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The aims of this paper are to reveal the surface failure behavior of 70Mn martensite steel under abrasive impact wear by impart wear tests. The wear tests were performed with the MLD-10 abrasive wear testing machine, using SiO 2 abrasive with three different impact loads for 30000 cycles. Worn surfaces and white-etching layers (WEL) were analyzed by scanning electron microscopy, x-ray diffraction and transmission electron microscopy, and the abrasive impact wear mechanism was analyzed. Strain-hardening effects beneath the contact surfaces were researched by Micro-hardness profiles. Results indicated that the main formation mechanism of white-etching layers (WEL) in test steel were the formation of twin martensite and accumulation of dislocations attributing to plastic deformation during impact wear tests. The thickness and hardness of WEL were both increased with test load, which led to an increased brittleness of WEL. Under the effects of impact load, the micro-cracks initiated at subsurface and extended to surface, eventually led to delamination and fracture. Therefore, the delamination and fracture resulting from plastic deformation fatigue were the primary surface failure mechanism of the steel at abrasive impact wear.

The hot deformation and dynamic recrystallization (DRX) behavior of austenite-based Fe–27Mn–11.5Al–0.95C steel with a density of 6.55 g cm−3 were investigated by compressive deformation at the temperature range of 900–1150 °C and strain rate of 0.01–10 s−1. Typical DRX behavior was observed under chosen deformation conditions and yield-point-elongation-like effect caused by DRX of δ-ferrite. The flow stress characteristics were determined by DRX of the δ-ferrite at early stage and the austenite at later stage, respectively. On the basis of hyperbolic sine function and linear fitting, the calculated thermal activation energy for the experimental steel was 294.204 kJ mol−1. The occurrence of DRX for both the austenite and the δ-ferrite was estimated and plotted by related Zener–Hollomon equations. A DRX kinetic model of the steel was established by flow stress and peak strain without considering dynamic recovery and δ-ferrite DRX. The effects of deformation temperature and strain rate on DRX volume fraction were discussed in detail. Increasing deformation temperature or strain rate contributes to DRX of both the austenite and the δ-ferrite, whereas a lower strain rate leads to the austenite grains growth and the δ-ferrite evolution, from banded to island-like structure.

The microstructure evolution and tensile properties of the Fe–10Mn–10Al–0.7C low-density steel annealed at the temperature range from 700 °C to 1200 °C for 1 h were investigated in the present study. The phases in the annealed specimens mainly included ferrite (α), austenite (γ) and κ-carbide (κ). The dissolution temperature for κ-carbide is between 850 °C and 900 °C. At the annealing temperature of 700 °C, all the γ phase transformed to α phase and κ-carbide by eutectoid reaction. As the annealing temperature rose from 700 °C to 900 °C, α phase and κ-carbide fraction decreased and γ phase fraction increased, and ultimate elongation increased, while ultimate strength and yield strength had a decreasing trend. The γ phase fraction in the specimen dominated the ultimate elongation, and the κ-carbide strengthened the specimen and weakened ductility. As the annealing temperature rose from 900 °C to 1200 °C, the phase fraction change was small but the grain size increased greatly. The rapid growth of the grains was the main reason why ultimate tensile strength and ultimate elongation decreased with the increase of annealing temperature over 900 °C. The steel designed here possessed a density of 6.80 g/cm3, which is about 13% lower than pure iron. Keywords: Low-density steel, Annealing, κ-Carbide, Tensile properties

In situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis were performed on the duplex Fe–27Mn–11.5Al–0.95C steel at room temperature to examine the tensile deformation behavior. The steel consisting of stable austenite matrix and a small amount of ferrite exhibited excellent combination of high strength and ductility (46.5 GPa%) in solid solution state due to the continuous strain hardening behavior. In situ SEM revealed that slip bands appeared in the austenite grain at the early deformation stage, and different slip systems intersected with higher density as the displacement increased. The deformation strains of austenite were obviously larger than that of ferrite, which resulted into the ferrite crack propagation at the later stage. With the stack fault energy (SFE) of ∼80 mJ/m2, the evolution of dislocation substructure with increasing strain shows typical planar glide characteristics, namely, dislocation pile-ups, Taylor lattice, high density dislocation walls, domain boundary and intersected microbands. Grain subdivision by microband intersection at high strains results in stable work hardening rate and continuous strain hardening behavior.

The dry impact wear behavior of bainite ductile cast iron was evaluated under three different impact loads for 30000 cycles. The strain-hardening effects beneath the contact surfaces were analyzed according to the surfaces’ micro-hardness profiles. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the worn surfaces. The results indicated that the material with the highest hardness was the one continuously cooled at 20°C, which exhibited the lowest wear rate under each set of test conditions. The hardness of the worn surface and the thickness of the hardened layer increased with the increases in impact load and in the number of test cycles. The better wear performance of the sample cooled at 20°C is attributed to its finer microstructure and superior mechanical properties. All the samples underwent the transformation induced plasticity (TRIP) phenomenon after impact wear, as revealed by the fact that small amounts of retained austenite were detected by XRD.

Precipitation hardening stainless steel has the advantages of both austenitic stainless steel and martensitic stainless steel, including good corrosion resistance, excellent processability and high strength. With the evolution of microstructure and properties of semi-austenitic precipitation hardening stainless steel (D631) during drawing process and aging treatment, the working hardening behaviors, law of phase transition, dissolution and precipitation state of alloying element are investigated to gain the toughness mechanism of D631. The results show that the tensile strength increases with the increase of the reduction of area, on the contrary, the plasticity decreases gradually. The tensile strength is 1529 MPa while the reduction of area is 54%. By means of X-ray diffraction (XRD) and metallograpic observation, the content of martensite increases with the increase of deformation, and makes the higher strength and lower plasticity. The alloying element dissolved in the matrix precipitates in fine particles by aging treatment, resulting in a higher strength of 1948MPa.