Precipitation Kinetics and Strengthening of a Fe-0.8wt%Cu Alloy.

Abstract

Precipitation kinetics and strengthening have been investigated for a Fe-0.8wt%Cu alloy. Microstructure evolution during aging at 500°C has been studied by a combination of Transmission Electron Microscopy and Small-Angle X-ray Scattering to provide information on the nature and location of the precipitates as well as a quantitative estimate of their size and volume fraction. The associated mechanical properties have been studied by hardness and tensile tests.The precipitation kinetics measured in this study are fully compatible with results reported for alloys with higher Cu levels. Nucleation of Cu precipitates is promoted by the presence of dislocations whereas coarsening rates in the later stages of aging appear to be not affected by fast diffusion paths along dislocations.The strength of individual precipitates increases with precipitate size based on the analysis of the mechanical test results. However, the strength of the largest precipitates observed remains approximately half of the strength required for the Orowan by-passing mechanism. The Russell-Brown model for modulus strengthening has successfully been applied to the current data.Study of the plastic behavior shows that the maximum initial hardening rate is related to the highest strength of the material. This unusual result may be explained by a dynamic strained-induced phase transformation of the precipitates from the bcc to the 9R structure. Consequently, the hardening potential of Fe-Cu alloys is associated with good plastic properties close to peak strength thereby indicating the excellent potential of copper as hardening element for the development of novel high strength interstitial free (IF) steels.KEY WORDS: iron-copper alloy; precipitation kinetics; precipitation strengthening; strain hardening; smallangle X-ray Scattering.formation to the 9R structure has been initiated. 10,11,19) The strengthening is usually described by employing the approach of Russell and Brown which is based on modulus strengthening. 20) This approach allows for the prediction of mechanical properties during an aging treatment assuming that the strength of the interaction between the dislocation and the precipitate increases with particle size. An alternative approach has recently been proposed by Osamura et al.,19) assuming that the hardening during the initial stage is controlled by coherency strains. The decrease in strength after the peak strength is attributed to the loss of coherency of the precipitates. Currently available experimental data do not allow to give preference to one of these two models.The effect of precipitation, coupled with the evolution of solid solution content, on the overall work hardening behavior is still poorly understood. Current knowledge derives from the pioneering contribution of Hornbogen et al. 21) where a few curves of initial work hardening rates are presented. More generally, a limited theoretical framework including the effect of bypassed precipitates has been proposed recently by Estrin,22) but the complete picture is still ...

High-Strength Low-Carbon Ferritic Steel Containing Cu-Fe-Ni-Al-Mn Precipitates

“…[50] The source of this controversy is possibly a result of a combination of a number of precipitation strengthening mechanisms include lattice mismatch, modulus mismatch, and chemical hardening. [51][52][53][54][55][56][57] Also, when the dislocation enters the precipitate two partial dislocations are created that combine when the dislocation leaves the precipitate. Energy must be supplied to move the dislocation out of the precipitate.…”

Mechanism of Toughening in Ferritic Iron by Solute Copper at Low Temperature

“…1) Therefore, most of interests in Cu bearing steels have been concentrated on the behavior of precipitation hardening by Cu. [1][2][3][4][5][6] On the other hand, few efforts have been made for investigating the effect of solute Cu itself on microstructure and mechanical properties of steel. When the Fe-(0ϳ2)mass%Cu alloys transform to massive ferritic structure on air-cooling from an austenite region, Cu exists as supersaturated atoms in solid solution, hence the ferritic steel is hardened somewhat due to the solid-solution strengthening.…”

Microscopic modelling of simultaneous two-phase precipitation: application to carbide precipitation in low-carbon steels

“…The phase transformation leading to an optimum distribution of hardening precipitates from a supersaturated solid solution (SSS) is often complex, involving a sequence of metastable phases, which compensate a higher Gibbs energy by coherent or semi-coherent interfaces with the metallic matrix. Important industrial examples of such precipitation sequences include SSS 0/e 0/Fe 3 C in iron Á/carbon alloys [3], SSS 0/BCC copper 0/9R copper0/FCC copper (e ) in iron Á/copper alloys [4], SSS 0/GP zones 0/ bƒ 0/b? 0/b (Mg 2 Si) in Al Á/MgÁ/Si alloys [5] and GP zones0/h?…”