Microstructure, mechanical properties and deformation behavior of Cr-containing triplex low-density steels with different C content

Abstract

In this work, Fe–20Mn–9Al–3Cr-xC (wt.%, x = 0.8–1.4) steels were designed to investigate the microstructure, mechanical properties and strain hardening behavior of Cr-containing Triplex low-density steel with different C content. Due to the presence of 3 wt% Cr, all the steel strips with different C content consisted of ferrite and austenite matrix with κ-carbide precipitation. With increasing the C content from 0.8 wt% to 1.4 wt%, the ferrite content decreased from 36 vol% to 4 vol%. Simultaneously, the precipitation and growth of κ-carbides in austenite was accelerated significantly. Quantitative analysis of the yield strength indicated that the strength contribution by κ-carbides increased from 36.3 MPa in 0.8C steel strip to 409.4 MPa in 1.4C steel strip, and became the primary strengthening factor when the C content exceeded 1.0 wt%. Fortunately, due to Cr addition, no intergranular κ-carbide was observed even in the 1.4C steel strip, and the steel strip demonstrated a good elongation of more than 33%. During plastic deformation, the slip band-dominated dislocation substructure made the 0.8C steel strip show a three-stage strain hardening, whereas a four-stage strain hardening occurred in the 1.0C, 1.2C and 1.4C steel strips due to the successive formation of slip band and microband. In addition, it was found that the plastic deformation in ferrite was prior to that in austenite, and the formation of ferrite improved the strain hardening capacity of steel strips at the early deformation stage. The findings provided valuable insights into the design of high-performance Triplex low-density steels by composition optimization.