Superior High‐Temperature Properties of Low‐Density Steel Enabled by a Tunable Hierarchical Microstructure

Abstract

The tensile properties, microstructure characteristics, and fracture mechanisms at 500 °C of Fe–Mn–Al–C–Mo–V steel processed by hot rolling (HR) and warm rolling (WR) are investigated. The HR steel obtained by rolling 1150 °C, consisting mainly of equiaxed austenite and banded ferrite, exhibits a tensile strength of 695 MPa, accompanied by an elongation of ≈45.5%. In contrast, the WR steel processed by rolling at 750 °C shows a hierarchical microstructure that consists mainly of lamellar ferrite/austenite + fine carbides, rendering a significantly increased tensile strength to 1040 MPa and an excellent elongation to ≈20.0%. This is mainly attributed to the remarkable refinement of ferrite and austenite in the WR steel, strengthening finely dispersed carbides, and obtaining numerous low‐angle grain boundaries in the matrix. The tensile fracture morphology is a ductile failure in both types of steel. The fracture of HR steel is attributed to the cracks enabled by the austenite localized slip deformation in the austenite and the fracture of the precipitates; the failure of the WR steel is mainly ascribed to the cracking along the lamellar structure due to the κ‐carbides pinning lamellar ferrite phase boundary leading to high strain localization.

Effect of Al Content on the Microstructure and Mechanical Properties of the Sintered Fe–Mn–Al Porous Steel

“…The Fe–Mn–Al porous steel combines the merits of Mn‐containing steel (e.g., high strength, toughness and wear resistance) and Al‐containing steel (e.g., low density and high ductility), resulting in the comprehensive characteristics of light weight and high mechanical properties. [ 14–18 ] In recent years, many studies revealed that Al had a significant impact on the mechanical properties and microstructure of steel. [ 19–28 ] It was reported that the density and Young's modulus could be reduced by 1.3% and 2% with the increase of 1 wt% Al in the steel, [ 23 ] respectively.…”

“…[6][7][8][9][10][11][12][13] At present, sintering is the most common method for preparing porous steels, which has the combined advantages of low preparation temperature, simple process, short cycle, less composition segregation, and tailored porosity.The Fe-Mn-Al porous steel combines the merits of Mn-containing steel (e.g., high strength, toughness and wear resistance) and Al-containing steel (e.g., low density and high ductility), resulting in the comprehensive characteristics of light weight and high mechanical properties. [14][15][16][17][18] In recent years, many studies revealed that Al had a significant impact on the mechanical properties and microstructure of steel. [19][20][21][22][23][24][25][26][27][28] It was reported that the density and Young's modulus could be reduced by 1.3% and 2% with the increase of 1 wt% Al in the steel, [23] respectively.…”