Electropulsing-induced strengthening of steel at high temperature

Abstract

Electropulsing usually reduces the stability of metastable phases in materials. This work reports the opposite effect, where electropulsing drives the stable -phase at high temperature to be decomposed. This enables both γ-phase and σ-phase in duplex stainless steel to survive and hence to strengthen the steel at high temperature. The hardness of the quenched sample after electropulsing is 49.4% higher than that without electropulsing treatment. The scientific understanding to the observation has been developed.

Application of High-Density Electropulsing to Improve the Performance of Metallic Materials: Mechanisms, Microstructure and Properties

“…As a non-equilibrium process, the EPT-induced unstable solid phase in the sample at high temperature could be retained after the rapid cooling to room temperature. Electropulsing not only promotes a metastable phase to evolve towards its equilibrium state; it also enhances the stability of the metastable phase if its electrical resistivity is lower than that of stable phase [ 76 ]. As Lu et al reported, the decomposition of stable δ-phase in 2205 stainless steel was accelerated after EPT, because the phase transition δ → γ + σ was promoted at the high temperature, which was equivalent to stabilizing the phase of γ and σ, mainly for their lower electrical resistivity than δ.…”

Influence of κ-carbide interface structure on the formability of lightweight steels

“…Theoretical calculation predicts the maximum current-induced temperature rising of around 200 o C [29][30].…”

Stability of martensite with pulsed electric current in dual-phase steels

“…intersection and annihilation of dislocations) in cold-formed materials [35]. This is due to the electron wind force generated by EPT, which can scatter unevenly around dislocations and which, subsequently, reduces the kinetics barrier between two neighbour dislocations [28,[30][31][32]. Therefore, the mobility of dislocations can be enhanced, which can be expressed as [36]:…”

“…For the thermal effect of EPT, the temperature increase induced by joule heating can be expressed as [28,[30][31], where j the current density (5.67×10 9 A/m 2 ), ρ is the electrical resistivity of the steel sample (9.64 ×10 -7 Ωm), Δt is the pulse duration (110 μs), C p is the specific heat of steel sample (450 J/kg K) and d is the density of steel sample (7. C, for periods of (300s) and (5400s) , respectively [6], as shown in Fig .5b.…”