Abstract
The formation of Mn–C short-range ordering (SRO) has a great influence on the mechanical properties of high-Mn steels. In the present work, the formation of Mn–C SRO during recrystallization of an X60Mn18 steel was investigated by means of a combined study employing small angle neutron scattering (SANS) and ab initio ground-state energy calculations based on density-functional theory. The SANS measurements prove the presence of Mn–C SRO in the recrystallization annealed X60Mn18 steel and indicate the evolution of the SRO during recrystallization. The results show that with the increase in annealing time, the mean size of the Mn–C SRO decreases, whereas the number density increases. The ab initio calculations well describe the energetically favored condition of Mn–C SRO and provide the theoretical explanation of the clustering formation and evolution in the X60Mn18 steel. The stress-strain curve of the X60Mn18 steel exhibits a high strain-hardening rate and the plastic deformation is characterized with a series of serrations during a uniaxial tensile test. In the end, the correlation between Mn–C SRO and the serrated flow of high-Mn steels is further discussed.
Highlights
High-Mn (15–30 wt %) austenitic steels are well known for their high ultimate tensile strength over 1000 MPa and total elongation over 60% at room temperature [1,2,3,4]
In order to compare the impact of annealing duration on the Mn–C short-range ordering (SRO) formation, the specimens were recrystallization annealed in a salt bath at 800 ◦ C for 2 min and 30 min, followed by quenching in water to room temperature
The small angle neutron scattering (SANS) results show that an increase in the duration of recrystallization annealing at 800 ◦ C from 2 min to 30 min leads to a decrease in mean particle size and an increment of annealing at 800 °C from 2 min to 30 min leads to a decrease in mean particle size and an increment both particle number density and volume fraction, which indicates new clustering formation and a finer of both particle number density and volume fraction, which indicates new clustering formation and distribution of the particles with smaller size
Summary
High-Mn (15–30 wt %) austenitic steels are well known for their high ultimate tensile strength over 1000 MPa and total elongation over 60% at room temperature [1,2,3,4]. Due to the excellent strain hardening of the high-Mn steels, the superior combination of high strength and ductility makes these steel grades a good choice for the automotive industry for the manufacture of complex body geometries, yielding improved crashworthiness and reduced weight at the same time [5,6,7]. A unique characteristic of high-Mn steels is the significant serration phenomenon (jerky flow) during deformation. These serrations strongly influence the mechanical properties of the materials, for example, they increase the flow stress, the tensile strength and the work hardening rate, etc. It has been suggested that DSA in Fe–Mn–C steels involves the interaction of dislocations [4,16,17] and stacking fault regions [12,13] with point defect complexes that include interstitial C
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