Static strain aging phenomena in cold-rolled dual-phase steels

Abstract

The effect of low-temperature aging, with aging temperatures up to 170 °C, on a cold-rolled CMn-CrMo dual-phase (DP) ferrite-martensite steel was investigated. This material was processed using three different intercritical annealing treatments, leading to DP structures with different microstructures and properties. It has been found that both the aging in the ferrite phase and the tempering in the martensite play an important role in the mechanical behavior of the material with regard to the strain aging phenomena. The yield stress increase accompanying the aging phenomenon revealed three separate aging stages. In the present study, those stages were determined to be the result of the pinning of dislocations in the ferrite, the C-cluster formation, or low-temperature carbide precipitation in the ferrite and the volume contraction of the martensite due to formation of low-temperature carbides, leading to the relief of residual stresses in the ferrite. In the absence of a clear yield point, a new method is proposed to measure the increase in yield stress due to aging only.

The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions

“…This steel possesses smooth stress-strain curves with continuous yielding, low proof to tensile strength ratio, high work hardening rate and high uniform and total elongation. Static [6,7] and dynamic [2] strain aging behavior have also been reported. During low temperature bake hardening processes, both static strain aging behavior of the ferrite and tempering of the martensite have been observed.…”

“…Cottrell atmospheres, carbon-clustering and precipitation can appear. It has been found by means of precision dilatometry and Xray diffraction [7] that redistribution of carbon atoms occurs below 120 • C and precipitation of -or -carbide takes place in martensite at temperatures 120-200 • C during the tempering of DP steel. temperature range 250-450 • C [2], accompanied by increase in yield strength (R p0.2 ) and ultimate tensile strength (R m ) with increasing temperature.…”

Characterization of mechanical properties by indentation tests and FE analysis – validation by application to a weld zone of DP590 steel

“…For the experimental result of the longitudinal specimen, the yield point elongation is observed at the initial stage, which is the material characteristic of the annealed steel (Waterschoot et al, 2003). Since the yield point elongation was not observed for the base material here, it might be related to the weld properties, which was not observed in the indirect measurement.…”

Local Laser Heat Treatment in Dual-Phase Steels

“…Tempering of martensite is reported as the main reason for softening of multiphase steels. [24][25][26] The investigations are part of a project within the Collaborative Research Center SFB 675 ''Creation of high strength metallic structures and joints by setting up scaled local material properties.'' The goals of the project are to analyze the effect of the local influence and to develop processes that are able to induce a locally restricted strengthening effect for DP steels.…”