Tensile stress-strain analysis of single-structure steels

Abstract

In an effort to establish a universal model to predict the mechanical properties from processing conditions, tensile tests have been conducted of four single-structure steels, namely, ferrite, pearlite, bainite, and martensite; the data obtained were analyzed in terms of the Ludwik, Hollomon, and Swift equations to characterize their work-hardening behavior. It was found that the differential Crussard-Jaoul (C-J) analysis, based on the Ludwik equation, can describe the work-hardening behavior of these steels fairly well.

The differential C-J analysis has shown that the ferrite and pearlite steels deform with two stages of work hardening, each stage associated with a distinctive value of the work-hardening exponent n. Martensitic steels exhibit single-stage work hardening. In bainite, the behavior was found to be dependent on transformation temperature; upper and lower bainite exhibit a behavior similar to pearlitic steels and quenched martensite, respectively. This can be well understood in terms of the similarity of the corresponding microstructures.

On the basis of these results, the work-hardening behavior of single-structure steels falls into four categories, according to the n value. This classification may serve as a useful guide to predict the flow behavior of steels with a known microstructure or to judge the microstructure merely by stress-strain curves, without microstructural observations.