength Wires

“…The source of the initial static strain ageing for the electric current treated 4.09 mm sample is reasonably the ∼ 50 o C (Figure 2) increase in temperature during electric current treatment for a duration of 10 minutes (600 sec). In work by Buono [12], pearlite wire of similar composition 0.82C 0.7Mn 0.23Si wt.% were drawn to a true strain of 2.0 and aged at 60 o C for 400 and 900 seconds experiencing a percentage increase in yield strength of 1 and 1.4% respectively. Analogously, lower yield strengths in this study showed percentage increases of 2.4% for sample 4.09 mm (true strain of 1.79) which is thought to have undergone static strain ageing.…”

Kinetics of Strain Aging in Cold Rolled Low Strength Multiphase Steel

“…(1), 12) in which Y is the transformed fraction (aged fraction), k V is the rate constant, t is the time, and m is the time exponent.…”