PMC

(a) Uniform elongation and (b) reduction of area (during necking) during tensile testing of both material conditions vs. strain rate at the two testing temperatures (293 K and 473 K).

(a) Engineering (tensile) stress-strain curves after Q&T and Q&P heat-treatment, at testing temperatures of 293 K and 473 K under quasi-static loading conditions (10⁻³ s⁻¹). (b) Strain hardening rate vs. true strain highlighting the extraordinary, almost constant strain hardening rate of the Q&P-processed material at 473 K.

Microstructural model of the key deformation mechanisms that dominate the material behavior at ambient and elevated temperatures. Retained austenite remains stable up to higher macroscopic strains at elevated temperature. Plastic deformation in austenite and the martensitic transformation itself operate up to higher strains. These mechanisms in combination with interface plasticity contribute to the increased ductility at an elevated temperature.

Microstructure of Q&P heat treated steel. (a) Secondary electron (SE) contrast reveals the presence of carbides in martensitic areas. Subfigures (b–d) and (f–h) show results of ESBD measurements: (b) image quality map (IQ), (c) inverse pole figure map (IPF) and (d) phase map (PM). (e) Retained austenite fraction (measured by XRD) vs. (tensile) plastic strain during tensile testing at testing at temperatures 293 K and 473 K. (f) PM superimposed with IQ of unstrained microstructure and after 3% tensile plastic strain at g) 293 K and h) 473 K.