Retain the austenite via diffusion control under electropulsing to improve the mechanical properties of the AISI 420 stainless steel

Retained austenite (RA) can efficiently increase the plasticity of steel with high tensile strength. In this work, electropulsing was used to improve the mechanical properties of the steel by stabilizing RA. AISI 420 stainless steel with ultra-high strength (1720 MPa) and 7.9 % elongation was prepared by electropulsing quenching (EQ). The extremely fast heating rate of the pulsed current results in an instantaneous phase transition, which limits the growth of the prior austenite grains (PAGs) and rapidly dissolves part of the carbide, enriching the carbon element near the carbide and obtains the RA during the cooling process. After electropulsing quenching then tempering (EQ + ET), the volume fraction of austenite increased from 4.4 % (EQ) to 11.8 % (EQ + ET), which is attributed to pulsed current promoting the diffusion of carbon from martensite to austenite in the tempering process. And the process leads to austenite reversion and improves the stability of RA. As a result, the EQ + ET sample had a good strength-plasticity combination (ultimate tensile strength 1527 MPa, elongation 14.1 %). These findings provide guidance for the regulation of the microstructure and mechanical properties of AISI 420 stainless steel.